Minimum dome size for pump gas - 787

[merlinbasenji]

Can anyone tell me the minimum dome size that can safely run on 93 octane pump gas? 96 XP / 787 carb engine, currently with stock head (145-150psi both cylinders) no engine mods. primarily intended for recreational use.

Sorry if this is already posted elsewhere, but I can't seem to find any info on dome size vs octane requirement either here or from head manufacturers.

Maybe someone could post a table showing engine/cc/octane for all Seadoo engines?

 

[Dans97challenger]

I am not sure on the answer you are looking for but you should be running 93 octane pump gas no matter what anyway even with the stock motor. All 2 stroke motors should be run on high octane pump gas. The highest you can get in your area anyway. Some can only get as high as 91 octane. I can get 93 though and I use nothing but that in the boat and in my motorcycle.

 

[12nvy]

Boy that sux!!!!!!!!
Our pump gas here in Oz is 98

 

[spunkyone]

98

y guys have leaded fuel down under or what??atriot:

 

[seadoosnipe]

Wrong answers you guys!....

There is some confusion going on here. Let me help.

The fuel requirements for the 787 cc engine is 87 octane, as stated in the fuel requirements from the shop manuals. The only engine that requires a higher octane is the 4-TEC and any 2 stroke designed to use racing fuels.

The 4-TEC, perse the 2006 RXT or RXP, have a minimum fuel requirement of 91 octane (RON + Mon)/2.
The 1999 XP limited with the 947cc 2 stroke, requires 87 octane. All other 2 strokes have the same fuel requirement as the 947, which is the largest of the Rotax 2 strokes.

If you burn a hotter fuel, your looking at the possibility of detonation problems. I doubt that you'd have any problems with an 89 octane but I wouldn't burn anything over 90 octane. :cheers:

 

[Dennis]

Hotter Fuel???

I gotta disagree with you on this one SEADOOSNIPE. The higher octane of the fuel the slower and cooler the burn and therefore LESS chance of detonation. Using higher octane fuel then recommended won't hurt the engine although it may burn too slow and therefore make the performance a little sluggish compared to the lower octane fuel that's recommended.
Debate anyone????? LOLO!!!!
DAWG

 

[Dans97challenger]

I agree with you 100% Dennis. The higher the octane the slower the burn for sure. I have never used anything lower than 91 octane in any motorsport vehicle I have ever owned.

 

[Dennis]

Higher Octane

Yea, I'm a believer in higher octane than is recommended in powersports vehicles and watercraft. Most people know that when they hear their car "pinging" (detonation) that it's not a good thing and have their vehicle looked at by a mechanic or go to higher octane fuel. The problem with motorcycles, quads, boats and jet skis' etc. is that you can't always tell they are detonating because of the enviroment they are being used in. The sounds of wind, water, sand, rocks and a high pulse rate make "pinging" inaudible and the last thing the rider is concerned about. Another reason I recommend higher octane fuel is that a jet ski or jet boat can easily pick up debris that clogs the cooling system and causes a overheat condition which can cause detonation. By the time the user hears the warning beeper (if it even works!!!) and shuts down the engine some detonation probably took place. Higher than recommended octane will keep the detonation, caused by the overheating, to a minimum and therefore avoiding possible engine damage. Lastly, I 'm not convinced that we always get the octane in the fuel that we think we're getting, especially at a marina!! Fuel at these pumps is not necessarily "fresh" and alot of times can be flat out "stale". 87 octane might actually only be 85. Therefore I always opt to be "safe rather than sorry" and use higher octane fuel than what is recommended.
DAWG

 

[jeffz0rz321]

higher octane means you need higher compression to detonate it properly. 145-150 is about right for 87. after that your wasting money on higher octane fuel if you have a lower compression ski. IMO.:cheers:

 

[seadoosnipe]

Octane?.....

:agree: with you on that one. But, like religion and politics, oil and fuel requirements are a stickler. Once someone chooses a brand of oil and fuel, it's like choosing the Bible or the Koran, there is no changing the learned impression of what the best requirements are..............so, I just leave it at that.:cheers:

 

[jeffz0rz321]

:hurray::hurray::hurray::hurray::hurray: well put. there, now everybodys happy. :rofl: