NineMeister

My 2nd to 3rd shift times across the H gate for the two runs were 0.38 and 0.35 seconds respectively, the corresponding 3rd to 4th shifts down the slot were 0.32 and 0.21 seconds, which obviously accounts for the majority of the time difference between the two runs.

I know that this has probably been covered previously, but since the shift times are critical to getting a good run time for the purposes of hp prediction gearshift times should really be deducted from the run time to make the runs comparable between all driver abilities and transmission types (i.e. manual, tip & sequential). I know that it would be a lot of work to pull this out for every run but it would definitely normalise the analysis of just the actual time the car is under acceleration, in practise using the AX22 data we could simply paste the max speed at the end of one gear onto the same mph start of the next.

Without wishing to trawl through 64 pages again, have you already done this Jean (if not I would be more than happy to pull out the data for the current top 20)?

Kiko

Where did you see that Toby? On their site all I can see is 0-100 and 0-200km/h times...

That's odd... theoretically the 508Turbo has ALOT more torque then the M6 (and you can certainly feel this when driving one), the same power and nearly 200kg less and although the 0-60 time is 0,5s faster in the 508 RS the 100-200 time is the same...

TB993tt

Er.......just subtracted the 0-200 from the 0-100........
Don't know much about BMWs but the test weight for the 8.6s M6 test was 1761kg so not that much heavier than the 996tt.
The M5 weighing 1838kg takes 10s and is only 75kg heavier ?
The M6 cab weighing 1988kg takes 10.3 secs and is a whopping 150kg heavier than the similarly timed M5 - is the M6 more aerodynamic ? quicker seq gear change which negates the 996tt torque advantage ?
8.6sec is plenty quick for a 508hp 996tt regardless

Kiko

The thing is I drove a frend's M6 and I was conviced my Turbo was quicker, it was probably the Turbo's torque which deceived my perception... but I could swear!

BTW This was the first time that I felt my Turbo was dated, the head up display and the SMG-F1 gearbox left me gobsmacked, it felt like a proper straight teeth, no clutch gearbox but with the smoothness and lack of drama of a Playstation console.

Stummel

Could you run side by side with the M6?

PS: The 996 is dated as the 997 is on the market for years now

Kiko

I will eventually test the turbo against the M6. About the 997... you're correct and the truth is I still haven't had the chance to drive the 997 Turbo but I've drive C2S's and although theres an obvious progression it didn't make me feel MY 996 Turbo (with its mods) was particularly dated. With the M6 even the 997 feels dated. The M6 felt alot heavier not as agile but most of all not as sure-footed as my Turbo or a 997 C2 S.

Red9

You must work for Porsche--they think everything but the current model is "old"!

Stummel

No, I did always like the pre-current model. But no more. Still like the 993 best.

The problem is that I do not grow old as fast as the Porsche models are targeted more and more for older people - limo style...

Sorry for OT!

AVoyvoda

"gearshift times should really be deducted from the run"

I have to disagree with you Colin. Say, for example, that you have two cars with identical times: The first with a very narrow power band and plenty of gears requires 3 (!) shifts for 100-200 vis the second with a wider band and a different box, needs only 1 shift.

Deducting shift time gives the advantage to the first car, while in real life, the second would be generally quicker.

I think adjusting for sequential, crash, SMG or egear is valid, in so far as these allow faster shifts than manual boxes. But as to the shifts themselves, that's part of the design to optimise engine output, so they should be counted.

In other words, if you think that your souped-up 993 suffers because you need too many gear shifts, you should fit a 964 box, or re-gear. Then you'll get fewer shifts and you may even be faster overall.

Interestingly, Porsche itself suffered from that issue. Here are the numbers:

964 C2, 1,485 kgs, 250 hp, 100-200 in 15.5 secs
993 C2 non vario, 1,478 kgs, 272 hp, 100-200 in 16.5 secs

Similar cars, similar weight, the 993 has more power but it's slower. Why? Wider car, wider tires and it needs one extra shift. In the event anybody thinks this is an abberation, the 993 C2 vario with 285 hp needs 16.3 secs. Faster than the non-vario but still slower than the base 964.

To pre-empt howls of protest, the 964 RS (260 hp, 1,305 kgs) needs 13.8 secs. 1.7 secs improvement for 180 kgs weight loss and a 10hp increase in power output, sounds about right.

935racer

The problem with including the gearchange time is it makes the maths a lot harder when trying to evolve a simple formula. I think that if we could have a simple program that required the acceleration time, the weight and the overall gear ratio (gearbox, diff and tyre size) we would have a quite powerful tool!
How about doing an acceleration run in a single gear? If you decided to do, say, 50 to 90 mph (in second or third) this would excercise the engine over its entire useful rev range and would take away the "unknown" factor of the gear changes. Afterall, I think the idea here is to calculate engine power, not to see who can change gear fastest! Of course, the formula would, by definition, only give the mean power between the two speeds. If you want to calculate maximum power you bring in the power of calculus and reduce the starting and finishing speed differences to almost nothing. Then, of course you need to repeat the excercise many times to cover the entire range! If you want to do that, take it to a rolling road!!!!
Aero drag at 90 mph is going to be significant. Either its ignored (the easiest option) or we could include it. Probably the best way, from an idea originally from the "Ninemeister", is to take the car to 90 mph, slip in into neutral and time how long it takes to get to 50 mph. This way we will have an identical drag component to the acceleration run. It would also take into account the rolling resistance, the tyre drag and everything else slowing down the vechicle.
So, if its a good idea is anyone up to doing the maths? I hope so because otherwise I will have to do it! In fact, I think its pretty simple so I may have a go this weekend. I will watch the replies and if no one like the idea of a single gear run I wont bother!
Let me know.
Cheers,
Richard.

NineMeister

I totally agree with you with respect to comparing the performance of one car against another, the examples you give back up your point nicely, but my aim is not to measure who has the fastest car, it is (and I suspect the ultimate aim of the thread) the concept of accurately estimating the "area under the power curve" from the acceleration times. As I see it if you have a closer set of gearbox ratios you only have to run in a narrower rpm band, therefore this narrower band is all we need to be interested in for maximum acceleration.

To make the power estimate more accurate we have to measure air resistance and rolling resistance, therefore given that we all have an AX22 or Driftbox to play with anyway, the simple solution would be to log the coast down time from say 100 to 60mph and then from 40 to zero. Use this data with the total weight of the car as tested and we should be able to build a very accurate mathematical model to give rear wheel power. Transmission losses would still have to be estimated to calculate engine power but this should not be too difficult as the majority of us use the same type of gearbox.

TB993tt

Avoyvoda
If you accept that the 60-130mph measurement was created to prove to oneself that you have got the improvement you have paid for and not what some dodgy chassis dyno tells you.
Coming from this premise as long as you keep the same gears and allow for faster/slower changes there is no need to allow anything for gear changes.

If we try to use the measurement to calculate accurate power/power curve data then of course the various factors including gears/gear changing need to be taken into account.
You said:
In other words, if you think that your souped-up 993 suffers because you need too many gear shifts, you should fit a 964 box, or re-gear. Then you'll get fewer shifts and you may even be faster overall.
This is obviously true but it doesn't help in determining power/shape of curve - this is not a competition for who can optimise their car for the 60-130 !

935racer's suggestion of examining a run through the power curve in one gear is surely the best way of determining the charactaristics and size (when other elements are taken into account: weight/drag/climate/4WD/2WD) of power curve.
I have a chart of a run from 50-90mph in 3rd gear which is from 3750rpm to 6750rpm so covers the full usable power range.
I have extrapolated the rpm points and put them on the chart -you can see the long G curve acts as an on road torque curve and whilst it does not correspond to my engine dyno curve in shape (engine dyno peaks at 4300rpm -presumably it is the slight delay between engine hitting peak torque and peak torque hitting the tarmac -looks like under 0.3s on the chart) it is actually what the engine can do on the road:


50-90mph in 2.77s 1483kg 24DegC any takers

Colin:
Jean and I have tried using the AX for coast down losses and it was hard to get consistancy mainly because coasting down from 130mph takes a lot of room - we need to rent out Bruntingthorpe. You organise it and I'll chip in

Red rooster

Looking at the 2.7 sec single gear plot I would be careful that turbo/motor response times were not going to play a major role in this test !
In other words it could have the accuracy of a lightly loaded inertia chassis dyno !!

Geoff

Woodster

I thought this was a competiton...

TB993tt

Properly done powerful tts need higher gears to load up to their optimum compared to lower power. for example a stock 993tt, its little K16s would be fully loaded doing this 40-90mph run in 3rd and takes over 5s -plenty of time to get things loaded.
With the caveat of what I say above I agree with your statement although I don't see it as "response" but agree that because there is not a significant brake on this powerful motor (eg as on a 5th gear similar run) the turbos will not have chance to build up to their optimum levels - a bit like a chassis dyno run
Here is a fully loaded 5th gear run, unfortunately this takes a lot of space !