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Just like it says i have a 78-79 KZ750H 4 banger engine sitting on the shelf thats going in a ATV project im working on, I need to find a shim to lower compression or a set of low compression pistons, I have a MS II fuel injection system and 2 IHI RHB5 turbo's going on the engine and dont really want to pop the head gasket or worse.. any info would be greatly appreciated.

its probably allready pretty close to 8:1 stock, aint it? i dont know how much boost youll be able to get away with with the stock cast pistons but id atleast want to pop the head off and check things out before you start pumping it up too far,have you run a leakdown test on the motor yet?

1980 model year was the first year for the 750 fours, the only 750's in 78-79 were 750 twins.

A set of GPz750 Turbo pistons would work, either stock or the Wiseco 810 kit for the 750 Turbo.

Search the site for 750 turbo and check out Lorcan's GPz750 Turbo, 234 RWHP with a single turbo (and 211 mph). You sure you need the complications of two turbos?

You might want to take a look at www.750turbo.com

Post edited by: steell, at: 2006/11/29 07:06

Ok thanks for clearing the year issue up..i wasent sure... As for boost the stock cast pistons wont have a problem with 5psi of boost..the reason im useing a set of twin turbo's is to keep lag down,i dont want to start making boost @ 9k rpm like some of the other turbo kawa's that iv seen. and yes i have done a leakdown on the engine, shes tight as a drum as far as i can see, only 3k miles on it.....

Kool wrote:

Ok thanks for clearing the year issue up..i wasent sure... As for boost the stock cast pistons wont have a problem with 5psi of boost..the reason im useing a set of twin turbo's is to keep lag down,i dont want to start making boost @ 9k rpm like some of the other turbo kawa's that iv seen. and yes i have done a leakdown on the engine, shes tight as a drum as far as i can see, only 3k miles on it.....

cool;)

haha you've got a lot to learn about turbos..if you think two will help you make boost down low.. you had better stick to a single turbo, run it on alcohol and pig rich to keep yourself from blowing it up....

Im a IHI rebuilder and work with turbo's most every day, due to useing the 2 smaller RHB5 turbo's inplace with my lag controller and bypass system they will net me less lag then a single T3 or G20 turbo, 5psi wont even come close to hurting that engine after i lower compression a bit. Now i need to find a set of stock GPZ 750 pistons, any one here got a set for sale?

also im looking for a turbo Kawasaki stock timing map to base my fuel management systems timing map off of. Thanks

Just to clarify, you want the stock GPZ750 Turbo pistons, the standard GPz750 pistons are around 9.5:1

Here's another 750 Turbo site for you (someday I'll own one ) Horsepower Unlimited

Thanks mate thats a nice little site, and yes im looking for the stock turbo 750 pistons.

Do you have compressor maps for these turbo's? I would speculate that just one of these IHI's your talking about will be more than enough turbo for a 750 at 5 psi....A t3 is just a monster. Why you would even consider putting that on a 750cc 2 valve motor is beyond me...thats about the size of the turbo on my talon with 2000cc's. a T3 is commonly used on huyabusa's that are set on kill to make upwards of 300 hp.

I would also watch out about saying you won't break anything at 5psi with low compression...especially runnin cast pistons...if it goes lean under boost, it will destroy it's self. it will burn pistons, crack ringlands, blow head gaskets and worse yet pound rod bearings out of it.

Just becuase you "rebuild" IHI turbos dosn't mean you have a clue about desgining a useable turbo system. Any clown can rebuild a turbo...it's a shaft a couple bearings and some seals...how hard can that be?

I'm not trying to say I am god of all things turbo, but I have been around forced induction cars a long time, and i have a realativly good idea of what it takes...it's not like i have building a turbo kl250, a chassis dyno, or a flow bench or anything...haha

i'll post pics of the turbo 250 on my home built dyno soon as i get homr for xmas break...

Listen, Ill say this 1 time, I rebuilt turbo's because i work at a speed shop as there machinist and custom fab guy. Im 43 years old with over 30 years working on race engines. A T3 isent "massive" its a smaller turbo, when compared to a IHI RHB3 yes it is massive but 750cc isent exactly small in the eye's of a turbo that was built for a 1100~2200cc engine making a meager 3 to 7 psi in a varying rpm range,depending on intercooled or not, Iv built small engine dyno's in a few flavors myself..nothing special there iv seen 17yo kids build simple fluid brake dyno's for karting engines, And NO for the last time 5psi will not hurt this engine, Its fuel injected with a standalone FMS and im running a wideband O2 sensor, id know well b4 the point of destroying the engine if i was running lean. Dont reply to my thread if your going to act like a ass. The COP of this turbo is a bit higher then most turbo's thats why i chose it, that and iv since replaced the thrust bushings with ceramic bearings, as to rebuilding a turbo, yes it is hard, we dont do kit jobs, we balance,machine, and refit every part after the center chunk is machined.