Anyone running 9:1 or higher on the street? Options

[-JR-]

I'm still hashing over compression ratios. I've been reading online that these motors don't or won't run compressions as high as 9:1 without taking extra steps. Like aluminum cylinders or electronic fuel injection. Mainly just because of the heat involved.

Has anyone "got away" with running higher compressions like this on stock cylinders?

*** IF anyone has any feedback on what fuel grade they are running at their higher compression and if they are getting any knocks ect... I would also greatly appreciate that information too.

Thanks everyone!

James

[lapuwali]

QUOTE

I have had 10:1 2270s pass emission tests in CA and many other states without me even trying to make it happen!

Only because they don't measure NOx for pre-'80 cars in CA. Well, they measure it, but there's no limit. Higher compression will help HC and CO, since, as you say, those numbers improve with better efficiency, and higher CR improves efficiency. In other states, they use the Federal limits where they test emissions at all, and the Federal limit for cars pre-'75 cars are quite high, and actually pretty hard to not meet in a car that's running properly. Some early 911S cars with MFI had some difficulty in CA until they became exempt, because the factory tuned the cars so close to the CA limits in effect at the time. When dyno tests came in, they'd reguarly fail even when running perfectly in stock trim. Too much cam overlap, I believe. These weren't "torque" engines.