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- 29.
What should the compression be? - Top
- Based on the original design compression ratio of 6.3 to 1, the compression would be 95 PSI. In fact, original test data recorded compression values very close to this value. However, most in-service engines will have average compression readings of 100 to 115 PSI. There are several reasons why compression is usually higher than the design specification: 1) carbon buildup in the cylinders, 2) heads being milled, or the use of only one head gasket during overhaul, and 3) variations in combustion chamber depths within cylinder heads. NOTE: While Universal never officially changed the specification for the depth of combustion chambers in cylinder heads, many of the later engines (circa late 70's and early 80's) have considerably shallower combustion chambers than earlier heads. Fortunately, new heads sold today (both our aftermarket heads and the more expensive heads sold by Westerbeke) have combustion chambers of the original depth. It's important to point out that since the Atomic 4 is a low compression engine by design, performance does not seem to improve by artificially increasing the compression ratio above the design specification of 6.3 to 1. - Updated:
December 6, 2003
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