6MT spec b vs STI trans

Strength wise, can a spec b trans handle as much power as an sti trans? the reason i ask, im considering whether swapping PPG gears into my spec b swap would be overkill or not...

What power levels are you sporting that you are now concerned with transmission's ability to handle power?

 

I know people who broke stock transmissions at stock power levels. And I know people who -while on borrowed time- have 500 hp on stock transmissions.

 

The two transmissions are essentially the same, except for the DCCD and the front LSD. But I think that if you are so concerned, even PPG gears in an STI tranny would not do. I think you should simply park the car and not drive it. Sure way of maintaining your transmission in top shape.

nothing with my current power concerns me, but when the build is finally finished itll be anywhere between 450-550 with the purpose of drag/time attack. i want to prevent paying to pull and install the transmission twice so before i go ahead with the swap, if im going with PPG gears i want to do it while the transmission is out.

 

I know people who -while on borrowed time- have 500 hp on stock transmissions.

 

so if i do end up around those levels i might as well get it done to prevent transmission failure? do you know anyone that has built a transmission?

I believe 600hp/ ft-lbs is where a stock 6 spd goes. It might just be cheaper to blow it up and fix it though.

 

IMHO those power levels (approaching 600hp) are best left for 'merican V8's (at least in drag racing).

 

I'm sure BAC5.2 / Andrewtech in MD know a lot more on this subject as Andrewtech does a lot of rebuilds.

I believe 600hp/ ft-lbs is where a stock 6 spd goes. It might just be cheaper to blow it up and fix it though.

 

and if im right on the cusp of that, itll probably just be a matter of time. would rather wiggle room so if its good up to 650-700 and i stay around 5 then, in theory, i should have a reliable tranny? how do you figure it would be cheaper taking it that route?

What are you really going to be doing with the car?

 

Drag racing? There are a bunch of people who make a bunch of power that drag race on stock 6-speeds. You run into gear ratio problems before you run into strength problems (well, not the shift forks and pivot arms, they snap when you shift REALLY fast). Gear ratios are a problem, and so is shifting quickly.

 

PPG's in a 6-speed are unbelievable. It's the easiest dogbox I've ever driven. The 4-gear drag set is the most affordable, but it's still not cheap. IIRC it costs somewhere in the $6k range. The 5-gear Group N box with the HD 6th is the money-box, but that pushes $11k. I daily drove a dogbox in my 5-speed for a while, and you get used to it. I actually really enjoyed having a dogbox, and I'd do it again in a heartbeat. Most people hate driving dogboxes.

 

If you want to make 500 wheel, the 6-speed is reliable enough. You'll have to watch out for the shift fingers and the forks if you drag race it, and the rear transfer gear bearings go out easily (so you'll have to have a keen ear for them). Other than that, you should be in good shape. I've not seen anyone put that much power through a viscous diff in a 6-speed, but it should hold up fine for road racing. Lots of drag racing will probably destroy it, though.

 

Keep in mind that 500whp is no trivial amount of power. It requires a lot of involvement, and it becomes much less of a daily driver at that point.

I think there is absolutely no reason to have a 500 whp Subaru. Ok for those people who actually race or drag race professionally with a fully supported shop car i can see it. But not a Legacy gt. It is the wrong platform. Ultimately the Subaru's we own are 4 cyl cars and should be treated as such. 500 whp is definitely possible but aside from a technical exercise it is a gross display of futility. It is my opinion that you should add more "lightness" and less whp.

 

What are your drag time slip ambitions? Dont be that guy who likes the numbers but has no real reason or need for them

What are you really going to be doing with the car?

 

Drag racing? There are a bunch of people who make a bunch of power that drag race on stock 6-speeds. You run into gear ratio problems before you run into strength problems (well, not the shift forks and pivot arms, they snap when you shift REALLY fast). Gear ratios are a problem, and so is shifting quickly.

 

PPG's in a 6-speed are unbelievable. It's the easiest dogbox I've ever driven. The 4-gear drag set is the most affordable, but it's still not cheap. IIRC it costs somewhere in the $6k range. The 5-gear Group N box with the HD 6th is the money-box, but that pushes $11k. I daily drove a dogbox in my 5-speed for a while, and you get used to it. I actually really enjoyed having a dogbox, and I'd do it again in a heartbeat. Most people hate driving dogboxes.

 

If you want to make 500 wheel, the 6-speed is reliable enough. You'll have to watch out for the shift fingers and the forks if you drag race it, and the rear transfer gear bearings go out easily (so you'll have to have a keen ear for them). Other than that, you should be in good shape. I've not seen anyone put that much power through a viscous diff in a 6-speed, but it should hold up fine for road racing. Lots of drag racing will probably destroy it, though.

 

Keep in mind that 500whp is no trivial amount of power. It requires a lot of involvement, and it becomes much less of a daily driver at that point.

 

can shift forks etc be upgraded without full gear sets? maybe thats the route ill take for the time and see how goes it.

Yes they can be. PPG makes some. I HIGHLY recommend getting a front LSD if you are serious about racing the Spec-B trans. DCCD you can do without, but you will be MISERABLE trying to handle that much power without a front LSD.

 

Give Andrewtech a call to talk about options: 240-683-1000.

I heard of Andrewtech but they are a hike for me. RallySpec is a little closer, know anything about them? I saw a CHEAP front lsd in the market but just seemed to good to be true

Andrewtech is the worlds largest distributor and installer of PPG.

 

You decide. They might even have some other options for you.

I heard of Andrewtech but they are a hike for me. RallySpec is a little closer, know anything about them? I saw a CHEAP front lsd in the market but just seemed to good to be true

 

RalliSpec is a quality shop. They aren't very big, nor do they do tuning, which is why they aren't well known. However, they have an excellent reputation. I can't say I've ever heard a bad thing about them, other than being too busy.

 

Numerous members here have had their STi front diffs installed there and at least one 5mt gearset that I know of.

 

Rallispec uses Albins gearsets.

Three other things to note:

 

Bias: STIs 6MT center diffs are biased for more torque to the rear, either 35/65 in the early years (04-05, I think) or 40/60 in the later years (you should double-check). That's good for drag racing as it sends more torque to the wheels that have more weight on them when you launch. Mine is 35/65, and I spin my rears, not my fronts.

 

Also, it acts a lot like rear wheel drive in that throttle is more likely to induce oversteer rather than understeer. So for road racing I think you'd find it easier to rotate, and therefore faster.

 

DCCD: It allows you to run the diff open, which I also think is preferable for drag racing. I talked with a guy who'd been through a few front axles, he believed that if he had an open diff he probably wouldn't have that problem. Thing is, after the rear axles break, the fronts get everything the center diff can give them, and the fronts are weaker than the rears. Open center diff means you only need to upgrade the rear axles.

 

You might think that powering the fronts would give you better launches but I'm not sure that's worthwhile. Really fast drag cars don't power the fronts, they lift them. Even if they stay on the ground, they don't have enough weight on them during a launch to be very useful.

 

I haven't had my car on a road course yet but my limited hooning suggests that the car would be much more fun with the diff open, due to the oversteer I mentioned earlier. More challenging, probably not faster, but much more fun.

 

Ratios: Spec B gears are longer than STI gears, and more evenly spaced. I had Rallispec put spec B gears in my STI 6MT mostly for DDing. But you may find yourself with enough power that Spec B gears would allow you to make one less shift before the end of the strip. You'd need a pretty fast road course for the taller gears to make a big difference, but I doubt they'd do any harm either. You'll shift less, which is probably good.

i called rallispec today to no avail. ill email them tonight and see what they suggest/offer in terms of a "best fit". i think my best bet is to take what i have and run with it, enter a solo event or two, see how it feels, tweak from there. I wanted to keep it as cost effective as possible but in hindsight it really doesnt work like that without hands on testing/experience.

NSFW, do you know of any aftermarket dccd options that can be retrofitted into a spec b? i know the casing on an sti trans is bigger but do you think it possible?

 

Ratios: Spec B gears are longer than STI gears, and more evenly spaced. I had Rallispec put spec B gears in my STI 6MT mostly for DDing. But you may find yourself with enough power that Spec B gears would allow you to make one less shift before the end of the strip. You'd need a pretty fast road course for the taller gears to make a big difference, but I doubt they'd do any harm either. You'll shift less, which is probably good.

 

These could have been JDM STI Forester gears depending on the year of your STI tranny. My 08 STI tranny required ther JDM gears. Same ratios though.

 

The thing the SpecB transmission is built like the older 04-06 STI trannies, keyway size wise, albeit without the oil pump (which is now missing on STI tranny as well).

 

 

Also +1 for Rallispec. Good guys. They worked on both of my 6MT trannies. Installed front LSD in 08 SpecB tranny and installed the Forester gears in 08 STI tranny.

 

<--- As you can see one is still sitting around, hence only 11MT not 12MT

i called rallispec today to no avail. ill email them tonight and see what they suggest/offer in terms of a "best fit". i think my best bet is to take what i have and run with it, enter a solo event or two, see how it feels, tweak from there. I wanted to keep it as cost effective as possible but in hindsight it really doesnt work like that without hands on testing/experience.

 

I think that's a good plan. To the best of my knowledge the spec B and STI transmissions are similar in strength, just different in ratios.

 

Rear axles will probably be the first thing to fail. I'm going to buy a set of spares this week, actually. At 375whp I'm pretty sure I will break mine eventually. With your goals, you might want to buy a set before your first trip to the strip.

 

I'm not aware of a way to put DCCD into a spec B transmission. That doesn't mean it can't be done, I just don't know where to start. I'm sure Rallispec would know if it's feasible, probably Andrewtech would too.

 

Putting spec B gears into an STI transmission gives you essentially the same thing in the end. I think that added about $2k to the cost of refurbishing the used STI 6MT that I put in my car, but it was a while ago so I don't remember for sure.

Added $2k??? I doubt it. It cost me grand total $800 to swap these gears. Parts & labor (with tranny out of the car). If the tranny was overhauled already it should be only $300-400 for the parts.

You might think that powering the fronts would give you better launches but I'm not sure that's worthwhile. Really fast drag cars don't power the fronts, they lift them. Even if they stay on the ground, they don't have enough weight on them during a launch to be very useful.

 

Its misleading to say AWD does not give you "better launches". Better launches than what? A trailer queen RWD on Hoosier race slicks? AWD does give a "better" launch, but better than WHAT exactly. A hell of a lot better than FWD anyhow.

 

Really fast drag cars have really fast suspension setups that keep the drive wheels on the ground and making contact. Anyhow, remove squat from the rear = more weight on the front wheels.

any of you ever drive a stage 4 clutch? im getting anxious ill have to learn how to drive all over again

What brand clutch are you looking at? If you're driving this on the street, you definitely want something with a sprung hub. This is your DD right?

 

Personally, I hate my Spec stg 2+ and lwfw for my former daily commute. Although, I attribute most of the drivability issues to the lwfw. For the daily grind I hate it, but for rev matching it's lovely.

 

I'd make my decision based upon what clutch can be used with either the stock FW or the STi FW.

Its misleading to say AWD does not give you "better launches". Better launches than what? A trailer queen RWD on Hoosier race slicks? AWD does give a "better" launch, but better than WHAT exactly. A hell of a lot better than FWD anyhow.

 

Really fast drag cars have really fast suspension setups that keep the drive wheels on the ground and making contact. Anyhow, remove squat from the rear = more weight on the front wheels.

 

Better than the same 500whp LegacyGT with an STI diff, since that's the power the OP has in mind, and he was asking about the pros and cons of STI vs Spec B transmissions.

 

Removing squat does less than you might think to keep the front end weighted. Squat only causes weight shift to the extent that the car's CG moves back when you tilt it back, which is what... half an inch? Squat doesn't cause weight shift, it's an effect of weight shift. If you have enough power, the fronts will come off the ground, no matter what suspension setup you have.

 

500whp won't lift an LGT's fronts off the ground, but if you have a 50/50 center diff, and you launch too aggressively, you'll unweight the front tires and spin them. At that point your launch is limited by how much lockup your center diff provides. If it provides little lockup, your launch is weak. If it provides a lot, you could still launch hard, but will the spec B's center support that? I honestly don't know but it seems unlikely for a car that comes with about 200whp.

 

DCCD will let you lock it up as much as you want, but bring a full set of axles to the track. As I mentioned, one drawback to putting lots of power to the front is that if your rear axles break, your front axles break an instant later.

 

My best launches so far have been done with wheelspin rather than clutch slip. I'm I launch more consistently that way. And I'd rather replace tires than clutches. And I'd rather replace as few axles as possible.

 

Perhaps I could launch a little faster if I was more willing to risk my axles and slip my clutch, but I've already done a couple of launches using wheelspin that were faster than I thought my car would ever be capable of so I don't really care. I had one sixty-foot of 1.38 that might be a glitch or a fluke, but also a 1.5X the same night. I was hoping I might get 1.7X, so I'm happy to open the center diff and spin the rears.

What brand clutch are you looking at? If you're driving this on the street, you definitely want something with a sprung hub. This is your DD right?

 

Personally, I hate my Spec stg 2+ and lwfw for my former daily commute. Although, I attribute most of the drivability issues to the lwfw. For the daily grind I hate it, but for rev matching it's lovely.

 

I'd make my decision based upon what clutch can be used with either the stock FW or the STi FW.

 

i have a competition stage 4 clutch sitting in my shed. i also have a used act stage 2 that came with the tranny. its my dd now, but hopefully soon well have a third vehicle so this one can sit and be my weekend warrior. my biggest concern is traffic. with the way i travel for work and how completely f*cked 95-476 is around 430 i might carry a pistol to blow my head off after 1 week

I use an Exedy Twin, and I don't mind it at all. It makes some noise when you're shifting but it's not bad. However at 500whp you'd want the HD version, which I have not used.

stop and go doesnt bother you?