Lites class ski setup

[Half flip95]

You have a loss of 14.73% air flow capacity, a gain of 12% air velocity, and increased backpressure of 17psi. Multiply by the Yamaha efficiency coefficient of .028, then round to the nearest whole number and you get 50mph.

 

[Jhucke]

You have a loss of 14.73% air flow capacity, a gain of 12% air velocity, and increased backpressure of 17psi. Multiply by the Yamaha efficiency coefficient of .028, then round to the nearest whole number and you get 50mph.

I think you mean 50.1. In all seriousness though, I was just wondering how much faster I might expect a 760 cylinder compared to 701.

 

[37]

For the cost of an OEM 760 cylinder, pistons and head, you could spend that in fuel and practice time and be exponentially faster. Concentrate on practicing your starts and making your ski accelerate hard enough to get out front, then have the physical stamina to stay out front.

 

[Jhucke]

physical stamina to stay out front.

Major key, thanks!

 

[user_error]

What did you end up going to jetting wise on a 760? I'm at 80p 135m 2.0n/s 25psi popoff. Seems alright but almost like it could be better

 

[Vortex]

Q.bosshe was killing it on a 701 against 760s and big bore sxrs in lites class.

The whole class is based on an 85hp estimated output to balance everything across the manufacturers.
Wet pipe over a 760 seems to balance it out better imo. 52mph with the r&d wet pipe on a 701 61x. That's right on line with a big bore 830cc sxr top speed.

 

[N3vrSat1sfied]

Any inputs/updates for the original post?

 

[user_error]

The rulebook has the specific gasket info, and I can elaborate how I did my cooling lines on the sxr. The sj is more simple and all I did for water lines was remove the line between the head and oem muffler and put a little cap on the two nipples. I'm sure you could put a restrictor in place somewhere but it doesn't seem as necessary as on an sxr.

I have always used exhaust reducers on sxr's and I see that now they are available for superjets so I might have to try one

 

[Christian_83]

A few of my riding buddies are racing Stock lite on superjets. They put the OEM Yam 760 cylinder on, but with a 701 superjet head on (i told them this is not right with squish and comb area) BUT, is it legal to put a 701 head on a 760 cylinder regarding IJSBA regulations.
My point is, the engine is not homogenised with this cylinder/head combo ?

 

[alwaystandingup]

A few of my riding buddies are racing Stock lite on superjets. They put the OEM Yam 760 cylinder on, but with a 701 superjet head on (i told them this is not right with squish and comb area) BUT, is it legal to put a 701 head on a 760 cylinder regarding IJSBA regulations.
My point is, the engine is not homogenised with this cylinder/head combo ?

Yes it is legal, there is a special part in there stating that if the ski is under a certain cc that a different cylinder from the same manufacturer may be used to achieve more cc's etc. (Obviously not exact verbiage)

 

[Christian_83]

Yes im aware of that. My question is
is it ONLY legal to run the OEM 760cc cylinder with the OEM 760 cylinder head
or is it legal to run the OEM 760cc cylinder with a OEM 701cc cylinderhead?

 

[Jhucke]

Yes im aware of that. My question is
is it ONLY legal to run the OEM 760cc cylinder with the OEM 760 cylinder head
or is it legal to run the OEM 760cc cylinder with a OEM 701cc cylinderhead?

I would imagine you would have a hard time maintaining the use of the stock pipe without the 61x head, so you are forced to.

 

[alwaystandingup]

Yes im aware of that. My question is
is it ONLY legal to run the OEM 760cc cylinder with the OEM 760 cylinder head
or is it legal to run the OEM 760cc cylinder with a OEM 701cc cylinderhead?

Yes it is legal to use the 701 head, the pipe will not bolt up to the 760 head. Almost every superjet that has won lites at havasu and tech'd which is a long list has ran a 760 cyl with a 701 head

 

[Christian_83]

yeah okai, but im just a little surprised that its legal, because the engine is not homogenised this way, and its a mismatch with dome vs cylinder But thanks for the answer

 

[Big Kahuna]

I would be more concerned with the 701 head on the 760 cylinder. Need to check squish.

 

[alwaystandingup]

It's not like this is a new thing, been that way since 2008. I've ran it for multiple years with zero problems, yes the squish band isn't ideal but it works, and what happens when you put an 84mm piston to a 701 dome? You get an increase in cylinder pressure.

And no it's not a homogulated motor combo but there is a specific addendum in the lites rules for the use of this setup on a superjet in the rulebook.

 

[Big Kahuna]

It's not like this is a new thing, been that way since 2008. I've ran it for multiple years with zero problems, yes the squish band isn't ideal but it works, and what happens when you put an 84mm piston to a 701 dome? You get an increase in cylinder pressure.

And no it's not a homogulated motor combo but there is a specific addendum in the lites rules for the use of this setup on a superjet in the rulebook.

I dont put an 84mm piston under an 81-83mm dome.

 

[alwaystandingup]

I dont put an 84mm piston under an 81-83mm dome.

I was referring to a lites class superjet build, as in a 84mm piston to a 701 head/dome

Obviously if you where allowed to run a head, you would run 760 domes, again it's not an ideal squish band but it works

 

[TehXshizzit]

So what jet specs see people running in their lites boat? I'm thinking up going up. Maybe 140 main, 80 pilot 2.0NS at 30 psi?

 

[vcolf]

If anyone is looking for stock 760 cylinder for a lites build, pm me. I have an extra one I no longer need .


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