A really interesting thread. But in one respect the question of noticeable
difference in performance sounds similar to the investigation that I did a
couple of years ago on a completely different subject.
i became aware that in current motorcycle racing engines, there were some
tuners who were getting significant increases by making the intake ports
smaller, to promote high velocity. One expert claimed a 5% increase in
torque. I tried this on the flowbench and was astonished to find that I
could make a TR port 40% smaller at the bend and see very little difference
in flow (as measured on the flow bench, remember). So I reasoned that the
guy was probably right and that flow would remain at least as good,
resulting in increased velocity.
I prepared a head this way (building up the short side radius with epoxy)
and took a trip to the chassis dyno, where I tested a head using my normal
prep against this high velocity port head. Guess what? Performance was the
same, within the accuracy limits of chassis dyno testing.
I went back and found dyno charts on the 'high velocity' approach and sure
enough -- there was an increase, starting at about 6000 rpm and continuing
right on up to 14,000 rpm. Hmmm. That's just a little outside my rev range.
I concluded two things from this. One thing was that hp increase claims
need to be looked at pretty carefully. The other was that changes to the
short side of the port probably don't mean anything. Unless, of course,
somebody has found some neat trick there.
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