To all the people who have had their S2s dyno tested

[Mihnea]

Originally posted by Lee
G-Force have an inertia dyno which is mean to be 0.1% accurate at the wheels. They build racing racing cars, specifically Porsches (GT1s, 935s, etc) and the have derived some software to calculate power losses for various transmission and engine configuratioms. THeir derivation had proved accurate on many race cars and some silly power Skylines and Cosworths I believe. Stock RS4s were putting out a derived 380bhp at the flywheel which is spot on. Maybe we should have a rolling road session there so Mihnea can find out how its done! They estimated the losses on my S2 to be 42 BHP although I have also had it measures at 81bhp on mine by someone who has a bit of a reputation for being anle to cook the figures so I am told. Explains some of my power figures though!!

lol, dunno if I could figure how they derive the driveline losses, I'm not the mechanical engineer here

@Mihnea, I suspect that frictional losses are more a function of Torque than power too. Just a thought!

That's correct too, just because HP is only a function of engine revs and torque, what you guys feel with your butt dyno in your seat is torque, not HP

[Lee]

Yep, its all about Torque profile through the revs. Horsepower means nothing as a single figure.

[Pisobiker]

Originally posted by Mihnea


.......I know frictional losses increase with heat and that a 1000 HP engine generates more heat than a 136 HP one, but can one just generalize and say that the driveline losses are a 25% constant?

I'd say no...

Mihnea, some time ago answering to a question on my thread "My latest chiptuning full report" I expressed my idea of the problem which is much similar to yours.
this is what I answered:

"Both mechanical and aerodynamical losses increase more than linearly with speed.
Then saying a transmission has 25% or whatever percentage mechanical absorbtion of delivered power is wrong (or at least not correct) for two main reasons:
1) Power losses depend on speed, and only very little of power delivered by engine;
2) Power losses are not a fixed percentage through the rpm but increase with speed.

Statement n°1 mean that a given car with 100 hp and running at 100km/h, will have lets say a 30hp of power losses. If same car @ same speed gets a 200hp engine on it power losses will be the same as before or very close to the same.
If you would have applyed the "fixed percentage" rule to the second example using data of the first one, you would have guessed 30% losses which would have been 60hp....

Statement n°2 mean that the car of example 1 would have power losses that increase while increasing speed but with a parabolical curve, totally different from its engine power curve.

The right statement would than be:
"car has 25% power losses at peak power rpm and whatever speed"


Marco

[Dr H]

Stock ABY :

228 bhp at flywheel
161 bhp at the wheels

Ambient temp about 30 c :wacked:

[martinjs]

Mihnea, i have some figures from geforce earlier in the year when it was stock, ill post them when get home in morning:wacked:

[Mihnea]

Originally posted by Pisobiker The right statement would than be:
"car has 25% power losses at peak power rpm and whatever speed"


Marco

Marco,


This is exactly the problem, I don't think your statement is really correct, here's an example:

Mark's car last monday: 327 HP flywheel, 225 wheels= 102HP= 32% loss

Mark's in July: 393 flywheel, 301 wheels= 92HP= 23% loss

My friend's S4 with RS2 bits= 352 flywheel, 299 wheels= 53HP= 15% loss

Tom's S2 with K26/27= 305 flywheel, 252wheels= 53HP= 18%

Sal's S2 with RS2 turbo, EM and IC: 292 HP flywheel, 243 wheels= 53HP= 18% loss

Leigh's car: 228 flywheel, 161 wheels= 67HP= 30% loss


So where's the truth???? If it weren't for Mark's car and my friend's S4, we could say that PTS's dyno was calibrated on purpose to display "default" values as tranny losses, but I just don't think it is so...

The idea is that there's been like a constant through cars with different HP levels, at around 50-70 HP loss, no matter what the peak HP was, except for Mark's...


Cheers,


Mihnea

[Vagsport]

It would seem there are quite a few variables to take into consideration. There was a suggestion that an incorrectly caliberated platform (to suit different wheelbases) could be at fault. I go along with this theory.

An incorrectly set platform, +/- will increase friction losses as far as tyres go. I observed the platform was not adjusted all the time, i.e each time a different S2 went onto the rollers. Due to suspension setups, 3 S2's with the same (factory) wheels can have slight variations in wheelbase length. Wishbones / bushes can also have a direct effect.

One thing the caliberation in RR platforms can NOT take into account is the driveshaft angles, a lowered car will generate greater losses, if the driveshafts have less 'plunge'. The same applies to camber / toe angles. The operators generally apply a factor to acount for transmission losses, but there are so many variables, I don't think their estimates can be applied to all cars.

Another way (if the engine is out of the car) is to have it on an engine dyno, but I guess that would probably give the same results as you would get @ the flywheel on a RR.
HTH

Siena

[newsh]

This is from my first run in the morning with the bad missfire.

Mihnea chipped 3B
Milteck Exh, no cats.

Flywheel 247.7
Wheels 165.8
Loss 78.5

My best run was 267 but I only have the graph for that one.

[Pisobiker]

Mihnea, I might not have expressed the statement clearly but we are saying the same thing.
What I mean is that if you find that your tested car has 25% drag, this will of course be referred to the top hp which is obtained at a well defined engine rpm but also at a well defined speed of vehicle.

This means that you can say (just giving example numbers) your car has "25% drivetrain losses @ say 160 km/h".

You could compare those losses only on another car at same speed.
It is absolutely nonsense comparing the 30hp losses of lets say a Fiat Punto whose 4th gear peak power speed is 120 Km/h with the 60-70 hp losses of an S2 whose 4th gear peak power speed is 170 Km/h.
S2 at 120 km/h might even have less losses than the fiat Punto thus showing a higher drivetrain efficiency !!


Marco

[APNess]

When AMD did it (woot!) ;

Stock: 256hp@Flywheel, 294lb ft
Chipped: 312hp@fly,319lb ft
At wheels: 197bhp, transmission losses 115bhp (in 5th)

(Optimax fueled, car had just been fully serviced - plugs, fuel filter, the lot, ALL READINGS TAKEN IN 5TH GEAR, 20 degrees ambient, 120mph rolling road speed, barely legal tyres on 16s. The tires *cough* sort of passed the MOT a month later *cough, cough* failure*cough)

Presumably there should be more @wheels in 4th, and it's on my list o things to do. Car has since had decat, cat back Milltek, and lag is much reduced (comes in 500rpm sooner), so I'll need to get a reading before the RS2 bits/Hybrid blower goes on.

It's well known AMD *might* (Disclaimer!) be generous when it comes to quoting hp figures. The car will leave a standard impreza turbo, with the S2 in a higher gear, in 6th vs 5th, from 70 to 150mph. Couldn't do that before!

I recall struggling (pre chip) with all manner of 200hp fwd machines. No such probs these days (and hopefully in a few months I can say that about porsches!) Damn these things are heavy (and I add 115kg. Burp.)

PJ

[tacq]

Oldest measurement?...

A few years back when I had my S2, and it was almost in stock except for an MTM ecu upgrade (3bar map & 270hp chip) showed this result results.

[Mark Halligan]

Mihnea, I just found the old plot from AMD from back in November 2000, this was when my car was a bit more normal with just a K&N panel filter and a re-chip.

Power at flywheel was 290.2 Bhp

Power at wheels 208.1 Bhp

Transmission loss 84.7 Bhp

So putting them together in date order:

Nov 2000, 290.2 Bhp with 84.7 Bhp transmission loss

July 2003, 393.4 Bhp with 83.9 Bhp transmission loss

December 2003, 326.8 Bhp (overfuelling problem) with 97.5 Bhp transmission losses.

So over the three years that I have had it my transmission losses have always been high :wacked:.
Now I am not even going to pretend that I know anything about rolling road calculations, and how figures are arrived at, I suppose I just need to know is my gearbox/diff fooked in someway .

Confused,

Mark

[Vagsport]

I wouldn't worry about your transmission, Mark. I reckon they're ok.

[audiman]

Mark, i know this is just a stab in the dark, but you do have wider section tyres. Could that cause the greater drag? Also if you had a sticky caliper or something? Just doesnt make sense. My car has only ever been on the rollers once so I have no other figures to look at and compare. Will have to wait until next time to see if my figures for drivetrain loses are the same as before. Maybe its an age thing :nana:

[Mark Halligan]

Well young Thomas me lad

I've been thinking a lot about this, and I thought that it might be that, but they are only 18x225's and besides the first re-map I had done (Nov 2000) was with the standard wheels.
I thought that maybe it was an alignment problem, but my tyre wear is OK, in fact the SO3's I have on there have been fitted for almost a year now and are hardly worn, I havent even had to swap front to back yet.
So I have no idea.

Just a question to anyone really, in simple language, how is the transmission loss calculated .

One thing though, the other times I have been on the RR it was done in fourth gear, this time it was in fifth, does it matter?

even more confused,

Mark.