TH350 max HP
Burning Brakes
Joined: May 2014
Posts: 1,094
Likes: 16
From: Los Angeles California
My uncle has a 700 hp mud racer with a th350 says they can withstand a lot of hp depends on how you build them the th400 adds unwanted weight for him and he could make his th350 stronger and better for less than it would a th400. I'm using a th350 but I only have 370hp but built tranny to handle 600hp at least that's what I was told lol but they are reliable my car sat for 15 years tranny was still good I only rebuilt it cuz I sprung a leak in hose and replaced it with oil hose which burst in fw drove home like that messed up all gears. But it still gave me a few more trips after that.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Stock seems to be around 400hp??
This guy on the Chevelles forum seems to know his stuff - see below......
My TH350 builds:
5 clutch direct piston (piston machined for 1 additional clutch)
Sun gear bushings doubled up and lube holes drilled, de-burred.
NEW intermediate roller clutch (sprag) and hardened race. Race inside diameter specially prepped.
Direct clutches MUST be dual fed. This can be accomplished internally or by using a TransGo Kit. I do it both ways depending on application.
Valve body modifications to firm up shifts. Nothing fancy needed, and not too fimr on the 1-2 shift.
Heavier pressure regulator spring for increased pressure.
Governor modified for higher rpm shifting.
Pump machined for better sealing and pressure.
700-R4 low/reverse roller clutch and support.
Endplay setup on the tight end of spec,
Borg Warner or Alto Red plates.
Snap rings tack welded for high rpm applications.
That's about all you need on a TH350.
I have a couple running Reliably 10's in the 1/4 in ~3600 lb rides with nothing more than this.
The key is, not overly hard shifts from 1st to 2nd, proper sprag race prep, and dual feeding the directs.
really nothing fancy at all.
This guy on the Chevelles forum seems to know his stuff - see below......
My TH350 builds:
5 clutch direct piston (piston machined for 1 additional clutch)
Sun gear bushings doubled up and lube holes drilled, de-burred.
NEW intermediate roller clutch (sprag) and hardened race. Race inside diameter specially prepped.
Direct clutches MUST be dual fed. This can be accomplished internally or by using a TransGo Kit. I do it both ways depending on application.
Valve body modifications to firm up shifts. Nothing fancy needed, and not too fimr on the 1-2 shift.
Heavier pressure regulator spring for increased pressure.
Governor modified for higher rpm shifting.
Pump machined for better sealing and pressure.
700-R4 low/reverse roller clutch and support.
Endplay setup on the tight end of spec,
Borg Warner or Alto Red plates.
Snap rings tack welded for high rpm applications.
That's about all you need on a TH350.
I have a couple running Reliably 10's in the 1/4 in ~3600 lb rides with nothing more than this.
The key is, not overly hard shifts from 1st to 2nd, proper sprag race prep, and dual feeding the directs.
really nothing fancy at all.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It depends on how hard you are on it. if you are power braking or manually shifting with sticky tires. A shift kitted th350 will die with under 400 hp out of a 350 ci motor. I killed mine and had it hopped up to 550hp /500 tq level and it lasted a couple of years in a low 400 hp 7200 rpm 355 ci with slicks at the drag strip
Le Mans Master
Joined: May 2007
Posts: 5,025
Likes: 1,120
From: North tonawanda NY
My uncle has a 700 hp mud racer with a th350 says they can withstand a lot of hp depends on how you build them the th400 adds unwanted weight for him and he could make his th350 stronger and better for less than it would a th400. I'm using a th350 but I only have 370hp but built tranny to handle 600hp at least that's what I was told lol but they are reliable my car sat for 15 years tranny was still good I only rebuilt it cuz I sprung a leak in hose and replaced it with oil hose which burst in fw drove home like that messed up all gears. But it still gave me a few more trips after that.
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