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Xpl exhaust ???
- Thread starter oct6454
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Just wondering why you are planning on putting on an after market exhaust? Sound? Performance?
If you are looking for performance...it prob won't be worth the money. You may actually end up decreasing the performance of you doo. If it is sound you are looking for and you think it is worth the money go for it!
Matt
If you are looking for performance...it prob won't be worth the money. You may actually end up decreasing the performance of you doo. If it is sound you are looking for and you think it is worth the money go for it!
Matt
Exhaust?.......
If you want to mod up the enigne a little, I don't think the exhaust should be your first choice.
The 951 engine is the largest of the two cycle engines with the RAVE (Rotax Automatic Variable Exhaust) system. This system is designed to increase the volume of exhaust gases by increasing the size of the exhaust port with an automatic guillotine slide valve.
As it stands now, with the stock engine, you can increase the fuel flow by changing the jets in the carbs and lower the resistance in the flame arrestor to increase output, without changing the exhaust system. You cannot change the jets in the carbs, without changing the flame arrestor. These two work hand in hand.
The exhaust system should only be changed in extreme or complete engine modification kits, like for racing.:cheers:
If you want to mod up the enigne a little, I don't think the exhaust should be your first choice.
The 951 engine is the largest of the two cycle engines with the RAVE (Rotax Automatic Variable Exhaust) system. This system is designed to increase the volume of exhaust gases by increasing the size of the exhaust port with an automatic guillotine slide valve.
As it stands now, with the stock engine, you can increase the fuel flow by changing the jets in the carbs and lower the resistance in the flame arrestor to increase output, without changing the exhaust system. You cannot change the jets in the carbs, without changing the flame arrestor. These two work hand in hand.
The exhaust system should only be changed in extreme or complete engine modification kits, like for racing.:cheers:
ok Thanks
this is what has been done. i want it for a little more power but mostly for the sound.
ADA Head with 49cc domes (pump gas 91 octane)
Rinaldi Reeds
R&D ported intake
Stock Carbs (re-jetted for Flame arrestors and no accelerator pump)
UMI Steering with bar risers and Pro-Taper fat bars
UMI Finger throttle
WORX one piece sponsons
Mel Miller Billet fuel pickup
Deans Team re-mapped MPEM (with one key,
Stock Pump with a shaved and balanced impeller
Upgraded the driveshaft system to a carrier bearing assembly
Bilge pump
Custom cooling with additional cooling pissers (visual effect).
Hydroturf medium slip seat cover
Hydroturf Mats
ODI Rouge locking grips
this is what has been done. i want it for a little more power but mostly for the sound.
ADA Head with 49cc domes (pump gas 91 octane)
Rinaldi Reeds
R&D ported intake
Stock Carbs (re-jetted for Flame arrestors and no accelerator pump)
UMI Steering with bar risers and Pro-Taper fat bars
UMI Finger throttle
WORX one piece sponsons
Mel Miller Billet fuel pickup
Deans Team re-mapped MPEM (with one key,
Stock Pump with a shaved and balanced impeller
Upgraded the driveshaft system to a carrier bearing assembly
Bilge pump
Custom cooling with additional cooling pissers (visual effect).
Hydroturf medium slip seat cover
Hydroturf Mats
ODI Rouge locking grips
Last edited by a moderator:
Now that's modded!.......
Well you didn't put all that in on your first post.........it sounds like you already know what's going on.
It seems like your ridin a nice machine!.........
One more thing to look for.
The 91 octane fuel will burn hotter, so keep an eye on your plug conditions. Higher octane fuel is thought to cause detonation. With the mods you have and if you go with a high flow exhaust system, then you'll probably be o.k. with the fuel type................:cheers:
Well you didn't put all that in on your first post.........it sounds like you already know what's going on.
It seems like your ridin a nice machine!.........
One more thing to look for.
The 91 octane fuel will burn hotter, so keep an eye on your plug conditions. Higher octane fuel is thought to cause detonation. With the mods you have and if you go with a high flow exhaust system, then you'll probably be o.k. with the fuel type................:cheers:
Exhaust........
I didn't answer your question........
With the mods you have, I'd say you could probably get a couple more miles per hour from a performance exhaust system.
There isn't many choices out there for the 951, but here is a link for you to read about and help get you started...........http://www.jetworks.net/sde951.htm
I didn't answer your question........
With the mods you have, I'd say you could probably get a couple more miles per hour from a performance exhaust system.
There isn't many choices out there for the 951, but here is a link for you to read about and help get you started...........http://www.jetworks.net/sde951.htm
Thanks!!!
I have only found a few exhaust systems one is a coffman and the other which is a factory twin pipe. This ski had a factory twin pipe on it but it was removed when it was no longer used for racing. Any info on either of these two?? i think i might have to try that jet works out !! not nearly the price of a coffman or factory pipe.
I have only found a few exhaust systems one is a coffman and the other which is a factory twin pipe. This ski had a factory twin pipe on it but it was removed when it was no longer used for racing. Any info on either of these two?? i think i might have to try that jet works out !! not nearly the price of a coffman or factory pipe.
Well........
Well, if you got a $1000 bucks to spend, I think I know where you can get the Coffman pipe.
With what you have on it and if it were a race machine, then everything should be set up for this pipe......
Here's the link....have a look http://www.coffmansexhaust.com/
Well, if you got a $1000 bucks to spend, I think I know where you can get the Coffman pipe.
With what you have on it and if it were a race machine, then everything should be set up for this pipe......
Here's the link....have a look http://www.coffmansexhaust.com/
Price!!
I like the coffmans but $1000 allota money. Is there anything less expensive but still will work without have to rework to much cooling. I have the extra cooling already. But since i am not super knowledge able with these machines i was hoping i could use the stock cooling setup. Any ideas???
I like the coffmans but $1000 allota money. Is there anything less expensive but still will work without have to rework to much cooling. I have the extra cooling already. But since i am not super knowledge able with these machines i was hoping i could use the stock cooling setup. Any ideas???
Dans97challenger
New Member
I am with you on that one Dennis. Higher Octane fuel burns slower than lower octane fuel. You use higher octane fuel to minimize detonation in any vehicle.
Octane?.......
Dawg, I was with you on that one till I started my research on it. The Seadoo shop manual sets the requirement on the octane we burn in our skis/boats.
Like you, I was always taught the higher octane, the better. Then I started learning about detonation and pinging..........
The higher octane stands to damage the engine due to the higher temps to which it burns.......
Dawg, I was with you on that one till I started my research on it. The Seadoo shop manual sets the requirement on the octane we burn in our skis/boats.
Like you, I was always taught the higher octane, the better. Then I started learning about detonation and pinging..........
The higher octane stands to damage the engine due to the higher temps to which it burns.......
Sorry about the thread derail!
Sorry Seadoosnipe, but you have it backwards on this one. I had to take this in school many years ago, and the octane ratting on fuel is given to show how well it resists detonation and pinging. The higher the number the slower, cooler, and more resistant to preignition the fuel is.
That is why any high compression engine, or one that has forced induction (supercharger/turbo charger) requires a higher octane fuel. With too low an octane ratting an engine runs the possibility of burning a hole in a piston, or becoming a diesel. The worst case scenario of running a fuel with too high an octane ratting is the engine will run a bit rich due too how "cold" the fuel is.
I found a good write up that explains it better.
The Simple Definition
An octane rating (87 vs. 89 vs 92, etc.) is a measure of a gasoline's ability to resist detonation, which manifests itself in a pinging or "knocking" noise. Higher numbers indicate that the fuel can be compressed to a higher level before detonation / knock occurs in an engine, which occurs when. As described in "Detonation, Knock, and Pre-Ignition 101", detonation / knock occurs when air and fuel that is ahead of the combustion flame front ignites before the flame front arrives.
The Complicated Definition
Octane is actually more than just a rating - it is a hydrocarbon just like methane (single carbon atom), propane (three carbon atoms), butane (five carbon atoms), and heptane (seven carbon atoms). Octane (C8H18) is a hydrocarbon with eight carbon atoms and eighteen hydrogen atoms. 100% octane fuel is remarkably resilient to compression (i.e. it does not combust when compressed) and is thus resilient to detonation / knock. This resilience is derived from the branching of octane's carbon chain (see figure). Because of the nature of octane as being resilient to detonation, all fuels are compared to 100% octane as a benchmark fuel, from which an "octane rating"can be obtained. Heptane, a hydrocarbon with seven carbon atoms, compresses very poorly and spontaneously combusts even under small amounts of compression. In other words, Heptane's behavior when compressed is diametrically opposed to Octane's behavior under the same conditions. For this reason, Heptane (which has an octane rating of zero) is the other benchmark fuel used in the octane rating system to determine a fuel's octane rating. A fuel that spontaneously combusts (knocks) under the same amount of compression as a fuel composed of 87% octane and 13% Heptane would have an octane rating of 87. This is not to say that 87 octane gasoline is made up of 87% octane and 13% heptane, rather that the 87 octane gasoline "knocks" in a laboratory knock engine at the same compression ratio as a fuel composed of 87% octane and 13% heptane.
The composition of an octane hydrocarbon.
Unfortunately, it gets even more complicated. Because various fuels respond differently under varying engine loads, a gasoline may get a different octane rating on a free running engine and one under load. For this reason, the octane rating label that we see at the pump (monitored by the U.S. Cost of Living Council) is actually an average of two octane ratings - the motor method rating (where the engine is run under a load) and a research method rating (where the engine is run freely). The formula used to get the CLC Octane number on gas pumps in the United States is thus: (Motor Octane Number + Research Octane Number) / 2.
:hat:What's the benefit of higher octane?:hat:
Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On modern engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!
When should I switch to a higher octane fuel?
First off, never run lower octane fuel than is recommended by the vehicle's manufacturer. If the vehicle manufacturer recommends 89 octane gasoline, this means that the engine has been tuned to perform optimally without detonation on 89 octane fuel. Once you've done some modifications to your engine, the manufacturer's recommended gasoline may no longer suffice. Obviously, if you can hear detonation inside your engine in the form of pinging or "knocking", try a higher octane fuel. You will also need to run a premium grade fuel (91+ octane) if you have a supercharger, turbocharger, or if you have an ignition programmer that advances your ignition timing.
Why is higher octane fuel more expensive?
Higher octane fuels are more expensive because they must go through more refining steps that increases the octane rating. These additional steps do not make the fuel better in any other way.
How is it possible to have 100+ octane gasoline?
There are some fuels that are even more resilient to compression than 100% octane. Some additives, like tetraethyl lead, increase the gasoline's ability to operate without knock. Some racing and airplane fuels have octane ratings of 110+!
Sorry Seadoosnipe, but you have it backwards on this one. I had to take this in school many years ago, and the octane ratting on fuel is given to show how well it resists detonation and pinging. The higher the number the slower, cooler, and more resistant to preignition the fuel is.
That is why any high compression engine, or one that has forced induction (supercharger/turbo charger) requires a higher octane fuel. With too low an octane ratting an engine runs the possibility of burning a hole in a piston, or becoming a diesel. The worst case scenario of running a fuel with too high an octane ratting is the engine will run a bit rich due too how "cold" the fuel is.
I found a good write up that explains it better.
The Simple Definition
An octane rating (87 vs. 89 vs 92, etc.) is a measure of a gasoline's ability to resist detonation, which manifests itself in a pinging or "knocking" noise. Higher numbers indicate that the fuel can be compressed to a higher level before detonation / knock occurs in an engine, which occurs when. As described in "Detonation, Knock, and Pre-Ignition 101", detonation / knock occurs when air and fuel that is ahead of the combustion flame front ignites before the flame front arrives.
The Complicated Definition
Octane is actually more than just a rating - it is a hydrocarbon just like methane (single carbon atom), propane (three carbon atoms), butane (five carbon atoms), and heptane (seven carbon atoms). Octane (C8H18) is a hydrocarbon with eight carbon atoms and eighteen hydrogen atoms. 100% octane fuel is remarkably resilient to compression (i.e. it does not combust when compressed) and is thus resilient to detonation / knock. This resilience is derived from the branching of octane's carbon chain (see figure). Because of the nature of octane as being resilient to detonation, all fuels are compared to 100% octane as a benchmark fuel, from which an "octane rating"can be obtained. Heptane, a hydrocarbon with seven carbon atoms, compresses very poorly and spontaneously combusts even under small amounts of compression. In other words, Heptane's behavior when compressed is diametrically opposed to Octane's behavior under the same conditions. For this reason, Heptane (which has an octane rating of zero) is the other benchmark fuel used in the octane rating system to determine a fuel's octane rating. A fuel that spontaneously combusts (knocks) under the same amount of compression as a fuel composed of 87% octane and 13% Heptane would have an octane rating of 87. This is not to say that 87 octane gasoline is made up of 87% octane and 13% heptane, rather that the 87 octane gasoline "knocks" in a laboratory knock engine at the same compression ratio as a fuel composed of 87% octane and 13% heptane.
The composition of an octane hydrocarbon.
Unfortunately, it gets even more complicated. Because various fuels respond differently under varying engine loads, a gasoline may get a different octane rating on a free running engine and one under load. For this reason, the octane rating label that we see at the pump (monitored by the U.S. Cost of Living Council) is actually an average of two octane ratings - the motor method rating (where the engine is run under a load) and a research method rating (where the engine is run freely). The formula used to get the CLC Octane number on gas pumps in the United States is thus: (Motor Octane Number + Research Octane Number) / 2.
:hat:What's the benefit of higher octane?:hat:
Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On modern engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!
When should I switch to a higher octane fuel?
First off, never run lower octane fuel than is recommended by the vehicle's manufacturer. If the vehicle manufacturer recommends 89 octane gasoline, this means that the engine has been tuned to perform optimally without detonation on 89 octane fuel. Once you've done some modifications to your engine, the manufacturer's recommended gasoline may no longer suffice. Obviously, if you can hear detonation inside your engine in the form of pinging or "knocking", try a higher octane fuel. You will also need to run a premium grade fuel (91+ octane) if you have a supercharger, turbocharger, or if you have an ignition programmer that advances your ignition timing.
Why is higher octane fuel more expensive?
Higher octane fuels are more expensive because they must go through more refining steps that increases the octane rating. These additional steps do not make the fuel better in any other way.
How is it possible to have 100+ octane gasoline?
There are some fuels that are even more resilient to compression than 100% octane. Some additives, like tetraethyl lead, increase the gasoline's ability to operate without knock. Some racing and airplane fuels have octane ratings of 110+!
Last edited by a moderator:
Octane.....
I had a nice write up on research that I did last year on this subject, but it was just lost in posting.
Rookie, what you have posted is good information, but is nil and void in the use of our 2 stroke engines.
While I agree with you and DAWG, it would only be useful if I were rebuilding my 350 cid engine.
The fuel requirements in the 2 stroke Rotax are 100% different from what you printed. The only engine that requires an octane over 90 is the supercharged 4 TEC's.
One of the things you fail to mention is spark plug. This single component is what determines which fuel we should burn. Each of those numbers on our NGK plugs has a specific meaning.
For me, I run the BR8ES which mean, it's a 14mm thread, resistance type with a reach of 19 mm with a standard 2.5mm center electrode.
Since I want to keep this short, the one big difference that you don't go over, is the octane that is dictated for our 2 strokes because it's the best fuel rating to run efficiently without heating the engine to hot while allowing enough burn for power and some left over for lubrication. To achieve this, the designers of the Rotax engine put a cooling path across the top of the head that cools the upper end (pistons) before going into the exhaust for preheating as it makes its way to the cooling jacket around the pistons. This in itself was done to help reduce the possibility of detonation.
While you have a good handle on octane and detonation occurance in the 4 stroke engines, your reseach has very little use in the 2 stroke motors.
Also, adding the oil changes the fuel flash point and therefore, the end result in whether it's cool or hot.
If you were to run the iridium or platinum plugs, with the double or quadriple electrodes and a 91 octane fuel, I can promise you, the 2 stroke engine would last no more than one season............:cheers:
I had a nice write up on research that I did last year on this subject, but it was just lost in posting.
Rookie, what you have posted is good information, but is nil and void in the use of our 2 stroke engines.
While I agree with you and DAWG, it would only be useful if I were rebuilding my 350 cid engine.
The fuel requirements in the 2 stroke Rotax are 100% different from what you printed. The only engine that requires an octane over 90 is the supercharged 4 TEC's.
One of the things you fail to mention is spark plug. This single component is what determines which fuel we should burn. Each of those numbers on our NGK plugs has a specific meaning.
For me, I run the BR8ES which mean, it's a 14mm thread, resistance type with a reach of 19 mm with a standard 2.5mm center electrode.
Since I want to keep this short, the one big difference that you don't go over, is the octane that is dictated for our 2 strokes because it's the best fuel rating to run efficiently without heating the engine to hot while allowing enough burn for power and some left over for lubrication. To achieve this, the designers of the Rotax engine put a cooling path across the top of the head that cools the upper end (pistons) before going into the exhaust for preheating as it makes its way to the cooling jacket around the pistons. This in itself was done to help reduce the possibility of detonation.
While you have a good handle on octane and detonation occurance in the 4 stroke engines, your reseach has very little use in the 2 stroke motors.
Also, adding the oil changes the fuel flash point and therefore, the end result in whether it's cool or hot.
If you were to run the iridium or platinum plugs, with the double or quadriple electrodes and a 91 octane fuel, I can promise you, the 2 stroke engine would last no more than one season............:cheers:
Research....
I have thought about the research Rookie 101 did on this issue and do not want to completely dismiss it. It is important to understand the theory and terminology of the fuels and oils we use in the Rotax.
I did some research last year on this subject and whith our stock engines, the conclusion was if we thought we gained something extra in using a higher octane, we were mislead.
I use 87 octane in my truck and all my skis and boats because it is the manafacturers requirement. I know many members in the forum that use a higher octane and they've reported no ill affects to their ski.
I do specifically remember reading about detonation, fuel requirements, oil and engine cooling.........and to read to much into our fuel requriements is not necessary.
Rookie 101 has provided us with some excellent reading and I just want to take a second to acknowledge his work. He is a smart man and though, I too had to take a course on fuel, I don't remember it specifically remember it covering octane. My school was on testing it for composition, flashpoint and bottom sediment and water............
One more thing............several members address me as "Mr. Snipe" or something other than what I see as equal to all other members in this forum. I put my pants on just like you guys do and I don't consider myself any better than ya'll. I am equal to and always open in debate and discussion. If I make a mistake or if my post is not quite accurate and someone points it out, I"m man enough to say I was wrong.
Please, don't address me as "Mr.". I choose the word "snipe" because when I was in the Navy, snipe was a nickname for an engineer and it stuck with me. My name is Louis and if you so choose to address me by my name, then I'm fine with that........................:cheers:
I have thought about the research Rookie 101 did on this issue and do not want to completely dismiss it. It is important to understand the theory and terminology of the fuels and oils we use in the Rotax.
I did some research last year on this subject and whith our stock engines, the conclusion was if we thought we gained something extra in using a higher octane, we were mislead.
I use 87 octane in my truck and all my skis and boats because it is the manafacturers requirement. I know many members in the forum that use a higher octane and they've reported no ill affects to their ski.
I do specifically remember reading about detonation, fuel requirements, oil and engine cooling.........and to read to much into our fuel requriements is not necessary.
Rookie 101 has provided us with some excellent reading and I just want to take a second to acknowledge his work. He is a smart man and though, I too had to take a course on fuel, I don't remember it specifically remember it covering octane. My school was on testing it for composition, flashpoint and bottom sediment and water............
One more thing............several members address me as "Mr. Snipe" or something other than what I see as equal to all other members in this forum. I put my pants on just like you guys do and I don't consider myself any better than ya'll. I am equal to and always open in debate and discussion. If I make a mistake or if my post is not quite accurate and someone points it out, I"m man enough to say I was wrong.
Please, don't address me as "Mr.". I choose the word "snipe" because when I was in the Navy, snipe was a nickname for an engineer and it stuck with me. My name is Louis and if you so choose to address me by my name, then I'm fine with that........................:cheers:
Octane debate
Ok Snipe and I are having a debate about the affects of octane levels in the 2 stroke engines, so if anyone would like to add their thoughts or opinions we would love to hear them.
I should also mention that I am referring to pump gas that you can get at any corner station typically ranging from an 87 to a 94 octane rating, as some but not all race fuels have additives that raise the "heat or energy units" of the fuel which could bring up combustion chamber temperatures and cause damage to an engine that is not purpose built for the application.
I am a strong believer, and all of the reading I have done suggest that there is no link between to a high octane rating and engine damage. The reason for this is octane as a hydrocarbon does not contain any higher energy levels than other hydrocarbon elements, in fact the structure of it forces it to burn slower at a more controlled rate, and resist the tendency to combust upon compression.
I did look through some of the Sea-Doo manuals for the 2 strokes, and agree that they recommend 87 octane. I don't feel they are suggesting that this would be the maximum that you could safely burn, but more of a guideline to follow. All of the dirt bikes, quads, and even my Utopia with its 2 stroke Mercury have listed the octane requirement as a "minimum" so I am puzzled as to why rotax chose to just put the number 87 with no minimum or maximum behind it.
The outboard manuals that I read chapters of online, even went as far as to suggest that if the engine is being used for commercial work or towing to consider using a fuel with a higher (87-91) octane rating.
PS: I am not suggesting that you should run a higher octane fuel, just that it will in no way harm the engine. Premium fuel for the most part is a complete waste of money unless your engine is designed with it in mind, such as the supercharged 4Tecs.
Here are some of our thoughts so far.
Aaron:cheers:
Re: Octane and the 2 stroke
--------------------------------------------------------------------------------
Quote:
Originally Posted by rookie101
Sorry Louis but 2 or 4 stroke does not matter when it comes to the octane rating. You are right that too hot a plug will destroy or shorten the life of an engine, but the only thing too much octane will hurt is your wallet.
I have been a licensed automotive mechanic for a lot of years, and in Canada we have to go to school in order to get our license. One of the things we had to take was understanding fuel make up and how it affects an engine.
I could not find any articals that delt specifically with Sea-Doos, but here is what I could find.
Aaron
This is from VP racing fuels.
Two-strokes stand to benefit more from higher octane fuel than four-strokes. The design of a two-stroke’s exhaust pipe (expansion chamber) keeps more heat backed-up against the cylinder and creates the potential for hot spots that could lead to detonation.
Here is one about Rotax 2 strokes. (I know it's aircraft not watercraft)
Diagnosing Rotax 2 stroke aircraft engine piston failure from detonation, or pre-ignition.
2 2A
Seized Pistons - (Ref: 2 & 2A)
The piston shows yellow spots on the dome and seizure marks on the skirt but there is no sign of metal aluminum.
If you inspect an engine and find yellow or yellow-orange deposits on the piston dome, that engine has experienced an abnormal combustion condition known as detonation. In this situation, combustion begins normally with ignition from the spark plug but as the flame front moves across the combustion chamber, rather than burning smoothly, the unburned portion of the charge spontaneously ignites. This results in extremely high temperatures and a shock wave heard as "pinging." What has happened is combustion has been completed in about 29 degrees of crankshaft rotation instead of the normal 50.
The oxide of calcium, an element found in 2 - stroke oil additives, is normally near white in colour. At temperature very near that of the melting point of the piston, the oxide will change colour from white to yellow-orange and is an indicator that the engine was overheated. The excessive heat results in rapid piston expansion and possible failure of the lubrication film.
Possible causes:
"Too low an octane fuel used or fuel with too much alcohol used"
jetting too lean or failure of the fuel system, i.e., clogged fuel line or filter, fuel tank not venting, problem with fuel pump, carburetor, air leak into crankcase
spark plug heat range too hot
ignition timing too far advanced, possible failure of the c.d. amplifier box
restricted exhaust system: back pressure too high
overheated, loosely-installed spark plug
Seadoosnipe Wrote:
Aaron, I addressed your post in that thread on the fuel. You are completely correct, there is very little that can affect the fuel rating. Once it's 87 octane, it stays that way, though over the course of about 1 month, it will lose one percentage of it's octance rating.
I too, had to go to school on fuel oil. Mostly for the purpose of testing the composition, flashpoint, properities and bottom sediment and water.
In the end, I would like to understand why Rotax recommends 87 octane in their 2 stroke engines. The 89 octane is only processed a bit more to achieve that rating..........so, ?........? I'm left with some questions.
In the one thing that I was studying was cooling of the 2 stroke engines. We do not burn all our fuel in the 2 strokes. There is a percentage left over for lubrication.
I also read that the engineers for Rotax have not determined 100% the reason detonation occurs in our engines.......
PLease feel free to debate that thread in the forum. I look forward to reading your research and your opinions.........
Louis
Ok Snipe and I are having a debate about the affects of octane levels in the 2 stroke engines, so if anyone would like to add their thoughts or opinions we would love to hear them.
I should also mention that I am referring to pump gas that you can get at any corner station typically ranging from an 87 to a 94 octane rating, as some but not all race fuels have additives that raise the "heat or energy units" of the fuel which could bring up combustion chamber temperatures and cause damage to an engine that is not purpose built for the application.
I am a strong believer, and all of the reading I have done suggest that there is no link between to a high octane rating and engine damage. The reason for this is octane as a hydrocarbon does not contain any higher energy levels than other hydrocarbon elements, in fact the structure of it forces it to burn slower at a more controlled rate, and resist the tendency to combust upon compression.
I did look through some of the Sea-Doo manuals for the 2 strokes, and agree that they recommend 87 octane. I don't feel they are suggesting that this would be the maximum that you could safely burn, but more of a guideline to follow. All of the dirt bikes, quads, and even my Utopia with its 2 stroke Mercury have listed the octane requirement as a "minimum" so I am puzzled as to why rotax chose to just put the number 87 with no minimum or maximum behind it.
The outboard manuals that I read chapters of online, even went as far as to suggest that if the engine is being used for commercial work or towing to consider using a fuel with a higher (87-91) octane rating.
PS: I am not suggesting that you should run a higher octane fuel, just that it will in no way harm the engine. Premium fuel for the most part is a complete waste of money unless your engine is designed with it in mind, such as the supercharged 4Tecs.
Here are some of our thoughts so far.
Aaron:cheers:
Re: Octane and the 2 stroke
--------------------------------------------------------------------------------
Quote:
Originally Posted by rookie101
Sorry Louis but 2 or 4 stroke does not matter when it comes to the octane rating. You are right that too hot a plug will destroy or shorten the life of an engine, but the only thing too much octane will hurt is your wallet.
I have been a licensed automotive mechanic for a lot of years, and in Canada we have to go to school in order to get our license. One of the things we had to take was understanding fuel make up and how it affects an engine.
I could not find any articals that delt specifically with Sea-Doos, but here is what I could find.
Aaron
This is from VP racing fuels.
Two-strokes stand to benefit more from higher octane fuel than four-strokes. The design of a two-stroke’s exhaust pipe (expansion chamber) keeps more heat backed-up against the cylinder and creates the potential for hot spots that could lead to detonation.
Here is one about Rotax 2 strokes. (I know it's aircraft not watercraft)
Diagnosing Rotax 2 stroke aircraft engine piston failure from detonation, or pre-ignition.
2 2A
Seized Pistons - (Ref: 2 & 2A)
The piston shows yellow spots on the dome and seizure marks on the skirt but there is no sign of metal aluminum.
If you inspect an engine and find yellow or yellow-orange deposits on the piston dome, that engine has experienced an abnormal combustion condition known as detonation. In this situation, combustion begins normally with ignition from the spark plug but as the flame front moves across the combustion chamber, rather than burning smoothly, the unburned portion of the charge spontaneously ignites. This results in extremely high temperatures and a shock wave heard as "pinging." What has happened is combustion has been completed in about 29 degrees of crankshaft rotation instead of the normal 50.
The oxide of calcium, an element found in 2 - stroke oil additives, is normally near white in colour. At temperature very near that of the melting point of the piston, the oxide will change colour from white to yellow-orange and is an indicator that the engine was overheated. The excessive heat results in rapid piston expansion and possible failure of the lubrication film.
Possible causes:
"Too low an octane fuel used or fuel with too much alcohol used"
jetting too lean or failure of the fuel system, i.e., clogged fuel line or filter, fuel tank not venting, problem with fuel pump, carburetor, air leak into crankcase
spark plug heat range too hot
ignition timing too far advanced, possible failure of the c.d. amplifier box
restricted exhaust system: back pressure too high
overheated, loosely-installed spark plug
Seadoosnipe Wrote:
Aaron, I addressed your post in that thread on the fuel. You are completely correct, there is very little that can affect the fuel rating. Once it's 87 octane, it stays that way, though over the course of about 1 month, it will lose one percentage of it's octance rating.
I too, had to go to school on fuel oil. Mostly for the purpose of testing the composition, flashpoint, properities and bottom sediment and water.
In the end, I would like to understand why Rotax recommends 87 octane in their 2 stroke engines. The 89 octane is only processed a bit more to achieve that rating..........so, ?........? I'm left with some questions.
In the one thing that I was studying was cooling of the 2 stroke engines. We do not burn all our fuel in the 2 strokes. There is a percentage left over for lubrication.
I also read that the engineers for Rotax have not determined 100% the reason detonation occurs in our engines.......
PLease feel free to debate that thread in the forum. I look forward to reading your research and your opinions.........
Louis
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The great fuel debate!....
Because I’m pretty much a stickler for manuals and instructions, I have no reason to use any other octane than what is recommended by the manafacturer. That’s in any thing I own with an engine in it. The biggest difference I’ve seen in the past personally is, the difference in flashpoint. While Aaron is correct in that a higher octane fuel burn cooler and more complete, it also has the capacity to burn with the more advanced “hot” spark plugs.
This is a two part debate. There can be no debate over fuel if you don’t include the spark plugs (see attached PDF file for a visible explanation). We’ve all seen the new age plugs like the Pulstar, Platinum Ir Fusion (iridium/platinum) and others that are really super hot plugs. These plugs could fire the 89 octane but better served in the octanes above 90. Now, if you burn this plug with the 89 octane fuel, your looking to burn a hole in your piston. But if you burn the 89 octane with the plug recommended by your manafacturer, you’ll probably do no harm. It will just cost you a bit more money (for no real reason). The biggest difference between 87 and 89 octane fuel is the flashpoint.
An important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phenomenon known as pre-detonation (also known as knocking, pinging, spark knock, and other names). Deflagration is the normal type of combustion. Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are a number of different conventions for expressing the octane rating; therefore, the same fuel may be labeled with a different number, depending upon the system used. Higher-octane fuels allow for a higher compression ratio - this means less space in a cylinder on its combustion stroke, hence a higher cylinder temperature which improves efficiency according to Carnot's theorem, along with fewer wasted hydrocarbons (therefore less pollution and wasted energy), bringing higher power levels coupled with less pollution overall because of the greater efficiency.
OCTANE-the first and foremost rule for octane is; only use what your
car NEEDS. This means if your car knocks or pings with 87, then move
up to 89, then to 92. As many have stated, you are indeed wasting your
money with higher octane fuels....unless of course it is needed.
Higher octane ratings mean higher flash point. Which translates to
less pre-detonation that causes ping and/or knock. Usually this is
only required on high performance(read: high compression) engines
where the temps and pressures can easily cause pre-detonation. As far
as keeping your injectors clean, you wasted money for "premium" gas
would be better spent on a can fuel injector cleaner once every 6
months or so. Higher octane gasoline does not clean your engine. The
additives(detergents) in the gasoline are responsible for the
cleaning. Here's where I plug Amoco products--> Seriously though,
Amoco's Ultimate gasoline does go through a proprietary process that
removes the PNA's which are basically poly-nuclear-aromatics. These
are responsible for the slight yellowish color in gasoline and are
ultimately responsible for resid(tar-like) deposits that can
accumulate in your injectors, etc. I am not telling you to run out and
start buying Amoco-Ultimate, just informing you of the product.
GAS TANK PRESSURE- Gasoline and all other hydrocarbons have a chemical
characteristic know as "Reed Vapor Pressure". This can be expressed as
reed vapor pressure RVP or true vapor pressure TVP. They are similar
yet each has it's own calculating method. Anyhow....most gasolines
have TVP's in the neighborhood of 9 psig. Which basically means that
all gasolines evaporate until equilibrium(9 psig) is attained. If you
have a cup of gasoline with no lid on it, it will evaporate
"relatively" fast versus a closed or tightly fitted container. As
gasoline is used up in your tank, the void is filled by vapor until
that equilibrium is again met. When you remove your gas cap to fill
up, you are releasing the pressure that was built to achieve
equilibrium. So you see....it has nothing to do with carbonation(no
such thing in hydrocarbons) or oxygenation.
Believe it or not, octane mixes linearly as far as we
are concerned at the pump. 89 octane is actually an even
mix of 87 and 91 octane, for example. Hence, there's no
point in having 3 different hoses running from 3 different
pumps and tanks these days.
You can also notice more and more Shell tankers drive around
with a huge 2nd tank trailer and tank half the size in front.
I can only surmise the 2nd trailer is full of regular 87
octane stuff, and the small trailer is whatever they mix
in to get the higher octanes. It makes lots of sense.
So, you'll get a hose length's worth of whatever gas the
dude in front of you pumped into his car.
With respect to which octane gas you're using, if the
owner's manual says 87 octane, you're wasting money
pumping anything higher cause your engine wasn't designed
to use it, much less know the difference. This is especially
true assuming you don't have knock sensors.
Of course, you can argue that you can
manually advance your timing more with premium gas to get
more power out of it. FWIW, I run 3degrees beyond factory
spec using 87 octane and still have no problems on my 22RE.
I’ve come to the conclusion that, if you burn 89 octane and have been for a while with no ill affects, then continue to burn it. It’s your money. It’s not making your engine run any better than the 87.
I read that a way to decide if you need to increase the octane (quoted in this research) of your fuel is if you suspect pinging and knocking. If you hear this in your Seadoo (I’ve never heard it in mine), then increase the octane till it stops.
We have had about 5 skis this year who have posted pix and threads on destruction by detonation. Hind sight makes me wish I’d have asked what octane fuel they were using.
Researh in my own words but also I credit contributions to Aaron Lung and John Harville of the Amoco Corporation
Because I’m pretty much a stickler for manuals and instructions, I have no reason to use any other octane than what is recommended by the manafacturer. That’s in any thing I own with an engine in it. The biggest difference I’ve seen in the past personally is, the difference in flashpoint. While Aaron is correct in that a higher octane fuel burn cooler and more complete, it also has the capacity to burn with the more advanced “hot” spark plugs.
This is a two part debate. There can be no debate over fuel if you don’t include the spark plugs (see attached PDF file for a visible explanation). We’ve all seen the new age plugs like the Pulstar, Platinum Ir Fusion (iridium/platinum) and others that are really super hot plugs. These plugs could fire the 89 octane but better served in the octanes above 90. Now, if you burn this plug with the 89 octane fuel, your looking to burn a hole in your piston. But if you burn the 89 octane with the plug recommended by your manafacturer, you’ll probably do no harm. It will just cost you a bit more money (for no real reason). The biggest difference between 87 and 89 octane fuel is the flashpoint.
An important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phenomenon known as pre-detonation (also known as knocking, pinging, spark knock, and other names). Deflagration is the normal type of combustion. Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are a number of different conventions for expressing the octane rating; therefore, the same fuel may be labeled with a different number, depending upon the system used. Higher-octane fuels allow for a higher compression ratio - this means less space in a cylinder on its combustion stroke, hence a higher cylinder temperature which improves efficiency according to Carnot's theorem, along with fewer wasted hydrocarbons (therefore less pollution and wasted energy), bringing higher power levels coupled with less pollution overall because of the greater efficiency.
OCTANE-the first and foremost rule for octane is; only use what your
car NEEDS. This means if your car knocks or pings with 87, then move
up to 89, then to 92. As many have stated, you are indeed wasting your
money with higher octane fuels....unless of course it is needed.
Higher octane ratings mean higher flash point. Which translates to
less pre-detonation that causes ping and/or knock. Usually this is
only required on high performance(read: high compression) engines
where the temps and pressures can easily cause pre-detonation. As far
as keeping your injectors clean, you wasted money for "premium" gas
would be better spent on a can fuel injector cleaner once every 6
months or so. Higher octane gasoline does not clean your engine. The
additives(detergents) in the gasoline are responsible for the
cleaning. Here's where I plug Amoco products--> Seriously though,
Amoco's Ultimate gasoline does go through a proprietary process that
removes the PNA's which are basically poly-nuclear-aromatics. These
are responsible for the slight yellowish color in gasoline and are
ultimately responsible for resid(tar-like) deposits that can
accumulate in your injectors, etc. I am not telling you to run out and
start buying Amoco-Ultimate, just informing you of the product.
GAS TANK PRESSURE- Gasoline and all other hydrocarbons have a chemical
characteristic know as "Reed Vapor Pressure". This can be expressed as
reed vapor pressure RVP or true vapor pressure TVP. They are similar
yet each has it's own calculating method. Anyhow....most gasolines
have TVP's in the neighborhood of 9 psig. Which basically means that
all gasolines evaporate until equilibrium(9 psig) is attained. If you
have a cup of gasoline with no lid on it, it will evaporate
"relatively" fast versus a closed or tightly fitted container. As
gasoline is used up in your tank, the void is filled by vapor until
that equilibrium is again met. When you remove your gas cap to fill
up, you are releasing the pressure that was built to achieve
equilibrium. So you see....it has nothing to do with carbonation(no
such thing in hydrocarbons) or oxygenation.
Believe it or not, octane mixes linearly as far as we
are concerned at the pump. 89 octane is actually an even
mix of 87 and 91 octane, for example. Hence, there's no
point in having 3 different hoses running from 3 different
pumps and tanks these days.
You can also notice more and more Shell tankers drive around
with a huge 2nd tank trailer and tank half the size in front.
I can only surmise the 2nd trailer is full of regular 87
octane stuff, and the small trailer is whatever they mix
in to get the higher octanes. It makes lots of sense.
So, you'll get a hose length's worth of whatever gas the
dude in front of you pumped into his car.
With respect to which octane gas you're using, if the
owner's manual says 87 octane, you're wasting money
pumping anything higher cause your engine wasn't designed
to use it, much less know the difference. This is especially
true assuming you don't have knock sensors.
Of course, you can argue that you can
manually advance your timing more with premium gas to get
more power out of it. FWIW, I run 3degrees beyond factory
spec using 87 octane and still have no problems on my 22RE.
I’ve come to the conclusion that, if you burn 89 octane and have been for a while with no ill affects, then continue to burn it. It’s your money. It’s not making your engine run any better than the 87.
I read that a way to decide if you need to increase the octane (quoted in this research) of your fuel is if you suspect pinging and knocking. If you hear this in your Seadoo (I’ve never heard it in mine), then increase the octane till it stops.
We have had about 5 skis this year who have posted pix and threads on destruction by detonation. Hind sight makes me wish I’d have asked what octane fuel they were using.
Researh in my own words but also I credit contributions to Aaron Lung and John Harville of the Amoco Corporation
Now it sounds like we are saying the same thing as each other, just with bigger and bigger words.:rofl::rofl::rofl:
It's all in good fun, and informative reading ( for the few people that are going to wade through those monster posts of ours:rofl: ) In the end this is the only statement I had issue with.
Aaron
Oh........ one more thing. I run 87 in my Mercury because that is all the manual states I require as a minimum octane rating.:cheers:
It's all in good fun, and informative reading ( for the few people that are going to wade through those monster posts of ours:rofl: ) In the end this is the only statement I had issue with.
Aaron
Oh........ one more thing. I run 87 in my Mercury because that is all the manual states I require as a minimum octane rating.:cheers:
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Right again!...
Again, your probably right. But, in trying to bring this to a close, if BRP recommends 87, then that is what you should use; it goes on to say if you pay more, then your throwing away your money. If you research detonation, you'll see there are several things that can cause these failures but in the Rotax, they don't have a 100% sure reason for this.
In one more thing, trying to say it in lamens terms, although the octane does not change in mixing our oil and gas, the properties do. This is important that we get the efficiency of the fuel by octane and the oil for lubrication being burned by the proper spark plug. One that is too hot while burning the 87 octane will still cause you to burn off to much oil and lose your oiling properties, run lean and burn up your engine.
Your research had everything to do with octane but only in it's composition. When we look at the big picture, it's more than just the octane. I think the spark plug temperature is more important than what octance you use.
Have a good weekend and you'll don't spend much money for Christmas. I've already told my kids that Santa's sleigh broke down and the bad shape of the economy has him so broke that he can't afford to get it repaired!........:rofl:
Again, your probably right. But, in trying to bring this to a close, if BRP recommends 87, then that is what you should use; it goes on to say if you pay more, then your throwing away your money. If you research detonation, you'll see there are several things that can cause these failures but in the Rotax, they don't have a 100% sure reason for this.
In one more thing, trying to say it in lamens terms, although the octane does not change in mixing our oil and gas, the properties do. This is important that we get the efficiency of the fuel by octane and the oil for lubrication being burned by the proper spark plug. One that is too hot while burning the 87 octane will still cause you to burn off to much oil and lose your oiling properties, run lean and burn up your engine.
Your research had everything to do with octane but only in it's composition. When we look at the big picture, it's more than just the octane. I think the spark plug temperature is more important than what octance you use.
Have a good weekend and you'll don't spend much money for Christmas. I've already told my kids that Santa's sleigh broke down and the bad shape of the economy has him so broke that he can't afford to get it repaired!........:rofl:
Fuel differences......?
The biggest difference with the fuel in the 2 strokes is the added oil. This oil will actually lower the flash point. It is needed for lubrication.
If you look at the PDF file I attached to one of my posts, you'll see why and how these spark plugs differ in heat range.
If you choose a plug with a hotter heat range than is recommended by BRP, then you stand the chance of burning off more of the oil than intended, creating the possibility of overheating the piston dome and possible detonation.
Though BRP recommends 87 octance for their 2 strokes, I believe like rookie 101, there isn't enough difference in the properties to create any real hazards. But, this is what they ask you to burn.:cheers:
The biggest difference with the fuel in the 2 strokes is the added oil. This oil will actually lower the flash point. It is needed for lubrication.
If you look at the PDF file I attached to one of my posts, you'll see why and how these spark plugs differ in heat range.
If you choose a plug with a hotter heat range than is recommended by BRP, then you stand the chance of burning off more of the oil than intended, creating the possibility of overheating the piston dome and possible detonation.
Though BRP recommends 87 octance for their 2 strokes, I believe like rookie 101, there isn't enough difference in the properties to create any real hazards. But, this is what they ask you to burn.:cheers:
cstrainsgun
New Member
uh. oh...
WOW! Good info from both Snipe and Rookie. Now I have to ask the "stupid newbie question if you all dont mind." I recently bought a 2003 Utopia with the Mercury 240hp EFI M2. Not knowing when the last service was completed on the boat (dealer had no records, go figure) I was impelled to go ahead and do a 100 hour tune up on it. When I went to the Dealership I purchased the boat from (which sells both Yamaha and Sea Doo), I gave them the NGK plug number "NGK BPZ8HS-10" which was listed as the stock plug. They informed me that if I wanted a bit of more spark out of it to go with the "NGK BPZ8HN-10". Only difference I could see was the groove in the center of the plug. After hearing all of your thoughts on combustion and plugs heat rates, I am a little scared to keep running these plugs.
1. Should I toss them and get the correct plugs?
2. On the lake I am on (Lake Conroe, TX) most all the "on-water stations" carry only 93. Should I treck to my slip with 8 5 gallon tanks full of 87? Dont want to destroy my pistons yet!
3. I have used Quickleen on the last two tanks, does anyone recomend constantly using this or Sta-Bil every tank?
A little other information about the dealership that scared me. I asked for the fuel/water filter which I did not have the exact part number readily available. They said not to worry and gave me the complete wrong one. Maybe it is time to find another location for parts. I have torn down mod motors and rebuilt with blowers for mustangs on numerous occasions so I am not compeltely lost when it comes to motors for cars, just see quite a difference in these two strokes. Thanks in advance for y'alls help. Snipe and Rookie have already helped me in multiple forums without me even having to ask a single question. You guys rock. Thanks for all your time for all of us.:rofl:
WOW! Good info from both Snipe and Rookie. Now I have to ask the "stupid newbie question if you all dont mind." I recently bought a 2003 Utopia with the Mercury 240hp EFI M2. Not knowing when the last service was completed on the boat (dealer had no records, go figure) I was impelled to go ahead and do a 100 hour tune up on it. When I went to the Dealership I purchased the boat from (which sells both Yamaha and Sea Doo), I gave them the NGK plug number "NGK BPZ8HS-10" which was listed as the stock plug. They informed me that if I wanted a bit of more spark out of it to go with the "NGK BPZ8HN-10". Only difference I could see was the groove in the center of the plug. After hearing all of your thoughts on combustion and plugs heat rates, I am a little scared to keep running these plugs.
1. Should I toss them and get the correct plugs?
2. On the lake I am on (Lake Conroe, TX) most all the "on-water stations" carry only 93. Should I treck to my slip with 8 5 gallon tanks full of 87? Dont want to destroy my pistons yet!
3. I have used Quickleen on the last two tanks, does anyone recomend constantly using this or Sta-Bil every tank?
A little other information about the dealership that scared me. I asked for the fuel/water filter which I did not have the exact part number readily available. They said not to worry and gave me the complete wrong one. Maybe it is time to find another location for parts. I have torn down mod motors and rebuilt with blowers for mustangs on numerous occasions so I am not compeltely lost when it comes to motors for cars, just see quite a difference in these two strokes. Thanks in advance for y'alls help. Snipe and Rookie have already helped me in multiple forums without me even having to ask a single question. You guys rock. Thanks for all your time for all of us.:rofl:
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