Transmission losses

Fire & skill

Fire & skill

Vintage member
Does anyone actually know the losses between the flywheel and the wheels on a Gti-R? would this be a constant figure or is it % related to engine output?

Ive thought about it a bit and im of the thinking it would be a constant figure :?

Ive been told its around 100hp
 
PobodY

PobodY

Moderators
Staff member
It should be reasonably consistent, but not a constant figure; it will be a percentage loss rather than an absolute BHP figure. - It's dependant on the drive train, so logically a car with all new bearings in the gearbox and hubs etc should have less loss than a car which is worn; I think that lower-mass parts (e.g. carbon-fibre prop shaft) would help as that's less mechanical work required to get them up to speed.

A good dynometer can get a good measure of the loss during the run-down when you come off the power; I've got a figure of 20-25% in my head, and that seems like a lot so I'm not sure it's right... but that would give ~100BHP difference on a 400BHP car.
 
whytie

whytie

Active Member
I got a car dyno'd a few months ago, it was usual 1.2 boost, exhaust, fuel pump and fmic, it made 267bhp at the wheels. I'm guessing the car was around 320-330
 
B

Born Again

New Member
Fast Guy said:
The figures I saw years ago if I remember were FWD 12%, RWD 15% 4WD 25%ish


On the dyno, mine made 268bhp at the wheels which they showed as 339atf.
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I've always been lead to believe 4wd is around a 20% loss.
Based on your figures your car is losing just under 21% through the transmission.
 
red reading

red reading

Active Member
There is no fixed percentage, but the rule of thumb is 20-25%, on 4wd.....the reason for variation is down to dyno types,wheel size, gearbox type,tyre type and pressure etc etc, its all as pobody has said and is measured on coast down on some types of dyno or a preset formula on others....dyno dynamics on shoot44 is 20% hence why when mine made 500.9 atc it was 400.1 atw.

a dyno is only a tool for setting up really,hence why when building and tuning a car use the same dyno and operator to check your tuning as the figures will be more consistent .
 
vpulsar

vpulsar

Well-Known Member
stage 3 muppet said:
suprised you never twisted the mainshaft right round itself with that graph !!!
bet that felt naughty once spooled up and on boost

what turbo was that on if you dont mind me asking ??? just being nosy
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Was using a quaife gear set mate I never had any problems with the gearbox not in ten years of using it, I had it rebuilt a couple of time though just in case, Yes it was ballistic once it spooled up I left a DB9 that I let come up the outside of me at full chat while I just cruised in 3rd when he got along side still flooring it I put my foot down and it looked like he had stopped lol, Was a GT3076 R with external waste gate mate.
 
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