chrisp

Had my RA dynoed at John Nobles yesterday and good fun it was with the rest of the midlands crowd. One thing is interesting is the power at the wheels and power at the fly. mine came out at 258.5bhp at the fly and 195bhp at the wheels .

I am right in thinking that its power at the wheels that really matters ??

Been looking at dyno.scoobynet.co.uk and heres what I found with other cars around the 195bhp at the wheels figures (including a few tyoe Rs and RAs but all Japanese imports)

Fly (bhp) Wheels (bhp)
273 191
278 193
271 196
277 191
281 195
282 193
285 191
287 192
288 197
293 197
288 195
308 189
298 193


So I am a little bit confused there were a couple of P1s there running at the same at the wheels one was 193 and the other was 197 and both were over 280bhp so what gives, any ideas ??

Cheers

ChrisP


[Edited by chrisp - 10/6/2002 5:46:21 PM]

Ex_Pug

I don't understand why running a car in 2nd or 3rd gear will show significantly more power than 4th or 5th (or 6th). As far as I was aware, 3rd or perhaps 4th were allways the gears to run in because of the drive ratio (someone will need to correct me if I'm talking bull). I didn't think the gearing on one car compared to another made much difference at all, as long as they were both in the right relative gear.

I'm baffled by the figures shown on the dyno pages. Most of the figures on the Powerstation page show 40-50% (and in some cases more!) transmission loss. How can that be?? It also seems that the more powerfull cars run there have less trasmission losses compared to their less powerfull friends, but as far as I know, if there's more power/torque in the drivetrain, there is more to be lost.

Surely at wheel figures are, relatively speaking, far more accurate than those calculated for the flywheel. Even then, most of those published figures make very little sense.

Is anyone able to shed any light, and/or correct me where I have gone wrong?

Edited just to say that Chrisp's figures from the Noble rolling road show exactly what I would have expected to see from a 4wd car... that being 25% loss, and a sensible at the wheels figure.

[Edited by Ex_Pug - 10/6/2002 9:21:00 PM]

Ex_Pug

Well that's about 40%, where do these figures come from?? Just with some rough calculations, it can produce some very strange facts (I say facts, but if I've cocked up some where someone will have to say so, but as far as I know...).

Comparing my two cars;

MY00 UK turbo: 215bhp @fly (manufacturers figures)
Modified 8v 205: 162bhp @fly (calculated from 140bhp tested wheels figure)

Scoob: 40% transmission loss leaves 129bhp at the wheels (calulated)
Pug: 14% transmission loss leaves 140bhp at the wheels (measured)

Scoob: power to weight = approx. 100bhp/tonne driving the car at the wheels
Pug: power to weight = approx. 156bhp/tonne driving the car at the wheels.

Which one wins to 100mph??

So unless I've gone hopelessly wrong somewhere, my little 205 is going to be leaving my Scooby for dust. I know my pug has about 140 at the wheels, it's been measured twice in two different places, and if 40% is a reasonable figure for scooby transmission loss (as indicated by the many rolling road results published) then the figures these calculations are based on must be in the ball park. The end results don't make any sense though.

Although my 205 is a quick little car, it's just not that quick, so either I've made an **** of myself with all that, or the rolling road wheel and/or fly figures on the dyno page are nonsense.

[Edited by Ex_Pug - 10/7/2002 8:25:55 PM]

chrisp

Could you put all that 140bhp down on the ground without the wheels spinning . The scoob can use more of its power on take off as grip and traction is the scoobs trade mark and would be half a mile up the road before the 205s wheels stop spinning . The 205 is FWD motor so transmission losses will be a lot less though.

[Edited by chrisp - 10/7/2002 8:35:46 PM]

R19KET

IMO, PATW's measured on a RR, is just as unreliable, as PATF.

Gearing has a big impact on the results, so it will differ from car version, to car version, and depending in which gear the run is done. Even the g box oil type, and temp will effect the results.

The list you posted shows just how much it varies.

If you want some really impressive PATW's figures, run it in 2nd, or 3rd

Mark.

Andy.F

Chrisp

You'll find that UK owners get a bit miffed at RA's PAW figures
The transmission losses on the rolling road are (almost) proportional to speed, so if your peak was at say 85mph in 4th, then a UK car with peak at 110 mph is going to have approx 25% more losses.
PAW is what the rolling road measures and that is what actually pushes you forward. Anything else is a calculated figure.
To compare a UK to an RA PAW figure you would need to run the RA in 5th OR the UK in 3rd. As for the Sti's, they're somewhere in between

Andy

shunty

so Andy F - does that mean that the RA's run out of puff @ 110-120 mph then...that's why a P1 & 22 B are so expensive as they have low gearing for the first 4 to give great 0-60 & 0-100 but a very high 5th gear to obtain the 155-160 mph then ??
so theoretically then if you change the gearing on the RA's to get a higher 5th gear you get the best of both worlds but at a cheaper price??

shunty

boomer

FWIW,

my figures from Powerstation (Cheltenham) from May were...
PATW: 159.5 @108mph/5860rpm
PATF: 234.0
Drag: 74.5

whereas yesterday at John Noble it was...
PATW: 151.5 @114mph/6070rpm
PATF: 240.0
Drag: 88.5

both on Sun Power Diagnostics measuring equipment.

mb

ustolemyname??stevieturbo

iTrader: (1)

RA's, P1, and 22b are all short geared, with a 4.44:1 final drive. The gear ratios in between do vary, but they are still fairly short, with the RA being the shortest.
It would almost seem that from what people say about rolling roads, that they are almost no good for tuning a car on????
With so many variables that cause different readings, eg tyres, tyre pressures, gears, airflow, air temps etc etc are they any use at all????
Just out of curiosity, What way are the big HP skylines etc tuned?? on the road, rolling road, or dyno? or a combination of both.
Im sure it would be quite tricky setting up a 800hp skyline on public roads.

Denmark

iTrader: (2)

Hi All.
I just had my my99 on a 4wd dyno yesterday and it showed 302hk/6323rpm at the flywheel and 255 atw.the atw is precisly what my g-tec is showing.
There where another my99 with full turboback supersprint and a kn-kit showing 233hk/5882rpm.
Iam really happy with the result.

Skassa.
link-vf29.hks hiper-costumdownpipe-portet headers-runing 1,2bar to 6500rpm down to 1,1bar at 7000rpm

chrisp

Just add a few more bits to it mine was doing 103mph@7,600 rpm in 4th gear.



Heres my graph if you are interested


I was thinking about this last night (in the pub ) and the graph the computer shows first is the PATW at teh end of the run the TL's graph appears and so does the PATF so I assume that its

PATW+TL gives PATF

Which means if I had the same TL as a UK I would be well over 280bhp and closer to 300bhp. Strange isnt it

tinvek

couple of points

1 "rolling roads are no good for tuning" - rolling roads are as near to ideal for tuning as you can get unless you can alter fuel / ignition values on the fly from within the car whilst its being driven which can be awkward if your trying to optimise the power for full boost at the redline in 4th .

2, power outputs / lossescan differ for all sorts of reasons. your engine may be runninghotter / colder. the air may be hotter, your intercooler may be hotter. all of these can make large differences in power when nothing else changes (read any decent road test on the sunny 4wd turbo, they all found they could only get one decent 0 - 60 attempt before the intercooler became too warm) transmission losses are effected by the gear ratio as the gearbox is a torque multiplyer and horse power is just a simple formula based on torque and revs

horsepower = torque X revs
. . . . . . . -------------
. .... ... ........5252

transmission losses can differ due to temperature of gearbox oil, diff oils, tyre preasure and temp, tyre slippage on rollers, tyre deformation, make of tyre, even suspension heght can effect the reading due to the angle c/v joints are running at. being 4wd, subarus will have much greater losses than a 2wd car. all transmissions need energy to turn them over. consequently this loss is a bigger proportion of lower powered engines output. for example if you had a mk2 escort mexico witht he 1600 pinto producing 80 hp and the transmission used 20hp then the power at the wheels would be 60hp ie 75% of the engine output. now put a 2000cc pinto in and it produces say 100 hp. tranmission losses would be the same so now you have 80 hp at wheel ie 80% of engine output so now your transmission appears more efficient.

what you need to do is firstly ignore anyone elses power figures unless they were achieved ont he same rolling road under identical conditions. then you need to be sure that the person tuning your car is competent. watch for tricks like changin the gear the car is run in so it appears more powerfull after hes "tuned it"

if you an to be sure the rolling road / opperator is fairly honest check the torque and power figures at 5252 rpm they should be identical obviously its going to be almost impossible to get an accurate fgure at 5252 rpm but it you should be able to get an idea from the figures at close rpm

*edit - cant get formula to line up 5252 should be under torque X revs

[Edited by tinvek - 10/7/2002 10:37:08 AM]

[Edited by tinvek - 10/7/2002 10:38:38 AM]

chrisp

I think the bottom line is that my pretty much still catted standard car made 195bhp at the wheels (which is what the RR measured) and has a good curve (no dips) and wasnt detting. Thats good enough for me, power at the fly is not worth worrying about. There were a couple of modded P1s with about the same PATW figures which means on the road they would be very little in it from what I can gather. Also looked at the UK turbo dyno figures on dyno.scoobynet.co.uk and most needed 280+bhp to crack 190bhp at the wheels .

Cheers for the input

ChrisP

Ex_Pug

...which can't be right Chrisp. Does anyone else find from 32% right up to 50+% in some cases, a little un-realistic for transmission losses, even for 4wd?

Fuzz

I lost 90bhp due to drag / transmission losses
wheel output 131bhp
fly wheel 221bhp
torque 217lbft

don't ask me what percentage that is tho, I'm a suthener

Andy

chrisp

Ex-pug exactly why you should be interested in power at the wheels not at the fly, the rolling road measures power at the wheels not at the fly. It seems power at the fly is simple a maths calculation based on power at the wheels and transmission losses which could be close or way out. Go to the dyno.scoobynet.co.uk and have a look.

Interesting to see what it does on a few other RR may try a few and see what happens .

Ex_Pug

Chrisp, the reason I'm being so objectionable is because I've already spent a while looking at those dyno figures, and can't understand how apparently sensible flywheel figures, are linked with such low low at the wheels figures. It's as if the dyno run has been done, and a reading taken straight from the computer... a computer which has already worked out a fly figure FROM the wheels figure it obtains initially... and then then the operator has made his own calculation (by using coast down losses, or his own formula) to achieve a wheels figure! It sounds un-likely, and strangely complicated, but I don't know how else you come to the conlusion that an MY00 run at Powerstation (second one down) can have an expected 214bhp calculated at the flywheel, but publish with it an extraodinary WHEELS figure of 113bhp?! That's 47% lost through is (presumably by now) melted transmission.

Ex_Pug

I think you've missed the point I was trying to make with the calculations post. I can get 140bhp down without any problem whatsoever (except praps in first). My point was, a car with 100bhp at it's wheels, is going to be left behind by a car with 140bhp at it's wheels, but as most people can probably guess, the 205 is not quicker that the Subaru.

chrisp

What you have to take into account is where and how that power is delivered. Take a VTEC for instance makes large bhp but you have to go into serious rpms and has no low down torque. You need to look at your 205s torque curve compared to an impreza whats the torque like how much power does it have at 2000rpm whats the spread of that power, how much torque does it have at what revs. An impreza will have far more torque for longer than a 205.

I guess what I am trying to say if you have 140bhp at the wheels thats the maximum it doesnt have 140bhp at the wheels all the way across the rev range. If its high up the rev range and the power band is narrow then you will be done by a car with a car with wider power band and less at the wheels.

Mine has 195bhp at the wheels but only at 6640 rpm and 6641rpm it has less and at 6639 it has less. It comes down to how well the power it distributed across the rev range and how good the torque is accross the rev range. If I sit at 6640rpm in 4th sure it will be putting down 195bhp but it wont be going any quicker.

Andy.F

Just a thought......what would happen if you put a 100bhp engine in that scoob that has 101bhp transmission losses

Forester_GP

It.... would fry the gearbox, of course, if the 525 lbf comes around 1000 rpm or better, the negative energy (trnsm loss) will suck the scoob to hyperspace

George

Ex_Pug

Well, I understand what you're saying, I'm just not totally convinced that transmission losses can be as high as 40% on any car, let alone a Subaru. In a run up to 60, or 100, or whatever, it's only ever 1st gear where you're able to make the most of the Torque in any car, the rest of the run will be using the top of the rev range, where as you've pointed out as well, most of the power is to be had.

Perhaps in the name of science I should get the 205 back out of retirement and see what it feels like, but from memory, it wasn't pulling quite as strongly as the Subaru. If the figures are correct though, I still maintain that a car with an advantage of 56bhp/tonne should accelerate faster flat out. Which I don't think it does, leading me to my main point that transmission loss must be less for the Subaru etc. etc....

I think a reasonable comparison would be the BMW 330D... huge torque (288bl/ft) compared to the Subaru, but less power (and granted, more weight), and a significantly slower 0-60 time, even factoring for a 4wd take-off.

Not being argumentative for the sake of it, I welcome your feed back, and anyone else's for that matter, plenty of views on this thread, but no rolling road experts/physacists yet?

Andy.F

Sorry Ex-pug, not meaning to take the 'P' Just making the point of how unrealistic rolling road figures can be.

Regards RR drag figures, the measured drag on the rollers will be more than the 'real' drag on the road due to the 2 contact patches per wheel. If your car develops enough power, it can lift itself out of the rollers slightly, reducing that contact point to 1 per wheel. Your Pug probably was doing this with that power through one axle. Your scoob probably wasn't
So, compare the drag of the 2 points total on the pug vs 8 points on the scoob and you start to see where some of the questionable "transmission" loss differences come from as both cars obviouly have 4 contact points when rolling along on the road.
FWIW, my scoob developed 305 bhp at the wheels on the last dyno day, this was enough to lift the (lightweight ra) car out of the rollers. As a result, my losses were only 60 bhp or 16% of the flywheel figure (365) I also had the tyres fairly firm and the power peaked around 90 mph due to the short gearing. This all helped reduce the 'measured' losses.
I think this gives a better representation of what actually happens on the road.

Andy



[Edited by Andy.F - 10/7/2002 11:51:52 PM]

Sprint Chief

Ex_Pug

This is all IMHO

Transmission losses on a rolling road are driven by a lot of different factors, but tyre deformation is significant. Remember, when the tyre is on rollers it is effectively pinched between two points. The rollers have a small radius, which increases tyre deformation compared to the road as well.

So in total your 4WD roller is deforming tyres in a total of eight places! On the road the deformation will be in four places. For the 2WD car, on the rollers there is no measured loss through the undriven tyres - but they will drag on the road. But the 2WD also suffers an exaggerated loss from the front (narrow radius rollers, etc), so in fact the 2WD RR result is probably representative of what you might see on the road, the 4WD RR result is extremely pessimistic.

Plus it is not likely that you are dissipating 100bhp through your transmission - which would ultimately end up as heat - without melting your diffs, tyres and suspension

Rolling road results need to be treated with caution, should not be treated as "absolute" but as "relative" figures for setting up a single car. Beyond that, if you want to know which is faster, best get to a track

Forester_GP

Seriously, though, i've got 248 PS & 245 lbf at the dyno last week with a very flat torque curve from 2800 - 5800, PAW was 189 PS. My PAW figure and TQ curve is very similar to SAAB 9-3 Aero (FWD)and S3 @210PS, needless to say that i've smoked them both in different occasions with ease (SAAB accelerating from 100Km---> & S3 when caught up with him at 185Km and then hit 225Km), so i tend to agree with EX-PUG that the dyno PAW figures are erroneous and/or max BHP along with smooth TQ curve (ChrisP) is all that matters.

Regards,

George

Ex_Pug

Thankyou for your respective replies. I appreciate all the variables mentioned. Just out of interest, the only car I've had on the rollers as yet is the Peugeot. Subaru figures I've been questioning have been those on the Dyno pages. Power runs on the pug have been done on occasion with a body sat on the front of the car to reduce the very effect AndyF mentioned... that of the car trying to scrabble out of the rollers. This hasn't allways had to be done, but nevertheless, the power figure obtained at the end of the run has allways been to whithin 4bhp, body or no body (but allways nill slippage if ya gets me).

Anyway, is it really possible that the reason there are such consistantly high (and perhaps more importantly varied!!)indicated transmission losses on the Dyno pages, can be put down to tyre contact with the rollers? There are obviously all the other variables to take into account, most of which have been mentioned, but some of the results show huge discrepancies. What with Chrisps 25%, and many examples of between 40% and 50% from here, it begs the question, why do so many people feel they can quote power figures when comparing one car to another, if all they have to go by is there rolling road print out? It would seem that they aren't really worth the paper they're written on. Surely there must be something in rolling roads, or are we all being taken for a ride by the operators (who I can well accept, in some places, probably couldn't explain rolling road losses any better than I) of such devices.

Well, it must be late, I've started rambling, and I was going to say something else which I've now forgotton. Rest assured that it was indeed a very important and relevant something.

rex11

Losses of around 30-50% are reasonable for a all wheel drive car. I've seen comparable figures on DSM sites and have seen figures of around 1-20% on rear wheel drive cars.

Any time you tune a car it doesn't matter what your comparision baseline is, as long as it stays the same. If you do the baselining of the stock car on a two wheel dyno and than go to a 4 wheel dyno for the remap, your bound to not see as big of an increase as just sticking with the 2 wheel dyno. As for comparing with other cars just don't use HP numbers. If you want to compare run some 0-60 times and then compare. Whicle this factors in some driver bias, it takes into account areodynamics, weight, and transmission losses. The method of study just comes down to if it's a bragging or tuning issue.

Hoppy

Ex-pug, whadayamean it's late, you light-weight? I'll send you some of my insomnia pills - they'll work wonders for your Power-At-The-PC figures

Good debate. But don't we all know that rolling-road figures are very hard to compare? And in absolute terms, they are (almost) total bollox? With the same car on the same rollers at as near identical running conditions as possible, they are a helpful tuning aid for to the experienced tuner's eye. Everything else is pub-talk.

Of course, we all like to talk about them, because they're the only comparitive common currency we've got. But on the road, they mean diddly. You wanna talk real performace? Look at Andy F's standing quarters. His car is mega-quick, but in R/R terms he's some way behind other cars in pure bhp terms. Like a 550bhp Scoob motor that is known to be lurking in the midlands... There's more to it than bhp.

And Scoobs are especially prone to variations of temperature/cooling due to the top-mount inter-cooler flushed by static cooling fans on the R/R. Not real road conditions.

John Banks has just done a Tek3 ECU remap on my well-modded UK00, which involved a lot of hard driving, ECU tweaks, followed by hard driving and more ECU tweaks, etc etc. It takes a few hours, but it's great fun and you can feel the ECU improvements on every run, while it all shows up on the boost gauge and KnockLink. On the 400-mile drive home, I got 1.4 bar of boost and not a trace of det on the KnockLink. Fabulous

But on a warm day today (yesterday?) I could only manage 1.3 bar. Strange what a few degrees of ambient makes. I'll do a rolling-road test soon - prolly on the coldest day in Jan 03, at PE, with a tank full of octane booster and tyres at 50psi. I just want a piece of paper that says 300bhp-plus.

But privately I know it's quick anyway. Unfortunately for my bank balance, I also know how to make it even quicker

Sorry to ramble, but it's late. Or is it early? Whatever, bedtime either way.

Cheers,

Richard.

tinvek

as i said previously horspower is a mathematical conjuring trick

it was based on the maount of effort it was believed a horse could do and is calculated from revs and torque

ie (and i'm not going to try and post the formula the way i did before)

horsepower = (revs * torque) / 5252

so if you have two engines both producing 200 lbs torque but one produces it at twice the revs of the other it has twice the horsepower

BUT!

torwue is what accelerates you and working backwards 200 hp at 2000 rpm is 525 lbft torque whilst at 6000 rpm its only 175 lb torque in fact at 6000 rpm 550 hp is only 481 lb ft torque so which is the most powerfull engine? going even more extreme and tkaing an educated guess that the BMW f1 engine produces 880 hp in qualifying at 19000 rpm this is only 243 lb ft torque

the only way you can do a real comparison is to measure the total area under the torque curve on a graph. obviously its further complicated by how the gearing of the car suited the power / torque curve. often people will tune their cars and in doing so move the torque higher up the rev range which can then make in unaccesable with the standard gearing.Honda have actually managed to do this with the standard S2000 sports car where you cannot acces peak power in any gear higher than 2nd without risking a ticket.

tinvek

also don't forget anothe reason for high transmission,losses on a rolling road is that the transmission doesnt benefit from he cooling effect of the wind passing over it.

give your car a good thrash down the road and then feel the rear diff. then give it a couple of full throttle runs on a rolling orad and feel the rear diff