In article , "Mark" writes:


Hi All, thanks for the responses, was not meant to be a trick question but
definately a newbie question. I was curious after reading about people using
mazda 13b engines for various homebuilts, and porting them, adding on
various components to boost the hp from 200 to 260+. Seems at a point that
it's overkill if the 200 hp engine is going to provide you with the needed
ponies and rpms to accomplish the same as the 260 hp engine. What would the
advantge be of having the extra horsepower ?

Thanks,

Mark



NOW you have asked the question the right way and will see some good answers.
The advantage of more horsepower is the capability of increased thrust, which
is not a factor of just the RPM but of the ability to convert the horsepower to
usable thrust using a prop geared to the output of the engine. Thrust is
created by the prop and is determined by the RPM of the prop, the length of the
blades, the number of blades and the pitch of the blades along with a host of
other factors. Assuming for one example the same number of blades, the same
RPM, the same length of blades, and other conditions for two engines and two
props, the higher horsepower engine will be able to turn a larger pitch prop
than will the lower horsepower engine and will produce more thrust.

Think of it the same way as a race care. The higher the horsepower available
from the engine, the higher the gear ratio that can be used and the faster the
top end speed.

PS: This is a simple answer to your question but many factors are involved.
The effort to increase a 200 hp engine to 260 hp may or may not be worth the
effort and the 30% increase in hp wil not produce an equilivent increase in
thrust or speed. I don't remember the formula for calculating the increase but
it is far less than anticipated.




Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)