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Phil;
This all would be easy, if car motors worked at a fixed load at a fixed RPM...but in the real world a car motor is expected to work over a huge operating range....which is why we have performance curves, and transmissions etc. ...so if your "performance guy" specified a certain runner length, that clearly was (or should have been) a result of optimum preformance at a certain narrow RPM, and also a certain shape of the torque curve over the entire RPM range...so I wonder just how much diff 3/4" makes...
I recall the more recent SHO Taurus with the Yamaha develpoed engine...that intake had long short runners (from the airbox into the manifold) and a servo controlled vane under control of the engine management system which opened the shorties at high RPM, bypassing the longies. I don't know how much improvement (read widening/shifting of the torque curve) this resulted in...only the guys in the engine development department at Yamaha do, but it might be fun and enlightening the next time someone has a B20 on a dyne, to take some 1 3/4" tubing and another, slightly larger one (belled out at the end) which slides over it to make a (manually) variable length velocity stack, and then take some perfomance data for the different lenghts, to see what would really work the "best" (for that particular combination of cam, head, meetering needle etc.). Other than that, its really all just idle speculation if you ask me.
Cheers
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