What's Compression Ratio got to do with it? Options

[ThinAir]

When I built my 2.0L I had the understanding that if you wanted to run Regular fuel the highest compression ratio you could have was 8:1. I don't have any idea now where that came from.

In the thread about his air-cooled event, Jake just posted this: "The 356 engine is a 2.4, it made 224HP @ 9:1 CR on pump gas."

Now I know that there is more to one of Jake's engines than just the CR, but it got me to wondering:
1. What is the maximum CR you can run with Regular fuel?
2. What is the relationship of CR to performance? Do you always get more HP by running higher CR if everything else is the same?

Understanding this concept might be helpful the next time someone builds an engine, buys one from Jake, or has one built for them by someone else.

[Don M]

Compression ratio is directly related to environment and intended use. set it at 10:1 and talk to me after you've driven I-5 south from Sac to LA in mid-day August. Here in So Cal with beach, mountain and desert conditions, using my driving habits as base and allowing for dynamic correction I would never advise a client to cam and compress for more than 9:1
As well for amature air cooled road racing purpose the higher the (actual) compression the more restricted the use, fact is in this venue while staying within mean racing environmental conditions expect severely diminished returns when exceeding 12:1 compression.