ClaesM

Ninemeister.

Thanks for the clarification, it is a good point to know when discussion is up how much power that can be taken out from a 993TT. When the funds are in place I might "walk the line" to more power as well..

JamesE

Sorry if everyone has already worked this out (i've been following this thread but not read it front to back), but is the power difference between Porsche/RS bhp and other dynos less about engine dyno v chasis dyno, but rather the goal of the tuner. i.e. It is clear that the std 993tt ecu is configured to maintain a BHP level over a reasonably wide range of conditions. Eg If we consider air temps, the std ECU will allow increased boost to compensate for lower density of charge. Now this is clearly going to increase temps further and would not be an option if the mapping was right at the limit from the start. i.e. you had no head room. So can we conclude that althought the RS numbers are realatively low in terms of BHP, this has to be considered in the correct context i.e. it is a guarenteed minium rather than a potential max. Which brings us full circle, to how we view BHP claims. I suspect alot of the large(r) BHP numbers that are being discussed are accurate ( I know of at least one that is B*****s, mind), just they are mapped to produce Max BHP (should conditions allow) not a guarentee a Min BHP, over a wide range of conditions. It may well be the case that the conditions experienced under continued load actually reduce BHP materially (of the 'other' tuners) and potentially lower than the RS numbers under similar conditions. However, it does not mean the chasis dyno numbers are not accurate, just mapped to a different standard.

As I said sorry if this is old news, it's just I couldn't understand why Porsche/RS cars still put down the same BHP numbers on a chasis dyno, rather than "inflated" numbers.

TB993tt

Good post - spot on
If one owns a Porsche then one appreciates "Porsche type hp" which as you point out is what "RS hp" attempts to emulate hence why I find it difficult accepting other "types" of hp which may or may not be close to "Porsche type hp" and it is this variability which chassis dynos cannot determine it seems ?

JamesE

Well, I think it is perfectly possible for a chassis dyno to do it, just more difficult. And as a "small(er)" tuner it probably doesn't seem wise to put a lot of effort into reducing BHP numbers. I guess my point is really that, bhp claims should be considered in context before "the other tuners" integrity is questioned. That statement is not ment in a hostile way, BTW. Also, given the choice I think I would rather have my car mapped to produce the most BHP it can rather than maintain a Min. Although, this clearly makes comparing BHP across different tuners nice and subjective, which I guess where this thread came from in the first place...

TB993tt

But the problem with "the most" bhp is that whilst it reads "the most" on your chassis rig, on the road your most disappears in heat soak very quickly -great examples of this in the UK are the DMS "tuned" Porsche turbos

JamesE

Sure, I agree, my point is really that the engine will produce the stated figures (from chassis dyno) if conditions allow. What I was trying to workout is why people were claiming that chasis dyno "inflate" turbo charged cars BHP numbers, but when a Porsche or RS car is put on same chassis dyno it reproduces the numbers that porsche and RS claimed. i.e. no "inflation". So in short alot of these cars do actually produce more bhp than Porsche or RS, but Porsche and RS build in a material headroom such that they are able to maintain that bhp. They could of course give up that headroom and claim similar or greater BHP, but then they risk being undone by a "lower" BHP car (which had head room). I suspect that it really comes down to typical German overengineering, "we could quote BHP at 1.3X, but lets keep the 0.3 in reserve, Yaahhhh..."

So this thread takes a new dimension, now the requirement is to also calulate the headroom not just the BHP...

Rassel

I think it boils down to being able to reproduce the guaranteed BHP in a wide amount of conditions. Running on a Dyno is one thing, since it's a controlled environment. However running in real life, you'll find Porsches all the way from Alaska to Dubai. So if it rolls out from factory with 450bhp, it should always produce that figure. Then again, if certain conditions are found, you can produce more, but it's the guaranteed power that becomes the benchmark.

To be really typical about this, look at the starting grid at a German 6 hour VLN-race. Plenty of the cars produce less after 8-10 laps and after running for 3 hours, some of the numbers starts to decrease a bit too much to be top competitive. This being one of the reasons why RS have been so successful into supplying racing teams with turbo charged engines.

JamesE

The race environment is a special case of this discussion I think. All I wanted to do is shead some light on the notion that chassis dyno's cant produce real BHP numbers. I believe they can, it is all relative to the goal of the mapping. i.e. headroom or, not, in this case.

Jean

James,
You make very good points, however..Just to give another angle to this...

If a tuner, who after all is a person to whom people pay money to get a certain HP number, reliability and drivability) brags about a 820NM torque curve from turbos that cannot possibly produce such torque, however, his state of the art chassis dyno showed those numbers in all truth, and even better, also showed stock Porsche cars posting exact factory numbers, what would you say about that . Whose fault is it?

There is a limit, and while some tuners might not know they are having inflated numbers on their dynos, others do for sure, and brag about them to use them as a selling tool. This is what should not happen.

Even if a tuner is only reading his dyno numbers as they are, but he has not done the right due diligence to produce numbers per a standard (DIN or other) and used meaningful correction factors , right gearing, correct load on the rollers etc.. then he is just as much to blame. When a tuner does not know how much he can extract from a certain setup, then he is not a good tuner, and if he does know, and still posts numbers that cannot be true, then it is even worse.

Chassis dynos can produce close to real Porsche numbers probably, problem is to find one that does, it typically costs an arm and a leg and most tuners and builders cannot afford one. But this is why some shops rent their engine dynos to tuners, the outcome is unparalelled.

JamesE

Jean, as I said, i've not read this thread front to back, (and as I pointed out , I am aware probably earlier than most, of some BS numbers). All I was interested in was why Porsche/RS cars would not show inflated numbers on chassis dynos, where as other 'tuned' cars would. I just wanted to try and work out why that might be. I've been around this industry long enough to know that "every body is an expert", and by expert I mean they'll take your money and charge you for their service, regardless of results. I also believe that a chassie dyno can reproduce engine dyno (or rather tune to the same standard), numbers. It just might be more difficult. So, again, full circle, I suspect this conversation is more about how tuners choose to map rather than a engine v chassis dyno debate. Again, I only say that as I couldn't understand why a 'real' bhp car would not produce inflated numbers on a/any (quality) chasis dyno. So to be clear, I think it is less about dyno make/chassis/engine, but rather the goal of the tuner. Also, we should not consider other tuners numbers as fake, but rather different. Which takes us back to calculating headroom. Which I think is more intersting... I think it is 42...

Jean

James, the discussion about dynos is endless (and pointless?) and this exact Porsche vs tuner HP, engine vs chassis dyno topic, has been beaten to death many times before. I suggest you do a search about it or you can start a new thread about this topic also. Let me know if you need help finding threads and I will link a few in private to keep it off this one.
This performance thread is much more valuable than any dyno sheet, provided that the integrity of the data is secured, and the weight and setup of the car are accurately represented, it is not a shootout, it is one's personal dyno sheet to verify his own numbers.
cheers.

Carrera GT

I think this post rings a tone with me based on my humble experiences.

This has become a helluva Ground Hog Day thread.

ps. I'm perfectly happy with 800Nm. : )

pps. Don't ignore the rest of the machine.

Jean

Ok here is the AX22 data from the new 997GT3RS. Weather conditions about 25 degrees C and low humidity.
The 60-130mph was done on the track so starting from 100mph the car started entering a turn, reaching 0.8Gs at 130mph.

415BHP at 7600RPMs and about 3,150lbs of weight. Run made with 2 shifts, 2nd-3rd gear (about 7,700 RPM), 3rd-4th gear (about 8,300RPM).
Time 10.7 seconds, with half a tank. I have a run to 175mph too but it is irrelevant since the rear wing was set too high for max downforce and also had to lift during the run between 80-100mph. Drag is tremendous (so is handling )
This is a graph comparing it to the run I did with my stock 993TT.

Power to weight ratio
993TT: 8.4 lbs/hp -- Time 12.99s
997GT3 RS: 7.6lbs/HP -- 10.7 s

BTW 100-200kph: 9.18s. AMS in Germany tested the 100-200kph at 9.3s, so the car is "within spec"





And here is a pic of the car at home.

JJayB

Jean,
You mention drag, how does RS time compare to a standard GT3, if you tested one.

Jean

JJayB

I have not tried the 997 GT3, however the RS is 40mm wider in the rear and has a massive beautiful wing (the way it should be). The CDA is about 8% worse than the GT3 and this results in a top speed of 187mph for the RS compared to 194mph for the GT3.

But what I was referring to is that we had the wing set higher than zero degrees (it was probably as high as the highest setting on our GT2 wing), and one can clearly feel the drag at higher speeds. The car puts almost 100lbs of downforce at top speed at its zero setting! I cannot even imagine what sort of drag it would have at the highest setting (almost vertical!) but I have never driven anything as stable at high speeds, including BMWs and Mercs.

It blew the Porsche "street car" lap record at the autodrome in Dubai by 2 seconds which was held by a modified 993TT since last year, the GT3s were 4 seconds behind.