Miata Mailing List: February 1996, Message #106
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   From: Brian Goodwin 
Subject: dyno numbers conversion
   Date: Fri, 2 Feb 1996 18:22:57 -0500

Hi everyone

I did not say anything about crank numbers for my Autorotor originally
because I knew there would be a debate about what the crank numbers were.
Much easier to just talk dyno at the wheel numbers.  Since someone else
started this ball rolling anyway I might as well weigh in now.  

I too have heard that 1.28 is the GENERAL conversion number from wheel
horsepower to crank number.  I too agree that it is probably a bit high in
this case.  Mechtech's Jim told me that the 1.8 car which allegedly makes
128 at the crank tests regularly at about 108 at the wheels stock.  If we
back the numbers up that gives us a factor of 1.18 instead of 1.28 (128/108
=1.185185 etc).  Note that this assumes that the engine really makes 128 at
the crank like the factory says it does.  Anyway, assuming 128 at the crank
is real then a multiple figure of 1.185185 results.  The Mechtech dynojet
dyno (about the best there currently is) showed my car making 156.2
horsepower.  Multiply times 1.185185 yields 185.1 hp at the crank which
sounds reasonable to me.  Jim also tells me that a free flow exhaust should
get me at least 10 AT THE WHEELS with this supercharged setup.  We will see.
I will do the exhaust soon and another dyno run and we will know all these
numbers for real.  Jim told me it is relatively easy to calculate the
negative horsepower numbers for a car and that we can do that next time so
we don't have to debate it.


Brian