sweanders

When one starts using the word accurate and estimate in the same sentence my guess would be that it probably is unlikely that there ever will be any exact results.

GT3 Rob

No worries matey..
I would seriously struggle with the Swedish thing.. except maybe the girls..

uk trucks

As they say in the good old USA "Talk is cheap" etc I will gladly run your RS Tuning 993TT for free to establish a benchmark for you. You can then see if our rollers over or under read or perhaps they might just turn out accurate ?

As for transmission losses etc Dyno Dynamics produce the Low Boy 450 as a load type eddy current rolling road designed to measure tractive effort at the tyre contact patch. It then uses sophisticated and proven/benchmarked software to extrapolate this into a BHP at the wheels and further extrapolation for a at the flywheel BHP figure. I do not profess to be an expert on rolling roads. We do not suffer from traction problems, we do not suffer from air supply issues, we have had over 650 cars through and too many standard cars have recorded standard manufacturers figures for us to doubt the accuracy of the result. I could ramble on a while here but wont. Our machine and its transmission loss calculations are accurate. We run all powertests in the Shootout mode, whereby the operator has no influence on the outcome [before the cynics suggest otherwise] As a tuning shop what benefit would I gain by supplying overstated numbers to a client whose car we have never seen before ??

The car ran the numbers, get over it

Allan
Weltmeister Ltd

sweanders

I don't doubt that the car ran the numbers and that the dyno works great.

It is however impossible to calculate or measure driveline losses without running the engine in an engine and chassi dyno back to back.

I have done some dyno testing with a 996 on a Dynapack and a Dynojet on the same day with different intake configurations, different gears and different sweep times and rpm ranges, it is interesting to see the changes in the results.

uk trucks

Anders
Sadly we cannot compare a Dyno Dynamics with either a Dynapack [Hub Dyno-Partial load] nor a Dynojet [Inertia Dyno-No load]. That is an apples with bannanas comparison.
You are absolutely correct in what you say on engine dyno test then install in chassis and test to see installation losses. DD have done this in Australia and we have seen similar done here in UK with Mitsu Evo's so our estimations on driveline losses at peak bhp/revs are reasonably accurate.

Cheers

Allan
Myoffer still stands on the RS Tuning 993TT tho'

TB993tt

I don't doubt that (as long as I haven't b@ggered anything up since it was on the engine dyno) your chassis rig would calculate my hp right around the 540 level.
Would your set up be able to tell me how much power my engine was giving after 5 minutes at 6500rpm with a simulated 6th gear road run and 300kph airflow to match ?
Edit
Just in case it is not clear what I am saying - The Cargraphic motor will have produced its 411PS at 7000rpm (or whatever) with a constant throttle for a period of time allowing everything to get nice and hot under conditions which reflect top gear on the road with appropriate load and airflow - Are you confident your chassis dyno is mimicing this method of measuring power ?

NineMeister

Worms and large cans come to my mind....

Rob,
A chassis dyno is a great comparative tool, but even though the mathematical corrections used by dynos are reasonably accurate, in the real world different tyres (or even tyre pressures) can have a greater effect than a few degrees C or an extra millibar of pressure. What you have to do is trust the information that your tester has given you in comparison with similar cars that he has tested on the same dyno and under the same conditions, and if your car compares favourably to others that Alan has tested you are laughing all the way to the Pub.

I agree with Toby that a definitive engine power measurement can only be measured by an engine dyno.

However I completely disagree that power figures are only of interest if they are from steady state or fixed rpm tests. If we were all driving diesel trucks pulling 30 ton loads up hills I would agree, but since you only drive the car at full load to accelerate you should test the engine in a transient mode(inertia or inertia/part loaded) at a similar acceleration rate to that of the car in the gear you use the most on track. Who cares whether your GT3 makes 400bhp at 195mph, what matters is that it makes 400bhp in 3rd/4th/5th before it gets to the next bend. Typical chassis dyno runs in top gear simulate best the acceleration of the car in 4th gear on the road, so that is how I test cars on our dyno.

Which leads on to the comment about losses on a chassis dyno. When testing in top gear tyre losses build up far greater than internal gearbox losses, which is why you see overall transmission losses of 15-16% when testing at 170mph or above. Robs car lost around 55bhp at 410bhp, my car in similar conditions lost 58bhp from 415bhp, so the numbers stack up to a similar chassis dyno of another make (Bosch).

GT3 Rob

Colin
I appreciate your reply, also the one on PH..
The reason for me having the car dyno'd, was curiousty as to what the car was putting out, compared to my old GT3.

When I looked at buying the RS, my choice of cars was.. GT2 or GT3 RS..
Because I like to track, I chose the RS.. If I had been interested in big straight line power. I would have gone the GT2 route. Hence I have no reason to be bragging over a relatively modest 420bhp.

I know the guys at WRC, through my previous Porsche dyno day, with the old GT3.
They have sold me no upgrades, or tried to sell me any future upgrades.
I asked them to dyno the car, they did.. end of story.

Evo magazine, obviously use WRC because they have a reliable, realisitic dyno.

My car was dyno'd in 3rd gear.. this is the most commonly used gear for me on track.

I'm pleased with results, but the power is only a small part of the overall RS package.!

Cheers
Rob

Woodster

Rob,
great info, awesome car!
Colin, you are obviously very experienced, thanks for the info!
TB, get your car dynoed sometime so we know what the equivalent is to "TB H.P." > rest of
world H.P. LOL! mk

TB993tt

Woodster
You are missing the point somewhat.

A number of flywheel correcting chassis dynos would be able to measure my flywheel hp at the engine dyno level of ~540hp.

For standard cars these chassis dynos as has been pointed out are usually very accurate and are even used by some manufacturers.



The problem comes particularly with modified cars which can give some nice high readings on a relatively lightly loaded run - this is the basis of my disagreement with Colin FROM 9M (see other thread) where I claim that his chassis dyno measured 540hp is less than my engine dyno derived 540hp - from the components and boost levels he is using I can't see him getting more than ~500hp -Colin doesn't think that the loading heating up the intake and theoretical reduction in power is that significant in track use (see intercooler thread 993tt) and he may be right but - Time will tell on this one

Remember the highly modified Nissan Skylines which used to run ~800hp on the chassis dynos, when they were attempting to beat the Nurburgring record they could "only" run around the 550hp mark

Modified cars can perform well on these lightly loaded runs compared to being held at the constant revs on an engine dyno (as mentioned above) where the heat will cause the timing to be pulled and power reduced.

How many times over the years have we seen tuned cars with high chassis dyno power curves not producing the acceleration numbers they should ?

Getting back to the 420 hp GT3 RS, yes it is a production car (so it doesn't fit the tuned car argument) and maybe it is giving these numbers, but if there was a handy engine dyno I would have a large wager it is not.

Regardless, Rob is taking all this debate in good spirit and has a great car with a seemingly special motor

911 silverback

Hi i read somewhere how you run the engine in makes a big difference, at least 5%bhp in some cases, also don't know if its true but apparently different figures come out from the guys who build the engines at manufacture hence you can no longer trace who builds what engine.

911 silverback

well that was a conversation killer if ever there was one!!

JamesGT3RS

Rob yours has 420 bhp because its got the red wheels and decals, we're lucky, the blue ones have less power!

Going to Goodwood on Tuesday where the gauntlet has been thrown down against some replica GT40s!!