Converting a GT3 engine to reverse rotation?

[mike the snake]

What about a ZF box?

They can be had for around 10 G's, much less than cup car boxes. The ZF can probably handle 1st gear launches, although if you can live without 1st gear clutch drops, then that opens up a few other possibilities. My race car has 350hp and 350+ torque and has been raced for many years with a "wevo-ized" magnesium 915 box.

Custom geared 930 box would be hard to blow up.

"The race car sales site" has a "gearboxes" section with many exotic transaxles, you might look there.

A "Real" gearbox that can handle abuse will run 20G's or more.

[blue72s]

Originally Posted by Matt Monson

A 5spd evolution of the 930/935 4spd. Canepa might have one for sale. It's gonna cost more than a GT3 box.

I just checked Porsche's webite - 1982 Porsche 956 C Coupé - Racing Cars - History - Dr. Ing. h.c. F. Porsche AG - it says that a completely new 5-speed gearbox was introduced for the 956 (in 1982) and that the 962 gearbox was derived from the 956.

[blue72s]

Originally Posted by Matt Monson

Now that I know the application, I still think the inverted GT3 box is the way to go. It's been done already. It can be made to work.

Yes, 9ff has done one, but they had to cut out the trunk floor and also had to modify the chassis to give clearance to the angled drive shafts. A rather messy job if you ask me.

[vmax]

The Ultima GTR is mid engine and many have inverted G50's.
Many have well over 500HP.
The Ultima GTR - Z06 Powered Racer - Car Craft Magazine

[Cupcar]

Looks like the 1/2 shaft is at quite an angle in the Ultima and the CV presumably is surviving. Also I think the same was the case for the 9ff Cayman shown in Excellence some time ago that had a Turbo engine with upside down 6 speed.

[blue72s]

Originally Posted by Henry Schmidt

Sequential shift linkage tends to be easier to route and fabricate.
Sequential gear boxes also offer speedy shifts with less misshifts.

Does sequential down-shifting require throttle blipping by the driver? If not, how does it match the engine revs?

BTW, here is a good vid:
YouTube - radical sr4 sequential onboard @oulton park 07

[Jeff Alton]

It depends on the box and the engine management.....

[Wayne 962]

There's a lot of smart people here in this forum! I would perhaps suggest a 959 transmission, as I know where you could get one. Probably not suitable for your application though - sounds like 962 is the way to go.

-Wayne

[MarKoBrow]

There is a guy who is always in the Subaru Forums that had a ring and pinion made for a Subie box that reversed the rotation, perhaps this is a way to go for you? The problem is he had to get it made in India and the first set was about 10k sets after were cheaper. Here is his website http://www.subarugears.com/index_files/Page388.htm

[Matt Monson]

Originally Posted by blue72s

I just checked Porsche's webite - 1982 Porsche 956 C Coupé - Racing Cars - History - Dr. Ing. h.c. F. Porsche AG - it says that a completely new 5-speed gearbox was introduced for the 956 (in 1982) and that the 962 gearbox was derived from the 956.

Porsche can say whatever they want in their marketing blurbs. That doesn't make it so. 956 2nd and 3rd gears are identical to 930 2nd gears. 956 4th and 5th gears are identical to 930 3rd and 4th gears. The only difference being that certain versions of the gears had the backside cutout for lightening. There's also the issue of bullnose racing dogteeth, but those were always available as a motorsports item for the 930 box and weren't new when the 956/962 line of cars what created.

[Flieger]

What about the casing that carried the suspension members?

The PDK was all-new, anyway.

[Matt Monson]

Originally Posted by MarKoBrow

There is a guy who is always in the Subaru Forums that had a ring and pinion made for a Subie box that reversed the rotation, perhaps this is a way to go for you? The problem is he had to get it made in India and the first set was about 10k sets after were cheaper. Here is his website About the product

Just noticed this. A lot of guys have started using Subaru gearboxes converted to 2WD in their 914 swaps. While that may be ok for the Ej22e (140bhp) and Ej251/D (165bhp) engines, I think it's a questionable practice on the other turbocharged variants.

The Subaru 5MT was originally designed for a 2WD car that had about 180bhp. When they started chasing WRC titles and getting serious about rally they added a rear differential to the same gearbox and started putting the Ej20G engine against it. Initially those were 250bhp in Group N trim. Over time power levels went up, and by the time the 6MT gearbox was released the last generation of Ej207 engines was putting out a published 280bhp, and was often engine dynoing in stock trim right out of the box upwards of 350bhp. And by then they were consistently breaking gears in races and came to be known as the "glass gearbox".

Now let's take that gearbox and consider putting it against a 400+bhp GT3 engine. At that sort of power level (which is not uncommon in Ej205 powered "bugeye" WRXs) these gearboxes break second gear all day long. It just can't take it in stock form. And this isn't even taking into account the 2WD conversion. When in a Subaru they are a 50/50 F/R power split. The forces are shared over 2 ring and pinions. Putting all the power to the front one is way past what these things were designed for. If you're gonna even consider the Subaru 5MT gearbox for this sort of usage, not only will you want a replacement ring and pinion, but you'll want to replace all the gearsets. And you are also going want to add an LSD to it so that you can get the power to the ground since the front differential on that box is open from the factory unless it was a special STI-RA variant, which is hard as hell to find in decent condition. You're going to spend $10,000-$15,000 beefing up the Subaru gearbox to make it work for this. For that kind of money there's many other boxes one can buy and not have as many issues in making it work right in this particular application.

[Cupcar]

Maybe a Quaife Q-Tek 6 speed shown on the left, which has all the dimensions of the latest 996 gearbox could be used. It is designed for mid-engine or rear engine use.

Quaife do make a variant of this gearbox as a kit to go with the non-GT3 911 engine, which is shown on the right with the gear lever. The kit also includes clutch and flywheel in addition to bellhousing.

I understand they are now making a kit for the GT3 engine, which if set up for mid-engine use would work for a Cayman.

Available with helical gears for "road use", but it is a dog clutch gearbox.

[MarKoBrow]

Hey Matt, I was actually suggesting that he get a ring and pinion made for the G50 transmission and I was using the subaru transmission as an example. this way he could get to use a G50 in it's stock configuration yet have it rotate in reverse. Perhaps this is right up your alley?

[Matt Monson]

Originally Posted by MarKoBrow

Hey Matt, I was actually suggesting that he get a ring and pinion made for the G50 transmission and I was using the subaru transmission as an example. his way he could get to use a G50 in it's stock configuration yet have it rotate in reverse. Perhaps this is right up your alley?

Aha. I get it now.

Unfortunately we don't cut ring and pinions in house. It's something we have done by Ricardo and the minimums to get it done are a dozen units and the lead time is about a year.

Though it may be the kind of job that Albins is interested in doing. They've got their own Klingenberg machine and will work in smaller batches. It definitely wouldn't hurt to contact them and see if it's something they would at least bid.

[blue72s]

Originally Posted by Jeff Alton

It depends on the box and the engine management.....

Thanks, it makes sense. I remember I test drove a BMW with SMG gearbox, which is essentially sequential but with syncros. The throttle blipping during downshifting was done automatically by the engine management but rather slow, nothing like in the above video. I think the reason for slowness was due to the heavy (OEM street) flywheel/clutch assembly, and of course the syncros.

Anyway, if a true sequential transmission (dog box) was fitted with a street version flywheel/clutch, the downshifting process would be slow just like the BMW, wouldn't it?

I'm not sure if a lightened flywheel with say 5.5" triple plate clutch could be used for street as a daily driver?

[Jeff Alton]

The management needs a signal to to cut ignition on the upshift or blip the throttle on the downshift, usaully a microswitch in the shift lever. You would need to make sure your chosed ECU can do this. Otherwise you just end up with a sequentially shifting box that requires clutch and manual throttle blip on down shift, which is not a bad thing!

Anything you can do to reduce mass in the rotating assembly aids in the speed at which the motor will increase/decrease revs. The rest of it is in the tuning of the ECU. The VW/Audi DSG rev matches quite quickly.

Cheers

[blue72s]

Originally Posted by MarKoBrow

Hey Matt, I was actually suggesting that he get a ring and pinion made for the G50 transmission and I was using the subaru transmission as an example. this way he could get to use a G50 in it's stock configuration yet have it rotate in reverse. Perhaps this is right up your alley?

Unlike the Subaru 'box, the GT3/G50 case does not have any room at the other side.

[kenikh]

Originally Posted by blue72s

Unlike the Subaru 'box, the GT3/G50 case does not have any room at the other side.

It was my understanding that you cannot flip the R&P in a Subaru transmission to get reverse rotation, which is also the case in the GT3 box.

[Cupcar]

Doesn't the casting pocket for the shift rails protruding in the diff case get into the space the ring gear would occupy on the opposite side of a G50, thereby preventing a flip of the ring gear?