QUOTE(SirAndy @ Apr 20 2006, 02:08 PM)
octane/regular: usually mix 50/50 of premium and regular
pistons: euro P/Cs, not domed.
Unless you flycut the heads, the Euro P&Cs "should" give you 8:1 compression, not 9:1. That's quite a difference... Factory spec for the 8:1 2.0 motors is to run ~89 octane.
Stock 1.7s would be 8.2:1, and most of them are spec'ed for super-grade (91 octane) fuel. Though the later 1.7s seem to have been spec'ed for regular (87) stuff, while making the same power and having the same compression. (???)
Compression ratio is the sort of thing you can't easily change your mind about once you've made the decision. I would tend to go more on the conservative side--I'd probably stay at ~8.6:1 or less, because trying to find higher octane than 91 in CA is quite difficult.
--DD