Cristel993

I had my car remapped last year and a fellow 911uk member had their car remapped on the very same dyno by the same person.

Here are the results:

My C2 (Dansk 100 cell cat and mufflers):



Comparison C4 (RSRs):



Looking at the difference between whp and bhp for the two cars:

My C2

whp - 275.4
bhp - 309.4
lb/ft - 275.7
transmission loss = 12.7% (have I got this right, or is it 11.3%?)

Comparison C4

whp - 260.3
bhp - 309.6
lb/ft - 301.3
transmission loss = 18.9% (or is that 15.9%?)

Both cars were tested at the rear wheels only, as this was a two wheel dyno.

I wonder why such a difference in transmission loss is seen here?

If I was at 18.9% transmission loss, I would have seen the following figures:

whp - 274.5
bhp - 326.3

Would my torque go up by circa 6.2% as well? If so, would I be at 292.8 lb/ft?

If the C4 car was at 12% transmission loss, would the following figures apply?:

whp - 260.3
bhp - 293.4
lb/ft - 282.6

Not sure if I've got my numbers correct in terms of working out transmission loss, but certainly intriguing to see such a difference if both cars were tested at the rear wheels only?

Cheers

Sam

Stealth 993

How do you know both are 309 bhp? I'm not quite sure what you are asking.
The C2 did 274
The C4 did 260

Even with the "same" tune, weather, engine condition, & even tires can change the numbers. All I got from this is the C2 has a stronger engine. But if the C4 is stock, & the C3 has the cats & exhaust that would explain the higher numbers.

Cristel993

Am interested to know why the guy running the dyno has applied different transmission loss percentages to obtain bhp figures and if this has had an affect on torque figures.

mongrelcat

Seems like the obvious answer is to ask the guy that setup the dyno.

Running a C4 on a two wheel drive dyno seems like quite a bad idea.

Stealth 993

I think there is some information missing.

A C4 will have a higher drive train loss over a C2. But if you make a C4 into a C2 it should have about the same loss.

BHP is just a after calculation, it does not affect the dyno setup or numbers. It can not be reliable, as there is no real way to measure drive train loss unless you dyno the engine (engine dyno) then put the engine in a car & remeasure @ the wheels. Dyno's only measure wheel hp (wheel dyno) or crankHP (engine dyno). From the engine dyno, you can get accurate BHP.

TheOtherEric

I sure hope the C4 owner removed his driveshaft since he dyno'd it on a 2-wheel dyno. That being the case, there should theoretically be no difference between your results, just typical variances due to being different cars, weather, etc.

One thing I've learned in several years on Rennlist is that there are big car-to-car variances in power. Feel free to speculate as to the reasons for that.