Kz750 Cylinders - How big can you go?

but could you move the pin up a decent amount then use a thinner spacer under the cylinder?

Why would you want to? This seems like too much work just to gain a few more cc's.

I'm just looking for some brainstorming...just like we got going on!

I was looking for alternatives for a larger displacement. So far the turbo rods with the 810cc kit for the 750 turbo seems to be the best route, but I wanted to see what we could come up with otherwise.

The idea of using some off the shelf parts to try to get over 810cc appealed to me, but it looks like it will require custom sleeves/pistons to go over 810cc. Is that the general consensus?

I was really hoping Steell would jump in on this one as he seems to have a wealth of information regarding these 650/750 motors.

I know there were 880cc kits built at some point, can someone chime in about that?

T_Dub wrote:

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.

No the turbo has 16mm pins. The NA 750 has 15mm.

My 904 block has 17mm pins, custom rods, 73mm high compression Z1000 pistons and is designed to run on methanol.

The 880cc kit was sold by Mike Chestnut of HPU. To date, the 810cc kit is more reliable and faster

This is my KZ750 racebike. It has an 810 kit installed. The motor was built and maintained by Pete Hockenstad of HOK-N-Block racing. The secret to this motor is in the extensive head work done by Pete. I just finished racing the AHRMA national in Salt Lake City with it and I "spanked" the 1025's and 1040's with it. The motor redlines at 11,500 rpm's. It is very reliable and produces 100+ hp at the rear wheel.

ducati7044 wrote:

This is my KZ750 racebike. It has an 810 kit installed. The motor was built and maintained by Pete Hockenstad of HOK-N-Block racing. The secret to this motor is in the extensive head work done by Pete. I just finished racing the AHRMA national in Salt Lake City with it and I "spanked" the 1025's and 1040's with it. The motor redlines at 11,500 rpm's. It is very reliable and produces 100+ hp at the rear wheel.

Hei duc,
nice bike! I am currently building a GPZ750/810 vintage road racer and I would love to hear more about your motor. Definitely planning to go with the wiseco 810 kit.

What CR are you running? Cams? Carbs? Any info will be appreciated.

Ciao
TG

I think the physical limit on the bore spacing is 73mm and with a stock stoke that = 904cc.

I am running JE 70mm = 831cc, but those are custom and I believe they are in the $1200 range now... prices for that stuff shot up in the last couple of years.

Recently I had a block outfitted for that 70mm setup and it cost $500 to get liners machined, installed, bore/honed. The majority of the cost is in material removal.

Custom liners will cost somewhere around $500 unless you can scrounge 900/1000 liners but they will need machining to prep them ($200)

Its more cost effective to stay with 810cc, I just happened to have the 830 kit sitting around and my buddy said to replace those was over $500, so I used them... ended up costing around $300 more than just getting a bore job done.

If you were into racing I could see spending the $2K, but for a street motor I don't think it makes much sense unless you have the stuff already.

That big bore also requires some cylinder head work, a set of cams, and some bigger carbs to work properly... so there is another $1K minimum... and that's not including the tranny and clutch work that might be required also.

At that price point you could buy a used 900 with a 1075 kit and call it a day !

Have you concidered plating the cylinder with Nikasil like the current sport bikes are?
Would need to fill in where the lip at the top of the bore where the sleeve sits.
Just another option to think about.

Injected, you're bang on with cost. My build didn't feature much more other than engine work, and I was well over $3000 when all was said and done. Thats not including the cylinders, valve springs and cams, which I already had before I started keeping track.

Nebr_Rex wrote:

Have you concidered plating the cylinder with Nikasil like the current sport bikes are?
Would need to fill in where the lip at the top of the bore where the sleeve sits.
Just another option to think about.

there's a racer in the sohc4 forum that did such a conversion in a CB750, I think he had ally liners made with a specific alloy to accept the nikasil plating.

TG