| Consider this: On the VG30DETT, we do all sorts of modifications to them to improve their volumetric efficiency. This is, afterall, what makes the difference in how much power you will make given that we are all working with 3L of displacement. All that changes when you upgrade the components in the powerplant (short of oversized pistons, although marginal differences there), is the volumetric efficiency of the engine. Installing aftermarket exhaust manifolds allows the engine to evacuate the cylinders more efficiently in the exhaust stroke. This improves the pumping action of the motor, which directly ties into volumetric efficiency. Thermal efficiency of automotive reciprocating internal combustion engines does not vary all that much - from about 25-30% efficiency. Volumetric efficiency however, can vary considerably more and the amount of power you will make from a given displacement ties considerably more into volumetric efficiency than into thermal efficiency. Comparing the HP/L that two engines make, especially given that they share a lot of common design elements (60^ V6, 4 valves per cylinder, centrally located plug, similar static compression of 10:1 vs. 10.5:1, direct port injection, etc), will give a close relative understanding of how effectively the two engines are making use of their displacement.
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[ agpowers@bellsouth.net ] Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the tailor.
Albert Einstein
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