20B gearbox choices
 

I know... this has been around more than once, but being in Europe, I have different choices and possibilities.

Supra 6- speeds are very rare here and zo are the T56 ones...

So I have been reading up some (european)build stories on a variety of cars, including supercharged V12 engines etc.

It seems that the 6-speed Getrag gearbox used by BMW in a variety of V8 (and bigger) cars is working for those guys.

More specifically the Getrag 420G. It seems to be more compact/lighter than a Supra box

http://en.wikipedia.org/wiki/Getrag_420G_transmission
Gear ratios:


1: 4.32

2: 2.54

3: 1.62

4: 1.23

5: 1.00

6: 0.83

R: 3.75


Applications:
1996-1999 BMW E36 M3 (Euro)
2001-2006 BMW E46 M3
1988-1995 BMW E34 540i and M5
1996-2004 BMW E39 540i and M5
1995–2001 BMW E38 7 Series
1989–1999 BMW E31 8 series
2000–2003 BMW E52 Z8


Aside from a custom adapter plate, this could be fine as well.

Only remarks in the Wiki is the shift linkages.

I can only tell you that I've killed 2 E36 M3 3.2l 6 (s6s 420g) speed gearboxes / driveshafts / differentials with a stroked m50 2,5l@2,8l.
I've also killed 3 E34 M5 (also s6s 420g) gearboxes on an E36 with a stockish m60b40 v8 swap.

All this damages have been done using the car's for drifting, j4i.

I would stay away from BMW gearboxes / drivetrain components, they are weak and expensive. As you can see, I've killed 420g's and W210 differentials with power levels below a boostet 20B. )

The only gearbox I've never tried is the BMW 850csi 6 speed, its called S6S 560G.. rumors are, that these boxes share the same internals with the 2jz 6 speed boxes (be prepared to spend some serious €€€)

It really depends what you want to do with the car. If it's a street car, you maybe will get away with the 420g. If I were you, I would just buy a 2jz gearbox from england or a T56 from the US. These are tried and tested setups and especially for the T56 there is a TON of aftermarket support.

if you are going NA, this would be another story ;)

I am currently working on a 20B setup with a ZF S6-40 from a '90s corvette. There are some major advantages to this box:
Pilot bearing is the same size as the mazda one.
Input shaft stickout is the same as mazda.
With minor modification, starter can stay in the stock location
Includes mounting provision for PPF (modified PPF obviously)
Better ratios than T56 or Getrag for 20B (higher ratios)
Allegedly stronger and more RPM tolerant than the T56 in stock form

The main downside is that there are fewer aftermarket parts sources for the ZF. In the US the box itself is also pretty affordable.

My installation process will include a modified Mazda bellhousing w/hydraulic throwout bearing, a custom (simple) shift linkage, a modified PPF, and a custom clutch disk and driveshaft. All of this is required for most transmission swaps, and in this case most of it will be somewhat easier than usual due to the similarities between the ZF and the Mazda boxes.

Might be worth your time to see if there is a European application for this transmission from which you could easily get one.

Ok point taken...but untill recently all european sports cars were NA (M3, Audi, Mercedes) and have finally seen the light to go turbo.

Mostly V8's so torque wise they should all be getting in the neighbourhood of what a 20B turbo is making (I'm looking for 550-600hp, street use and occ trackday, no drag)

Although it will be hard to still find a manual gearbox all together in this range as the flappy gearboxes have taken over.

On the other hand, I'm in Europe, and BMW/merc boxes are almost as common over here as a Supra or T56 in the US...

This particullar thread mentions the 335I gearbox mated to an engine producing around 950 hp.

The 335i is a straight 6 turbo

gear ratios


Transmission





Transmission

6-Speed manual gearbox ZF GS6-53 DZ



1st

5.08



2nd

2.80



3rd

1.78



4th

1.26



5th

1.00



6th

0.84



Final drive ratio

2.81

Other Stock transmissions to handle Turbo Rotary power
 

Any updates on transmissions powerful enough to handle more power and adapters made for the Rotary ? 13B’s are making lot of power now and we are desperately needing them.

T56 Magnum is the best transmission option at the moment. They make adapters for them to the 13B/20B.

I got the CD009/JK40C Nissan 350/370z transmission adapter from careless for mine. It should handle pretty much whatever you want. There are guys running 1000HP on those.

right now i'm using one of those Dog Gear Straight Cut gear sets for the fd3s tranny, and for some reason its holding up KNOCK ON WOOD. Putting about 600ftlbs / 1100hp through it on full slicks and a large Nagasaki Noisy Boy with 4 Ying Yang Spinny Thangs. God only knows why its still together. Took it down for new clutch, has just a little input shaft play, swapping out a new bearing and throwing it back in.

The gear sets for the RX8 box were just way too much money to be worth it to me. Maybe if I start eating 370z boxes... I'm hoping to get the revmatching features of the trans working too.

Have same in my Cosmo, be interested to hear if you get the rev matching working.

How far along on this conversion are you? Would love more detail even for 13B/track applications.

I rarely visit this forum anymore. I had some kids, started a shop, and spend most of my free time SCCA racing and this got back burner-ed. That said I am planning to resurrect this project in the spring. I have everything fabricated and assembled just need to mount it in the car. I will update when finished.

Pat

I'd like to see some pictures of this work! Very interested. Marc

HGT doggy /thread