compression values

[PKRWUD]

Originally posted by mustangman65_79
Is the motor being warm really going to bring the #'s back up to 150?

Not if it's junk. I can't guarantee what your numbers will be, but I can tell you this, if the engine is cold, the numbers won't be accurate. Metal expands when it's warm, and it contracts when it's cold. As a result, an engine that would have great compression when it's running may have lousy compression when it's cold, because the piston and rings haven't expanded to their running size, and are allowing more blow-by than they do when driving. This could generate compression readings that are lower than they should be. This could mean performing unnecessary repairs.

Look, it's your car, time, and money. Do it however you want to. But don't ask my advice, and then act like I have nothing better to do than tell you to do unnecessary procedures on your car. You followed my advice about doing a compression test, but you did it wrong, and the numbers you came up with are meaningless, and don't tell anyone anything. This wasn't your fault, because no one ever taught you the right way to do a compression test, so I did. I'm not mad at you, Kaspar, but please understand that I don't have any reason to instruct you to do things that aren't necessary. If you want my help, you need to supply me with accurate information.

Originally posted by mustangman65_79
Hey, can a cast iron crank)stock 2bbl crank) handle 200 psi? I'm thinking of shaving the heads to this. Or do I have to buy a new forged steel crank?

Okay, first off, forget the cranking compression numbers. You don't use them to build an engine, you use them to diagnose an engine. It's cylinder compression that you would consider modifying, and it is that number that you need to be concerned with. There are too many factors involved with cranking compression, and they won't remain constant. Cylinder compression, however, will.

What kind of compression are you thinking about? Keep in mind that more compression means more octane will be needed to control the compressed fuel mixture's stability, which means running a more expensive gas. If you go much beyond 10.5:1, you should plan on having to use a mixture containing at least 20% AV fuel.

Take care,
-Chris