TB993tt

Whilst running alongside MOD500 on the vmax day my excitement got the better of me and I fluffed my third to fourth shift big time and ended up shifting into fifth gear.
You can see it on the trace below.
What is interesting is that this run still managed a trap speed of 191mph.
What is more interesting is how this mistake illustrates what a complete torquemiester my new motor is
By shifting to 5th, I missed out on the benefits of dropping the revs back in the power band of 4th gear - right ?

Well it seems that dropping the engine to approx 4350 in 5th gear (right around peak torque) was not a bad thing to do.
The trace using 4th gear resulted in 95-140mph ( 95 is just after changing into 4th and 140 is just before the change to 6th) in 7.08s
Using 5th gear only it took 6.96s.
I need to have a look at some new gear ratios !

JJayB

TB
I've changed out 6th gear to a lower ratio, which won't help you in your top speed runs like VMax, but in track events it is devestating for the competition.
Jimmy formerly the felon

Red9

Interesting topic is Torque.Usually overlooked and far more relevent to turbo engines than anyone seems to credit. A lesson driven home to me some years ago when using 5 spd and losing 3rd gear I had to spend the weekend racing shifting from 2nd directly to 4th. Taught me to pay a lot more attention to driving lines that kept momentum and flow.Not so busy changing gears and ringing its neck to distraction let me get back down to match times done previously with all gears. The next meeting some months later I shaved over a second off previous best using the lessons learnt when one gear down.The key part of all this is having the ratios well matched to the torque characteristics .

Acropora

Interesting. I'm going to try not downshifting at the track today and leave it in fourth. Hopefully the local vette chapter doesn't hang me out to dry. So, what's the best price on a secan?

Jean

I always believed that a taller geared and well staged 5 speed gearbox on a turbo will be faster than the 6 speed that we have for an accceleration run.

The short gear ratio gearbox is more suited for N/A cars, even on the race track. The longer time you are accelerating in a gear, the faster you will go on our turbo cars vs having to shift to a higher gear earlier.

Acceleration within a certain gear (i.e. 3rd vs. 3rd) from say 3000RPM to 7000 RPM will however be slower obviously.

TB993tt

Jean
RS Tuning claimed that this is why the Red Rocket in the link below was so fast. A five speed box with long gears 0-300kph in ~26s with 533hp and lots of low end torque.
https://rennlist.com/forums/showthre...ight=RS+Tuning

Jean

Imagine that with a sequential 5 speed gearbox

Jean

While we are talking about gearing, interesting to note that all the turbo cars across all models that POrsche has produced, have taller gearing than their N/A counterparts. Even race cars (GT1) had taller gearing than the 996TT. For N/A it is the opposite direction that they have taken, for high performance or track cars, they have shortened the gear, IMO because they don't have the torque a turbo produces, so shorter gearing is the torque driver. Since there not many professional turbo race cars put there, I cannot tell for sure how they compare, but I do know for a fact that Franz Konrad did use taller gears on his race 993GT2 cars, and used very tall tires as well.

Gearing can be in the form of gear ratios and/or taller tires.

Some comparisons:

911 vs. 911 turbo (930) 5 speed. And 964 vs. 964 turbo, notivce how the 964 turbo has suibstantially taller gearing. I did not facotr tire sizes here, but it would add somewhat to this, making them taller still.



993 vs. 993 turbo, notice how much taller the TT ratios are, and I have not factored tire sizes yet. Then I am comparing the 993N/A to the 993GT2 that came with the same gearing but taller tires. Tiresalone give the 993GT2 4.5% taller gearing.



Finally 996 vs. 996TT and 996TT vs. 996GT2. Notice the big difference between N/A and turbo. On the right hand side I have calculated the effective 996GT2 ratios based on the taller tires they wear (4.5% taller)



I might be mistaken, but it does seem to me that Porsche engineers have kept taller gearing for turbos in mind across all their models. This might be due to many factors, but certainly performance was one of them. RUF has mastered this art in all his cars, and one can see substantially taller gears (except 6th) on his CTR2 Sport for instance.

Kevin

Jean what is the gearing on your sequential? Nice gear charts..

You should add the Ruf 930 5 speed gear chart.

Jean

Kevin,

I have been trying to obtain the actual data for my gearbox but was not succesful, they had done some changes before sending it to me (they kept the ones they did not want in it basically).

I have done some runs with my AX22 to try and identify each gear ratio, it was not a perfect science because of the visual error with RPM reading, however I got to some approximations. I will post my findings tomorrow as I don't have the data. I can tell you that they don't make any sense for a street car and need to be changed. First gear is about 64mph, 6th gear is about 160mph or so
I will add the RUF 930 gearing tomorrow as well on this table.

TB993tt

Dumb question, but is the 996tt 6speed gearbox the same as a 993tt - ie is it a direct bolt on ?

Jean

TB
I your case (2WD) you can have a 996GT2 gearbox installed. It will need some work but nothing out of this world. They need to fabricate a bracket and do some work on the case. It also comes with the oil cooler which is a major advantage for your torque levels and prolonged autobahn usage.

The shifter is cable operated, which is smoother but needs more maintenance apparently. For a 4WD car there is much more work involved as the torque tubes are not the same.

I hope I am not mistaken, Kevin?

Kevin

Toby and Jean both gearboxes can be swapped back and forth. I would and use the 993TT gearbox and rebuild it with 996TT GT2 components.. The actual problem that we have failed to mention, is that we should built these boxes 993TT AND 996TT which includes the 996GT2 with the GT3RS Mainshaft. This will give us a bullet proof shaft and many gearing options. Haveing the GT2 or GT3 Cup center section gives us the oil pump and factory cooler..

The way that I look at it is, you can buy a used GT2 box and then have to spend 6-8K in it to re-gear it and install the mainshaft.. Or spend 8-10K on the 993TT box and include the GT2 center section and gearing and mainshaft..

Disclaimer, we haven't even discussed the options for the limited slip..

Kevin

I forgot to mention, there is no cheap solution. Once you are at the torque levels of Toby's and Jean's motor, the mainshaft and syncro's need to be addressed. This conversion costs a wad of cash.. The mainshaft alone is around $2,500.00

Jean

Kevin, I think the point is to bolt on a GT2 gearbox without any mods to its gearing. It has taller 2nd to 5th gears than the 993TT and the benefit of the oil pump/cooler + being lighter by about 5lbs+ quieter operation + a good differential .