SX/SXi/SXi Pro 85mm bore motor?

[Rossar]

Hi,

I'm looking to improve the power of my freestyle Kawasaki 750sx. (small pin)
http://www.x-h2o.com/index.php?threads/kawasaki-750sx-freestyle-build.152825/

I'm trying to keep the cost down, so lets forget those Dasa motors for now.
Eventho I would like to be able to flatwater flip with it.

Is there improvement to expect if I re-sleeve the cylinders and bore those to 85mm?
This could be done "easily" with LA sleeves and wiseco pistons.
This way the motor would be 840cc.
Is it going to be enough if I do that with 200psi head and dual 46mm mikunis?
Probably nobody knows, but if there is someone with similar setup I would like to get some feedback.

Also there is couple different sleeves to choose from.
Difference between those is port timing. If I have understood right, small pin port timing is the best for freestyle? So I should go KA-5166H sleeve? http://www.lasleeve.com/downloads/2013-Catalog-Watercraft-Section.pdf

This way I could get this done with 600$ on parts + re-sleeving work.

I've tried to find used 800sxr cylinders with bad luck, that would also do the trick.

I know GroupK would do this for me, but I'm from Finland so its abit hard.

Or is there some other sollution that I haven't found?

 

[theVetteman3]

The extra hp gained from going to an 85mm bore will be negligible. The main factor according to reputable tuners will be a good freestyle port job. That has way more impact on low end than bore. A bore increase will give you a small hp increase. Porting and changing the port timing of the engine will change its power band. You've already got the sx cylinder which is gold for low end. Tim Z at Z Force has told me the 750sx cylinder, ported for low end, will have more low end than a sxr cylinder, with the extra displacement, ported for low end.

Here's a really great set up which we run on my brother's sxi pro. Only reason he (and I) went with 800s is because they're newer engines and we didn't have the sx cylinder. A well set up sx cyl should have even more low end.

800 freestyle ported cylinder
93 octane domes/ compression
oem sxr mikunis
750 factory pipe limited pipe and head pipe, small head pipe dia is better for low end
Advent T3
VForce 3 reeds
C-75 big hub swirl impeller (matched to your weight, we're 155#-170 and run a 14-19)
Big nozzle (80mm+), freestyle pump cone

And a few handling must haves, to make the ski into more of a freestyle ski:
Blowsion destroyer tubbies
Take weight off the ski: Lightweight hood is about -10lbs, removing oem bumpers is probably another 5-10
D cut stock rideplate

Once all those mods are done, you could spend a few extra bucks for better carbs and bore the engine out for more overall hp. But only then.

With those mods you can give a SJ a run for its money. With those mods it makes his bone stock 95 SJ seem like a tank with no potential for freestyle, and it has more low end than one of our friends 144mm pump swapped factory piped FX1s. His ski actually feels like a more hyper-sensitive 2008+ sj with its carving and maneuverability. I rode them back to back the same day. Our square nose was not even in the ballpark. It was a tank. And that's saying something, because as they are stock, pros have absolutely no low end!!

Hope that helps!

 

[Rossar]

Thanks for the info..
I think that I could keep the "good" port timing by choosing the small pin sleeves. (KA-5166H sleeve)
But you think that I would not get much improvement on 840cc?
What should I do for more power if not go big bore? My hull is pretty much done , so now I would need improvement on motor+pump. Hull feels great, stock Yamis feels like battleships after this.
Anyone has a suggestions?

 

[sxipro02]

Im running a big pin 750 bored to 800, I didnt feel any power gains going to the larger cc until I raised the compression and advanced the timing. Im running the 98-03 ignition with a R&D advance plate with no issues. I noticed the most gain when I switched from a stock pump, bored nossle, stubby cone and 9/17 to a blueprinted pump, TBM stuffer with short cone and a 13/18 5mm setback and 650sx nossle. It really helped make use of the power the motor is making. long story short, Id keep the small pin cyl with a fresh bore to whatever size you need to clean it up and just raise the compression and advance the timing (or AM ignition, I like the stock for reliability) sounds like your carbs are more than enough to get you going great on whatever power your motor is making.

 

[theVetteman3]

Ha yea squares in particular do feel like battleships. It really has me questioning the whole "buy a superjet" mafia. I guess if you're really big and want something super stable, like for surf, then perhaps its good. Ours is great for beginners who have a hard time balancing. Our good friends just bought a very clean 92 750sx. That thing feels so light and nimble compared to our 95 SJ. All that said I rode a 2013 sj and the ski it felt closest to was my brothers pro with tubbies. That sort of nimbleness. Totally different ski.

If you are really bent on going to more ccs, then yea you can resleeve, but thats a big chunk of change. In my mind there are bigger bangs for your buck, such as pump mods, advent, ect.. other parts I listed which you don't have. Oh and if your cylinder isn't ported, I'd absolutely spend the money on porting and not the resleeve and bore like I said.

 

[yz125514]

I've have a couple sxi's one with 86mm and other has 85mm pistons in the 750 cylinders. These take a lot more work/money but give you the option to run a lower exhaust port depending on which cylinder casting you have. You must also use a non o-ring head because the top flange of the sleeve will start to rust over time and cause sealing problems.

 

[jetman624]

You must also use a non o-ring head because the top flange of the sleeve will start to rust over time and cause sealing problems.

Can you go into more detail on that-- I am not sure I am following exactly what you are saying. What does an o-ring head have to do with the "top flange of the sleeve" starting to rust?

 

[yz125514]

The stock cylinders have cast in sleeves which leaves an aluminum surface on top which is ideal for o-ring heads in my opinion at least. Once the stock sleeve is bored out to except the big bore sleeve the top of the cylinder has to be counter bored for the top flange on the sleeve. The O.D. of the flange is larger than the diameter on the inner O-rings so over time the outside edge of the flange starts to rust from the water and will start to work its way towards the o-ring. This problem does not happen over night but after a season or two of riding more or less. I guess I should have said that I would recommend using a modified stock head with big bore head gasket vs the aftermarket o-ring heads on the 750 cylinders at least. There might be some other modifications that could be made to prevent this from happening if you really want to use a o-ring head but both my motors are already done, too late now.

 

[jetman624]

The stock cylinders have cast in sleeves which leaves an aluminum surface on top which is ideal for o-ring heads in my opinion at least. Once the stock sleeve is bored out to except the big bore sleeve the top of the cylinder has to be counter bored for the top flange on the sleeve. The O.D. of the flange is larger than the diameter on the inner O-rings so over time the outside edge of the flange starts to rust from the water and will start to work its way towards the o-ring. This problem does not happen over night but after a season or two of riding more or less. I guess I should have said that I would recommend using a modified stock head with big bore head gasket vs the aftermarket o-ring heads on the 750 cylinders at least. There might be some other modifications that could be made to prevent this from happening if you really want to use a o-ring head but both my motors are already done, too late now.

I understand, and that makes sense. Do you think some silicone spray around the sleeve would help slow it down? Or is it just something you might want to pull your head for a couple times a season and make sure any rust isn't getting a good foothold in that area-- make sure it doesn't get any further than surface rust...

 

[yz125514]

I'm not sure if coating it would help or not but I did polish the top flange surface up after it had rusted and seemed to work but I got tired of messing with it. Of coarse I was not really watching it close enough to know exactly when the this started to happen but I'm sure some regular inspection/cleaning may keep the surface smooth and flat.

 

[baller11111]

I've have a couple sxi's one with 86mm and other has 85mm pistons in the 750 cylinders. These take a lot more work/money but give you the option to run a lower exhaust port depending on which cylinder casting you have. You must also use a non o-ring head because the top flange of the sleeve will start to rust over time and cause sealing problems.

can you point me to a non o ring head? thx