Diff type for Subaru drivetrain

They may not be LSD's in the Crosstrek or the Impresa.  It's VERY important to get the build sheet with the engine/trans assy. for the one you buy. Also the CPU that it came with.  If it dosen't have LSD, they are available from several sources.  I thought it was interesting that the Subaru unit is welded shut and the gears are not replaceable. If it's bad, you buy a new unit.  That's about all I know. Someone else can surely help you more................Bruce

Thanks Bruce. Yeah, I don’t love the idea of sealed…feels a little Camry-ish rather than performance-oriented, but I do feel like (for me and where I live / how I plan to use the car) this is probably the right drivetrain. Just wish I knew more about Subarus…and new knew more more Subaru enthusiasts personally.

@Goatfarmer posted:

I think the standard rear diff that pairs with the 2.5 motor is a LSD in the Crosstrek and Impresa.

I’m not a Subie guy, but my impression from posters here is that there’s a mixture of Subie 5 speeds and modified (for Subie engine) VW 4 speeds. You might want to call Greg at Vintage. AFAIK, he has Rancho build him a specially-geared VW trans to optimize the Subie powerband. Also just an assumption, but I think VW trans are easier to deal with, installation-wise.

I’m sure @DannyP will weigh in soon. I think he has as much experience with both as anyone here.

Yeah. So which diff? In a Crosstrek or Impreza, there are three. The only one that concerns us here in a Subaru transmission is the one in the transmission itself. The center and rear diff disappear when building a Speedster with either mid or rear engine configuration. Subaru does a cool thing with the transmission and has two shafts running one inside the other going to the center diff. A special piece is made to eliminate the diff and shorten the transmission, which also turns the transmission into two wheel drive instead of all four. A new and custom cover makes it a pretty slick option.

I've no idea if the FRONT diff in a Crosstrek is TBD(can we please use this term instead of LSD?). Say it after me: torque biasing differential.

I do know that in a rear-engine configuration the Suby trans gets a reverse ring and pinion allowing the Subaru trans to be installed and work in this position. You CANNOT simply flip the diff in a Subaru like you do in a VW.

Now, onto VW options. Yes, it is MUCH easier to simply use a properly geared VW trans with bellhousing/clutch adapter to Subaru. However, you'll have 4 speeds. The 5 speed options are both expensive and more difficult, but doable with wheelbarrows of cash. Same goes for the Subagears diff in a Subaru in a rear-engine installation. All you need to do is add the money.

You could also use a Porsche 901 or 915 trans. Add even MORE money.

I have almost 200 hp in a 1500 pound Spyder with an open diff VW 4 speed. With proper suspension setup and STICKY tires, you simply don't need a TBD or LSD or any of that fluff. Unless you drive it(or over-drive it?) on the track well beyond the limit of what most mortals here(including me) can drive.

If I start to hooning and say rev it up and dump the clutch, I lay down two equal and even patches, even with an open diff. Stop the madness, you don't need it.

If your building a subaru engined car I see no reason to not go with a subie tranny 5 speed.  I have 2008-2009 engine and tranny and the R&P is an australian product that reverse it.  hey you get VSS, they line up perfectly no adapter, use Subie clutch and the CPU can be used to even get you cruise control, heck it is built in.

It works for me in a Roadster cruiser style driving car, and I have no LSD it is too hard on the brain and no TBD .  The tranny also has the proper spacing in the gearing and you get to row 4 gears then get ODrive and It is not much more money IMO. If my budget was low I would add this at the expense of something else.  

We all know that If your using a VW engine you need to keep the engine spinning at 3K to cool it ... so you are limited to cruise at 3K rpm at least in any cruising gear.

Danny that a spyder or yours is so light it can do well with a Type-1 but in a speedster I find a 3:44-1 is still a compromise as the 3rd and 4th are not spaced properly.

Heck what do I know but I was going to do a 915 or 901 tranny in my build but some of the used stuff available have been driven for many many miles and rebuilt a few times and hence the cost and availability of GOOD trannies may be an issue and add to the cost... so Big Money ... Subie is available at every corner store nearly.

IMHO the best cheap setup for a type1 powered Speedster using VW trans is stock 1-2, early 1.32 3rd and early 0.93 4th with a 3.44 final drive. Gets rid of your 3-4 hole that your 1.26/0.89 trans probably had.

But otherwise agree with you Ray, you have a great setup.

My setup is working for me but I think there are many choices available and the use equation for your car is of primary importance.  A spyder is an awesome car if only I could fit in it  

In a speedster more options are available but again the use is really what you need to determine and of course whether you want the turn the key and go Subie style or the ACooled traditional car.

Phil has a great idea to do a TypeIV I would try to get a 901 but preferably a 915 but getting good ones are an issue and you cannot get the engine QUIET because of the rpm cooling limitations so the 5th is really a 4th most times but you get more evenly spacing of gears so a good 4speed like your suggesting Danny works well. IMO.

My Spyder has a 200hp Suby engine. Tranny is type 1 4 speed with 3.88 and an LSD. Geared low. 4000 rpms at 70 in 4th. I like it geared low. Never get on the highway. Danny says I don’t need the LSD but with such a powerful engine I think I’ll keep it.
Obviously I’m building a very powerful Type 4 for my speedster.  This car will be used more as a cruiser and highway car and rarely driven in anger. Using a 3.44 R&P with gearing similar to what Danny described. No LSD. Greg has promised me 70 in 4th closer to 3000 rpms. With an air cooled you need some rpm just to keep the engine cool. It will be fine.

Sounds like a good plan!

Wow, thanks for the very well informed responses.  I really appreciate it.  I have been lurking around for years, but now my spot in line to build a Beck Speedster is finally coming up, so I am starting to feel like an excited little kid that can barely stand it...and I need to firm up the plan. The current / default plan is a new 2.5 Subie motor mated with a 5-speed Subie trans. I get the sense they have done this a bunch, and people are very happy with the outcome, so it would probably be just fine not to get too involved in the details and just drive off with the "standard" Subie-powered package.  But I cannot help but feel like now is the time to ask a few questions and see if it makes sense to do something other than "standard."  Carey is so cool and accommodating, I think he would make any reasonable wish come to life...so is there something you wish had done or could do?  Thanks!

My advice after 3 spyders, an intermeccanica, and a Caterham Super 7 is to keep it simple.

Yes do something they are use to doing

@550 Phil posted:

My advice after 3 spyders, an intermeccanica, and a Caterham Super 7 is to keep it simple.

Absolutely agree!

Thanks all. Beck uses a Subiworks tranny, and a LSD (or TBD) can easily be fitted by them…so that’s good. There are four choices of final drive ratio: 3.90, 4.11, 4.44, and 4.88. Any wisdom there? Again, I will probably just go with whatever Carey recommends (who has done a bunch of these trannys in other builds), but I think it is at least an interesting question. It may be hard to answer without knowing the other ratios in the 5MT, but I don’t know that yet. Thanks in advance.

I believe the 3.90 final drive is the one that will give you 70mph at 2800-3000 rpm that for me is the one to use.  I have the 4.11 by error, so 70 is around 3000-3100 I forgot it might even be closer to 3200. in 5th anyway I hardly ever have to goto 4th for freeway overtaking, well unless I really want to get by quickly.  

For a goat farmer, you can choose whatever and it won't be too Baaaadddd.

You're in good hands with Carey. Tell him how you're going to drive the car and let him pick the gears. As others have said, super-close gear spacing isn't needed with the Suby engine, which has a very wide, flat torque band. But people like it anyway.

My guess:

If you live your life a quarter mile at a time, 4.88s are your gears. You're building a canyon carver? 4.44s. You want a GT car to rush over the High Plains with minimal drama? You want 3.90s then.

I think most subaru   gears use the standard gear set that the subie came with having the only exception of choosing the r&P.

Unless of course you use a Turbo gear selection which can be chosen as well as our cars are much lighter from the get go.  You can read on this if you want to see the different gear sets and the shift points that they produce and the final 5th gear selection and R&P will give you speed the rpm at 3000 gives you... Enjoy the ride

While the 901/915 transaxles are quite expensive - the '70 thru '72 Porsche 914 reversed pinion is inexpensive.  It was called a tail shifter and in '73 they went to a side shifter which gave more precise shifts.  Many early owners went to the later style transaxle.  Plus the 914 rusted quickly and up until recently, they weren't worth cost to repair.  The 914 901 version does require a different nose cone (real 901 one or a new available machined one) and a fabricated support brace.  There is an article online on putting one in a Bug - some clearancing of pan/trans horns is required PLUS a 5 speeds shifter! (Note solution is for IRS only).

Type 1 VW Transmission to Porsche 5 Speed Conversion - (aircooled.net)