TH-350 vs TH-400
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TH-350 vs TH-400
Just woundering who out there could tell me the strength difference between the two. The 350's are easier for me to find but I don't want to start with something that is too weak to begin with. How much power will each of them hold in stock form? Looking to handle 400-500hp.
Phil
Phil
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Just woundering who out there could tell me the strength difference between the two. The 350's are easier for me to find but I don't want to start with something that is too weak to begin with. How much power will each of them hold in stock form? Looking to handle 400-500hp.
Phil
Phil
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Phil, pushing out that much power, the 400 is probably your best bet. It is much stronger, but the down side is it saps more power to run it. At 400/500hp even the 400 is on it's limit though. I've had my 400 uprated to handle 800hp just to be on the safe side....you will also need a hi-performance torque converter. Having said all that, the 350 is a great box, and I've read stories of it running high HP without any probs!
Phil
Drifting
Joined: Apr 2006
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From: gold coast queensland
400 def stronger, indestructable on a stock motor.close to indestructable on a warm motor. no guarantees with a hot motor. in saying that i am running a B&M Th350. flog the hell out of it for 2 years and hasnt blown up yet so i cant complain with either choice you make because both can handle that power with a tweek.
Last edited by gingerbreadman1977; May 23, 2009 at 09:06 PM.
Thread Starter
Instructor
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400 def stronger, indestructable on a stock motor.close to indestructable on a warm motor. no guarantees with a hot motor. in saying that i am running a B&M Th350. flog the hell out of it for 2 years and hasnt blown up yet so i cant complain with either choice you make because both can handle that power with a tweek.
Phil
Drifting
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From: gold coast queensland
Le Mans Master
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I built a TH350 about 10 years ago for a guy running a 67 GTO with a 455. All he's doing is racing every weekend. He hasn't blown it up yet. And he's not the fastest thing around, but he is pretty quick. High 12's. I built a 400 for another guy with a BB Camaro. They told him to not bring it back without a cage.
FWIW: a 400 takes roughly 25-30 more HP to turn.
FWIW: a 400 takes roughly 25-30 more HP to turn.
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Melting Slicks
Joined: Jul 2005
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From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
The TH350 handles my 490hp ok, never had an issue so far. The trans I rebuilt ( clutches, valves etc) and installed a Trans Go stage ll shift kit with a 2800 stall. My rear gear is 456.1 so it has taken some abuse over the past few years, nothing has failed yet. 
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Phil
Heel & Toe
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400 turbo vers the 350
I've been building performance 400's and 350 turbos since the mid 70's and I can tell you right now, with anything over 475 hp that hooks up, you will be working on the 350 again. They are a good transmission but the 400 is probably the strongest transmission built. The one thing you will need to do is put the performance sprag on the early direct drum for endurance. The late model 400 uses a roller clutch drum and they are not worth their weight in dirt. I have guys running twin turbos at 1,100 plus hp and they hold up for a season at the track. The one in my 59 vet is behind a 600+hp 427 and will probably out last the engine. Even with the hardened sprag, the 350 just hasn't got the beef to take a really hard shift or withstand the use of a tranny brake. If you are running in the high 12's or 13's you can probably get by with it but like you said, why settle for something that's second place to start with.
The horse power loss you will hear about is something that has been going around for a long time. We pulled the 350 out of one of our Chevy II cars and put a 400 in it's place because we were tired of fixing the thing, still turns the same high 9's didn't loose so much as a tenth. We even used the same convertor. Can't find any loss on the chaissi dyno either.
Hope this helps, good luck
The horse power loss you will hear about is something that has been going around for a long time. We pulled the 350 out of one of our Chevy II cars and put a 400 in it's place because we were tired of fixing the thing, still turns the same high 9's didn't loose so much as a tenth. We even used the same convertor. Can't find any loss on the chaissi dyno either.
Hope this helps, good luck
Burning Brakes
Joined: Dec 2003
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From: Adelaide South Australia
I went down this path deciding what trans to fit with my 383 stroker..
TH-400 is a stronger box than the TH-350 in stock condition.
However, the TH-350 is popular as it is lighter, and with modifications, can be built stronger to cope with a 500hp motor.
Overdrive trannies are also worth considering....
as "you can have your cake and eat it too!"
You can run a lower diff gear to get good accelleration (needed with an auto) whilst still retain good cruisability with the OD ratio .
Here's a couple of overdrive autos to consider....
TH700-R4 is based on TH400, whilst TH200-4R is based on TH350 box
Here's an article on rebuilding the "weaker" box to handle 1000hp
http://www.carcraft.com/techarticles...ild/index.html
TH-400 is a stronger box than the TH-350 in stock condition.
However, the TH-350 is popular as it is lighter, and with modifications, can be built stronger to cope with a 500hp motor.
Overdrive trannies are also worth considering....
as "you can have your cake and eat it too!"
You can run a lower diff gear to get good accelleration (needed with an auto) whilst still retain good cruisability with the OD ratio .
Here's a couple of overdrive autos to consider....
TH700-R4 is based on TH400, whilst TH200-4R is based on TH350 box
Here's an article on rebuilding the "weaker" box to handle 1000hp
http://www.carcraft.com/techarticles...ild/index.html