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why do ported engines have less compression?

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Old 08-19-02, 12:20 PM
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Red Mist

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why do ported engines have less compression?

see title...
Old 08-19-02, 12:33 PM
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There is more overlap between the intake and exhaust, so at low speeds some of the intake charge can "leak out" the exhaust port. The less air you have to compress, the less compression you'll have.

Once the motor gets up to speed it's less of an issue - the rotor is turning fast enough that there isn't enough time for the overlap to cause intake dilution. You can also, in some instances, get a scavenging effect where the exiting exhaust gasses help suck in more intake air, giving a fuller charge at higher RPM.

Dale
Old 08-19-02, 12:42 PM
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Red Mist

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ooOOoohh.... i get it.... thanks dale

~Jeremy
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