Quote:
Originally Posted by flatspin911
You mentioned 10.5:1 is not much static compression with those cams. Can you expand on this a bit. Do you mean that with the large overlap of these cams I can run a higher compression? What will I give up here?
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Dynamic cylinder pressures are affected by valve timing and when one uses longer duration (or narrow lobe center) camshafts, one needs more static compression for acceptable off-peak torque as well as competitive power.
Engines must be configured as matched components and specifications otherwise overall performance will not meet expectation.
In your example, 10.5:1 CR would be appropriate for an aggressive street engine or an endurance race engine with 120/104 cams as that would make decent power and still run well on 92 octane fuel (with twin-ignition, of course). For an engine with 171/149 cams, I'd be at 11.3:1 or better to prevent severe torque loss below 5000 RPM.