High compression for the street

knight rider , meet jimmy

just drop a j head on there,instantly go from 13:1 to 11:1 or buy some 1197 turbo pistons and deck the cylinder to bring you up to 9:1-9.5:1 youd be suprised just how quick it will be with pump gas and a decent head and small carbs for a streetbike.

hey speacking of race fuel i just about fell over two weeks ago when i went to by a jug of c-12 a 5 gallon pail was 127.00 can. last year i was getting it for around 75.00 and i thought that was insane iwas going to try c-14 but that was 140+ and i still had another week before payday so that wasn't happening so i would definitly run lower compression unless of course your big in oil and money is no object.

I think the 3rd person is the guy standing on the side of the street laughing his ass off when the Knight Rider completely waxes the School Teacher in the 1/4 mile! :woohoo:

Go for it:

20:1 compression ratio; direct injection; diesel fuel.

keith1 wrote:

knight rider , meet jimmy

Knight Rider thinks that jimmy meets Knight Rider not the other way around. :laugh:

u cant just use a thicker base gasket. u would loose the squish clearance and be right back where u started. Needing higher octane.
How about a j head gpz1100 block with a .040" spacer and 1170cc 10.25:1 j pistons?
Or GPZ head with custom pistons?
Or just resleeve and bore to 1200cc with a good port and bigger valves.
Lots of options. what is the base motor? kz, J?

Everyone has given you some good suggestions. Maybe I could add a few thoughts. "Theorectically" if you use a cam with a later closing point to lower the cranking compression. This can work "but" then you start losing your bottom end power and your idle. You will then have a very narrow power band. This would be fine if you plan on keeping it wide open all the time. If you get the compression down to 11:1 with a j head it's still hard to run on pump gas. A j head with bigger cams (later intake closing) would put you alot closer. Something you should really think about is the fact those pistons have very thin rings. They are meant for frequent rebuilds, not high mileage. There is the possibility you may be working on it, more then riding it. Plummen had a good suggestion about the turbo pistons with the compression bumped up alittle. That combination would be a lot faster then what you would have, trying to get those other pistons to run on pump gas. Turbo pistons would give you deep valve pockets witch would allow you to run a wide range of cams and cam timing that would be more suitable (is that a word) to your riding style and needs. All I can say for sure is, I have seen 900's with stock 1015 pistons and drop in cams run 10.80's
Please don't get hung-up on piston size or compression ratios, they have been the down fall of many motors.