Gtech Pro RR

[s2driver]

Wierd that, I had 40bhp 'estimated' losses at G-Force too but closer to 80bhp at the same revs in the same gear when measured on 3 other completely different dynos.

[Dippy]

Wonder when the next Santa Pod "run what ya brung" session is? I feel a "calibration" session coming on.

You do remember what happened to Joshie don't you?

[KayGee]

Yes, the one MK meet i attended he told me all about it.... Still can't worry about these things to much, otherwise I'd still be driving an Astra. Don't see the point of having a performance car and not using its potential at least sometimes.

[Dippy]

True, but you have to accept it's limitations as well - is the gearbox really up to it?

[Verruckt]

Many dynos are ONLY useful for shootouts and modification comparisons when developing a car. The absolute BHP figures are often misleading but can be fantastic for pub talk. On my motor I have had 80bhp peak losses at peak power in standard and remapped forms at multiple outlets that measured the power profile on coast down. With the G-Force RR they 'estimated' 40 bhp losses based on some fudge of entering various vehicle specs....not reliable IMHO.

Driveline losses are not a percentage of engine power! If you double the power, you will not get double the losses unless peak power revs changes significantly and other drastic mods are made. We had several S2s on a Maha dyno and the loss profiles through the revs were very similar for S2s from 300 to 480 crank bhp running everything from 205 to 255 rubber.

Mihnea, do the US dynos have extra fudge factor built in? Most US car manufacturers quote their power figures (DIN?) based on an engine with all ancillaries removed. Could the figures be optimistic due to the correction factors used. Doesn't altitude play a part in the correction too?

Accelerometer based performance meters only produce reliable figures if they have been calibrated on a 1/8 and 1/4 mile track. They cannot compensate for vehicle pitching so their figures for acceleration are mostly optimistic. As the car squats under power the acceleration vector cahnges as the unit is no longer level so you start introducing a proportion of gravity into the calcs. Once you have calibrated the unit for your particular cars suspension settings, your acceleration times will be quite reliable but when it comes to guessing the power you are likely to be way off. These performance meters are like inertia dynos...great for checking the comparative improvement of certain mods on a car i.e how did the power profile change when a part was changed: air filter, ported head, exhaust, remap etc

Inertia dynos are great for shootouts too as they are consistent and if you compare tractive effort at the wheel surface you can compare the cars on test on the day.

Normally aspirated cars are more consistent on RRs. Turbo cars are so dependant on the cooling system employed at the facility. If the cooling is poor you may 'lose' a lot of power due to the test conditions (and the operator action..BTDT recently!).

There are a few things wrong with this statement. The MAHA measures coast down drag which will not change as horsepower increases. However, the actual parasitic drag the car encounters must increase with input torque. Basic Thermodynamics guarantees this. More power in means more heat in the drive line means more loss.

US cars are measured in SAE HP which is actually slightly more powerful than the Euro DIN ratings. The engines are tested as they would be in the car will full accessories.

The newer G-tech models do, in fact, take vehicle pitch/roll into account and you can adjust it. On a tightly sprung vehicle like an S4, the pitch/roll isn't incredibly significant from what I've seen.

My findings for my Golf were very consistent and comparable to the MFG specs of 105 hp and 185 ft-lbs.

My G-tech testing with the S4

[S2tuner]

Chris, agreed and fine for me with coast down losses, however, the real question I have asked was: how come that whenever I've had a stock car of a certain type on a MAHA/Bosch dyno, it had the power it was meant to have? How come that a car with a Lehmann engine-dyno-tuned engine and rated at a certain number (495 HP) got dynoed in France and got 495 crank HP from a 4WD dyno?

So far no one has answered these questions, neither here nor in the US....


Take care,

Mihnea

[Verruckt]

Chris, agreed and fine for me with coast down losses, however, the real question I have asked was: how come that whenever I've had a stock car of a certain type on a MAHA/Bosch dyno, it had the power it was meant to have? How come that a car with a Lehmann engine dyno-tuned engine and rated at a certain number (495 HP) got dynoed in France and got 495 crank HP from a 4WD dyno?

So far no one has answered these questions, neither here nor in the US....


Take care,

Mihnea

I can't answer that question by any stretch Mihnea. I take many dyno numbers with a grain of salt. In the US, most people use the dyno numbers for bragging rights and their timeslips for proof. Any place you go, a quarter mile is a quarter mile.

Anyway, I'd be happy to come visit you in Koblenz this weekend, thanks for the invite. Please email me with the specific info (times, address, etc) and I'll meet you there.

[Verruckt]

Double post.

[S2tuner]

Lol, no probs Chris, will email you in a bit with all details

Cheers,

Mihnea

[s2driver]

Thermodynamics would suggest that as you increase power, parasitic losses will increase. From practical experience on very similar cars with vastly differing power outputs it appears that there is no proportional correlation between losses and power. Seems that crank power increases have a very marignal effect on transmission losses in reality.

[KayGee]

So in conclusion, I'm now safe to calibrate my S4 and Gtech Pro on the drag strip as the gearbox won't explode with the extra HP being fed into it and if does, no worries, as either Chris or Mihnea is paying the bills?

Sweet

[S2tuner]

LMAO, hmmm, Chris? What do ya think, dude?

[KayGee]

Chris thinks it's a great idea!

[S2tuner]

Fine for me if he's ok to pay for it, that shows us Chris is a real gentleman

[Verruckt]

So in conclusion, I'm now safe to calibrate my S4 and Gtech Pro on the drag strip as the gearbox won't explode with the extra HP being fed into it and if does, no worries, as either Chris or Mihnea is paying the bills?

Sweet

Nah, the gearbox is pretty tough. You're more likely to do what I did...



FYI, Audi roadside assistance towed me from the track for free.