TOPIC:

ed spangler wrote:
"Throttle Response" is better with Higher Compression, what do I mean? I have drag raced for more than 40+ years,while its true increased compression may not make huge Horsepower differences, when you launch a car with a 454 Chevy Big Block that has factory 8.5 compression vs an identical one that has 11.5 .CR...The "Throttle Response" and or "seat of the pants feeling" is quite different. I believe for lack of a better explanation the engine "responds" to increased throttle quicker Does that same apply to a motorcycle engine?? I think so.....just my opinion, only thing i have not heard anyone mention on this thread is whether milling head's and or block's affects Cam chain length? Valve train dynamics?? and does that in fact affect performance and reliability.?? Just my .02/ opinion and obviously all of us have one. 650ED your thoughts??

I cannot speak from personal experience since my KZ650 is stock, but considering the bike in question is starting out with 9.5:1 compression I doubt one could bump the compression up as much as you did on the big block Chevy simply by milling the head without causing problems for a street bike. On the big block, going from 8.5 to 11.5 was a 35% increase in the compression ratio. A 35% CR increase on the GPZ750 would result in a 12.85:1 compression ratio; that's pretty high for a street KZ engine. In fact, there may not even be enough spare meat on the head or enough space between the valves and pistons to shave that much off, but I don't know if that is true. If you in fact did that, I suppose the chain tensioner would take up the slack in the cam chain, but I believe cam timing would need attention. Ed

The deck height limits everything. Anything over 9.5/1 requires special fuel. For street applications Wiseco offers 9.25/1 pistons that can run on regular gas. I use premium but the gas today is far from when higher compression was the norm in the 70's. Nothing to be gained here.
Steve

i run a 10.25 to 1 CR 810c kit in my gpz 750 with the head milled .i do not know what the real compression ratio is until i cc the chamber.i run dyna s with 34 degree's of total advance. i too have to run special gas but i usually find it at most gas stations its called supper unleaded LOL

the real question is what would be the best head to build for the 810 cc kit motor?i have a choice of 84 gpz head -85 turbo 750 head or 81 kz 750 head .that would include mill deck to clean up surface , valve job , minor port clean up.i would like to send 1 out to larry cavanaugh but do not know which is the best to start with.

kawi810 wrote: the real question is what would be the best head to build for the 810 cc kit motor?i have a choice of 84 gpz head -85 turbo 750 head or 81 kz 750 head .that would include mill deck to clean up surface , valve job , minor port clean up.i would like to send 1 out to larry cavanaugh but do not know which is the best to start with.

A late head with the "bathtub" shape would be the obvious choice I think. Not sure, but I think these heads do not have provision for a mechanical tach so that may be something to consider though.

Regarding milling the head to increase compression, again, as stated earlier, there is not enough deck surface to do this with a 750 head. The valve seats are already VERY close to the deck surface, so you can not take off more than a minor amount without hitting the valve seats. This is an interesting discussion and all, but you can't mill a 750 head to increase compression so the subject is mute.

i am not to worried about milling the head just a clean up pass.more concerned about ports- how well they flow and chamber volume.which head would you choose to build? if you could choose any casting that bolted up to 750 block.i have all three options except a late 70's 650 head.which might be a choice for smaller cc chamber.this is my 84 gpz head see pic.what it comes down to is i want to send a head out for port work, valves,decking, which one ?

gpz 750 head

I want to have my head ceramic or powder coated. Is there a problem with having it baked at 500 degrees with the valves and guides left in it? I'd rather not disassemble everything if it's not going to harm it.

Ceramic coating a cylinder head may not be a good idea. Ceramic coatings can reduce the heat transfer which could cause the cylinder head to retain too much heat. Check it out carefully before making a decision. Ed

500 F seems crazy hot. I'd be afraid of the valve guides falling out and/or the valve stem seals being damaged.

Ok so I need a trick to compress the valve springs and remove the retainers since I don't have the fancy spring compressor tool.

go on ebay and pick up cheap one .if not c clamp and cut away socket .use magnet to pick out keepers.