Anyone try Subaru STI 6 speed?

[George Liechty]

I am new here and thinking out loud about transaxle options. I have read quite a bit about available options, and thought about the Subaru STI 6 speed. It has proven to be very strong in racing applications and is readily available. It also has an available electronically controlled center differential. Depending on year.

My background is machining, auto technician and grew up around old and new mustangs, Shelby's and Boss's, etc. I am currently building a kit Cobra but I am thinking forward to doing the Gt40 kit that I always really wanted.

If there is a compelling reason not to try a STI 6 speed, I may go down that road. I have the equipement and capability to build adapters and a rear drive eliminator kit.

Let me know what your thoughts are.

 

[Randy V]

Hi George,

Welcome to GT40s.
While I can't answer your question here directly - I'm sure that someone can.
I would think that the challenges might be in regard to engine rotation direction and the reorientation of the transaxle for a mid-engine application.
Many transaxles need to either have their ring gear/differential flipped (if possible) or the transaxle must be inverted.
I know that there are many guys in the Suby world that are cranking a lot of HP through those boxes..

 

[Scott]

The subaru gearboxes are notoriously weak. Most Subarus used for racing have upgraded gearbox internals.

The gearbox is also All wheel drive meaning you have to defeat the AWD mechanisms, which may be improbable like the Audi all wheel drive gearboxes. Also you'll end up with a very long gearbox.

 

[George Liechty]

Thanks for the welcome.

I know the 5 speeds are weak. The 6 speed is a lot better. I will do more research. There are a lot of guys running the 5 speeds in a rear/mid engine/defeated rear drive situation. I am still researching the 6 speeds ability to do that.

BTW, the 2005 Legacy GT transmission is the only 5 speed that can handle more power. Still not up to the 6 speed capability.

 

[George Liechty]

06 WRX powered mid-engine TR-42 track/street car build - Page 3 - NASIOC

Here is a thread about how to convert the 6 speed.

Still doing research.

 

[George Liechty]

Possum Bourne Motorsport Ltd - TRANS & DIFF PARTS - STI Parts, Subaru WRX, WRC, APRC, Cody Crocker, Brakes, Fuel Systems, Engines & Engine Parts, Trans & Diff Parts, Rally Car Interior, Exterior & Underbody Parts, Suspension Parts, Roll Cages, Carbon

Lock out kit to eliminate rear drive.

 

[roaldin]

I have a fair amount of torque/power going through my 6mt with no strength related issues.
The 5mts are weak as water.

Biggest problem I've had with mine is worn dogs. They change gear so quickly... On a track it's hard not to take advantage of that...
I have also had a couple of selector issues, factory upgrades have been made in this area.

It's a great box IMO, just don't get it confused with the 5 speed... It's junk.

I have heard that newer versions and American versions of the box aren't as strong but I have no evidence either way for that.

I do hard launch starts with no problems - ie four wheels smoking. If I can do that in a 1450kg awd with race tyres and a 600+ bhp engine then I think a light rwd should be ok.

Tim.

 

[Scott]

Possum Bourne Motorsport Ltd - TRANS & DIFF PARTS - STI Parts, Subaru WRX, WRC, APRC, Cody Crocker, Brakes, Fuel Systems, Engines & Engine Parts, Trans & Diff Parts, Rally Car Interior, Exterior & Underbody Parts, Suspension Parts, Roll Cages, Carbon

Lock out kit to eliminate rear drive.

That's cool but what's the benefit of using a subie box (other than being able to use the subie engine) over one of the more common transaxles? Defeating the rear drive you still have a fairly long gearbox and would the front diff handle 100% of the torque versus a front to rear torque split?

 

[roaldin]

Making the box fwd isn't too difficult I believe. I think in so doing the box can be made shorter (with a bit of work). Making them temporarily rwd is common in places where awd dyno's are unavailable.

Tim

 

[roaldin]

The front diff is an r180.

Btw the electronic centre diff isn't going to be much use in a GT... Unless you want a power take off for a thresher or something...

Also btw, the 6mt has an internal pump for an oil cooler. I believe on later boxes this may have been deleted.

There have been several stages of factory upgrades in the 6mt. Not sure of all of them anymore. Cars haven't had the same priority over the last few years.

Tim

 

[George Liechty]

The biggest reason to look into using the Subaru transmission is availability and cost. And no I wouldn't put a Subaru engine in a GT40. I would build an adapter to run a sbf.

Thanks for the feedback. It will be a while before I go down the GT40 road. I still have a cobra to build.

 

[George Liechty]

Scott, are the Audi boxes durable and available? Is the 01e 6 speed the way to go? How durable, and what changes are required?

 

[roaldin]

Fwiw I have the Audi 6 speed in my GT. Seems strong but standard ratios are pretty wide. So far I am happy with it. It's behind a pretty strong 6 litre and has held up well so far.

I will at some point put a new set of ratios in mine.

I think the Subaru box is likely to be more numerous but I'm led to believe they aren't as good a fit in a GT as the Audi box is.

Tim.