Dyno question>>>>>

[Greg]

I had my 95 M tested on the dyno in 3rd gear. Apparently the gear to test in is fourth...

Does anyone know what the difference in reading might be?

The guys at ERT said that the reading in 3rd gear will come out lower than actual readings.

Any input?

Thanks

Hellred Kompressed
95 M3 ERT blower
:confused:

[PM3]

I had a car tested in both gears and it didn't give that big of a difference (within a HP and pretty much the same curve). 4th gear is probably easier to read, especially with higher HP cars, because it gives more time to actually read thru (this is just my guess)..but some tunes like to use 3rd gear because they don't like having the wheels spinning up to 120mph..

I think you're fine in 3rd gear. We do most, if not all of our testing in third gear, at McMullen Argus. what did you get? CYA>PM3

[Jim//M3]

Some people will use 3rd gear on a dyno if they still have a speed limiter in place.

[Greg]

When I got to this place after an 1 1/2 hour drive on the highway, I barely got a chance to let the car cool down before we tied it down to the dyno.
My first run, I got 283hp at the wheels. 260 or so tq
By my second run I dropped about 12 hp! And more as it went!!!
One thing the power curve was almost a perfect 45% angle.
The guys at the shop were also surprised that the torque curve and hp curve did not cross where they were supposed to at 5252rpms or something like that.
That pushed me to believe that 3rd gear was not accurate for testing.(I realized this later)DUH
I think that if the car had cooled a little more, and they had a strong fan acting as forced induction, I would have gotten a more accurate reading.
I'm running about 6psi, and have not yet gotten a chip burned for the setup.
Hopefully that will balance things out.
I could be running lean...
I'll re-post when I go to ERT in April for the chip burning.
I may do cams... Not sure yet.

95M3
ERT blower/pulley/injectors/software
SS headers/ES tuning exhaust

[V Shah]

Originally posted by Greg
The guys at the shop were also surprised that the torque curve and hp curve did not cross where they were supposed to at 5252rpms or something like that.

This is not possible. Please see http://www.bimmerforums.com/forum/showthread.php?s=&threadid=1078 for more information on why torque and hp must cross at 5252 rpm.

[Greg]

I kid you not... The guys at the shop were shocked. Again this is why I feel testing should be done in 4th gear not 3rd. Maybe the dyno was a piece of shit?
G

[E36 Fanatic]

Someone correct me if i'm wrong, but 4th gear is usually 1:1 ratio, and that's why they dyno in 4th. (again, i could be wrong, but i'm pretty sure that's the reason.) Here are a couple of vids of my roommate's WS6 formula firebird at a dyno. They let it cool down, and as a result, it kicked a MAF sensor error, and it sputtered and whatnot. The vid called robsws6dyno shows a proper dyno run, and the other is the f'-up. I think you'll have to download and then open the vids. I couldn't get them to work directly off my site. Anyway, just rambling.
Nick
http://communities.msn.com/BMWPlayground/dyno.msnw

[RS]

from the ever helpful Bob///M3:

>The transmission gear ratios for a E36 M3 are:
>1st Gear 4.20
>2nd Gear 2.49
>3rd Gear 1.66
>4th Gear 1.24
>5th Gear 1.00

ya, since hp = 550 ft-lbs/sec = torque (ft-lb) * rpm (rev/min) * (1 min/60sec) * (2*pi radians/rev)

or hp = (torque * rpm) / 5252

so hp and torque have be equal at an engine rpm of 5252 rpm. So for the dyno, it measures torque from the wheels and I guess it measures the rpm of the big drum the wheels are spinning. Since the dyno knows the torque and the rpm, if they aren't equal at 5252 then it sounds like the dyno rpm measurement needs to be recalibrated or something. But if the dyno is taking your engine's rpm measurement, then your gear ratios may not be accounted correctly for the gear your in, or your wheel size is a little different than stock......????

[Greg]

Wheel size is correct, and the diff is stock.
Thanks for the input BobM
Greg