D666S

Very helpful information as usual ...

Seems to be interesting upgrade to 996 cup LSD + 993 with shorter ratios (and 6th gear in addition.

But, you didn't mention anything about sequential gearboxes, why? impossible to fit in a 964 shell? is it really worth the effort?

Geoffrey

A sequential gearbox needs an ECU for it to work. You need a strain gauge on the shifter console so when you pull back on the gear level the ECU cuts the ignition timing and allows you to physically pull the trans out of one gear and into the next. Further, you need a rotory potentiometer on the gearbox so the ECU knows what gear it is in. I could very easily install a sequential gearbox in my car because I have MoTeC, however, the costs to rebuild are cost prohibitive. The recommended rebuild is 30 hours and the gears are $2k each set.

Jeff Lamb

Bill, thanks for putting together your spreadsheet AND for sharing it. I found it to be incredibly helpful !!!

I ended up buying a G-50/52 for my race car (see my avatar) for the strong ring and pinion. I am using the stock sizes for first and second gear and I am going to change 3 through 5.

Now, I need to decide where to buy my gears and what diff to run.

Best regards,
Jeff

Jeff Lamb

Geoffrey, couldn't a guy run a sequential box without the ECU connection if manual throttle lifts were used to shift gears?

Jeff

Geoffrey

yes, I suppose so, but what would the advantage be? My normal shifts in my race car take approximately .25 seconds from throttle off to throttle on. At WGI on the back straight, I lose 4mph during that shift. A sequential geabox will shift in <.1 seconds with no lifting of the throttle and no loss of mph. THAT is the advantage of the sequential gearbox, the mph lost due to shifting.

When I'm running against a 997 Cup, my car has slightly more acceleration than a 997 Cup, however, when I shift, I lose 1/2 a car length immediately, and it takes a long time to make that up, then I have to shift again and lose another 1/2 a car length.

D666S

Geoffrey try with an anchor.. in its spoiler

NineMeister

Don't worry, the new engine will sort out those wasserpumpers once and for all at which point you won't have to worry about the upshifts.
Although that said, maybe someone should design a mechanical KERs type device that only drives the output shaft of the gearbox when the clutch is depressed and recovers its speed during braking? That would be cool, accelerating through the upshifts.

Bill Verburg

Yes, it does

Bill Verburg

Paul Guard(Guard Transmission) would be a good choice for both

Jeff Lamb

Unfortunately for me, my experience with manually lifting to shift a sequential box is limited to driving my 125 shifter kart. Assuming that shifting a Porsche sequential box is reasonably similar to shifting the sequential box in my 125 shifter kart, then I know that I could shift the Porsche sequential box just about as fast (if not just as quickly) as using the ECU method to shift without lifting.

There is a certain technique that is used to shift a sequential box with throttle lifts that results in VERY quick shifts. Basically, right before the shift you pull tension on the shift lever with your foot still flat to the floor, then at the designated shift point you quickly lift your foot (not completely) and the trans "automatically" makes the shift once the rpms drop to the exact point where the gears mesh (because you have "pre-tensioned" the shift). The instant the shift happens, you mash your foot to the floor. Using this technique requires a certain "feel" but it results in very quick shifts that I bet can rival the speed of the ECU controlled shifts.

If anyone has any experience shifting a Porsche sequential box to the contrary, I would like to hear it . . . because I have to admit that I do not yet own a Porsche sequential box.

Regarding buying a Porsche sequential box, does anyone happen to know how many different alternatives are available from Porsche? And, what do they cost to buy?

Jeff

Jeff Lamb

Thanks Bill. I continue to hear good things about Guard Transmission so they will be at the top of my list. Regarding the diff, I still haven't been able to take the time to research whether or not a torque biasing (the type that uses gears) diff would work well for racing. I already know that pretty much everyone says use the limited slip (clutch plates) version for racing . . . but when I read those articles, the logic still doesn't completely address all of my questions.

The advantages of the torque biasing diffs that are hard to ignore are as follows:

* cheaper to buy.
* no maintenance costs -> does not wear out and require maintenance.
* should allow the car turn in and move through the corners better because the rear wheels are free to rotate at different speeds (whereas, the clutch disc type diffs try to force both rear wheels to rotate at the same speed all the time).
* transfers more power to the rear wheels because its gear driven design does not convert energy into heat.

Jeff

Geoffrey

No, you won't ever be able to manually shift a Porsche sequential transmission as fast as the ECU can. I've done the programming on these cars with MoTeC as well as an Emco Daytona Prototype gearbox, so I speak from experience.

There are fundamentally two different sequential gearboxes from Porsche for the 911. The standard G50 version and the latest one which shares the internals with the RS Spyder. The G50 version is $40k from Porsche.

Regarding differentials, you want the plate style for circuit racing because it adds a stabilizing effect under deceleration as it also locks under that condition whereas a torsion diff will not and is better suited to something like autox.

As far as cost, the plate style differentials are not that expensive and readily available from both Porsche Motorsport and Gaurd Transmission.

Cupcar

There are only 2 plate repair sets shown in PET for 2 WD cars, one for the G50 20/21 and another for the G50 31/32/33 which I suspect is a 4 plate.

PorscheII

*No question that they're cheaper, **but they most certainly do wear out. As a matter of fact, 911-based Pro race teams that have experimented with them have literally fried them in a single test session.
***Porsche LSDs can be set up in so many different ways, that I can assure you an LSD can be tuned to get any rear engined car (with more than 300 hp) through a corner more quickly than any open or torque biasing differential.
****All types of locking diffs create heat, but since max hp can't be utilized through the turns anyhow, you can't really say that any difference in hp loss (between LSD and TBD) is an issue for a race car. JMHO

kos11-12

Hi sorry to jump in ,


I have a friend is has a golf 4 wheel drive rally with a turbo , with a special engine and ECU ( 370 bhp) but not a special gearbox or shift ,he took me aurround in his car ... flat out and he was changing gears without using the clutch , he is in NZ at the moment, I need to ask him again how does this work , Geoffrey would you have any idea , is it because it 's a turbo ? his gearbox is lasting by the way .

Konstantin C4 92