Too much HP

Speedemon · Oct 11, 2004

I went to the subaru dealer today to talk to the guy at the parts department about more HP and he said that if you get over 300-310 hp then the cluth will start losing teeth. He also said that the transmission in my car can't handle over that much HP. I was wondering if this is true. If it is true what do you suggest and if it is false then let me know. He said this about my 02 WRX. Thanks Evan.:???:

kickin_81 · Oct 11, 2004

Which dealership? I went to Morries Brooklyn Park Subaru and spoke with Brett from the parts department, also.

My car has around 320 hp at the crank. If I drive right and don't abuse the clutch when I shift (I always do), the tranny will last a long time. Abuse a car with double the traction of a standard car will affect the car by burning up wearing out the clutch or losing teeth in the tranny. There are a few cases on nasioc.com where the member's MY02 WRX trannys not able to withstand tranny abuse and break.

Zola · Oct 11, 2004

The guys who work at dealerships are not generally reliable sources of information. Anyway, why would you even want to tell them that you're modding your car? It'll probably increase the likelihood of them giving you a hard time about it.

My car makes very similiar power to Fong's, and my clutch is fine. Clutch wear and gearbox is strongly correlated to the driver's habits. If you are a real butcher you could torch one of both of them on a stock WRX. On the other hand, consider Clark Turner (AZScoobie) down in Arizona. He swapped an EJ257 into his WRX with stock 5MT and was pushing well in excess of 450bhp and sick amounts of torque. That tranny even withstood some drag passes but--as was inevitable--it grenaded itself just accelerating hard in 2nd (not even launching).

Speedemon · Oct 12, 2004

I went to the same dealership and talked to a guy named Brian. Thats what he told me.

morganm · Oct 12, 2004

He prolly was just warning you. Will it work? Yep. Can you blow it up easy? Yep. Can you burn a clutch more easy? Yep. Will it kick some seriouse ass?! YEP!

Yang · Oct 12, 2004

NO2 will solve all your problems.......:I.....

bikerboy · Oct 12, 2004

LOL a clutch has no teeth

5mt is good up to 350 ft/lbs ot torque to the wheels

6mt 450 hp to the wheels

These are relitive figures to the drivers habits or his ability to shift like a butcher.

the reason the tranny gives up is the flex of the cases. Hard to explain in writting but if you want a further explaination let me know

WRX1 · Oct 12, 2004

Actually, we would have a good way to explain AND show it once we have our next meet. Brett has a tranny and motor waiting to get ripped apart.

Russ

zapman · Oct 12, 2004

As long as you learn how to launch correctly and don't drop the clutch or smoke the **** out of it i should last for a while. the tranny isn't as bad as alot of people think it is, as long as you drive it smart, aka always use the clutch. I know a guy who has 350 to the wheels on a completely stock tranny.

Dream · Sep 27, 2007

Damn subaru trannys...

AWDimprezaL · Sep 27, 2007

Speedemon said: ↑

I went to the same dealership and talked to a guy named Brian. Thats what he told me.
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LMAO back to the 04s

DISCOPOPE · Sep 27, 2007

holy bump batman!

piddster · Sep 27, 2007

bikerboy said: ↑

LOL a clutch has no teeth

5mt is good up to 350 ft/lbs ot torque to the wheels

6mt 450 hp to the wheels

These are relitive figures to the drivers habits or his ability to shift like a butcher.

the reason the tranny gives up is the flex of the cases. Hard to explain in writting but if you want a further explaination let me know
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Case flex isn't real. The main reason they fail is due to small gears in the transmission.

Taken from Phil at Andrewtech:

Case flex is a myth.

People have argued with me about this, and they were all wrong.

It's not an issue with shaft flex or case flex or anything like that. There's no "stock gears are strong, it's the case's fault that they break!"

PPG's use the stock case.

If you look at the transmission case, it's a 1" thick aluminum cradle with 10mm bolts running all through it. Plus, it's split vertically. If the case DID open, the gears would be forced downwards and upwards, and that would damage the front ring-and-pinion too.

Because of the case design, the shafts cannot flex either. The main cradle has a section width of 6". 1st through 4th gear are crammed into a highly reinforced, 6" wide, 1" thick box. PLUS, the bearings are held in place by some massive bearings (the rearward output shaft bearing is actually bolted to each half of the case). AND, if the shafts flexed, the output shaft would seize. There is an inner and outer shaft on the output side. Flex that (which would be impossible), and the two shafts would contact eachother.

The shift forks are pretty low-quality cast aluminum. They are plenty strong to handle stock-ish power and they don't really break with a synchronized transmission
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Case flex isn't real. Trust me. Over 800 wheel horse power, and we've never, ever, ever, ever, ever, ever seen a failure of the case.

First gear on the output shaft rides on a film of tranny fluid a few hundredths of a mm thick. If the gears are pushing apart, first gear on the output shaft would contact the output shaft. Yet, that doesn't happen, does it?

The 99+ transmission cases are identical internally than the pre 99 cases. I know, I've had them next to eachother. Actually, the pre-99 cases have more gussetts externally than the newer cases. The only thing that changed in 99 was the synchro engagement hub design. A WRX gearset will drop into the Legacy Turbo case without case modification.

The pre99 case is design is exactly the same as the STi RA design, which was running 276hp. The post 99 case design is the same as the 5-speed STi's from MY00 in japan, again running 276hp.

Rallispec's 276ft-lbs rating was against a stationary output shaft. They locked the input shaft and output shaft, and applied a load. To assemble a gearset, the locknut on the input shaft is torqued to something around 250ft-lbs. Either Subaru is stupid, or Rallispec is wrong.

The 6-speed gears are MASSIVE compared to the WRX gears. Easily twice the size. And the case is different because of an entirely different internal design. The 6-speed and the 5-speed, are like apples and oranges. They are two totally different beasts.

The rotational speed of the shafts doesn't impact the effects of gravity. Someone who says that clearly doesn't understand physics. Gravity is a constant force, there can be forces opposing it, but gravity is a given, and the acceleration due to gravity is constant unless other forces are introduced to oppose it.

Think of it like this. A straight cut gear is stronger than a helical cut get. This has been well proven, despite what some vendors would like to tell you to boost RA gear sales. A straight cut gears produce only seperative forces. The gears spread apart as loads increase. Helical gears produce lateral loads as load increases. It would stand to reason that if case flex was really a problem, a straight cut gear would be weaker than a helical cut gear, because the case would flex more with a straight cut gear.

The reason Subaru gearsets break, is because the gears aren't strong enough. Plain and simple, the gears are just weak. That's all. There's no bandaid fix. The case is bolted to the motor, and bolted together. Unless you stretch one of the bolts, or crack the case, it's not going to flex apart. I've seen more blown transmissions than your average person. I'm speaking from actual experience.
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I've spent a LOT of time with subaru transmissions.

The shafts in the transmission are not transmitting very much torque to the case. The axes of rotation of the shafts are perpindicular to the axes of support. The shaft is also supported on two ends by journal bearings. IF a load is placed on the shaft (from the shafts being forced apart), there are two points of support that lie in the plane of the case half helping to oppose that load. If the case was split horizontally instead of vertically, I could see the potential for seperation, but since it's split vertically, you have a better chance of STRETCHING the case than actually flexing it.

The shafts simply cannot move apart when they are bolted inside of the transmission. If that were the case, first gear would break far more often, because it is the only gear that doesn't ride on a needle bearing.

The only thing that I can visualize for the causes of gear breakage is the following:

Shockloads that exceed the shear strength of the gear tooth.

That's it.

It's not really possible for the teeth to lose mesh with it's complimentary gears, because that would mean that the shaft would need to flex and back off more than a centimeter (to totally disconnect). I don't know if that's what your saying or not, Nick. I think you mean back off enough to no longer be in it's designated place.

The problem with that, is that helical gears don't LIKE to back off. Helical gears like to walk apart from one another laterally, rather than pushing apart and backing off of one another. That's why the thrust surfaces are so critical to the 5-speeds operation (which, again, is a film of oil, not an actual bearing).

So really, I think the fact of the matter is that the stock gears are just not strong enough to handle the shock loads placed by higher output.

But does it explain how transmissions blow up while "just driving along"? Well, when you aren't launching and you aren't shifting like an idiot, the impulse loads aren't as high as if you were driving like every stoplight was a drag strip. So it does stand to reason that at certain power levels, the standard loads created by the engine are enough to match or exceed the shock loads created by launching hard or shifting fast. At that point, your ****ed, and the trans is going to blow up.

I ran some arbitrary numbers through some calculations for gear strength between straight cut and helical, and if the stock gears were straight cut, they'd be somewhat stronger. But is it enough? I don't know. Plus it places different loads on the transmission that it might not have been designed for. Through experience, however, I've found that the straight cut gears in the Subaru 5-speed case are plenty capable of holding up to power.
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Again, first gear on the output shaft rides on a film of oil. Any significant increase in runout would shove it against the output shaft and weld the two together. Even when disengaged, first gear on the output shaft is still spinning, and any flex would surely manifest itself there first. At least with some scoring or something. But that never happens, at least I've never seen it.

I HAVE seen a first gear FUSE to the output sleeve, though. It was the result of using some bobo-brand gear oil in a high horsepower application. The fluid sheared, and first gear contacted the sleeve. It welded the gear to the sleeve. Don't use Some ghetto gear oil. This also happens when you have no gear oil in the tranny at all.

What I meant was that the amount of runout between the gear teeth (which there is some, as most all machined parts have a wee bit) could cause the breakage of teeth when a shock torqueload is placed on them.
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It could be, but I'd think the effects of runout would be marginal at best.

Again, first gear on the output shaft rides on a film of oil. Any significant increase in runout would shove it against the output shaft and weld the two together. Even when disengaged, first gear on the output shaft is still spinning, and any flex would surely manifest itself there first. At least with some scoring or something. But that never happens, at least I've never seen it.

I HAVE seen a first gear FUSE to the output sleeve, though. It was the result of using some bobo-brand gear oil in a high horsepower application. The fluid sheared, and first gear contacted the sleeve. It welded the gear to the sleeve. Don't use Some ghetto gear oil. This also happens when you have no gear oil in the tranny at all.
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Too much HP

Speedemon Well-Known Member

kickin_81 Well-Known Member

Zola Well-Known Member

Speedemon Well-Known Member

morganm New Member

Yang Well-Known Member

bikerboy Subie GOD Staff Member

WRX1 _ Staff Member

zapman Well-Known Member

Dream Well-Known Member

AWDimprezaL has more posts than you

DISCOPOPE Well-Known Member

piddster Lone Wolf