Craig and Anthony,
I find it very confusing talking of WHP. Do you think you might keep to BHP (flywheel) as that is what most of us compare.
Thanks.

 

Yep, it takes a bit of getting used to.

I had only ever discussed Fly HP in the past.

As long as people make it clear which they are talking it is not too difficult.

A bit like mph and kmh I guess.

 

I think the whole thing is a big can of worms; there's no real way of comparing car to car, as each dyno or rolling road is different and the flywheel from rear wheel horsepower calculation is dependent upon tyre type, pressure, resistance and wear in the rollers etc...
I've seen discussions on this explode into giant "flywheel versus rearwheel" flaming matches before! eek!

 

Maybe I'm getting this wrong....
Just to clarify: when the porsche handbook, and magazines refer to BHP, are they talking about flywheel or rear wheel?
For example 1994 3.6turbo is 360bhp, which is this?

Whichever it is this is the format that would make sense to keep to as we will be comparing 'apples with apples'.

 

Manufacturers figures are all at the flywheel. The problem with that is that unless you have access to an engine test rig and willing to drop the engine out of your car, there's no accurate way of comparing a result on a dyno or rolling road to it.

Most dynos give you rearwheel figures and then apply an error correction to it to guess the flywheel figures. You just have to take it all with a pinch of salt

 

Yes, I believe there is a standard factor to multiply which converts rearwheel to flywheel. Do you know what it is? In any event we should be able to compare flywheel as it is meaningless to compare one claimed flywheel number with another rearwheel number.

 

The reason we refer to to Wheel HP is because our cars have been on a chasis dyno. Of course this is not the most reliable way of measuring HP but eaiser than having your engine removed and put on an engine dyno (which is more reliable measure of HP).

When we talk about WHP just take that number and add about 18% (about the drivetrain loss for a G50) to get BHP numbers. So 315 WHP equals 372 BHP. Hope this helps.

By the way, drivetrain loss is another number that is widely argued 15-20% is what I have heard.

Craig

 

The correct way to convert is:

so using you numbers it's:


Most believe that the G50 is around 15-18%. You can actually measure drivetrain loss on some dynos.

As for horsepower with bolt on mods, I would tend to agree with Anthony's ranges. If you took a 3.3L and did headers, cat bypass, gutted the wastegate cat, J pipe, and a 1 bar spring, I think you are more in the 355fwhp range. If you swap in a K27HF you might bump that another +20 to 375fwhp.

 

Well put. Although I have heard two authorities tell me different numbers. One insists the G50 on our cars is 15% and 18% for the 4 wheel drive system of the 993TT and another insist it is 18% for our cars and 20% for the 993TT's. I was also told that the LSD can consume as much as 2%. So your guess is as good as mine. In either case even in this world of 5 and 600hp monsters I still think our cars are damn fast and it gets to a point where all the extra Hp gains you nothing but braging rights because there is no place to test how much faster all the extra HP has made the car. Although something about 400 RWHP that sounds like a good number.

It is easier to use the wheel hp as stated and that is also why many seem to like the DynapacK chassis dynamometers. The rear wheels are removed and the units are bolted directly to it. This eliminates a lot of unecessary corrections and calculations.

Power to weight has a lot to do with it also like this little puppy down below I make parts for. It has less than 1 hp and can do over 200mph and pull 113 G's. Unfortunatly you can't ride in it and it only goes round in circles.

 

Rat mobile ?

 

38D/Colin,
the examples you gave with the 355-375hp, although the HP number is not that impressive, I'll bet the real world performance and response (torque) will be something else!

As an aside, I guess standard 3.6 (360bhp) and a modded 3.3 at 360hp may well be quite different beasts in their characteristics.....

 

LOL

Tether cars. A strange obsession that has been around since the early 1900's. I can't understand why people pay as much as $30,000 for these little beggars but it is all in the bragging rights to say mine went fastest.

I don't think you will find that much difference between the 3.3 and 3.6 other than the low end performance. Once on boost they should respond pretty much the same.

 

Agreed. On boost, they are a very similar. If both are stock, the 3.6 is that little bit faster.

 

Never heard of them Anthony, must be a USA thing.