Hi Larry,
I'm from Belgium and belgians have the all time reputation of being stupid. So
I'm not responsible.
I don't want to blame dyno operators. They are in a difficult position. If a
dyno operator find out that his bhp figures are always lower than what
customers get on other dyno's, his conclusion may be that he is too honest. I'm
still interested to know how an operator can adapt the results. I may be wrong
by assuming that it could be by exaggerating the inertia value (of the car
and/or the dyno cylinders).
Marcel
Van: "fot" <fot at autox.team.net>
Aan: "fot" <fot at autox.team.net>
Verzonden: Woensdag 5 september 2018 16:41:38
Onderwerp: Re: [Fot] 89MM piston question
Marcel,
I suspect if you brought this question up with the dyno operator he would look
at you like you were from Mars. I think it is a safe assumption that the
inertia of the engine/drivetrain is small relative to the inertia of those
large drums. I've often wondered about the differences in rolling resistance,
since it depends on road surface and weight (including strap down force). I
suppose this can all be lumped into drive train losses.
- Larry
On 9/5/2018 3:33 AM, van.mulders.marcel--- via Fot wrote:
It seems I've a chance someone here knows what the inertia is of the rotating
parts of a (standard) TR4 and TR6 engine?
PS : most chassis dyno's are measuring horsepower out of the acceleration of
the very heavy cylinders (great inertia). The wheels of the car are resting on
these cylinders and accelerate them during the runs. But the engine has also to
accelerate the rotating parts of the car(crank, transmission, wheels..). I
suppose that the dyno operator has to make a guess of the inertia value of
these parts and add it to the inertia of the cylinders. Here is a comfortable
opportunity for the operator to make the customer happy : if he is adding an
exaggerated number for the inertia of the rotating parts of the car, then the
horsepower is exaggerated. As far as I know , chassis dyno operators never
mention or ask about the car inertia. It would be very interesting though to
know the value he is using, because then you can always use this same value for
runs on different occasions and compare the results a bit better. A chassis
dyno is really only usefull to compare the results of changing things on the
engine during one and the same session.Don't be fooled by the absolute numbers
: Once I went to a chassis dyno with my TR3 : my car must have looked pitiful
against the modern cars the operator was normally testing, because the result
was 210 bhp at the wheels and I knew it surely had no more than 180 bhp at the
flywheel! I don't know if some chassis dyno's have a brake to hold the engine
on a constant rpm at WOT : then the inertia of dyno and car doesn't matter and
you know the right horsepower at the wheels. About right at least : you can
cheat yourself a bit by overinflating the tyres and the dyno has still to be
calibrated rightly.
Marcel
_______________________________________________
fot at autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/pipermail/fot
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://autox.team.net/pipermail/fot/attachments/20180906/d8517a6f/attachment.html>
|