10.25 on the street?

Greetings. Its been a while... I want to de-mothball my KZ1000, and rebuild the top end that it needs. I wanted to ask some advice, though. First- can I run 10.25 CR on the street, with pump gas (Wiseco 1075 kit)? I am at 5200ft elevation, if that helps. Also- I have milled my head- and I read somewhere that I can't use a 10.25CR/1075cc kit because of interference. Does anyone here have firsthand knowledge of this? Naturally, I don't have a heap of cash for this project, so suggestions are appreciated. The bike will be ridden on the street in a normal, adult manner, not like the old days... Thanks

pump gas is fine for a 10.25:1 but since we dont know how much u milled the head that is a tough 1 ? it will have higher comp.
i would suggest that u buy the pistons and then measure the v to p clearance. if it is not enough then buy a head. since u said u need to redo the head anyways it wount cost much to buy a stocker.
u could also add a thicker base gasket. if u new how much was taken off the head.
i run a thicker aluminum gasket in my kz1200.

Ive run it in my 1105/900 in Billings Mt @3700 ft for 31 years with no problems, I just use what passes for premium gas in it. A stocker will run fine on regular. Maybe the big motor will too, Ive just never tried it.

The higher the altitude the higher the compression you can run. I run 11.25:1 in a 1150 motor in Chicago, with no problems at all. Cams will also make a big difference.The higher the duration and greater the overlap the higher the compression you can run.

Was the head surfaced or was it milled .100, makes a big difference? If it was a blown head gasket or something Id guess they just skimmed a few thosandths off of it, We have no way to help you without all the info. If you want to know if you can run 10.25 on the street, the answer is yes

otakar wrote: The higher the altitude the higher the compression you can run. I run 11.25:1 in a 1150 motor in Chicago, with no problems at all. Cams will also make a big difference.The higher the duration and greater the overlap the higher the compression you can run.

Higher duration cams yield less cylinder pressure.

Increasing overlap involves advancing the cam which increases cylinder pressure.

BOOM! I would use the numbers on the gauge for reference.

The higher the duration, the more overlap can be used without pressures that will

Boom! I'm just guessing here so ..... but I think I'm right.

No, I know I'm right

And my bike is fast, 34mm carbs and I'm passing a gpz so fast it'll spin like a bottle as I go by it. :woohoo:

NADS.COM???? www.nads.com/ :woohoo: :woohoo: :evil: NIIIIIICCE ;)

I'll have to disagree with the rest of the guys. I also live at 5200 ft in Denver and once tried a 10-1 compression in a GPZ1100 that was otherwise stock. It did not work, the engine would ping so bad after about 5 miles worth of heating up it was not ridable. Also had high compression pistons in my 1974 Kawasaki H2 that was the same result. My wife and I rode that H2 15 mile once and it overheated and we had to let it cool to continue home. Stock 8 or 9 whatever compression results in detonation on my KZ1000 and KZ650s in warm weather. My other KZ650 with GPZ750 pistons which I'm not sure of compression, but I doubt higher than 9-1 demands premium and keeping the ignition timed to the retard setting or it will ping and overheat in less than 10 miles. So I either have 10 junk motorcycles or have proven to myself at least that higher than 9-1 compression does not work. Results vary of course, other guys run 12-1 but it don't work here for me and never has.

Take a look at the compression on the modern bikes. If you had 10:1 knock with premium fuel, you must had something adjusted wrong. The lower the altitude the more severe the detonation would be. Here in Chicago the elevation is 600ft. i know of guys who run 12:1 with little problem. Only when it gete 90+ in the summer is there a problem with detonation.

Of course usable compression ratio varies by engine design. No problem with new engines with new technology in combustion chamber design running 11-1. Old KZ a different animal. Like I say, some guys it may work. It doesn't work for me at 5200ft on any of my KZs. Also had a Yamaha IT465 dirtbike that was the fastest dirtbike I've ever owned, but the previous owner saw fit to mill the head. Big mistake as it would not run hot, as I found on 25 previous attempts at this botched idea for higher power, so luckilly Yamaha stll offer the head at that time, so return to stock compression and all was well.

Have you ever noticed those modern bikes are mostly liquid cooled & use much more advanced combustion chamber designs?? A lot those engines are also computer controlled.

Well, I'm gonna try it. I'll let you know what happens, although I've got plenty of other work to do before I actually get to the motor, so it'll be a few weeks. I can't wait to get it out of my living room! Thanks for your inputs, and I'd still welcome more from others, too.