Twin Carb Transplant?

[Brant]

Hey out there! I have a 94 GTS with a 580 single carb. If I could find a twin carb set up complete with intake and cables would this be a worthwhile addition to my machine? Would I notice any significant power gain or just more fuel consumption. Are there any differences in engine itself or would it just bolt on? This machine isn't bad but I'd like a little more. Thanks...BRANT

 

[Dr Honda]

Not really. For the effort, it will only net you a few HP. Also, it makes tuning harder.

Just an FYI... I have a single carb Si... and I have all the parts sitting in my shop to do a swap (so it's free) but I won't do it.

If you have a single SBN 38... that's plenty for that engine.

 

[Brant]

Thanks for the reply Tony! I've heard similar things from some friends about snowmobiles. I somehow don't want to believe! The twin carbs just look way more impressive!!! I guess I'll have to wait till April and put both machines out for a run side by side......is it April yet????....Yet???.......Hmmmm...

 

[Dr Honda]

OK... if you are going to do it anyway... why ask?

It will make a difference, but not enough to cover the price tag of the parts.

Also... one thing to remember... your engine's top speed is set with a rev limiter, so with twin carbs... all you may accomplish is bouncing off of it more.

Finally... twin carbs on a little SeaDoo engine will effect the bottom acceleration. From a stand still, you will get a huge vacuum drop if you open the throttle quickly, and in turn, creating a low RPM stumble that is hard to tune out. Because of that... I would recommend raising your compression a little to help. But, if it's an old engine... it may be hard on the crank bearings.

As far as the "It looks cool" comment... I don't know about you... but I ride my skis with the seats on, and the engines hidden.


OK... I'm not trying to be a jack-off... but if more than one person has told you that it's not a big improvement... then you should listen. The money would be better spent on a good impeller, a high compression head, or a tuned pipe.

BUT... if you do the swap... please post up some pics, and ask questions... we will be here to help you get it tuned again. :cheers:

 

[Brant]

QUOTE:As far as the "It looks cool" comment... I don't know about you... but I ride my skis with the seats on, and the engines hidden.:rofl:

The thought has now passed!!! .....Tuned PIPE???:bigear:

When I bought this machine the ad said it had a tuned pipe What does that involve and how can I tell?......

 

[Dr Honda]

The thought has now passed!!! .....Tuned PIPE???:bigear:

When I bought this machine the ad said it had a tuned pipe What does that involve and how can I tell?......

Post a pic of your engine, and I will tell you.

The stock pipe is purple... and they are pretty good... but an aftermarket pipe can bring in huge mid RPM gains, and 10 to 15 HP up top.

For the older engines... a pipe can be had on eBay for $200 or less.

 

[Brant]

Here are a few shots of the pipe on my GTS. It's a Bombardier pipe could it be tuned? The GTX pipe looks the same but it is purple and seems to be a little louder.

 

[Dr Honda]

That's a stock pipe.

As far as tuning... it could be done, but you will need to cut the pipe, and weld it back together. Since you can't change the diameter of the expiation chamber... you would cut it at it's fattest part...change the length, and weld. I have done this to smaller pipes, but never to a a SeaDoo pipe, so I can't tell you what length to use.


BUT... if you can find a Coffman, or better yet... a "Factory Pipe" for your ski... it will perform better. Factory pipe uses an external box to control the water injection, and raises the rev limiter.

 

[Brant]

Wow! That sounds like more work than installing some carbs! I have a mig welder but not aluminum capabilities. So what does adding a few inches to the pipe do that gives such an increase in performance? It makes me wonder what the down side is. Less fuel economy etc...You would think that the manufacturer would have tried to milk that performance gain! I've been looking on everyones favorite auction site and can't find anything so far.

 

[Dr Honda]

No... Manufactures don't look for every last drop of power. Their goal is to make something that performs well, and be used in many regions, and is reliable.

a 720 engine from the factory makes 85 hp, but with only adding a "Factory Pipe" they have gotten over 100 hp with no other mods.

The technical on a tuned pipe is too evolved... but changing the diameter, and length will affect the pressure wave leaving the engine, and in turn, forcing the cyl with air and fuel. (Kind of like a supercharger)

Without doing any real tests... I can say that the stock pipe is short and fat. This gives a good mid punch, and an overall good performance. A longer pipe will give you gains in the upper RPM's. (top speed) Controlling the injected water can help bring back the mid punch, and letting the pipe dry out, will give you top.