Daniel -
Since horsepower (or kilowatts, or whatever) is calculated in terms of
torque (twisting force) and RPM, it can be measured directly by replacing
one of the front motor mounts with a load cell (pressure transducer) and
multiplying the readout (vs. RPM) by the action distance (load cell to
crank center line). Since there are some non-symmetrical factors acting
here, you would need to calibrate the system on a chassis dynamometer
(rolling road) to be able to get absolute readings. Lacking that, you
still can measure relative changes due to tuning (changing to Weber, adding
blower, etc.). This was discussed and an implementation described (with
photos) in one of the car mags (R & T, SCI, or such) around the mid-sixtys.
Clay L.
'67 Sprite
At 06:03 PM 9/27/01 -0400, Daniel1312@aol.com wrote:
>You make an extremely interesting point here that I have not seen made
>before. I only know what bhp the engine in my car makes when I have it run
>up on the chassis dyno so all the numbers I see are RPM specific. So, the
>bhp the engine produces to drive at 60mph in 3rd gear are in fact much higher
>than the bhp the engine produces to drive at 60mph in 4th gear because the
>bhp is always rpm specific. I think seeing all my power figures in relation
>to dyno testing has blinkered some of my understanding because.........
>
>On that basis your statement below would appear to be incorrect. HOWEVER, as
>far as I know the chassis dyno readings are always taken under a full load
>which the dyno operator applies to the rollers (I guess this explains why the
>power figure as indicated on the dyno station jumps about while the rpm and
>speed remain constant (say 5000rpm, 6000rpm, etc). It would also explain why
>for any given speed (say a steady 85mph cruising in 5th gear) my car consumes
>much more fuel with the softtop roof down than with it up. What is happening
>is that because the aerodynamic drag increases the engine is required to burn
>more fuel (the max efficiency for any given rpm) to generate optimum power at
>that rpm simply because it needs to.
>
>I guess that the chassis dyno power figure for any given rpm is the max rpm
>the engine produces is not necessarily what is required to drive the car at
>that given speed (as I had previously thought and always puzzled me).
>
>Does all this make sense? Have I seen the light or was I always thick? Any
>comment?
>
>Daniel1312
>
>In a message dated 27/09/01 12:50:48 Pacific Daylight Time, TMHEFFRON@aol.com
>writes:
>
><< It doesn't matter what mod's you've made to the
> engine, if you need 20 HP to go 60, that's all your engine is called
> upon to
> produce when going 60. >>
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