Seqential Tranny in ACO GT class?

[RacingManiac]

I know that the sequential box is available in GTS now, but in the Road Atlanta race last week, AJR Porsches are running new sequential gearshift now in GT. They are legal in GT as well now?

[Lee Janotta]

Apparently. Just plain wrong in my view, as if the Porsches weren't fast enough already? What the hell happened to homologation?

[JAG]

Gearbox type is not really to do with homologation. Almost ever series now runs sequential boxes.

They are cheaper to run and quicker than H-pattern. The 360s now run there paddle shift sequential box.

[Lee Janotta]

I know how you love taking the driver out of the equation, but heel-toe downshifting is an art. The paddleshift gearbox in the F360 is a homologated production piece, _not_ the pure race unit in the Porsche. And because it's a production piece, it doesn't shift much faster, and it's not exactly the most reliable.

How the hell could it be cheaper, Jag? The H-pattern 6-speed is an off-the-shelf Porsche production part!

[JAG]

Its not of the shelf. It needs lots of mods in order to be fit to race. Check out the problems in the ETCC with 'standard' gearboxes which went bang at every conceivable opportunity.

The internals of the racing h-pattern gearbox are unchanged it is just the actual gearshifter itself that is changed

They are cheaper as they allow less oportunity to over rev the engine through missed gears and such like. Volvo had incurred MAJOR costs in blown engines and gearboxes in the ETCC last year using 'standard' production h-pattern gearboxes.

[Lee Janotta]

When's the last time you saw a Carrera GT3R/RS blow it's engine?

A racer should be able to downshift into the right gear 99.99% of the time, or they need to make modifications to the shiftgate and linkage to make a clearer distinction between gears.

[pirenzo]

Come on, i've never driven a car, but honestly how hard could it be to get the right gear!?

[pirenzo]

Originally posted by Lee Janotta
I know how you love taking the driver out of the equation, but heel-toe downshifting is an art.

OK. I've heard of heel-toe downshifting, and i've seen it done in some in car footage of Sir Stirling Moss driving a Lotus 18 about 5 years ago (slowly of course)

But,
1) What, if you like, is the theory behind it, and
2) What advantages does it have...



I've heard you say before that it saddens you to think you might have to explain this to a 16 year old some time, when we have auto shift and TC as standard, and well i'm that 16 year old, and i'm sorry for bringing it upon you earlier than you thought

[JAG]

Originally posted by Lee Janotta
When's the last time you saw a Carrera GT3R/RS blow it's engine?

A racer should be able to downshift into the right gear 99.99% of the time, or they need to make modifications to the shiftgate and linkage to make a clearer distinction between gears.

Sure, but they also want to be the quickest car.

Sequentials are the quickest gearshift.

I've heard mothing but positive comments from drivers who use them. First time I saw them was in the BTCC in 1993/4. They allowed much more intense racing as the gears could be changed so quickly.

[Speck]

Mind you, there are 2 parts to a sequential shift system. The gearbox is one part, and the electronics for rev matching the other.

I've seen in car shots from both the FIA GT and the JGTC where drivers are shifting using a sequential 'box, but are heel-toe-ing and rev matching with their feet.

[RacingManiac]

Sequential does not equal to paddle shifter automatically.....for example most motorcycles nowadays shift sequentially, that just means you cannot do 1-3 or 4-2 in one shift, you would have to do 1-2-3 and 4-3-2 to do that. In between each shift you'd still need to match the rev and use the clutch on the downshift. The sequential part can just be some linkage pulley setup to how the gearbox being operates from the driver.

Like the Porsche one that was used in Road Atlanta, the shifting action is sequential now, but everything else is still the same as far as I know, except not they have clutchless-no-lift upshift. The driver still heel-toe and use the clutch on the downshift. As far as this type of the box goes, the gearshift is a little bit faster, but not like Formula 1 fast, the main benefit is you never miss shift a gear. Even the Corvette C5R's sequential box too, it is the same gearbox as the H-pattern one, just the method of shifting have been changed to sequential action....

Now with the SMG or F1-type gearbox, there are no longer any mechanical connection. The paddles are like buttons, they receive a command, and the TCU does the clutch, rev-matching, on the mechanical end via electrohydralic or pneumatic devices. They can be a lot faster because everything now is done by computer, where it can just control the engine to cutoff for a fraction of a second to complete the gearshift, while it'll take longer for human to physically complete the action....

[gttouring]

alright racing maniac
god no more questions from the class thank see you tomorrow...

[Lee Janotta]

Ah, thanks RacingManiac.

JAG, I'm not arguing with Porsche or Alex Job Racing for using it. I'm arguing with the ACO for allowing them to! It's a philosophical argument I have with them, not a technical one.

Et tu, pirenzo?

Alright, the theory is that before you downshift, which of course provides engine braking on the drive wheels, and sets you up to get on the throttle exiting the corner, you want to match engine revs to approximately the speed it'll be turning once you downshift. So, entering the brakine zone, you place part of your foot (either the heel, or if you've got big feet like me, the left side of the ball of your foot) on the brake pedal and press down, threshold braking as best you know how (holding the pedal right on the threshold of lockup). At the very same instant, you pop out the clutch with your left foot, and in the same motion as you press the brake pedal, with either your toes, or the right side of your foot, you momentarily press down on the throttle, blipping the revs upwards. As soon as the revs are going up, you have to lift off the clutch. If you've down it right, the grabbing of the clutch will barely produce any shudder from the car. If you don't match revs before you downshift, the car will jerk, and the drive wheels will hop violently as you engage the clutch, likely damaging the drivetrain and causing you to lose control.

It's pretty much an essential skill for getting the most out of a car. If you watch a NASCAR road race, you can see the guys at the front, heel-toeing, while the guys at the back pop out the clutch entering a corner, roll in on the brakes without downshifting, then select a gear as they start leaving the corner. Costs a lot of time.

It takes about 10 minutes to learn, and a lifetime to master.