I was wondering if any of you have run a THM400(I assume some one has.) And if you have any experience upgrading one for a significant amount of HP and Torque. I am looking at about 400hp and right around the same for torque. I run one ton gear with 5:13s and 42inch TSL's. Also my t-case is a plain jane 205. I have already went with a B&M Hi-Tek cooler with fan, and a ratchet shifter (so I dont bind on the rocks or whatever). I know there are shift kits, but I am not fond of them. "Banging" the gears has never sat well with me. Seems like those kits make your tranny wear faster.

So what about Kevlar clutches? I have heard that they too wear quick... but they dont dissinegrate. What kind of converter should I run? And what stall set should I choose?

Any help would be greatly appreciated!!  

That HP level is not a issue for a good stock THM400 because some "lead sleds" of late sixes had those power levels everyday. What can cook a 400 is if you are not geared deep enough and you ride converter stall a lot. I would say that 5.13's are not really deep or best gear for use with 42's by any means as it is equal to about a 3.73 with stock tires in performance before you factor extra load/drag for lift and tires. You really should be running 5.57 or more and a sweet setup would be 6.14's with a 4L80 as a 4L80 is nothing more than a THM400 with OD added to it with a electronic valve body too. This would give you more low end grunt, better tranny reliability due to reduced average torque loading AND a lower RPM cruise too.  

a stock th-400 will handle 400 hp and 400 ft/lbs all day long. don't go with a 4l80. they are a lot weaker than a th-400. stall is gonna depend on what your engine is set up like. mainly what the camshaft is.  

1978k-20:
a stock th-400 will handle 400 hp and 400 ft/lbs all day long. don't go with a 4l80. they are a lot weaker than a th-400. stall is gonna depend on what your engine is set up like. mainly what the camshaft is.

A 4L80 IS NOT weaker than a THM400. A 4L80 is nothing more than a THM400 with OD added and a electronic valve body. The 400's day has long passed and there are better solutions today. BTW a 4L80 is "rated" at 440 Ft lbs constant state and 20,000 lbs GVW.  

for what he is gonna be doing yeah it is. if the th-400 is past its day then why do so many people use them. from my experience there is not much that a th-400 can't take  

No many people use them because they do not know any better or know how to proper gear axles either thats all. As 4L80's with deep axle gears is better than any THM400 any day because you can run deep gears for power and reduced tranny strain and yet cruise nicely too while with a THM 400, you are forced to limit gear ratio in axles to get a reasonable cruise RPM at the expense of performance and MPG. (a 4L80 with a 5.13's would cruise at a lower RPM than a THM 400 with 4.10's and have a lot more stump pulling power too) Furthermore, a THM 400 has no ability to lock converter either which means more wasted $4 a gallon fuel on the road. If you ran a 4L80 is drive instead of OD position you would have the exact same gears and same gearbox. (except 4L80 is electrically controlled too) Some are just stuck in the past though and handicapping their overall performance too. Just like some believe that 4.10's are great no matter what tire size you have!!!  

thats great if you want to drive your truck on the road. i have no interest in driving my truck down the high way. maybe a short drive into town every once in a while. i have 4.10's in my truck currently but i know i am going to have to change them when i switch to my 40's.  

1978k-20:
thats great if you want to drive your truck on the road. i have no interest in driving my truck down the high way. maybe a short drive into town every once in a while. i have 4.10's in my truck currently but i know i am going to have to change them when i switch to my 40's.

But it is even more great if you do not because you can run even deeper axles and have a4 gears to choose from over a ratio range of 3.3 to one in tranny with a 4L60 vs 2.48 with THM 400 or a range of 4.3 to one with a 700R4. Why some stick with 3 speed trannies today is beyond me. Saying a 3 speed is better than a 4 speed is like saying a 2 speed power glide is better than a 3 speed tranny.  

it all depends on what you are going to be doing with it. i under stand why you said to use the 4l80. but for what this guy is going to be doing with it i don't think its the best choice  

More gears is ALWAYS a better choice as you can run even deeper axle gears for even more power with same top gear performance. If you think a 4.56 is good for you with a 3 speed, then a 5.57 is better still with a 4 speed.  

i am not talking about gearing. i am talking about durability of the transmission.  

I am to duhhh. A 4L80e is a THM400 with OD added and it rated at 20,000 GCVW. And gear is all about axle ratios too because the deeper the axle ratio the lower the average torque load on tranny when it is working hard because less average tranny torque is needed to get same effort to ground with deeper gears which mean less strain and lower life in severe duty. Again, it is all about the gears. BTW, I have a 4L80 in a 2000 K3500 that has plowed snow every winter since new and at times it works very very hard, like clearing 1500 foot lanes pushing hard for several minutes non stop in deep drifted snow in 1 st and  2nd gear low range and maxed out and at a GVW of 9000 lbs and more while doing it. That is strain harder than on a 4x4 off road and tranny has been fine. I would never swap in a THM 400 today. It would be a 700R4 or 4L80 with deep gears. BTW, I have a 700R4 that is over 18 years old and has over 180K miles on it and a heavy 4x4 burb and it still work really sweet and it has towed and been across rockies a dozen times. I know what works.  

your truck has a 4l80e not a 4l80. i have a th-400 in my mud truck with a big block. the truck is in low range either in 1st or 2nd gear. i am turning 6000 rpm. your 4l80e would never live if it had to go what i would put it through  

Well there really is no 4L80 as they are all 'e's  but many call them just 4L80's anyway. BTW there is a 4L60 and a 4L60E except the 4l60 is just a renamed 700R4 with not internal changes at all and there is a 3L80 too, a renamed THM400. (notice the same "80" rating which is short for 800 metric Newtron torque class) As far as HP, it would handle it just fine. Again you just do not get it. a 4L80 is just a THM 400 with another range added, a locking converter and electronic valve body. It takes same internal part as 400 plus, there is even a 4L85 version that is beefed up more(beyond a 400) and a 4L90 too. If you are turning 6000 RPM it is because your lack of proper gear ranges have you taching it out in one gear because you cannot pull the next gear. Only thing 6000 RPM is fueling here with BB is ego because your are well past its best torque range. Also the 400 got its name best it was rated at 400 ft lbs of continuous torque capacity. The 4L80 was rated at 445 Ft lbs when it was born and and since gone beyond that with a 4L90 used in big panel trucks that is rated at 500 ft lbs plus.  

yeah there was for a couple of years before gm went to the e. it sounds like to me you don't play in the mud very often. been to a mud bog lately? i was at one on saturday and there wasn't a truck running with a 4l60 or 4l80. every one of those trucks was sitting on all of what i turn. besides rpm equals wheel speed with the gearing i have. the only time the lock up converter is good for any thing is when you are crusing at a steady speed. the lock up is to lock the torque converter together so it doesn't slip when crusing. i don't want a ton of gearing in my truck any ways. over gearing means i loose all my wheel speed. engine torque also make up for a lack of gearing. why do you think diesel trucks with large tires still cruise fine without massive gear ratios.