View Full Version : BHP: Fly v At the wheels (loss for Manual and Auto) ????
Last time my Auto was Rolling-Roaded I lost about 30% (mainly due to the transmission) between Flywheel and Wheels.
What does a manual lose?
Yes I'd be VERY interested in this, particularly from an S14 point of view.
Guy at the RR day yesterday said mine was putting out only 130bhp at the wheels (even though on his printout he'd written that it's putting out 150.
He reckoned I was losing about 50 bhp which on his figurs would put my FBU'd car at 180BHP at the fly :eek: :eek: :eek:
Well according to the SX brochure I should be putting out 197 bhp.
Oh yeah, he also had a figure of 185lbft of torque which is almost exactly what Nissan quote in the borchure, so how come not much power loss there??
Oh and he reckoned my car was running fine before anyone says there's something wrong with it.
C'mon, someone must know, there's always someone on the board who knows everything ;)
It's a very difficult subject... The only way to accurately know flywheel power figures is to take the engine out the car and use an engine dyno, not very practical, as you also need all the ancilliaries and fittings as per if the engine was in the car, or it's not a realistic figure. Most RRs have software to calculate it, and some seem to be better than others. I prefer RRs who give you the wheels figures, as that's what they measure.
Measuring power at the wheels can be equally tricky, as there are so many factors that can affect it, like the alignment of the car on the rollers, tyre pressures, heat, air pressure, air flow into the intercooler etc. Don't get me wrong, I'm a firm believer in using Rolling Roads, they are invaluable as a set up tool. As a means for measuring power, they are only as good as the set up and the operator.
For power losses, there is no fixed way to tell. Generally, for a Manual 200, I would guess 15 - 20%, based on inline engine, RWD, and this is a guess so don't shoot me down if I'm miles out. Autos seem to have higher losses, but I don't really know much on autos. If a transmission loses 30% though, even on a 4wd car, I'd say there was something wrong. Think about it, you have an engine with 200BHP, that's 150kW. If you lose 30% of that in the tranny, that's 45kW, going where? Stand by a 3kW Electric fire and see how hot it is, then tell me where 15 times that energy is going while your car is on the rollers...
If you're worried that your car is down on power, maybe take it on a 1/4 mile day (or find another 200 and a private road ;)), and compare times with others on here. If the times are up with others, then the car is obviously fine, and the power is there, just a problem with the way it was measured.
Does having a Limited slip diff increase or decrease losses? What do FWD cars loose? Do MR cars MR2's get alot let tranny losses?
mickstreet
24-03-2003, 12:02
MR2's loose around 15% through transmission. You are obviously going to looses slightly more in a 200, I would guesstimate 20%.
barryjdart
24-03-2003, 19:47
I agree that an auto will have more losses than amanual but, going on factory and road test figures there seems to be next to nothing between them. Only downside being higher fuel consumption. I could well be wrong though.
i'm currently doing quite a bit of reading on this topic, and from RR days and other such resources i've found that trying to estimate the fly figure, and guessing tranny losses is a waste of time.
If the rolling road is accurate then the value at the wheels is the only number worth knowing.
Interesting article here. http://www.g-force-motorsport.co.uk/dyno/rolling%20road%20detail%202.htm
I agree with the above. Also, when you look at all the factors that can affect an at the wheels figure, you realise why comparisons between cars can be completely meaningless at times :(
A Rolling Road is a Tuning Tool first and foremost. Use it to get the best set up possible, the numbers are just a bonus - if they're high enough!
Originally posted by Ripper
Last time my Auto was Rolling-Roaded I lost about 30% (mainly due to the transmission) between Flywheel and Wheels.
What does a manual lose?
My autos running 233bhp at the wheels, if I'm losing 30% through transmission that puts my at the fly figure at about 330bhp, cant see I'm getting that much on std injectors and tubby ( not for much longer tho:D )
Originally posted by dunc
What do FWD cars lose?
Rubber and traction!:D :D :D
Coming back to my original comment, mine was RR'd at Thornbury and the results were 186-197bhp (due Auto, can have upto 5% adjustment, hence the lower 186bhp figure) and 130bhp at the wheels.
That's about 30% if you take 186bhp as the lowest attainable figure.
Originally posted by Ripper
Rubber and traction!:D :D :D
Chortle, chortle :D
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