Compression Ratio

[mpollock]

I want to do a complete engine rebuild for increased power while maintaining reasonable street driveability. I'm just in the beginning planning stage, but I'm going to use a 1.8L head modified for performance on a 2L block. I want to increase the compression ratio but I'm concerned about going too far and ending up with detonation. My question is how far can I go with compression ratio before I start causing unwanted problems. What have people done - what piston and head configuration, or if you have actually measured volumes what is the actual CR? I would also like to hear from people who have gone TOO far and ended up with problems.

[BEEK]

10.0-1 should be the magic number for a street engine on premium fuel. with proper attention to timing and air / fuel ratio you should be fine. also better camshafts will help with the detonation issue

[baltobernie]

As Beek suggests, CR and camshafts go together (along with every other aspect of engine specs ). Here is more info:
http://classicinlines.com/CompressionRatio.asp. It is impossible to give you an exact answer without knowing all of your proposed components and measurements.

As a general rule, most amateurs (myself included), when confronted with their first opportunity to rebuild an engine, typically apply the "more is better" rule, and end up with too much cam, too much carb, too much static CR, too big an exhaust, too quick an advance, etc. etc.

If you want to build a great street motor, buy all the engine bits from somebody who has a proven success rate with the Fiat TC, and follow his recommendations regarding machine shop target specifications, carb(s), jets, advance and so on. Conversely, you could take advantage of Fiat's body of knowledge, and copy the Abarth specs. We have a local club member with an original Abarth Spider. He is also an experienced Fiat mechanic, and his car is in a near-perfect state of tune. I'd bet dollars to donuts that car outperforms 99% of all Spiders you'll see on this forum.

[Daniel]

10.0-1 should be the magic number for a street engine on premium fuel. with proper attention to timing and air / fuel ratio you should be fine. also better camshafts will help with the detonation issue

The only problem with this is finding pistons that will give you 10to1, if your keeping the engine mostly stock
like the cams etc on the internal parts i'd say buy stock pistons and save the hassle you'll end up with 9to1
CR and be just as happy the gain with 10to1 vs 9to1 on a almost stock engine would be about 5 HP if that.
About the only way you can find 10to1 with the 1800 head would be custom pistons starting in the 500+
price range and a lot of work for a amateur to help design with a piston company. If you are a little more
experienced then it shouldn't be a problem to try to have a set made then theres the waiting time.

[Daniel]

Also larger cams might (depends on over lap) lower CR the larger duration the cam the lower your static CR will be at
lower RPMs...