This stuff makes for great conversation here at home!
Al suggests that on a rear-drive car, up to 40% can be lost. What he also
includes to rob horsepower is the inertia of the rotating masses; ie,
driveshaft, axles, differential, tires, wheels, etc. Front-drive cars tend
to lose less, simply because they have less stuff to spin.
Small ways to increase your efficiency would be things like slicker oils,
lighter wheels and tires, etc.
We've got a Clayton chassis dyno buried under piles of boxes and car parts.
Probably the best thing we got from Al's last employer! We don't seem to
have enough time to clean off the dining room table, let alone get this
thing running. It'd really come in handy for this thread, wouldn't it?
A chassis dyno really isn't a good indicator of your engine's horsepower. It
is an incredible tuning tool. The most important thing is to always make a
baseline pass before you tinker. This provides you with a benchmark number
to see if your adjustments are improving or hindering. What the actual
number turns out to be is not as important as how much of an improvement it
is from your baseline number. The numbers are only relevant to that
particular day's work. If you're going to tune again tomorrow, you need to
get a new benchmark before you make any adjustments. Of course, if you end
up with a big number at the end of the day, you can really impress you
friends later on at the local pub!
Cheers,
Wendy (& Al) Hart
75 TR6
76 TR7
> What would be the typical expected % difference in hp from a engine
> tested by itself in the lab dyno verses one tested as installed in the
> car at
> the rear wheels?
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