building ahrma middleweight superbike--need advice

You mentioned a 750 head... if I were you I would stick with the 650 head if you stuck using a stock bore size - the 750 while having bigger valves also has a bigger combustion chamber which is great with a 810 kit but not so great with stock pistons.
Your going to give away a lot of precious sealing area using the 750 head on top of the stock pistons.
What you should look at doing is deck the block to get the piston crown as close to the combustion chamber as possible (.035-.040") and use 750 valves sunk onto the stock seats in conjunction with a stage 2 port job which would require at least a .390" cam.
Your gonna want to make a Bondo cast of the piston crown and the combustion chamber at TDC to see what your working with.

Thank you. I'm wondering if the head that was on the 750 engine is actually a 650 head. It has the top idler bolt holes and appears to have the same diameter combustion chamber. I need to get some plex before I can measure the volume, but it looks identical. Valves are definitely larger.

What is the advantage to decking the block rather than the head?

I think for racing you end up decking both anyways... you end up doing both after porting and boring just to make everything square to each other so it happens anyways.
Decking the block intentionally will bring the piston up into the chamber slightly, but you have to be really careful at this point... some builders prefer Zero deck, some -.005" and some +.005".
It depends on that Bondo cast and how closely your piston crown matches the combustion chamber... ideally they should be offset around .040" all over.
The most critical thing is making sure those rods are up to snuff and won't cause any issues at high RPMs.

like injected says, good match of piston crown edge area is the most important thing when you bump up compression.

a bondo casting is a great idea but you could also use plasticine blobs, put them in the fridge and then slice them.

kzrider.com/forum/2-engine/410994-gpz750...=20&start=180#438549

0.8mm is a safe number to go with.

in all of my builds, it all starts form what pistons are available and deciding what CR to use. wouldnt go for more than 11.5 to begin with (on pump gas)

New to this type of web surfing,always before just looking.Could not stand it anymore have to throw my 2 cents.I currently race in ahrma,vintage superbike light and middle.sr500 yamaha and kz650.I will help if I can.Did not race in 2011 built a house racing and building don't go together.The kz is mostly stock,kz750 head,gpz cams,29mm carbs, zeypher swingarm.modern brakes,suspension,wheels,kerker.Bike is not fast enough to run with leaders.Turns like a battleship may have to much rake.Bought a clapped out spetre for ignition and electric tach.This bike came ebay 250.00,2010 placed 4th at dayton 2nd at vir.still has points,clutch cover has never been off.

Welcome! Thanks for posting!

What bikes pull away from you?

If you don't mind, would you send me a private message with your email? I'll send you one with mine - I'd love to get in contact with you and discuss.

Thanks!

Hello, ride-safe, and WELCOME to KZr forum!

We're glad you're here, and looking forward to your participation.

Good Fortune!

to begin with the reason i built a KZ650 was because ahrma threaten to combine light wt and middle wt so i took a look at the middle wt. There's a racer in Columbus, Ohio that won the championship on a KZ650 and it is very fast! Our championships are won on the interstate not the track. At Daytona a racer from Calf. always wins on a Ducati, second GS650 Suzuki and bunch of GPZ 550.

Cool! My buddy who is going through this with me is doing a 1982 Honda Cb450 Hawk so he'll be in lightweight.

Why were they going to consolidate lt. and middle?

Can I ask what wheel/brake/tire combo you chose and what was involved in making it happen?

hei welcome RS, not many road racers round here...

ever put it on a dyno?

some pics would be nice

italy, though not as big as the USA has also a distance problem, most people cant really do all races because of logisitcs. I am taking it race by race....

Yeah, I don't personally expect to make it to more than 1-3 races a year. 4 if I can really stretch the budget and vacation time.

I'm looking at the WERA vintage series as a secondary option to get some more track time in, but I'm not sure what the rules/regs differences will be.