We all like to quote BHP, flywheel and at the wheels/hubs right...

 

Well does torque have a concept of flywheel/wheels? Itsa just you only ever hear one figure quoted.

 

Cheers

 

Pete

RR's actually measure torque & then convert to BHP!!

Torque is just potential energy, its a rotational force which has to be applied through a turn (angle of rotation rotation)

 

then you have your simple power equation.

 

Power = Torque * rotation rate

 

 

To convert to BHP you divide by 5252

Really? Interesting, so is the RWBHP still an estimate then?

Really? Interesting, so is the RWBHP still an estimate then?

 

 

Well the applied force will be to the rollers, so the only actual measurement you can take as real is the one where the actual work is being measured, everything else is just an estimate. If you stuck the measuring decivce to the flywheel then that would be the actual figure.

So RWBHP is the "true" measurement - everything else ("at the flywheel", "at the crank" "allowing for transmission losses") is just an estimate. (Unless, as Mike says, they drop the tranny and bung the dyno on the flywheel or wherever. Which they don't.)

 

When they are estimating 300ZX autos there is a real problem as 300ZX autoboxes are not normal torque-converter type auto boxes - so almost no-one has a real idea of what the "transmission losses" are and you can't estimate them the way you can with a manual transmission. (Boot the engine then take your foot off the throttle and dip the clutch - the deceleration of the rollers gives you an idea of the drag in the transmission which you add back to the rwbhp to get a pretty good estimate at the flywheel).

 

It has been alleged that some unscrupulous tuners / dyno people (no one here, natch) simply guess what figure they need to add back to make the customer feel he's got a really good engine....

 

Now, don't get me onto the subject of the SAE measurement of BHP - is that with or without aircon? Alternator? Lightweight oil? etc etc hehehe

Ok, in the rollers. RW torque is actually measured, RWBHP is then calculated from that.

although FWBHP is estimated, it is actually measured. after the power run the clutch is dipped (or put into neutral) the dyno then measures the torque (& therefore bhp) that the transmission is sapping due to frictional losses.

 

autos lose far more than when being driven, due to all that oil, rubber bands & feathers that slosh around in there! :D

But what about torque? Is that estimated at all, or is it a "true" figure

LOL Cheers Paul. I saw ChrisC's figure in the dyno section so had a look at mine from the SE RR day, I got 369lbft which is remarkable high considering he has way more BHP.

certainly givesscope for unscrupolous (i am so pure of thought i cant even spell it) people to estimate down on the RR before engine work and estimate up after to make it seem like the thousands charged have been worthwhile

(Sorry- backtracking a bit to what power means...)

 

This all makes sense now. So in real-world terms, power is not terribly meaningful (other than being a nice big number!), while torque on the other hand tells you how well the car will accelerate.

 

In a way yes but power takes into account at what revs the torque is made..

A diesel creates big torque but low bhp generally. So compare that with a petrol car producing the same torque but more bhp...

Fine they pull the same for a while, but the deisel will have to change up into 3rd much early than the petrol, efectivily reducing its RW torque...

 

So a greater bhp figure lets u take advantage of better gearing..

 

Another way to put it....

if you were turning a handle...winding in a rope, you would have more torque than an engine...But the engine could wind it in much quicker with a bhp figure about 10billion times greater than you.

Ok, so I take it back! :D

 

Just think back to the times when people only had horses... and imagine telling them that some people had transport equivalent to 500 horses pulling a cart round the corner to pick up a six-pack of mead!