Skinny On The 5 Speed

[Gollum]

So I sat down with my friend who knows subies through and through to really talk turkey about all this and gleam some info off him so I can be prepared.

The big thing that stood out, was his input on the 5 speed transmissions. Reality is, they WILL blow, at a wonderfully documented rating of around 370 torque. Stock power levels are fine, but if you're venturing beyond 300 wheel hp, you're going to be at risk.

We talked it over and over, and this is just the reality. Having two less wheels won't matter. These trannies aren't blowing with shock load. You can get going, put it into 2nd, then slowly ramp up the throttle, and getting into WOT with enough torque you'll just shred the gears.

The solution? Aftermarket gear sets. These can get pretty pricey, but you'll also have to find someone who KNOWS subaru transmissions well, not just a joe shmoe tranny shop.

The other thing is that the WRX trannies are all open front diffs. This might not be a huge issue depending upon the suspension design, but for those looking to upgrade, expect to spend over 1k for that+labor for install. This is an install you most likely won't want to do yourself.

Also, it should be noted, that converting to E85 will almost guarantee enough torque to shred gears.


Conclusion: Sub 300hp levels might be really affordable from a WRX donor, but if you want 400 wheel hp expect to put an extra 5k into your budget for 5 speed work. The other alternative would be getting the STI transmission, which we don't know if it'll fit yet. But if you look around those aren't cheap either...

[Steve91T]

I disagree. 2nd gear with a 400 hp 3200 lb all wheel drive car WILL HAVE more traction and load than an 1800 lb, rwd car.

A 400 hp, 1800 lb, rwd car will light up the tires in 2nd gear. Not hook like the big car with 4 tires digging into the ground.

There's no way this little car will tear up a tranny....unless someone is driving like an idiot, which means they could tear up any tranny in any car.

Steve

[MDRex]

The tranny thing is blown out of proportion. There are a lot of guys that blow them up, but there are also a lot of guys that run good power and don't blow them up. You also have to remember you are much more likely to hear from the people that have problems, than those that don't. The ones with problems tend to be more vocal on the Internet forums when something happens.

[Nativo]

I don't know about you guys but I planning on using R compound (and as wide as I can fit) tires in mine and that will definitely have enough grip to avoid spinning the tires. That's when it won't be necessary to be an idiot since torque alone will break the gears.

I've been working on subies long enough to know that if one wants power one should start from the bottom up.

Thanks,

[Benji]

I've mulled this over and over and..... quite clearly you and your friend don't know much, mostly about the laws of physics :D

[PhyrraM]

I would counter with: Unless your drag racing, 300HP is all your ever going to need at the target weight. It's not a Enzo, McLaren F1 or even the GTM. Anything more than 120ish MPH is largely not realistic in a light, open roadster (the current, stated goal).

Correct me if I'm wrong, but most folks who build stock 225HP 5.0/4.6 Roadsters still feel like they are driving the fastest car in the world, right? Also, I would venture a guess that anything more than about 300HP in a Roadster requires your virtually undivided attention most of the time. Fair to say?

My version of the Cliff's Notes go something like this: Yes, the trans can be weak. But the majority of builders will never feel the need to push the car near that point. And for the few that do there is always a better trans that fits with some modifications.

Now, from a engineering standpoint, the torque load the gears see will be the same whether it's 2WD or AWD. The TIME that the gears see the load is less because the lighter weight is manifested as faster acceleration. All other things being equal, at low speeds the tires may break loose before the transmission pukes. However any time the wheels do not lose traction, the transmission will see the same load, albeit for less time.

[Steve91T]

I don't know about you guys but I planning on using R compound (and as wide as I can fit) tires in mine and that will definitely have enough grip to avoid spinning the tires. That's when it won't be necessary to be an idiot since torque alone will break the gears.

I've been working on subies long enough to know that if one wants power one should start from the bottom up.

Thanks,

No you won't. Because there is less weight, you have less load.

I didn't fully understand this concept until I tried to dyno my 99 F-250 Powerstroke. On the street, my lightly modded diesel would hit 25 psi of boost. On a dyno, I was only able to get about 18-20 at redline. The reason, because the drum was only about 3500 lbs or so. Not 7000-8000 like I actually need to put a similar load on the engine like I get on the street.

Spinning that 3500 lb drum, in 6th gear, just couldn't generate the load required to spool the turbo.

WOT in a 400 hp car that weighs 1500 lbs less isn't going to generate the same load....even if you are in a high gear and not spinning.

My 450 hp 97 Camaro would probably rip the rear end out of the car if I put drag slicks on it and did multiple launches. So, how do I fix that? I don't put slicks on the car and drag race!!!!

When you have R compound tires, you are probably doing track days or auto-x's. You will have cold tires when starting from a start. Once they are warmed up, you probably aren't going to be doing a drag start.

Steve

[PhyrraM]

Steve, what you say is true. However it has nothing to do with the weight of your truck vs. the weight of the dyno rolls. It has to do with the amount of time the motor was allowed to build boost.

My guess is the dyno run was over before full boost was reached. Or phrased anothe way..the RPMs climbed faster on the dyno than they do on the street.

This is really common on turbo cars and will also be seen on the FFR Apex (ha! see what I did there?). Faster acceleration will see a boost reduction vs. the full bodied car. Most turbo cars also see this phenominon as slightly different boost levels in each gear. If they don't it's only because it's programmed out from the ECU (a stock WRX does this).

[mn_vette]

I've mulled this over and over and..... quite clearly you and your friend don't know much, mostly about the laws of physics :D

Interesting, perhaps you should state some reasons for disagreeing with him.

When you look at the transmission as a black box, you have engine torque going in and shaft torque going out. Assuming that you are getting traction you can put the engine torque through the gears to the ground to propel the car forward. Reguardless of how much the car weighs if you are putting 370ft# or torque out of the engine that has to go through the gears to get to the ground. If the gears can not take that much force then they are done.

Does having a lighter car help you? From a stop yes, from a roll, not really. From a stop you have to get the mass moving and you are dealing with clutch slip and a bunch of other junk. From a roll, instantaneous torque is the same as long as you maintain traction. F=M*A If you take the same engine and put it in a car with half the mass you end up with twice the acceleration, but the force still has to go through the transmission to get the car to go.

If the 5-speeds are breaking from people doing quick launches and quick slamming shifts then having a lighter car will help, but if it really is just the power limit of the gears then we have to be careful.



Since the cars are going to be accelerating at twice the speed of the WRX people may want to adjust the overall gear ratio as well, which will involve cracking open the tranny anyways. I'm currious to see how these cars will do with out an LSD as well. I'm sure the first few people done with their cars will let us know.

[Kasmodean]

PhyrraM beat me, but he is right.

The only effect weight has on engine load is increasing traction of the vehicle. A 200 HP load is the same load regardless of if your RPMs are raising slow or fast.
If the tires aren't spinning then a 2WD RWD has the same traction as a tracked vehicle.

[Kasmodean]

I've mulled this over and over and..... quite clearly you and your friend don't know much, mostly about the laws of physics :D

Nothing Golum said is incorrect. The question becomes does the lighter FFR car accelerate fast enough to prevent hitting full boost. If not, then if you hit 370 lb*ft then you will have problems if what he states is correct form historical information. If the car does accelerate fast enough that you can't hit 370 lb*ft because you can't build full boost before needing to change gears then there will be no problems.

[Gollum]

Thank you for the backup guys, I clearly stated that "from a roll" they break at 370 toruqe. My friend has seen it happen time and time again, some times on car's he's had his own hands on. This is more than just myth, which is why I wanted to start a thread.


I've mulled this over and over and..... quite clearly you and your friend don't know much, mostly about the laws of physics :D

I just want to go into detail here for you, so that you can hopefully understand why I said what I said. Don't take it personally, because I understand where you're coming from, AND YOU'RE RIGHT!!!!

USUALLY, when a tranny manufacture like g-force says "our tranny will hold 500toruqe" they mean in almost any application intended. So you can take a T56, rated at only 500 torque and put it in a 4000 pound GTO with huge slicks and it'll be fine. But put it into a 2300 pound datsun and it'll hold A LOT more power.

But what normally breaks trannies is shock load. The "moment of inertial" when you're getting that weight moving. There's severe strain on all the driveline parts and when you have huge sticky tires and you dump the clutch it all SCREAMS under the load. But this isn't what's shredding the gears in these 5 speeds.

You could be in 5th gear, on the freeway, and decide that you want to pass a semi before changing lanes and BLAM!!!! Bye bye tranny. Some gears are weaker, thus more likely to blow, but that's the hard truth. 370 torque, and you're throwing dice.

You could also consider it a HP rating versus a Torque rating. If you say a tranny can hold 200hp, then if you add more weight to the car then the static traction rating of that will change. But torque doesn't require any RPM to have a force. Torque is just that, rotational weight no requiring speed to exist. It's just there. You can hold a 10 pound rock and it's pushing 10 pounds onto your hand. You can throw that rock with a certain force with speed, and it could create a much larger load, but it's still a 10 pound rock. 18-wheeler transmissions are huge not because of the HP they hold, but because of the torque they have to use to convert such a massive load.

So again, weight DOES matter, but not necessarily in the way these trannies have been brreaking.


No you won't. Because there is less weight, you have less load.

I didn't fully understand this concept until I tried to dyno my 99 F-250 Powerstroke. On the street, my lightly modded diesel would hit 25 psi of boost. On a dyno, I was only able to get about 18-20 at redline. The reason, because the drum was only about 3500 lbs or so. Not 7000-8000 like I actually need to put a similar load on the engine like I get on the street.

Spinning that 3500 lb drum, in 6th gear, just couldn't generate the load required to spool the turbo.

WOT in a 400 hp car that weighs 1500 lbs less isn't going to generate the same load....even if you are in a high gear and not spinning.

My 450 hp 97 Camaro would probably rip the rear end out of the car if I put drag slicks on it and did multiple launches. So, how do I fix that? I don't put slicks on the car and drag race!!!!

When you have R compound tires, you are probably doing track days or auto-x's. You will have cold tires when starting from a start. Once they are warmed up, you probably aren't going to be doing a drag start.

Steve


To be honest, your dyno operator should have been smart enough to run the dyno in a higher gear like 4th or 5th unless his drums are RPM limited (which I doubt). In a higher gear your transmission will have less TORQUE MULTIPLICATION factor, thus won't move the drums so easily.

You can actually take your max engine torque, multiply it by your 1st gear ratio (we'll say) then by your gear ratio (we'll say 4) then by tire (we'll say 2, meaning 24" tall). If you have 300 crank torque that means without any drivetrain loss you'll see 7200 lbs of torque at the wheels. How so much? You're giving up speed for torque. This is how we move such large objections from a stop so easily. When you have to push a car it's really hard right? You're probably capable of pushing 100+ worth of pound if not a lot more, and look at how long it takes to get a car rolling.

[Gollum]

I would counter with: Unless your drag racing, 300HP is all your ever going to need at the target weight. It's not a Enzo, McLaren F1 or even the GTM. Anything more than 120ish MPH is largely not realistic in a light, open roadster (the current, stated goal).

Correct me if I'm wrong, but most folks who build stock 225HP 5.0/4.6 Roadsters still feel like they are driving the fastest car in the world, right? Also, I would venture a guess that anything more than about 300HP in a Roadster requires your virtually undivided attention most of the time. Fair to say?

My version of the Cliff's Notes go something like this: Yes, the trans can be weak. But the majority of builders will never feel the need to push the car near that point. And for the few that do there is always a better trans that fits with some modifications.

Now, from a engineering standpoint, the torque load the gears see will be the same whether it's 2WD or AWD. The TIME that the gears see the load is less because the lighter weight is manifested as faster acceleration. All other things being equal, at low speeds the tires may break loose before the transmission pukes. However any time the wheels do not lose traction, the transmission will see the same load, albeit for less time.

This is all totally true, and I'm not starting this thread to scare people. I'm just wanting to clear the air because there had be talk about the tranny and what it'll hold. I agree that most people will never need even 300hp, but thanks to the lower displacement and dynamic nature of a turbo a 300hp 818 (or whatever it gets called) should be more "drivable" than a 275hp small block roadster kit.

I also know how easily some of these motors will make power, and people deserve to know what they're in for if they go crazy with the mods. It might only take 3k to get to 400hp, but I want people to know that there's some serious supporting mods to consider before doing so.

And who's kidding themselves? There's people with 500hp elises. :-D Some of us are just speed junkies.

[Steve91T]

Well, like I said, the dyno was done in 6th gear, to get as much load as possible. When done in 5th, it generated even less boost. The dyno operator should have told me that this dyno wasn't going to work in the first place. Still managed 550 ft/lbs of tq though!

Anyway, I completely understand what you are saying. You are probably right, that even with the reduced weight, tq is tq. I was just thinking of the car, at WOT at top speed. Doesn't matter the weight at that point.

I guess it is good to know that if you want 400 hp, you're going to need to upgrade the tranny. It'll probably keep a lot of people towards the 300 hp range, which is where I'll be.

Those people with 500 hp Elises are nuts. I think a 250 hp Elise would be just about perfect. This car at 300 hp is going to be a rocket.

But you are right, there are people who just love to go fast, no matter the cost.

Steve

[AVIONX]

Conclusion: Sub 300hp levels might be really affordable from a WRX donor, but if you want 400 wheel hp expect to put an extra 5k into your budget for 5 speed work. The other alternative would be getting the STI transmission, which we don't know if it'll fit yet. But if you look around those aren't cheap either...
Gollum,??
You say this will cost 3-5 more Gs for LSD and Bulletproof tranny like it's a deal breaker. Ummmmmm. How much $$$ do you think it takes to get 400 WHP? Any body silly enough to think they can double the crank horsepower in ANY CAR EVER MADE and not spend some corresponding dough on the driveline deserves to have his tranny end up as filing filled 90 weight pudding I have no pity for. :) And oh yeah Nativo. 1800 pounds, 400WHP and theres not a tire compound in the world that will eliminate wheelspin.

All that being said...there is some really useful info in your post if you ignore the hype, so thanks and keep the useful info coming

[Steve91T]

The other problem with high hp levels are heat. If you plan on tracking the car, you need a good intercooler, and low boost. Otherwise things will get too hot.

[audsyn]

Stock WRX has 220-some hp at the flywheel. If you double that, the tranny is at risk, but so are the rod bolts, the pistons, the bearings... That's into the range where you should expect things to break.

However, if you aim a bit lower...A 2.0 WRX with full exhaust, bigger turbo plus supporting mods, a good tune, can routinely get to 270 or more whp, let's say >325 at the flywheel (WRX's have lots of driveline loss). Obviously that's much more than stock and lifetimes will definitely be reduced, but it is routine, reliability is reasonable, and you can do it without breaking the 5-speed (unless you shock load it by dumping the clutch, as mentioned). In a 2000 lb car, that's like having >500 hp in a WRX-sized car.

That's probably going to be enough for most people. If you want more power then that, then yes, the stock gears in the 5 speed are not for you.

[Steve91T]

That drivetrain loss is due to the all wheel drive. You can expect the normal 15% or so loss.

Steve

[Gollum]

Well, like I said, the dyno was done in 6th gear, to get as much load as possible. When done in 5th, it generated even less boost. The dyno operator should have told me that this dyno wasn't going to work in the first place. Still managed 550 ft/lbs of tq though!

Anyway, I completely understand what you are saying. You are probably right, that even with the reduced weight, tq is tq. I was just thinking of the car, at WOT at top speed. Doesn't matter the weight at that point.

I guess it is good to know that if you want 400 hp, you're going to need to upgrade the tranny. It'll probably keep a lot of people towards the 300 hp range, which is where I'll be.

Those people with 500 hp Elises are nuts. I think a 250 hp Elise would be just about perfect. This car at 300 hp is going to be a rocket.

But you are right, there are people who just love to go fast, no matter the cost.

Steve

Wow, I didn't see that you posted what gear you were in. My bad.

Usually most dyno operators run in 3rd or 4th to prevent over stressing the engine, which has it's merits. On turbo cars built right I prefer 4th or 5th myself. Gives the turbo time to spool like it would in the real world.

[Gollum]

Stock WRX has 220-some hp at the flywheel. If you double that, the tranny is at risk, but so are the rod bolts, the pistons, the bearings... That's into the range where you should expect things to break.

However, if you aim a bit lower...A 2.0 WRX with full exhaust, bigger turbo plus supporting mods, a good tune, can routinely get to 270 or more whp, let's say >325 at the flywheel (WRX's have lots of driveline loss). Obviously that's much more than stock and lifetimes will definitely be reduced, but it is routine, reliability is reasonable, and you can do it without breaking the 5-speed (unless you shock load it by dumping the clutch, as mentioned). In a 2000 lb car, that's like having >500 hp in a WRX-sized car.

That's probably going to be enough for most people. If you want more power then that, then yes, the stock gears in the 5 speed are not for you.

For the 2.0 motor you're reasonably correct. Though the 2.5 WRX motors and STI motors main weak link is the ring lands. Stock rods are good for some 500+hp, same with the crank. But you'll be risking the rings, depending on the condition of the motor, at anything over 400 crank HP. That being said I've seen those people willing to risk it push some pretty insane numbers on those stock STI pistons. You just have to be ultra careful and conservative on the tune.

But this is also why I'm really eager to find out if we'll be able to use the STI 6 speed, because that makes things simpler in my mind. Sure STI trannies are expensive, but it's easier than finding quality and affordable gear sets and LSDs and then paying to have someone put it all together.

Point being, for those that have a 2.5 WRX donor (like FFR has in shop from what Dave Smith said) then the most likely FIRST thing to break, providing you're not in detonation city from a bad tune, will most likely be the trans. That's kind of my point here. With a motor that was turbo from the factory, doubling the HP isn't that unheard of. I can go down the list of motors that can do it, and the WRX motors are darn close. One of the other big reasons why this needs to be address here ahead of time, is that you'll spend more money beefing up the tranny than you will getting the motor into tranny breaking territory. So my advice is to just steer clear, or go with a STI setup from the get go, if it'll be compatible with the final product. By contrast I can get my turbo datsun motor to almost 3 times stock power before having to worry about the transmission or driveline even. It's always application specific, and I'm just shedding light on our application. :-D

[Oppenheimer]

One thing that people seem to be missing is that engines don't produce their full HP & torque values simply by virtue of revving to the level they can produce those values at. Say your legs can produce one full HP (you're as strong as a horse). You pedal a bicycle that is towing a heavy load uphill, and are cranking at your 'redline' of 100 rpm, you're producing your full 1 HP output. But if you pedal that same 100 rpm with no load at all, you're producing much less power.

Your WRX engine has been built to produce 400 HP, but its in an 1800 lb car, with gear ratios setup for a car weighing much more. No matter how hard you floor the gas, you may not be able to force the engine to produce its full output in the lower gears, on a level surface. With higher gears, higher speed (more drag, etc), uphill, you'll load the engine more, and pull more power out of it.

All I'm saying is just because 400 HP in a WRX shreads gears even just in a roll-on acceleration does not necessarily mean the same engine & trans, at same rpm, same gear, same road will be a problem in a much lighter car. In other words, its not just that less load (less weight (& 2WD)) puts less torque between the crank and the wheels, its also because less load translates to less engine output (all other things being equal).

[Gollum]

The effect of power not being present at the wheels when there isn't load isn't a principle of physics that will continue to give you varied results under various loads. There is either load, or there isn't. You can get ANY engine to produce the same power in ANY vehicle provided the drivetrain losses are the same. This is because you can always get a motor to full load relatively easy. You can't create load when not in gear, but you can even produce enough load going down hill for the engine to produce full power, unless you have a large turbo like steve who can't create full boost without a good amount of load.

For example, if you take a NA motor, it'll be within 1% HP on a dyno when comparing various gears. Usually running in a higher gear will give you a few more HP, but more than anything else this has to do with the engine having more time to stabilize the mixture and air flow rather than having more "load" seen. The only time you really see a huge difference between gears on a dyno is when there's a turbocharger, which is a LOAD and TIME sensitive device. Thus if there's more load the turbo will spool SOONER, creating power sooner. This has nothing to do with the engine actually seeing more load thus it makes more power. The extra power is directly related to the turbo being spooled.

But lets look at this from another perspective. You can have a compressor side of a turbo that's just way too large for your application, thus you have disgusting surge during WOT on the bottom end, but up top your engine starts to breathe enough air and the surge goes away. Let's presume it'll surge between 1500rpm and 4000rpm under full boost. In 1st gear you might hit full boost at 3000rpm because there hasn't been the TIME under LOAD to spool the turbo, so you have surge for 1000rpm. 2nd you'll hit full boost earlier, thus having more surge. You're not getting more surge because you have more load thus making more power. You're having more surge because you're spending more time under load.

There's a chance the transmissions will hold more power because they won't spend as much time under load but I have a feeling it will only shift at most 5-10%, not directly relative to weight like some transmission breaking points. For example, the T5 is heavily susceptible to shock load breakage. A 3200 pound fox body with about 300hp and drag radials can kill it with a good launch on a sticky track. Because it broke under a shock load we can then presume it was directly related to the load it was seeing. So you take a T5 and put it into a 2200 pound @0bra kit car and with the same tires there won't be the same problem, because the moment of inertial doesn't take as much energy, thus less energy is transferred into the transmission.

As we all know though, bench racing gets is nowhere. I personally DO expect to find the limits, and once I do my findings will be shared.

[audsyn]

Gollum,

You're right...I guess I still think of non-STi WRX's as 2.0, even though the 2.5's have been around since 2006! It's easier to get big power out of the 2.5, and we will undoubtedly see 5-speeds with stripped 2nd gear just like on nasioc. With the 2.0, it's a lot more work to get over 400 hp.

There are plenty of people with big power and stock 5-speeds, so you may get lucky, especially if you avoid the drag launches. However, if you are going to this power you should not be surprised if a gear lets go.

[BrandonDrums]

Yeah, everything has a breaking point. I do firmly believe that in 2wd fashion and only around 2k lbs the 5mt can handle 350-400 whp without grenadeing itself without some serious abuse.

[Gollum]

Well, knowing this, we can also do our best to avoid torque bulges in the power curve. If you're shooting for 400 crank hp, you can pull some mid range timing and fiddle with your cam timing to flatten out the torque curve some. You could even shoot for just rich of rich best torque to drop the hp a few percent too, at the obvious expense of fuel mileage.

Knowing the weak points can help us to best accommodate them.

I'm not extremely familiar with the subie ECU boxes yet but they might have gear specific timing pull ability too, which we can use to make 2nd gear a little "soft" which is fine on most circuits/tracks.

[LS MAN]

Hey guys, a quick question - how much are used 5 speed transaxles? $500? $750?
I think sometimes we worry a little too much about things that might be a weak link or might break. I'll take my chances on a stock box. I'm not going to do crap to it, other than the AWD eliminator & cover. & if for some reason it has a problem, I'll just get another one. I'm going to beat the crap out of it, & if it breaks, I'm going to laugh, & figure I got my moneys worth out of it. That's one of the benefits of this platform. We are not using the expensive Subie (STI)components, so I'm not too worried about it. It's not the $8500 G50 or Mendeola like the GTM.

http://cgi.ebay.com/ebaymotors/05-06-07-IMPREZA-MANUAL-TRANSMISSION-2-5L-OUTBACK-/120690133722?pt=Motors_Car_Truck_Parts_Accessories&hash=item1c19b14ada

[PhyrraM]

Not so well kept secret:

Subaru made FWD transmissions that will bolt to a WRX motor. Before '96 all Subarus were avaialbe with FWD or AWD. The FWD transmission won't need the conversion kit, but they came with a cable clutch (WRX is hydraulic) and a slightly different shift linkage (but same basic design). They even have a longer final drive ratio that might suit these cars better. You will need a non-turbo flywheel and aftermarket clutch for it, but other than that it will all bolt together. WRX CV axles should work. To top it off, the FWD transmissions are basically free because few people need them. '90-'95 FWD Legacies and '93-'95 FWD Imprezas are the cars to look under. Subaru never went 'AWD only' in most overseas markets, so newer FWD transmissions can be imported if desired. (no idea on cost)

[Evan78]

I wonder how those trans would hold up with the additional power of a turbo 2 or 2.5L. I assume that they all came with cars with significantly less power than a WRX. Any idea on the differences?

[PhyrraM]

No evidence on power handling, however - before there were alot of AWD dynos and before the 2WD conversion kits - Folks would swap to a FWD trans to get Subies dyno tuned.

The gears are basically the same, but some of the shafts and the differential itself might be different. I *believe* that a LSD for a WRX will also fit the FWD transmission.