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What should my PSI Be on the topend?

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Don't know the spec on the 426, but I would guess somewhere between 180 and 210, or even higher with the compression ratio they have.

An even more valuable thing to test for is to observe how many kicks it takes to arrive at the max. Compression on the guage should more or less peak after 4-5 kicks.

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Compression on the guage should more or less peak after 4-5 kicks.

Good to know, I always thought the rule of thumb was to kick it (or turn it over) until the reading stopped increasing.

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Most contemporary ring designs cause them to seal better under pressure than otherwise, so that compression and combustion pressures help force the rings against the cylinder, and allows a little less friction during the exhaust/intake strokes.

If the compression readings take too long to run up to their peak, it can mean that the rings are loosing their tension on the cylinder, and have become more dependent on compression pressures to seal than they should. In a dynamic sense, this can result in low intake vacuum and poor low speed and idle performance. Hard starting, too.

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