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**Lee** · 25 December 2003, 17:24

Kim from QST said that he may be able to support an S2 rolling road day. Not sure how good his setup is but it sounded pretty good when I spoke to him recently. It's wasn't 100% finished but it might be worth a try if there is a slot available and it isn't too expensive.

We can still use the inertia dyno at G-Force. Very accurate (sorry, 'consistent') at the wheels and this is the most important figure. Problem is, you can fool an inertia dyno by fitting lighter flywheels and things. This doesn't actually make our cars much quicker in the real world because aerodynamic forces dominate at higher speeds as they are a function of velocity squared.

The best dyno has to be the engine test cell...only an option if you were creating a monster and wanted to fine tune it before install into the car! Comparisons are time consuming. LOL.

Maybe the best thing to do is to find a good, reputable dyno and with the same (skilled) operator it should be pretty consistent. Use the same place as there is huge variation between facilities and staff. Horsepower is just a pub figure anyway so maybe the actual values are not important. Do we want a comparison between modifications or a definitive "here is my maximum horsepower at 6600rpm blah blah"? My biggest interest in a rolling road is to understand the effect of modifications. Understanding is the biggest key to improving further.

A stock S2 would cane a T5 yet they have similar peak horsepower. Study their torque profiles and rev range and you'll realise why. T5 has an impressively flat torque curve but the S2 can stay in each gear over 1000 revs longer. Closer ratio box in the S2 helps too.
My mates TT produced 110 bhp at a rolling road session but it was as quick, if not quicker than mine. Horse crap rolling road!

Rolling roads are good for comparisons and shootouts only. Never expect any definitive or accurate power figures. Engine dyno only for accuracy!!

**Pisobiker** · 26 December 2003, 22:15

Mihnea, I have been thinking a little more in depth on this subject last couple of days (while eating italian "lasagne" and "panettone"

) and have some considerations I would like to share:

What I was previously thinking, about detecting drivetrain + tyres + aerodynamical (if needed) power consumption, was a curve that could represent the effective value of the particular dissipating layout at each speed reference point (which will, given the gear, give rpm reference points).
In this case I still cannot find any physical factor which could explain why, having two stages of engines, at same rpm and same speed of drivetrain+wheels we should get power (or torque) consumptions proportional to power (or torque) outputs.

BUT

I now figure out that probably the most interesting numbers are not the real power consumption of the drivetrain assembly at each steady speed and rpm, but how much power the layout will "suck" when you ACCELERATE the whole thing the quicker the engine is able to do.
In this case, then, I have to recognize that your "consumed Force" will be some how proportional to power output. This because the more powerfull engine will impress a higher acceleration to the whole masses thus increasing theyr inertial forces reaction, which are proportional to acceleration.
We will still not have perfectly proportional to Hp output power consumption (because acceleration here is affected by non linear forces), but at resonably low speeds and not taking into account aerodynamical forces (perfect on a dyno), it will be very close.

Any comments? Am I wrong?

Marco

**Glen Chamberlain** · 26 December 2003, 23:05

A stock S2 would cane a T5 yet they have similar peak horsepower.

Sorry Lee but no way man! S2 may beat it yeh but no way cane it! I have driven thousands of miles in both these cars (both the 225 BHP T5 and the 250BHP one too) and performance is similar mate! Yeh granted the S2 can definalty use the power better due to 4x4 but engine muscle there are close! The S2 does have more tourque but also has to constantly power through a quattro system, so it's pretty much even stevens i say m8! "Iam sure that this fits in somwhere with the whole drivline loss thingy?"

**Mihnea** · 27 December 2003, 00:15

Marco, nice one, I've had lasagne last week and I've eaten as much panettone (genuine Italian panettone!!!!!! mamma mia!!!!!) as you like since the 24th until tonight and I'll have some more tomorrow! Man I love that "cake", it's just brilliant!!!!!!

Okay now, let's stop talking food, I've had too much for today already

Originally posted by Pisobiker
Mihnea, I have been thinking a little more in depth on this subject last couple of days (while eating italian "lasagne" and "panettone" ) and have some considerations I would like to share:

What I was previously thinking, about detecting drivetrain + tyres + aerodynamical (if needed) power consumption, was a curve that could represent the effective value of the particular dissipating layout at each speed reference point (which will, given the gear, give rpm reference points).
In this case I still cannot find any physical factor which could explain why, having two stages of engines, at same rpm and same speed of drivetrain+wheels we should get power (or torque) consumptions proportional to power (or torque) outputs.
BUT
I now figure out that probably the most interesting numbers are not the real power consumption of the drivetrain assembly at each steady speed and rpm, but how much power the layout will "suck" when you ACCELERATE the whole thing the quicker the engine is able to do.
In this case, then, I have to recognize that your "consumed Force" will be some how proportional to power output. This because the more powerfull engine will impress a higher acceleration to the whole masses thus increasing theyr inertial forces reaction, which are proportional to acceleration.
We will still not have perfectly proportional to Hp output power consumption (because acceleration here is affected by non linear forces), but at resonably low speeds and not taking into account aerodynamical forces (perfect on a dyno), it will be very close.
Any comments? Am I wrong?
Marco

Ummm, too fecking technical for me but I can see where you want to get... damn, where are my engineering courses????

Ohhh god, I can't think properly right now....

BUT, one thing is for sure after reading Greg's post with the link to that tuning company that only relies on wheel horsepower, I think that from now on we should all think in terms of wheel HP and not crank HP....

My idea for the next months (years?) is to build an engine dyno, I've already read a few DIY guides and it doesn't look all that complicated. A separate cooling system as well as hybrid wiring harnesses (for 3B and ABY/AAN/ADU) will be necessary but that's not my main concern.

Then my other idea was to use accelerometer software in order to measure HP dynamically while driving on a road/airfield/whatever, and finally, to use that sort of accelerometer stuff on 4 rollers with brakes that would simulate real world driving conditions.

Now, I'll need a serious garage budget but if I get my company running, that should be no big deal if all's well....

Mihnea

**Pisobiker** · 27 December 2003, 00:42

Hurray for AT THE WHEELS figures !!

Mihnea, nice projects you have for your tuning career. Wish you'll succeed

Marco

P.S. Would you need a "spalling partner" for the hardware stuff?

Announcement

Dyno issues, drivetrain losses and so on

Dyno issues, drivetrain losses and so on

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