Re: ABF power

"Conor" <conor.turton@xxxxxxxxx> wrote in message news:MPG.2112aaeac148133a98a319@xxxxxxxxxxxxxxxxxxxxxx
In article <O5ppi.896$rr5.250@xxxxxxxxxxxxxxxxxxxx>, Burgerman says...

> Oh do *** off you sanctimonious twat. There is no method that can
> guarantee to correctly calculate transmission losses on a per vehicle
> basis which is why the power at the wheels is what counts but you can
> "roughly estimate" the flywheel rating.


Err how? I used to design and build dynos and ship them all over the world
and I cant!
Only at the engine (a engine dynamometer) or at the wheels can ever be
totally accurate.

Did I say otherwise?

Experience will tell you roughly what the transmission losses are on
certain vehicles but not accurately.

For an example if an engine builder building CVH's and sticking them in
Escrotes sees 120BHP at the flywheel when dynoing them that way and
100BHP at the wheels on the rolling road tune on a regular basis, it's
safe to use a 20BHP/ 1/6th power loss "guesstimate" due to the
drivetrain on a Escrote running the same drivetrain.


But 1/6th means a 120 bhp engine will give 100 as you say.
But you cant reliably use 1/6th on that transmission on a worse or better motor.

Say you stick a turbo at 2 bar boost for a spot of weekend drag racing. It may make 280bhp on the engine dyno.
Now put it in the car and you are expecting your 1/6th to be a 46bhp loss rather than 20bhp.
What you would expect to see would be 280 less 1/6th which is 280 - 46 = 234.
But you will get more!
Because once the frictional and bearing losses and oil drag has been overcome and these are all speed/rpm only dependent then that leaves only the minor component of extra losses caused by increased torque transmission. This typically is 5 to 20 percent of the total losses. Now in reality you will get nearly all of the power increase you saw at the motor, with only the small increase in torque loading losses to be lost since the original 120bhp motor has already overcome the speed/rpm related losses already. And they dont increase with torque loading.

So you would get say 25 brake hp transmission losses rather than the 20 you had with 120bhp.

Now do you see why a fraction or a percentage (same thing at the end of the day) can never be right?

Now its nowhere near a 1/6th and your power figure at the wheel would be around 25bhp better than the 1/6th rule would have suggested.


Say you put a 1.3 (60 bhp on the engine dyno) in it on the same gearbox/car. The losses are STILL going to be almost as great. The power needed to turn the transmission, tyres on the road/drum, drive shafts etc doesent really change much.

But now the majic number would be about 1/3rd of the power was transmission losses...

If you pulled a couple of plug leads off and engine dyno it it might make 25 bhp.
Now 20 go in the transmission if it now had the power to get to that speed so your losses are about 80 percent...








--
Conor

It arrived at their repair center last week so only another month or so
to wait


.