Kz750 Cylinders - How big can you go?

I've read that the mid-80's GPZ900R rods can be used to get piston pins the same size as the 900/1000 machines.

Can you use 70+ mm pistons from the 900/1000 kits with new sleeves (specifically the low compression MTC pistons)? Or would custom pistons be necessary ($$$)?

How big can you go? How big is reasonable before things get a bit hairy?

I know there are a few members here who have tinkered with this in the past...what's the brain trust's consensus?

i think lorcan has a 900plus kit still! :laugh:

Wiseco use to make 890 pistons that you had to put bigger sleeves in that LA Sleeve sold. Bigger pistons well only give you so much power, it's when you start porting and bigger cams is when you really make some power.

Mark

The plan is to force feed it. I just wanted something "different", but wasn't sure what was reasonable/worth the $$$.

I see what you're getting at Dub! You get this figured out let me know, I'm very interested. I want to force feed one of these too, probably start next year.

Hey DD, I was just perusing the carillo catalog, and it seems they already have GPz750 rods designed. I don't know how much they would cost but it might be worth a try, I'm sure they could make them with a bigger wrist pin hole easily.

Also, according to the APE site, the KZ900/1000 piston pin is 17mm, which I was told is the same as the GPz750 Turbo. This means that with these GPZ900 rods, you might be able to use wiseco 810cc GPz750 turbo pistons.

I did some digging and it turns out the ZX900 big ends are the same diameter as the KZ650/750 ones. We will still need to either measure or find out from someone who knows if the rest of the dimensions are correct.

I had found a post saying that the '84 and '85 Gpz900R rods were the same big end as the 650/750, same small end as the 900/1000, and 4mm longer than the 650/750. Not sure I what effect the extra length would have, but they also said that they were heavier than the smaller motor's rods. This would leave me with the impression I could use the pistons from the bigger motors if I could get a sleeve from a Kz1000 installed - that's what I'm not sure of. Are the Kz1000 sleeves too big to be installed in the 750 cylinders?

Be sure to check pin height.

Lorcan does have a 900cc block, but it was a custom billet block. Not cheap, and not many places would be willing to make you one like it.

The turbo guys had a 880cc kit made up, it included custom sleeves and they claimed the sleeve thickness was actually greater than the stock 750 sleeves after being borred to 810. The idea was larger pistons and more support.

Another gent on the turbo forums has a 902cc block using pistons 1mm larger than the 880 kit, however he had to bore through the block in places to fit the larger sleeves, making that motor useless for the street (the aluminum block cools the steel sleeves, if you bore through it you loose cooling and develop hot spots...alright for a quarter mile at a time but not good for a weekend road trip).

I personally want to have a 880 kit made up for a NA motor using piston crowns that would match the 84 gpz head (bathtub shaped combustion chambers). LA sleeves made the sleeves for the turbo guys and it would be easy enough for them to make some more up. However the turbo kit had a stepped sleeve (so you wouldn't need to bore the upper case) and they were prone to leaking. I would rather have a traditional sleeve and just get the case borred to fit it. That with some decent head work would make a screaming motor.

I have a set of carrillo gpz rods sitting on my shelf waiting for me to get on with my motor and install them. They cost me $300 used off ebay then another $300 to have the small ends re-bushed and the rods shot peened, carrillo said after that treatment they are just like new. I still need to get the 6 speed trans back cut and I want to see about adapting a 2005+ zx6 clutch basket.... it will probably never all get done but it is nice to chip away at it slowly!

Sounds like these rods wont work. 4mm longer is a huge difference. I'd say we keep trying to find GPz750 turbo rods or we could investigate the carillo option.

Edit: I just emailed carillo, hopefully they'll get back to me. For the price of this build I'd be willing to buy aftermarket rods if they weren't crazy expensive.

PS - I've been investigating turbos all day, I think a GT20 would be the best bet for a 810cc engine running moderate to high boost. Lorcan runs a GT22 I believe, so for a street bike a GT20 or even a GT15 would be good I think.

Hardrock, thats great, I look forward to seeing what you come up with. We're all in this together, getting some crazy 650/750's built will be much easier with us all collaborating on info.