One of the things I ran into back in the 50's before I got the engine dyno
was the heat of the tires. Slippage of the tires on the rollers, not
significant but another bit does not help the accuracy. I also found I
could use more ignition timing on the rollers as opposed to the engine
dyno, to the detriment of the engine at the race track.
*Never be beaten by equipment.*
On Thu, Sep 6, 2018 at 3:02 AM, van.mulders.marcel--- via Fot <
fot at autox.team.net> wrote:
>
> 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
>
> ------------------------------
>
>
>
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>
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