TOPIC:

Nessism wrote:

Nebr_Rex wrote: Another option is to use three bond instead of a base gasket.


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Surely you jest. Right?

No I do not. Done it several times. ( KZ440 & KZ1000/1105 )
It takes the piston up to almost zero deck height with a Wiseco piston.
Why do you think they have different thickness copper base and head
gaskets.


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My '82 GPz750 has pretty fair cleaned up ports from the factory, so unless you are going to put in Mt Everest sized cams I don't think you'll pick up a lot there. I think the biggest bang for the buck would be a big bore kit - punch it up to 810cc. re-jet, and ride. One drawback - you'll be at the premium pump.

I question your expectations of the effect on horsepower if you mill the head or otherwise raise the compression ratio. Do you expect a meaningful boost in horsepower? If so, I fear you will be disappointed. While there are ways of boosting horsepower in KZ engines simply bumping up the compression ratio is not near the top of the list.

Consider the following -
The stock 1985 GpZ750 came from the factory with approximately 87 HP. It came with a compression ratio of 9.5:1. So let's say you went through the trouble, expense, and risk of milling the head enough to bump the compression ratio to 10.0:1. What would you expect the resulting HP to be? How about 88.21 HP Big deal? No; not even noticeable.

Ah, but wait - let's say you took a bigger bite and milled the head enough to bump the compression ratio to 10.5:1. What would you expect the resulting HP to be? How about 89.34 HP Big deal? No; still not even noticeable.

OK, doggone it you throw caution to the wind and chop off enough of the cylinder head to raise the compression ratio to 11.0:1. NOW, there should be some big gains; right? Wrong. That only yields 90.39 HP. Still not a noticeable bump above the original 87 HP, but with an 11.0:1 compression ratio you may find your engine is no longer the happy street engine it once was.

If you're looking for a good running, quick bike I would start by getting the engine to turn out the stock horsepower. If you find that is not enough, you can install a big-bore kit, have the cylinder head professionally tuned, add different cam/carbs, etc. If that does not yield enough power you can go full-tilt and turbo charge it along with more radical upgrades and get the turbo 750 up to a point where it can go 211 MPH (no joke). Just be sure to have the checkbook handy. Ed

What calculation did you run to come up with such specific horsepower numbers 650ed?

tachrev wrote: What calculation did you run to come up with such specific horsepower numbers 650ed?

I used the Wallace Racing HP calculator at:

www.wallaceracing.com/hp-cr-chg.php

Ed

tachrev wrote: What calculation did you run to come up with such specific horsepower numbers 650ed?

And I bet it was calculated for static compression.


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Could be. I can't say that the numbers in the calculator are exact for any particular KZ motor, but it gives a general indication that simply bumping compression does not yield huge HP gains. Ed

Fair enough.

Just a thort.... sometimes its not about hp numbers but about the sensation.
Dynos give a bunch of numbers but don't always log the change felt at the throttle. A bit more compression often gives a crisper FEEL through the lower to mid rpms but little acctual hp gain.
long ago we stripped and balanced a new gsx750 motor. Match ported and minor rejetting to suit. Made for the smoothest crippest loveliest gsx motor all that rode thought it had been hot rodded. Made a couple of extra hp but FELT like a lot more......
just saying there is more to tuning than outright hp.

EdwidjR wrote: Just a thort.... sometimes its not about hp numbers but about the sensation.
Dynos give a bunch of numbers but don't always log the change felt at the throttle. A bit more compression often gives a crisper FEEL through the lower to mid rpms but little acctual hp gain.
long ago we stripped and balanced a new gsx750 motor. Match ported and minor rejetting to suit. Made for the smoothest crippest loveliest gsx motor all that rode thought it had been hot rodded. Made a couple of extra hp but FELT like a lot more......
just saying there is more to tuning than outright hp.

"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??

If you mill the head is 100% sure you will have to get your cam gears slotted to adjust timing.

You can't go that far on the head.