^ agreed as above. OEM fluids only for tranny life and the 0.5 decreased oil capacity means heat is that much more of an issue. And it's really heat that's the killer, not raw torque. In addition to an oil cooler you can also over fill your trans for better heat capacity. Even if tre rebuilds your trans the same problem will exist.

You can still keep your 6spd but just be mindful of the heat and use an oil cooler/over fill/change regularly to replace oil that's already been broken down by heat. I still miss my 6spd from time to time. Replacing it with a built 5spd was a real turning point for my car, it started to get my car away from DD status and ultimately less day to day enjoyment.

 

I had my trans, t-case, and rear diff rebuilt by TRE. Jon told me that over 400 wheel torque will eventually kill the 6 speed. I believe that the gears are actually smaller in the six speed to accommodate the extra gear inside the same basic trans case. An oil cooler would definitely help, but if you plan on building toque levels above this number, I would not spend the money required to fix your trans, add the cooler, then potentially see it fail not long after.
On the other hand, get it rebuilt, buy a five speed, and then sell your rebuilt six speed to someone like me who loves their sixer and doesn't wish to switch!

 

+1

i hope the 400wtq number is accurate. i'll forever be under that number with my seasonal fluid changes. i still want to build a cooler, though.

 

Torque is NOT the killer as people in threads dating back to 2008 have said again and again. I have killed my 6spd with 300wtq. Many others have killed it on stock turbo too. Even after being rebuilt by TRE people have killed it below 400wtq (ex: razorlab). And then many others are doing just fine at 450wtq+ for a long time (ex: mrfred). There was a MR in approx. 2011 with a stock block and gt35r than even ran 10.9@130+mph with it. Don't make the mistake of thinking you're safe under 400wtq.

Bottom line if you street drive and don't beat on it hard and use OEM fluids you'll be ok. If you track, its time is limited, regardless of torque.

 

i haven't read every thread buy yeah, i know heat is the killer. i've run my car and a 5spd on the same course and really prefer the gearing of the 6. i'll have to find a way to make it work because i really, really would hate to go with a 5spd.

 

I believe what Jon was referring to was the weak nature of the input shaft and the smaller gear sets. He was quoting a somewhat "safe" torque figure that was intended as a guideline by which to safely operate the transmission without failure. Of course, there are production tolerances in mass-produced components and in the materials themselves that will cause some components to fail prematurely while others will withstand significantly higher than average stress levels without failure, but as a whole, it is considered to be a best bet figure to build around.
The other issue of course is thermal loading. The fluid thins out as temperatures rise, causing a reduced film between the gear teeth. With enough loading, the film strength cannot hold out and the teeth make metal to metal contact. This is where a thicker base oil, and of course an oil cooler, can be the difference between success and failure of the transmission.
So if you want to road race/hpde your six speed, then an oil cooler is almost a necessity. And also, don't expect 600wtq to last forever, that's all.
The 400 figure was for a rebuilt 6 speed with shot peened gear sets and additional oil passages. I could not quote any kind of safe figure for a factory built 6 speed...I would reckon its not much above stock levels at all.