Chi_San

I got a 2002 WRX. It's an awesome car, though I have wanted to convert to RWD for a while now.

Well, I blew my center diff up, and now I have to decide if I want to weld up a center diff, buy a spool, or put a RWD trans in the car. Oh, I should mention, the front axles are totally toast as well, passenger side has two ripped boots, the drivers side has the inner boot ripped.

So, I have heard that the RX-7 bolts right up to the WRX engine (basically, ever subaru motor mass produced, in other words). Making a trans mount is something I can do pretty easily. Converting the rear diff from a WRX unit to an STI unit is something I would be doing anyway.

The question is, is the FD manual box the same bolt pattern as the FC, or did the bellhousing pattern change? What's factory final drive and tire size on the FD? And can an FD gearbox hold up to the 270 HP and 270 FT-LBs my engine makes?

Down the road, I will be stuffing an FC steering rack and front suspension in this car, for weight savings and because I don't really need AWD.

FC slide

iTrader: (1)

Buy a transmission out of a wrecked frs or brz if you can find one haha

nicdchris

iTrader: (1)

Meh, if it was me I would just buy a used transmission and some axles, for dat resale value.

Shouldn't be too hard to come by, i've seen more wrx's parked in trees than any other car.

leftcoastdrifter

iTrader: (17)

FD and FC TII gear boxes can handle that and then some. Fitting it to a boxer, that's a different question that I have no answer for.

Chi_San

Yeah, but the WRX gearbox is awful. There are more stories of people blowing second gear up than you could imagine. And on top of that, the WRX gearbox is like $1k used, for a good one. For that money, I could get a RWD gearbox and a rear diff. I'd just need to spend a little more on conversion axles, and I'm gonna splurge on a new exhaust, as my hackjob catback (which is welded on) is starting to rust.

Apparently, Subaru and Mazda used the same bolt patterns on the Subaru vs RX-7. I think there's like one bolt hole that doesn't line up. Trying to confirm it before I pull the trigger, though.

Biggest issue people have with going RWD on the WRX is wheel hop on hard launches, but I don't really plan on doing much of that.

rotary-guy

iTrader: (24)

My buddy put a toyota r154 with custom bellhousing in his subaru.

198713bt

iTrader: (2)

how did you get 270hp AND 270tq out of the wrx?? im curious because mine holds its own with hp but is lacking in tq. thats one of the main reasons i've been considering an sti swap or a forester xt, that extra .5 liters does wonders for tq lol

twilight slide

This is all stuff that can be found quickly with a search dude. Randomly off the top off my head, and this may be totally incorrect but... Yes, they have the same bolt pattern. I assume you know FDs use a pull type clutch system. FDs have a 4.10 diff ratio in the manuals, 3.9 in the automatics. 225/50/16 is the stock tire size. An FD or TII trans will survive fine at that power level. One thing to note, I don't think FDs transmissions have your standard crossmember supporting them. I believe the PPF supports the aft end. If this is true, making a mount might be a little more interesting than with an FC trans.

Chi_San

I self tuned it. I don't REALLY know how much torque or HP that my setup is making. I do know that it makes most of the power in the 3-5k area, and the turbo is making 17 PSI by 2,500 RPM.

Factory turbo sucks at 7k, but it spools incredibly fast for what it is.

4.10 rear in the manual... Interesting. Means I have to play with a calculator if I'm going to use a 3.545 STI rear diff... And holy crap, that would be stupid tall gearing. Makes things interesting.

twilight slide

Don't STIs come with various diff ratios over the years? Is there something closer to a 4.10, assuming that's what you want?

RotorMotorDriver

iTrader: (1)

Why not replace the center diff and the axle boots and be done with it? The center diff is an easy enough job with the transmission IN the car. Piece of cake, it's like 10 bolts once you get the exhaust and drive line off (all 15 bolts/nuts and 2 plugs for that). I did one in my 2001 Legacy GT not too long ago in about 4 hours working at a slow pace on the floor with just jack stands stopping for lunch. I put a center diff in it I got for $100 from an 05 WRX transmission with a blown second gear (haha).

The boots are simple to do yourself also and are only about $20 per kit. So for less than $200 you are back in action, and/or could sell the car and get something non-AWD. Or, you could put money into a decent transmission like an STi 6 speed. Get one from an 06/07 STi and you don't even need to swap the rear diff. Get some stub shafts from an 04 STi to convert the front axles to fit and it's plug and play. Remove old trans, install new. Plus, you can get an aftermarket center diff controller down the road to play with the center diff bias in manual and auto modes.

As for the steering rack and front suspension, get yourself an STi rack with a quicker ratio, and I highly doubt the suspension weighs all that much less so I don't see the point. A Turbo FC is about 2,850 LBS, and an 02 WRX is about 3,300 LBS, the majority of the difference being the AWD I'm sure. So it's not like you're saving a ton of weight by converting the WRX or anything.

~T.J.

MrGoodnight

iTrader: (1)

An even better idea has arrived!

Sent from my iPhone using my finger.

Chi_San

Hum. That's an aweome idea, except...

1) I've had bad boots on the front axles for ~2 years now, and have driven logging roads, on the beach, and close to 50k miles on the freeway. I COULD replace the boots, however, axle failure is going to be a certainty anyway. How do I know for sure? Because the front passenger side is making all kinds of fantastic noises all the time, and the driverside front is making fantastic noises when turning.

2) With my discount from work, a center diff runs $560, or thereabouts, while an RX-7 gearbox could be had for around $300. A center spool conversion from RalliTek is going to run about $500. I'd be going the RX-7 tranny way, except the rear diff is... Not an easy match. Closest is a 4.11 from a 2000 Legacy GT, but it's an R160, so would break pretty fast.

3) My factory rear diff is worn out. I is making all kinds of neat sounds, most notably a whine under constant throttle cruise, that is getting louder over time. I'm sure it will last at least a little longer if I left the car AWD, but it will need replaced sooner or later regardless. Hence, I'm going to be finding an STI R180 rear diff and drop it in, regardless of AWD or RWD.

As for the ratios the R180 comes in, they were limited to 3.9 and 3.545. The only final drive ratios Subaru has ever used are 4.44, 4.11, 3.9, 3.7, and WRX/STi rear ends in 3.545. 3.9 isn't too far off from 4.10, but it would still make tall gears even taller... The factory WRX box has kind of middle of the road ratios, I'd like them taller. Going rom 3.9 to 3.545 would be an improvement, but it would still be a little closer than the stock FD gearbox setup with factory rear and tires. (I've driven a few RX-7's.) My tune is for powerband, not peak power, so longer gearing would be nice.

Right now I'm eyeing the center diff spool. If I can get one cheap enough, I will go for it. If it's too expensive, I'm putting a factory rear diff and two new front axles in, an R180 3.545 rear diff, and if I have money left, an exhaust. If the spool isn't too expensive, I'm getting the spool, rear diff, conversion axles, and if I have money left, an exhaust.

RotorMotorDriver

iTrader: (1)

Get a used axle cheap that isn't making noise and re-boot it. Re-boot the other one that isn't making noise.
I ran an R160 with 130,000 miles on it behind a JDM version 8 EJ207 and STi 6-speed making 300+ WHP for nearly 2 years before I took it out to replace with an R180. I still have the R160 sitting around the shop somewhere, it held up fine. There is only a 0.7874" difference in ring gear diameter between the two, it isn't much of a difference in strength IMO.
The rear diff has to match more than just the transmission (center and front diff ratios) for it to fit and work. The rear R160 axles wont work in an R180 rear diff, and if you tried to use the R180 axles in the rear diff, the other end wont fit into the WRX hubs. There used to be a company that made conversion axles but they were over priced, and I don't think they're still around anyway. In order for the R180 axles to fit, you need the matching rear hubs from an STi, which then means the WRX suspension and brakes would no longer fit either, so you need the STi struts and brakes. Also, the wheel bolt pattern changes from WRX to STi, so you need new wheels. Stick with an R160 if you're trying to save money.
I don't think this matters since you should be sticking with an R160 as explained above.
Center diff spool will really be hard on everything on the street. If I have the center diff on my 6-speed set too tight, let alone locked, the car does not like to turn. It clunks, binds up, etc just backing out of my driveway, let alone parking lots, etc. Driving down the road it isn't too bad, but as soon as you need to make a turn at a light, you will be fighting it and making noises and clunks. The inside tires have to turn slower than the outsides obviously (this is a function of the front and rear diffs), but the front to rear needs to turn at different speeds too (front faster than the rear typically when turning). The spool is REALLY hard on that. You think you have axle and diff problems now... Haha

I'm just trying to pass on some advice after many years in both the Subaru and RX-7 world. I didn't mention it before, but in addition to my RX-7, I have a 1998 Outback, a 2001 Legacy GT, and a 2002 WRX with a JDM version 8 STi engine (with AVCS), ball bearing turbo, 2007 STi transmission (with working DCCD), driveline and R180 rear diff (STi axles also), aluminum control arms and lateral links, STi sway bars and end links, Brembo brakes, STi BBS wheels, blah blah blah. Needless to say, I have swapped around a few parts in the Subaru world, lol.

~T.J.

Chi_San

The idea is to put the spool in, remove both front axles, put in an R180, and go RWD. There are conversion axles that allow you to use an R180 diff with R160 hubs.

Eh. Comes down to price. And both front axles need to be REPLACED, not re-booted, if I am going to stay AWD. >_> I'm pretty shocked that neither has snapped yet as it is.

RotorMotorDriver

iTrader: (1)

Custom axles are typically expensive. Custom inner races are cheaper/easier, but you still need the STi axles first to make the custom rears yourself. What do you plan to use to plug the holes in the side of the transmission where the front axles used to go? I suppose you could disassemble the fronts, pull the shafts out of the inner cup and reinstall those, but it seems like a lot of work to take a couple steps backwards with the car, haha.

~T.J.

Chi_San

Well... It's harder than just getting STI axles and WRX axles and making a hybrid.

But, regardless... I am running out of time, as this is my only car, and by the time I find a RX-7 trans and figure out how to swap it, my car won't be drivable anymore. I picked up a new center diff today, I will be swapping it in, taking the currently broken one apart, and if it's just the clutches in it that are broken, weld it up and hold it until I have an R180 or R200 rear diff I can swap in, with axles.

Edit: For the front axles, if you leave the front diff in, and the axle stubs, then you can remove an axle and not worry about it leaking.

mellow65

iTrader: (2)

wont work, the starter is on the wrong side and there is no clearance for on the block for the starter being on the other side. the brz is not using an EJ motor.

Here is what I did,



that's a ej22 with a w58 from a supra,

the guy who built it an awesome old man named Bill, he makes a bunch of stuff for making 4g63s to rwd, but after about a year of begging and then waiting about a year and a half i got the first bell housing. he can do the W series or a r150 from toyota.

here's his web page, i think he charges around mid $400s for the bell housing.

Bill's Auto Fabrication - Toledo, Ohio

personally i took all that and crammed it in a first gen

SAY WHAT?!?!

there is a guy on legacy central that put a w58 in his lego turbo.

Lego awesomeness

as I have taken my car from a random idea to a driver i can answer any questions about the bell housing you would have.

mellow65

iTrader: (2)

I used to always read that too when I was first looking, but I happen to have a rx7 tranny and a subaru tranny in my garage at the same time, i can tell you, they aren't the same.

XXXLSFD

what you need to do is either get a spool to eliminate the center diff or weld a stock one in the trans. 2nd is get a 03 or newer wrx transmission. they have updated stronger gears than the 2002 (6 speed would be the BEST idea but those are around 3k). for the rear diff the stock diff will be fine but ther BEST way is to get the r180 from a 2004 or 2005 sti and the rear cv axles from a 2005-2008 legecy SPEC B. uses the 6 speed and r 180 but the r180 they use has axles thay will let you not have to change out the rear hubs/ect.

if you need any help/parts lmk im a senior master tech for a dealer in oregon and have done rwd in subi's before.