How much power can a 5MT tranny take?

[keys2heaven]

Picked up a 5MT tranny from a 2004 Impreza last year. Low mileage and someone had already done the AWD to 2WD conversion to it. Was going to use it in a beetle. (dune buggy)

I wrote a thread about it during that time, but someone replied that the 5MT couldn't take big numbers. I'm looking to couple a STi engine with it and hope to get around 250 HP. Is this too much for this tranny?

[Mechie3]

My car dyno'd at 312hp and 450tq (at the motor, assumes 22% AWD drivetrain loss from wheels) on the 5 speed. It lasted 60k miles including several years of autocross and hard launches. Finally failed on the way to work. Using it in 2WD mode should be less abusive on it.

[FinishlineWRX]

Ive heard around 350/350 is the number to start to worry. But it really all depends on your driving style. My 2l car made 370whp and 330wtq. The 818's weight and 2wd like posted above will be less load.

With the STi 2.5 it not the hp you need to be concerned with it the TQ that breaks them.

[shinn497]

I wrote a thread about it during that time, but someone replied that the 5MT couldn't take big numbers. I'm looking to couple a STi engine with it and hope to get around 250 HP. Is this too much for this tranny?

Ummm the Sti is 300hp.

With the STi 2.5 it not the hp you need to be concerned with it the TQ that breaks them.

This would be true of any engine.

There have been humungous discussions on this. The short answer is that a lighter 2wd car will put less stress on the engine but this won't change that the drivetrain will be subject to the same level of forces regardless of car weight and configuration 2wd/4wd.

[metalmaker12]

Ummm the Sti is 300hp.



This would be true of any engine.

There have been humungous discussions on this. The short answer is that a lighter 2wd car will put less stress on the engine but this won't change that the drivetrain will be subject to the same level of forces regardless of car weight and configuration 2wd/4wd.

Not completely true, weight has a lot to do with transmission load and so does 2wd vs 4wd. Less sprung mass to move and less dry friction due the the lower mass, also there is less internal friction on the parts it is moving and its own internal parts( one diff, not two, or three). It is true that the same horsepower will go through the tranny, but with much less resistance from the cars lower mass and less attached parts. The brakes, engine, wheel bearing, tires, axiles, etc, will all fair much better on this lighter car. This is why lighter cars like a honda fit have less maintenance than say f150 truck if driven the same. Also hondas are made better lol, so that comparison is weak. All in all, the lighter car is less mass to get moving and keep moving which puts less stress on the internal moving parts (engine and tranny)....period

Not that any of this matters bro, but not all sti's are 300. The jdm's v7-v9 are 286-290 range--- and spec c's with big head ports are like 330hp.
The usdm 300hp sti has a fat low end due to more displacement, but the jdm ej207 v8-v9 can redline at 8,600rpms which gives it more top end grunt. There both great, but if you can tune a ej207 to get that fat low end and keep its high end you got a perfect balance. either will be awesome in this car.

[Rasmus]

Moore Performance is manufacturing bracing for the 5 mt transmission.







Not that the 818 will need it running only 818 kilos in 2wd. Tires will break traction long before the 5mt pops.

[metalmaker12]

cool stuff, like to see it mounted up on tranny

[SkiRideDrive]

I believe someone made a convincing argument earlier that case flex wasn't necessarily the issue but the main shaft flexing within the transmission due to a lack of bearing support. This would make those braces less effective. I am not too informed on the subject however.

[apexanimal]

^ i read that as well...

[shinn497]

300 torque is 300 torque regardless of how much resistance is being imparted to it. Resistance effects acceleration not force. The car will accelerate faster and spins the tires often, but I'm worried more about torque spikes. Of course I'm not entirely sure how parts fail, is it a progressive thing, an instantaneous thing, or some combination of both?

Anyway, I think the 5mt will handle higher hps just fine, but I don't think that the lightweight is an excuse to drive like a moron with a 500 whp engine.

[metalmaker12]

Lol, yes driving like a moron will get you no where but dead with 500 hp in 1800lbs. The force is the same here. Resistance does effect acceleration but I was stating how less mass will create less internal friction on the engine, tranny etc. Is it simple physics. It is like if you put the wrx engine and tranny in a big rig, not designed for that, its going to break,but put that in a light 818kg go kart and it will last. The horsepower was the same, what happened... see what I am saying. It has to do with the amount of load on the tranny which will +/- effect the internal friction of it's moving parts.
I only want 300-350 whp tops, over that and your in full race car land.

[wallace18]

I am having Andrewtech rebuild my trans from my donor. I am waiting on the teardown to see if I need gears. If so I may upgrade the 1 thru 3 gearset. I am going to have somewhere near 300 RWP. I am not too hard on gearboxes so I hope it will be OK.

[shinn497]

At 350 whp you are probably pushing 370-400 flywheel. That is .20555555 hp per pound. A lamborghini aventador pushes about .202. What excites me is that 350 whp is almost trivial for an sti engine. I'm sure it can be accomplished with maybe just meth/e85, a tune, up/downpipe and some other supporting mods (remember though that many exhaust mods won't fit). No turbo upgrade required, which means no lag.

One thing I am wondering is are all 5 speeds the same. For example, would a manual from an older 1996 legacy or impreza hold the same power. I plan to use on older car (Since I am using a jdm engine) for a cheaper donor, and am wondering if this will suffice or i should just source the tranny elsewhere. If I got one from NASIOC I could probably find an upgraded 5 speed anyway.

[PhyrraM]

.......One thing I am wondering is are all 5 speeds the same. For example, would a manual from an older 1996 legacy or impreza hold the same power. ......

It depends on who you believe in the Never Ending Tranny Debate.

The gears have been upgraded through the years, little else has. If you believe it's the gears that go pop, then upgrade. If you believe it's going to be the input shaft or the ring and pinion, early is fine. Keep in mind that early cars may need a different (but available) 2WD adapter kit.

[AJW Performance]

I had 375 WHP on my personal Subaru for a while, no issues.
I have seen 450 WHP no issues, I have seen 250 WHP many issues.

[StatGSR]

300 torque is 300 torque regardless of how much resistance is being imparted to it. Resistance effects acceleration not force.

Resistance is Force, without resistance you can't make (or measure) Torque. I really wish people wouldn't talk like an expert when they are not.....

go and try to apply 85ft-lbs of torque to a lug nut when its not tight if you don't believe me.....

[csdilligaf]

Saker motorsports runs the 5MT with 2wd conversion and gets away with it in a race car. What throws a stick in the spoke for me is.
1) The outer large mainshaft normally powers the rear wheels. With the 2wd coupler it locks the smaller dia inner shaft to transfer the power to the front diff. Just how small is that shaft?
2) Man these subie's have a tiny ring and pinion. Maybe I got to get over the bigger is better thing.

[Rasmus]

I believe the 5mt mythical fragility is not due to the number of torques run through the box, it's the TMOP factor. As TMOP approaches 100% somethings gonna break. TMOP? Total Moron Operating Pedal.

These kids think the 5mt is 'glass' because it can't take a clutch dump from 6500rpm in an attempt do an AWD burnout for 660 ft in a 3,400lb car on dry asphalt like Ken Block.

[metalmaker12]

by the way I measured the 6spd vs the 5spd housing portion with the back taken off, were talking two inches folks, the six will be part of this cars future.

[StatGSR]

^ last i heard you cant just put a block off plate in the back of a 6spd though. Thats why a guy had to switch from a 6 to a 5 on his TR42 build. I posted about this on the another thread here.

[BrandonDrums]

300 torque is 300 torque regardless of how much resistance is being imparted to it. Resistance effects acceleration not force. The car will accelerate faster and spins the tires often, but I'm worried more about torque spikes. Of course I'm not entirely sure how parts fail, is it a progressive thing, an instantaneous thing, or some combination of both?

Anyway, I think the 5mt will handle higher hps just fine, but I don't think that the lightweight is an excuse to drive like a moron with a 500 whp engine.

Oh god, didn't we talk about this already? F=MA is for rocketships that make the same force regardless of speed. A car running at redline in 1st gear CANNOT ACCELERATE MORE AND THEREFORE CANNOT APPLY ADDITIONAL FORCE. An internal combustion engine also must be under load to create it's maximum torque as the torque is being created by fuel burning under compression. Remove the flame crompression from the system and you loose torque at the flywheel as the mixture expands too quickly but it's a balance as you gain applied torque through the mechanical advantage of the gears down low. Most WRX's won't make peak torque on a dyno until 3rd gear or higher. Race engines like in F1 say f-torque, I'm going to rev to darn near 20k rpm and just make insane amounts of HP and apply a smaller amount of torque more often.

Back on topic: I know guys with 350 whp bugeyes with over 200k on the clock on the stock transmission. I also know guys who've replaced their 5mt 3 and 4 times.

The difference? Launching. In Japan where the WRX has been around since the 90's, transmission failures were so rare that subaru never changed the 5mt's gears for close to a decade and Japanese market drivers are even more power mod crazy than we are.

Then in '02, Subaru brought the WRX to the US market and transmission failures started happening all the time. By 05, they had revised the strength of the 5mt gears several times in an attempt to prevent the failures they were having to cover under warranty for unmodded wrx's.

If that tells you anything, it's how us 'merican drivers with our drag racing heritage drive our cars. We love torque and stoplight to stoplight racing and destroy transmissions more than any other market. The 5mt can handle however much power you decide to drive responsibly with or as little you decide to grenate by not properly engaging the clutch.

That being said, if you have an 05 or later wrx, chances are the gears will be beefy enough to handle some abuse with higher than stock output levels. Otherwise, just be careful not to repeatedly shock-load the transmission by revving to 5k and side-stepping the clutch.

Can we monitor these threads? There are far too many "how strong is the transmission threads". Maybe an admin can sticky a post linking to all of the existing ones or something.

[Mechie3]

FWIW, I always ran stock clutches on my car to help save the transmission. Make that the weak link rather than the trans.

[PhyrraM]

......If that tells you anything, it's how us 'merican drivers with our drag racing heritage drive our cars. ..........

Don't forget that Subaru added about 400 pounds to the cars at the same time. But, I agree, dead horse. Only a few miles on real builds will show exactly what the tranny will need for the long term.

....... There are far too many "how strong is the transmission threads". ........

I also agree. There are also far too many "this is how I wish it looked, but alas....." threads.

[BrandonDrums]

Don't forget that Subaru added about 400 pounds to the cars at the same time. But, I agree, dead horse. Only a few miles on real builds will show exactly what the tranny will need for the long term.

Wouldn't the acceleration just slow down and the stress would be the same as before? If removing 1500 lbs from the drivetrain doesn't increase how much power can be ran through a gearset then adding just 400 wouldn't cause all those transmissions to suddenly grenade [/SARCASM]


I also agree. There are also far too many "this is how I wish it looked, but alas....." threads. [/QUOTE]

True! But at least those are aesthetic discussions and lead to less arguments....

[shinn497]

I'm not going to argue this further, but I would like to know how subaru's can change engine torque depending on load.

[bromikl]

Whoever said "try to torque a lug nut that isn't tight" hit the nail on the head.

If there's no (or very little) force pushing back, it's like being in neutral. Or if you lift the drive wheels off the ground. You may have a 500Hp engine under there, but almost no torque produced.

[BrandonDrums]

Whoever said "try to torque a lug nut that isn't tight" hit the nail on the head.

If there's no (or very little) force pushing back, it's like being in neutral. Or if you lift the drive wheels off the ground. You may have a 500Hp engine under there, but almost no torque produced.

+1 :-)

I'm not going to argue this further, but I would like to know how subaru's can change engine torque depending on load.

It's not just Subarus, it's everything that applies force mechanically and not through inertial differential.

Just like you throwing a paper airplane as hard as you can vs trying to throw a cinder block over a 3 story house, one of them could tear the rotator cuff in your shoulder, the other will result in a crappy paper airplane flight. You're trying as hard as you can in both scenarios and yet only one of the objects can injure you back.

In order for Force to equal mass times acceleration (F=MA) which has your camp apparently so irreparably confused on this topic, the object that is applying the force has to keep up with the object that it's applying the force upon. F=MA is great for explaining collisions and short, single element systems of force exchange. Unfortunately, most of the world including your throwing arm have more than 2 objects bumping together to create movement.

An internal combustion engine driving wheels that roll on the ground via a mechanical linkage cannot continue to apply force past certain thresholds found at the rev limit in each gear (not to mention gears change the mechanical advantage it has PLUS an engine only makes peak torque at certain points in the revband, it's not constant).

So much of it's energy goes into simply keeping the system rolling at the rate in which the ground moves underneath it THEN it has to apply a net force above and beyond to further accelerate the object it's moving.

A rocket applies force by throwing a portion of itself the opposite direction to net a force in the desired direction. There is no medium it has to keep up with, the medium is the rocket fuel's kinetic and chemical energy. It burns the fuel and it is expelled in the opposite direction and the inertia (the resistance of mass to changes in motion) applies an equal and opposite force to the rocket itself.

So, with a rocket, changing the mass results in a proportional change in acceleration. In a car, a change in mass does not result in a proportional change in acceleration, friction, losses in applied force due to reduced load and the dynamics of mechanical advantage/disadvantage come into play.

I'm OCD about this stuff. I can do this forever but christ is it tiresome.

[/NERDOUT]

[wjfawb0]

Please don't put an airplane on a treadmill and ask if it can take off.

[jimgood]

I think I'll just start a new thread every day about how the 818 will be fine with the 5MT tranny. Do I have to break out my dump truck/lever arm/lug nut analogy again?

[Thorne]

I think I'll just start a new thread every day about how the 818 will be fine with the 5MT tranny. Do I have to break out my dump truck/lever arm/lug nut analogy again?

We shall see... I think it might hold..... I've broken a few 5 speeds in my day.

I'm using a STI-RA box on my build

[Leonard]

They will be fine. Production T5's are marginal in mustangs with upgraded power, but they do just fine in roadsters -- even behind big blocks. There are even a few builds that have used T5's from 4 cyl mustangs and they did okay too.

[apexanimal]

for what it's worth:

http://forums.nasioc.com/forums/show...093090&page=20

You're correct. Due to the weight of the car (1600 lbs) and the fact that only 2 wheels will be under traction (instead of 4), the load transfered to the transmission will be minimal.

Andrewtech even said that using any type of case bracing for the 5-speed was not necessary. They have never seen case flex be a cause of problems in any Subaru 5-speed in all their years of experience.

Bottom line - the 5-spd is more than adequate. They will be adding a Cusco LSD too so I can't wait for them to get it done and sent off to Danny.

[jimgood]

I drove my '02 WRX to 140k miles with lots of track days and rally crosses. I parked it when the engine lost compression in one cylinder with the original clutch, original transmission and a set of spark plugs changed somewhere around 70k miles. I drove the dogwater out of that car. What I didn't do was rev it up to 4k and dump the clutch on dry pavement. Ever.