Strongest tranny?

[FFRWRX]

Unrelated to 818's, but related to Subaru's.

My brother has an older kit car with a SBC in it with a Corvair transaxle. That was one of the only transaxles available 40 years ago. He is rebuilding/restoring the car (a Manta Mirage) and of course wants to upgrade the tranny and rear suspension. One option is a Porsche Boxster unit, but another is a Subaru 5 or 6 speed unit. There are adapter plates made to mate that to the SBC.

Apparently the 6 speed after a certain date (2007?) has different gears and my be stronger. He has had people tell him that is the one to get, and others tell him the 5 speed has larger gears and it stronger. I know virtually nothing about this, so am just reporting what he was told. Since there are those on this forum that race their cars and have increased the performance, any thoughts/facts on the strength of the Subaru transmissions?

Thank you,

Rick

[Hobby Racer]

I know from personal experience that the Subaru 6 speeds are MUCH stronger than the 5 speeds. They are also heavier and more expensive. Depending on how much power he is putting down a 5 speed may be all he needs. The Corvair transaxles were not very strong and if he has not broken that, a 5 speed would suffice.

But if he is also upgrading / modifying his engine for more power, just go to the 6 speed. 6 speeds from 2004 - present in the STI's are stout and will work great. Subaru also made a split case 6 speed which is essentially a modified 5 speed that went into the base WRX model from about 2014 onward. I do not know much about the durability of that unit.

[idf]

Unrelated to 818's, but related to Subaru's.

My brother has an older kit car with a SBC in it with a Corvair transaxle. That was one of the only transaxles available 40 years ago. He is rebuilding/restoring the car (a Manta Mirage) and of course wants to upgrade the tranny and rear suspension. One option is a Porsche Boxster unit, but another is a Subaru 5 or 6 speed unit. There are adapter plates made to mate that to the SBC.

Apparently the 6 speed after a certain date (2007?) has different gears and my be stronger. He has had people tell him that is the one to get, and others tell him the 5 speed has larger gears and it stronger. I know virtually nothing about this, so am just reporting what he was told. Since there are those on this forum that race their cars and have increased the performance, any thoughts/facts on the strength of the Subaru transmissions?

Thank you,

Rick

I don't know the answer to your question, but Zack at ZF Design will. His sole business is building Subaru transmissions for all uses. Was great to work with and fast turnaround in building one for my 818.

[Neeraj Ahluwalia]

From what I've heard, the split case 6 speeds from the newer models have similar durability to the 5 speeds. The split case design is really why the transmissions are like glass. The case halves flex and the two gear sets saparate a little. The gears then shred because of lack of tooth engagement. This can't be fixed with stronger gears. I'm experimenting with a brace on the outside of the 5mt which should stiffen things up a bit.

[Sgt.Gator]

6 speeds are stronger by far than 5 speeds. Over the years they have come in various gear ratios. I have the long geared JDM Forester STI (yes they made a Forrester STI in Japan) that I only get to 6th when I'm trying to give the engine a bit of a RPM rest on long straights. As in 135 mph + and want to keep the rpm down.

The main differences between the STI 6 speeds are the Front LSD type, the ratios, and whether it has an internal oil pump. The internal pump is useful for adding a cooler. Otherwise the splash and internal oil trays do fine on the non pump newer transmissions. By newer I don't mean the newest 6 speeds with the split case.
PM me your email address and I'll send you some pdf documents that will help, or possibly confuse you !

And a second plus for Zach @ ZF Design. You'll have to mod any trans to work as a 2WD. He does it all the time.