Th350 or Th400...Realistically?

[LongSixEight]

I'm not looking to start a huge debut over something that's been covered already. Just wanting advice for what actually works in our trucks.
I've got my big block out of my old bracket car I'm collecting parts to put it in my 86 long bed. Motor went 10.50-10.80 range in 3000lb car with a glide & brake. So I'm guessing 550-580hp. The truck is just gonna be a little toy to beat on on the street & track a few times a year. Probably shoot for 4:88's & 3000- 3500 stall.

So what would you guys run for a trans? I have a good cooler & an lines already. Also, I have a th350 that works perfect with 75k on it that would be worth building. Since I'll be doing driveshaft work putting my 9" in I'm not even factoring that in on my decision.
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[cableguy0]

Th400 will be most reliable. While a th350 can be built to handle the power the th400 will easily handle that power. The only real downside to the th400 is that it eats a fair bit more horsepower than a th350 but for a street bruiser that shouldnt be an issue.

[LongSixEight]

Thanks, that's exactly the debate I'm having w/myself right now. I'm really hoping someone can chime in on what they've used to make a 350 live behind a big block.
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[funnyfarmracer]

Originally Posted by LongSixEight

Thanks, that's exactly the debate I'm having w/myself right now. I'm really hoping someone can chime in on what they've used to make a 350 live behind a big block.
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Money and a good bit of it! A th400 will handle so much more than a th350 in just stock form. I love a 350 but the 400 is way more reliable and thats what counts when on a budget.

[Blue Rat]

Billet drum an input shaft on the TH350 for sure for starters. A lot parts will need to be upgraded for sure.
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[vin63]

Since you posted your question in the race forum, I would go with the TH400. It'll take more money to make the TH350 handle the torque levels (it'll be the torque that will be the primary factor for longevity) in a mild race application.

I've run Mike's Transmissions (http://mikestransmission.com) in all of my race cars with automatic transmissions, and Mike Stewart will not build me a TH300 or 700R4 for my Pontiacs. As a side note, I have run his TH400s behind my blown Pontiacs in nostalgia eliminator with zero trans failures - broke just about every other component, but not the transmission.

[mr. g]

...don't want a big debate either-
i had JW Performance build my TH350:
fully rollerized, ultrabell, 36 element steel drum, 2.75 low gear planetary, performance valve body, strip-sprag, etc.
it is some of the best money i have ever spent- i am confident it could take just about anything you can throw at it...
it's just money....cost was right at $3300 shipped

[LongSixEight]

$3300 is a little out of my budget for trans only. Im thinking around $2000-$2500 for trans & converter. I've managed to come up with a low mile stock rebuild th400 from a buddy. I'll probably take it to a local racer that builds some good transmissions & see what his opinion is on what it will need. Then probably get my stall ordered.
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[cableguy0]

A well built th400 with a good (read 7-800 dollar) verter could be done for under 2 grand without much of a problem.

[LongSixEight]

I really liked the Coan converter I had with this motor & the glide but it is waaaaaay too much for mainly street use. I'll probably call them again when the trans is done. Top notch folks to deal with in my opinion.
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[vin63]

Originally Posted by mr. g

...don't want a big debate either-
i had JW Performance build my TH350:
fully rollerized, ultrabell, 36 element steel drum, 2.75 low gear planetary, performance valve body, strip-sprag, etc.
it is some of the best money i have ever spent- i am confident it could take just about anything you can throw at it...
it's just money....cost was right at $3300 shipped

Yikes! That's exactly what I was talking about in my earlier post regarding the money required to make a TH350 handle the higher power/TQ levels. I ran Mike's Ultimate Turbo 400 behind my blown Pontiacs in NE 1 (7.60 index) and Pro 7.0 with no issues: http://mikestransmission.com/catalogsite400trans.html
The trans is $1895 today. Having a TH400 rebuilt locally is even cheaper.

[mr. g]

...generally agree with related comments...if/when budget is a concern the th400 is more cost effective- wanted to answer original question, though, so i was telling you what and how much/about my JW th350...can be done-just costs more; like what was being said.
if your th400 core/internals are in good shape and you have the opportunity to work with a builder local whom you trust, you can prob do something adequate for your application like this (just trying to help out):
kevlar/kolene kit: 300
perf valve body: 200
converter: 600-700
rebuild labor: 325
-you can prob complete this with $1700 or less using your core and have a mean th400 for nearly half the cost of a "built" th350
...also i like coan, but they didn't have all the parts i wanted for my th350- so i went with JW and am quite pleased with the results of my decision

[lil_sahara450r]

TH400 all the way!

Like others have said, a TH350 will handle a LOT, but it takes a LOT of $$$$$!! You could buy a few nice TH400's for what you will have in one race built TH350. Do some googling for a guy that goes by the name of "Jakeshoe", he has some awesome writeups on the 400's and he has a wealth of knowledge. He claims that the difference in power consumption between the 2 transmissions will not exist untill you start getting below tens in the 1/4 mile. He has it all in detail so I'll let ya do the digging on that. He usually frequents the hotrodders.com and other forum boards..

[lil_sahara450r]

found it! this is what i was talking about. this is a quote from the forum listed in the link. http://www.nastyz28.com/forum/showth...t=84090&page=3

"""Gentleman (term used loosely ) the whole "takes more power to turn" phrase is a pet peeve of mine. Misinformation being spread is another big one.

I think I wrote up a deal on this awhile back.
The short answer is:
Greater rotating mass consumes more HP but ONLY when you are accelerating or decelerating it. Not "turning" it.
Steady RPM in 3rd gear on either a Th350 or Th400 would be about equal. So cruising down the freeway at 2000 or 6000 rpm with either trans would basically only be consuming the power lost to the pump (obviously the converter also, but that's a whole different deal), and frictional losses internally. Frictional losses would be pretty low. ATF does a great job as a lubricant. Pump losses would depend on what the pressures are setup to be and actually running in the trans.
Obviously the higher the pressure the more power is consumed. Stock racers have been trying to lower pressures to run faster for years, which even resulted in the development of "racing" clutches that supposedly bind at lower pressures. (Blue Plate Specials).

Where the TH400 will consume more power is when you are accelerating or decelerating the greater weight.
TH350 is 125 lbs, Th400 135 lbs, dry no converter, both short shafts.
The difference in weight is in the rotating assembly.

The power loss is dependant on how fast you accel/decel the parts. If you accelerate the parts at a moderate pace (think 14 second car) there is virtually no difference in power, because you aren't trying to accelerate the parts fast enough to make any difference. If you are accelerating them quickly (low 10 second car) you will start to see some difference in ET, usually in the .01-.06 range slower with a TH400.
However at the low 10 second range, you almost always want the greater strength/reliability of the TH400. Bracket racers will give up .05, to be sure they don't break a trans and lose a race.

If you made the drums larger diameter it would consume more power.

I just think it is funny everytime I read someone state "Use a Th350 because a TH400 takes more power to turn".
While I understand what they are trying to say, they are stating it incorrectly , and usually don't have a clue as to why it would even be partially true.

A TH400 will take more power to drive through the planetaries in low and 2nd gear because of the larger tooth contact pattern also.

But you have to look at the REAL world difference. I'll take the .01-even a .1 loss in ET to have a stout unit.

I also see this stated about 4L80E's. How HUGE they are and HEAVY. Nobody knows what they actually weigh though...

I've seen estimates of just the trans being 250#+. LOL

I lifted one off the bench yesterday and while heavy, I'm not lifting 250 lbs off the bench and setting it on the floor. I probably could but maybe only once. """
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