Flywheels

[johneroberts]

Question?
How does a lighter flywheel increase BHP?
or does it?
I know that it effects the way in which it revs higher, which in turn allows quicker passage through the gears.
However i have tried to find out some information on flywheels, but non state that an increase in BHP occurs.
Comments appricated
Cheers
jr

[quattropaul]

John
It's doesn't increase the BHP figure as such,but by virtue of the fact that it's lighter it basically means that less torque is required to accelerate the flywheel,therefore more torque is available to accelerate the car instead [img]images/graemlins/smirk.gif[/img]

Power = force mutiplied by distance moved,then divided by the time taken to do this

[Andiroo]

Very well put [img]images/graemlins/laugh.gif[/img]

Effectively the normal losses throught the transmission (27% to 30% discussed on the Rolling Road day) are decreased because of the lighter flywheel - which means higher bhp at the wheels, but also flywheel.

But also going from flyhweel back down the crank, it means that the inertia required for the crank to speed up after combustion is less, so the engine will rev quicker - which means a better torque figure - and as bhp is a factor of torque probably more bhp as well [img]images/graemlins/laugh.gif[/img]

Taking Tanoga's figures on the rolling road, he has a higher bhp at the wheels, which probably means his losses are only 25% say, but it would be interesting to see what his flywheel bhp figure is at say AmD's or Kim Collins rolling road, compared to say yours John, just to see if his flywheel bhp is up on the rest of us. I'm sure it will be up 10bhp at least [img]images/graemlins/smile.gif[/img]

Andiroo

[tanoga]

There is not much else that I can add except to say that rolling road figures for bhp at the flywheel take account of already know drive line transmisson %loses.
As my RS4 has a light weight flywheel fitted we can no longer assume a % drive line lose figure to back track from "at the wheels bhp figures" to give an "at the flywheel bhp figure"
At the end of the day figures at the road wheels are more relevant to every day usage.
Karl

[Greg_S]

surely lightening the flywheel has negative effects also? otherwise audi wouldnt have designed it that weight in the first place.

[quattropaul]

surely lightening the flywheel has negative effects also? otherwise audi wouldnt have designed it that weight in the first place.

True,a heavier flywheel does help in making the engine run a little smoother,eg when at idle [img]images/graemlins/smirk.gif[/img]

[Andiroo]

One drawback I suppose, but if you deal with guys who setup on a rolling road then it can be ironed out.

The main problem is correct and accurate balancing on the flywheel so as it doesnt throw out the harmonic balance of the crank. This done correctly - no probs whatsoever [img]images/graemlins/laugh.gif[/img]

Why don't Audi do it as OEM? - probably the same reason they give you <beep> brakes, soft suspension, poor turn-in and bendy wheels [img]images/graemlins/wink.gif[/img] oh and a piss poor 380bhp [img]images/graemlins/blush.gif[/img]

Andiroo

[Nordschleife]

Drivability is improved with a heavier flywheel as it stores energy that masks all those fluffed gear changes, mismanaged throttles etc.
Amongst other items Audi and Porsche share is a preference for dual mass flywheels.
Anybody switching to a lightweight single mass flywheel should also switch to a different clutch as the standard clutch is not well suited to the lighter more aggressive flywheel. Not many people bother with this, its not expensive as you have everything out to change the flywheel.
This is the arrangement for MTM's high performance cars.
Incidentally, the McLaren F1 has no flywheel

R+C

[Andiroo]

Good point Robin [img]images/graemlins/laugh.gif[/img] my clutch is modified to take the beating [img]images/graemlins/wink.gif[/img] not sure about a standard clutch.

Andiroo