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Original Message
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| RE: Is the engine audibly pinging? |
| By Gerry Proctor - 09/26/2005 8:36:04 AM; IP 207.133.188.254 |
You say you’re not comfortable with the compression but express no problem you're trying to solve.
A shim head gasket is not designed to be stacked with another gasket, so that route to lowering compression is a non-starter.
There are some options but you're working in the dark at this point since you don't know your specifics. Felpro's off the shelf performance composition gasket has a compressed thickness of .041" This would help drop compression only if the gasket that is now installed has a thinner compressed thickness. Your other alternative is a Cometic gasket. These you can get in whatever thickness you need. But going too thick in an effort to drop compression can create or exacerbate the very problem you're trying to avoid by reducing quench, which is a key consideration in lowering your octane threshold.
To make a beneficial choice, you're going to have to pull the heads and measure your actual chamber volume and determine what head gaskets were installed. Because of the ambiguity with how terms are used, your heads may have been machined but rather than being milled to reduce chamber volume, they may have only been surfaced, which, while it too does reduce chamber volume, is intended to only provide a flat surface. Surfacing has no measurably significant affect on compression. The only way to know what was done to your heads is to measure the chamber and compare the displacement to the blueprint specs. If you can't do this, a machine shop can.
If you are not experiencing any real problems, whoever built your engine may have already addressed the compression issue with lower compression pistons. But even with a higher compression, it's possible to address marginal situations with some careful tuning in both the fuel system and the ignition timing. There are plenty of 10:1 and over iron-headed street engines running fine on 93 pump gas. Despite the conventional Internet wisdom, it certainly can be done but it depends on the tuneup.
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