Pavlo

What I am using isn't important.

Are you trying to tell us that an Sti 8 doesn't have the power we think it does because of the small turbo and intercooler (which isn't small but we'll get to that I am sure)? Or are you trying to tell use that the Sti 8 does have the power quoted, but has massive amounts of drag making it slow? Or is that it doesn't have the power AND has massive losses and is actually really really slow?

The intercooler on an Sti8 is not small by any stretch of the imagination. 65º inlet temps is what I have seen on an early impreza with the poor slanty intercooler which is very small. The sti8 in comparison has an I/C with a core about 3.5 times the volume of this and a much larger bonnet scoop. Even at 500hp (crank) levels the Sti8 intercooler has shown to perform very well.

Paul

Cosworth427

You just illustrated a possible reduction in performance. The dyno doesn't measure that, it measures the power and torque.

Yes, lower atmospheric pressure will cause some engine management systems to retard the ignition and lower the performance, and spool time will take a little longer, but that will affect the torque curve and not the transmission losses dynos claim to calculate. What you are supporting is that dyno software compensate theoretical power outputs for what the ecu has done for that given engine. And that's very misleading.

You have just implied that the difference in losses between RWD and AWD is minor. The tire accounts for 33-50% of the total loss in power through friction, heat and noise of each driven wheel.

Driving 2 extra wheels does not mean double the loss in aggregate power. For an AWD, assuming a 50/50 torque split, the front wheels will lose about as much power as the rears. Suppose the rears lose 10% of 100 HP, and the front's lose 10% of 100 HP. That would be a total of 180 HP net.

If a RWD car loses 10% at the wheels. It too would be 180 HP net. No real difference at all.

But in the AWD's defence, one of the axle pairs will lose more than the other, due to the losses in the transfer differential feeding power, which is around 1.5 - 2% additional loss.

Well, I am not attempting to be one sided, the only matter I refute is the misleading and overexagerated transmission losses. There are plenty of stock turbocharged AWD cars of various engine layouts on a chassis dyno, produce enough if not a bit more HP at the wheels to match the quoted flywheel HP. And the losses aren't much more than RWD cars.

Cosworth427

I haven't mentioned the STI8 regarding turbocharger performance.

STI's usually produce enough whp to fall within the 15-16% loss range. It's not so fast because of it's 1470 kg kerb weight, and the stock level of power has to shift all of that.

The small hot air blowers usually come from the classic UK turbos, YB cosworth engines, Vauxhall's c20let. Note that these engines are used in AWD, RWD and FWD cars. I have seen FWD, and RWD cars on the same dynos used to measure losses for AWD cars, and they still apply 20-25% loss on RWD cars.

I have seen dynos of basic modified supras on these dynos, that allegedly make enough flywheel HP that the ecu isn't capable of supporting.

Pavlo

Who is supporting any of that? Certainly not John nor I.



No I didn't imply such a thing, only that it's not the difference you will see measured by a number of rolling roads (Maha being the prime example) it will be less.


Aggregate power? We are not dealing in gravel here! I actually said "power absorbed by the tyres (which doubles for the AWD on the dyno but not on the road) is eliminated". And that as is true.

What about the losses other than the wheels? 180hp net of what? It most certainly will not be 180hp at the wheels. Drivetrain losses are not proportional to torque transmitted.

Not for a subaru, evo or cossie they don't have transfer differential (but a skyline does). The subaru and most AWD cars have a centre differential and unless there is a difference in speed between the axles, the centre diff can be eliminated from the losses. What isn't eliminated is the losses from the front CWP, drive shafts and CV joints. These losses combined with the extra tyre losses measured on an AWD car using a rolling road are what constitute the difference between AWD 2WD.

Well that is fecking weird, because you seem to have been arguing the opposite. Although consider that a standard WRX will produce about book power at the flywheel on a Maha rolling road, but exhibit about 110hp losses, which isn't exactly "a bit more HP at the wheels than the quoted flywheel HP" is it? In fact it's about half the wheel hp.

We are going round in circles here.

Paul

Tentenths

Note to self - check thread title before launching into tirade.

Cosworth427

There's a simple rule, there can only be a loss in a system if power is being supplied into the system.

AWD distrubutes power to 4 wheels. If power is distributed by 4 wheels, then the losses too should distributed by 4.

If the front wheels receive 50% torque, then whatever losses occur at the front tires, differentials, etc will only be the losses of the 50% power fed to it. The remaining 50% at the rear, the losses of the tires, differential, bearings, oil etc affect only that fed 50% power.

I already explained that tires account for 5% loss of power fed to the wheels. In a 50/50 torque split, for each axle pair, it is 5% of *half* the power fed from the flywheel.

Additional drive shafts, CV joints, oil constitutes only an extra 1.5-2% loss of flywheel power, this why AWD is marginally loses more power than RWD.

I don't understand why I have to pick a side, all I'm attempting to do is explain the losses between 2wd and 4wd cars aren't as bad as 4wd owners and especially tuning shops who sell performance upgrades as they make out to be.

If you only have 110 whp on a standard uk WRX, then that car has problems. The boost, ignition timing, cooling etc all plays a part to make anywhere near the quoted power. Why are you providing only 1 example of a car underpowered to refute several dozens of other examples that can easily make the quoted power?

Bubba po

Has anyone pointed out that donutman spelt "disappointed" incorrectly?

MadMark

Tentenths

Not too mention "tires"

Pavlo

lol

missing the point completely.......

john banks

The accelerometers and acceleration times give it away, the AWD losses are overestimated, but the flywheel power is reasonable IMHO. Otherwise there should be many hot hatches that will accelerate faster than a UK Classic as they develop higher power at wheels to weight ratios than 1235kg and 130 WHP. Yet the Scooby does 60-100 in 9.2 seconds. Apart from a Focus RS which does 9.0, I'm not aware of any unmodified hot hatches that will match that?

The atmospheric and temperature corrections are not some perverse way to deliberately skew the figures, they apply a minimal correction to DIN standards that practically corrects figures quite nicely. If the ECU is knocking the performance more than this, the figures will be worse not better even with the correction.

I'd rather make attempts to control for these variables plus the ones we've discussed that make the flywheel figure most useful to me, whilst accepting that rolling road figures for shootouts are pinch of salt material.

donutman

Has anyone pointed out that donutman spelt "disappointed" incorrectly?


Not too mention "tires"


Lol

now you know why i am called Donutman

Tentenths

Doh, maybe I should be Donutman - you didn't even mention tires (or tyres). It was Cosworth427.

Sorry Donutman

fromage

Just thought I would ask a question while on a smiliar subject, how do you work out the power at the flywheel figure If you get a power at the wheels figure from a road-dyno like on Deltadash ?

Thanks and sorry for going OT

willipdarling

GO BUY A SPEC C. EVO RECKON THEY BE **** HOT AND HAVE A VERY ANTISOCIAL TONE. BYE......

TonyBurns

iTrader: (3)

I believe i gave you the 255bhp@wheels figure for my car v the 260bhp@wheels figure that you gave.....
Now the good bit....

This is very true, in that case my car would have approximately 63.75bhp per wheel, whilst yours has 130bhp per wheel, or does it?
You talk about drag, saying that if you power all 4 wheels on an 4WD car it spits the power 4 ways, to the driven wheels, that would make your car extremely quick, so why is it not? could it actually have something to do with the laws of physics (im a bit knackered, having worked a 9hr day and 5 hrs driving so forgive me if im not 100%), but the 130 per driven wheel would eventually work out at a theoretical 65bhp per wheel, as it needs to push/pull the free wheels?, nothing worse than drag is there?


Interesting quote, but you dont actually need to power something directly, if there is resistance/drag on the same object, ie the 2 free wheels that you havnt counted.

Anyway, now that im fed up of this thread and the waffle of some people and it went totally off subject due to someone saying that their other japanese manufactured car was the be all/end all and yet cannot take the truth (there are quicker STi's than supra's out of the box ) and that STi's are slow (nothing wrong with a PPP'd car )
Its about time that this ended with this quote:-

"Smoother, longer power delivery can mean that a quick car doesnt feel as quick as a car with instant, shorter power delivery".

Tony

Bubba po

Their is a lot of technical language going on in this thread that excludes the casual reader, but each to their own.

chris's scooby

Yup, i'm lost as well!

Pavlo

thought for the day.

If drivetrain losses were just a fixed percentage of input power, we should be able to move our cars with a very small amount of torque to the input shaft, or just by pushing very genty on exterior.

Paul

R.B

Donutman

Get P.Cole to take you out in his, Its a very quick Sti8 now

I think you already know him he`s in your area.

R.B