Bond

Using my acceleration simulator program (Cartest 2000 from cartest software.com) over the years I have always been amazed at how accurate it is relative to the various car magazines road test numbers (R & T, C & D, etc). The program has a huge database of cars with virtually every parameter programmed in that affects acceleration. Its interesting to run the cars stock, then add horsepower, then change the launch techniques from clutch slip, dump, etc at different rpms - it even will find the optimum lunch technique for a particular car.

The above said, I have found that the true (calculated) flywheel HP for my 2001 TT 6 spd must be increased to 477 hp, and torque increased to 457 ft-lb in order to achieve the 12.3/12.4 @ 115 mph 1/4 mile, 3.9/4.0 sec 0-60 time and 0-100 time of 9.2 that both Road & Track and Car & Driver were able to get from the car.

I know that Porsche is conservative on their published HP numbers, but its hard to believe they are 50 hp low on the stock car. Does anyone know the true hp of a stock 415 hp 996 TT?

Bond

Bond

On a similar note - It also needed the 477 hp to achieve 192 mph (the 415 hp gave only 185 mph) - cd was calculated at 0.31

Bond

mjc123

You mean this wasn't possible with 415 hp?

TB993tt

Porsche publish figures based on their engine dyno results - for the 996tt 420PS maximum- your program is wrong. A 996tt with 420PS max is not necessarily the same as a 996tt with say a tuned GT3 engine giving 420PS max - the shape of the torque curve will make the turbo car give better figures.

cobra06

Crunch the numbers in here:

H.P. Calculators using 1/4 times

Bond

TB993tt - The program takes the turbo's unique (flat from approx. 2500-4600) torque curve into account, so this does not explain the descrepancy.

Bond

Craig S. Couris

The 192 MPH is quite impressive but I'm sure the 48 degrees F meant that the corrected altitude was well below sea level, for a very dense air charge. That was probably very helpful in acheiving the big speed.

GuyR

The calculators don't take into account many factors such as transmission type, gearing, traction, bhp 'under the curve' etc so I've always viewed them as being not much use in deriving actual bhp. However they are useful for incremental calculations, for example 'how much bhp extra do I need to drop 0.5 seconds for a given car.

As for the 996TT bhp, I have been to the engine dyno rooms at Porsche factory and they state that their policy is to dyno every engine made and they must make between 100% and 105% of stated power or they are rejected and rebuilt. The reason for the 100% is obvious, but the 105% is due the fact that excess power is likely the indication of a faulty part causing overboosting.

However, once the cars are run-in it is always possible that more power will be developed as is the case with most cars as they loosen up. In addition, in colder climates it can make more power as the turbo's efficiency rises and intake temp lowers.

I'm sure most stock turbo dynos back up the factory power within a few percent, or they would all be making about 400 at the wheels in stock form.

Turbo Racer

so how much hp and tq does a stock non x50 2001 tt make at the rear wheels?

TIA,

Geoff

MBailey

I would say ~350 rwhp and 355 rw torque.

1AS

MJC- do you really believe your speedo was accurate at 192? Can't see your tach, but did you multiply mph/1000 rpm X rpm to confirm? AS

Ruf-Racer

>>> You mean this wasn't possible with 415 hp?<<<

Indicated speedo readings don't really mean too much. Beat that against a GPS and you may see a difference.


keep having fun

R

scottramsey

bond, can you email me your model? I also use that program. Did you increase tire friction coefficients? The stock parameters are for street, track testing usually has the benefit of increased traction which is just as good as hp for acceleration (assuming you are spinning the tires).

I quickly used the 911 turbo model with a weight of 3480 lbs(not a perfect match, but close) in the program and it says 0-60 in 3.95 sec and 0-100 in 9.71 sec with a bump in tire friction (kinetic) from 0.85 to 1.1 and (static) to 1.0....numbers I came up with when evaluating other cars with timeslips.

also the variation in power curve could impact things a bit, esp if the power doesn't roll off as fast after HP peak in the real motor compared to the modeled profile...
*edit* here is the power sheet from porsche for the 911 turbo, there is no power roll off above 6k rpm, the cartest model has hp dropping to ~390 hp by 6800 rpm, there is your top speed discrepancy.

scottramsey

Unlike the freebie programs on the web, Cartest2000 takes all of this into account.