Andrew Cams Question...

Yes, I've looked at that a few times. Been researching quite a bit and then posting here when I can't find answers. Not much more than this in there about heads other than some stuff about milling them:

"The 82 GPz750 has a combustion chamber volume of 24.9 cc which is very good. The 83-85 GPz750 have chamber volumes of 25.9 cc . The Kz750 H 24.8cc and Kz750 L 25.3 cc. You can easily switch these heads between motors."

Franklin wrote:

Still looking into an '82 GPZ head that's for sale. I was wrong about how the combustion chamber looks. Seems the '82 will look very similar to the '83+. Here's a shot from a Cycle World article back in '82. I'm still wondering how the later '83+ heads flow better than the '82 head. '82 was cleaned up at the factory and has higher compression. Trying to decide if I should buy the '82 head or hold off and look for one from '83+.

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Where did you see the 83 GPZ head flows better than the 82 head? I doubt you would find flow bench numbers.

Why do you think you need to buy a cylinder head? I looked at your project thread, as far as I could see you have not turned over the engine.

This is the kind of thing I've found in a few places. Just that '83-'85 flow better but without explaining why and without including '82. This is just a post from another thread here:

"The turbo and N/A head's are the same other then the turbo head has a temp. senser. Turbo cam's are stock KZ650 cam's. 83-84 GPz head is the best 750 head flow wise."

I mentioned previously in this thread my recent bikes have been 175HP or so. First step for this KZ is to get it running but eventually I'll want to get more power out of it. Have some extra money to spend now so looking at collecting parts. Figure they'll just get harder to find as time goes by.
 

The later GPZ heads flow more because the ports are bigger.
I had a in depth discussion about the GPZ 750 head with our local porting guru who has since passed away (RIP Larry)
From what he told me there is not much porting to do on that head, they are near the limit stock as the factory gave them huge ports (actually too big) and the valve size is almost as big as you can go without having to install bigger seats (not recommended) He said the only thing they could benefit from is bigger cams.
The GPZ range bikes were designed to be factory racer so they would qualify for stock Superbike racing categories in the US.

Thanks for that! So here's how I understand it:

-Heads were reworked for the '82 GPZ750. Combustion chamber modified and ports cleaned up at factory. Combustion chamber only slightly larger than KZ750.
-GPZ heads were reworked again for '83-85. No longer cleaned up by factory but ports enlarged to flow better. Combustion chamber larger than the previous two versions.
-Valve size the same for all of them (although there is some confusion out there about this).
-Cams for KZ750 and '82 GPZ are the same except '82 doesn't have the tach gear.
-Cams for '83-85 GPZ are hotter with more lift and duration (no tach gear).

So in the end better to see if I can find an '83-85 head with original cams still in it. If I get an '82 head I'd want to replace the cams with some from '83-85. Or the Andrews cams which were the original point of this thread!

So I feel like I've got heads and cams pretty well understood. (Enough to choose what to buy at least.) Now I've found two options for a big bore kit: Wiseco and one from a Cruisin Image website.

I know Wiseco are forged and the best way to go but will cost close to $700. The Cruisin Image are cast and made in Taiwan for about $200.

I've seen the Cruisin Image ones mentioned on this site but not much detail about them. I'm wondering if they can handle near 100 horsepower and if they are reliable enough for the long term. Any thoughts?

My opinion is that if you are targeting 100 hp, go Wiseco.  That's a huge price difference, though.  I have a Wiseco 800 kit sitting on the shelf, purchased a few years back for less than $400, so the current pricing is shocking.  

As far as heads, cams, etc, I don't think it matters a whole lot, in the real world.  One of my favorite 750 builds on this site is Daftrusty's.  He used the Cruzin image piston kit, installed a 6 speed wide ratio transmission, ZX7 sprag type starter clutch, ZX600 carbs, and heavens know what else.  An absolutely immaculate build, with real world improvements.  You might want to look up his thread. 

Thanks, I found that thread, it was excellent! Good info about the Cruisin Image pistons. They seem reliable enough so I'm tempted but thinking better to spring for the Wiseco. They have higher compression so think it's worth the cost for me.

Franklin wrote:

So I feel like I've got heads and cams pretty well understood. (Enough to choose what to buy at least.) Now I've found two options for a big bore kit: Wiseco and one from a Cruisin Image website.

I know Wiseco are forged and the best way to go but will cost close to $700. The Cruisin Image are cast and made in Taiwan for about $200.

I've seen the Cruisin Image ones mentioned on this site but not much detail about them. I'm wondering if they can handle near 100 horsepower and if they are reliable enough for the long term. Any thoughts?


 

With the changes you were talking about you would be around 80HP at the wheel, and that would be with the Wiseco kit. There is only a slightly CFM increase using the GPZ head over your current head. +100 HP is where the Superbike teams were, race bike vs street bike.

If you really want to make maximum power you need to get some real carbs and cams in there.

 

My mistake was buying the Wiseco kit from Z1E and not from APE. They would have bored my spare block for free. 
Steve

Do you know if APE will still bore the block free? I just looked at their website and didn't see that mentioned.

I can find the kit a little cheaper elsewhere but would go with APE if they bore the block free.

If you plan on getting 100 horsepower out of a Kz750 motor, you better find yourself some stronger, better con rods. Just remember your motor is only as good as its weakest link. In the 750 motor I built for road racing I used some shot peened and polished GPz or Turbo 750 rods. I don't remember for sure anymore. Or if you could find yourself some Carrillo rods that would make your bottom end damn near bulletproof!!!! It really sucks when you spend all that money in a motor and it puts a rod through your cases!!!!