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In my prop-on-plane evaluation equations, I put in
sea-level rated HP at rated rpm and, where appropriate, boost, then I
adjust this value for design rpm, density altitude, and boost with delta
T* or stagnation pressure. The numbers I get from one CA engine shop are
always about 10% to 20% too high. Using the equation HP=PLANK, and solving it
for P=150 psi MEP, gives HP= DISP X RPM / 5280. Use this on an O-320 at
2700 rpm and you get 163 HP, an O-360 gets 183 HP! According to CF Taylor and
others, raising the CR from 8.5:1 to 10.5:1 will give about 9% more power. Sure,
you can up that even more with tuned intake, about 31" long at 3000
rpm, tuned exhaust, about 71" long at 3000 rpm, or a pretty-much linear
increase of power with RPM. But any time the numbers
depart significantly from values obtained with these methods,
they should be viewed with much skepticism! I still haven't had a chance to try
out my airplane dyno method yet. I bought the extra scale I needed to have two
to put under the main wheels, but haven't had someone to help me the few
times I've been to the airport recently. Designing airplane stuff has kept me
pretty busy lately!
p.s. Any time an engine builder tells you that he can not
get the highest power with an electronic ignition, but only with mags, that
must also be viewed with skepticism. There's one engine builder who
makes lots of money re-building mags, and he always puts down EI systems. If the
EI is timed the same as the mag, will the mag spark be all that much
better? With its much wobblier cylinder-to-cylinder timing? Keep in mind,
as little as 0.6 mJ will ignite a charge, and LSE's Plasma III puts out
about 140 mJ total each spark event!
* Keep in mind that boosted MAP doesn't really tell
you how much power you are getting if you don't factor in the induction
air temperature rise, delta T, to determine the charge density!
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