TH 350 or 400?
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09-08-2020 | 02:21 AM
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TH 350 or 400?
Hello Everyone,
I'm wondering what everyone with Modified big block Olds motors are running for transmissions. I purchased a very solid 1970 Cutlass Supreme about 6 months ago that I take to the track for the club clashes. It's basically bracket raced once a month and I do drive it on the street just for fun. I'm replacing the original 350 with a 455. Without going into a lot of details... I had a good standard bore 455 F block. The crank was bad from a spun bearing so the short block is now a 455, .030 over with a stroker crank (488 ci) with forged rods and pistons. Basically and Eagle after market rotating assem. kit. The top end will be Edelbrock heads, 10:01 compression, performer RPM intake and headers. In fact, might just purchase the Edlebrock power package including the cam and lifters. So I'm guessing the motor will make somewhere around 450 HP and 540 torque.
My question is... what are people running for transmissions behind modified 455s? I think I have 3 options.
1. Find a shop that can build my existing TH-350 to match the performance of the motor. Although I think there is a reason GM used the TH 400 on most of their Big block cars.
2. Purchase a TH 350 already built for performance. I have been looking on the performance parts web sites and see TH-350's by differernet brands that claim to hold up to 550 HP, but they never give torque specs.
3. Purchage a TH 400 already built for performance. Again I see HP rating but no Torque ratings (?).
The car will run a 3000 speed stall convertor and someone already swapped in a chevy (not and BOP) 12 bolt rear end with 3:55 gears.
Again just looking to get some advice. I've been reading the forum and see guy's saying a TH350 is fine if it's built right. The TH350 is lighter, takes less power to turn and will be fine if modified. Some are saying don't buy one, use the one you have and have it built by a local shop. I don't know of any good local shops that do that type of work. Others are saying junk the TH350 and find a TH400. GM already knew the TH350 would not hold the power of a Big Block, don't second guess the GM engineers and just go to a TH400. Some saying this brand of Transmission is OK and this brand is bad... I also read where one person is stating you need to buy the BOP to Chevy adaptor and run a Chevy bolt pattern trans if you plan on buying either a TH350 or TH400 that has been built to live with 500 Plus torque. I'm just looking for whatever works behind the motor I'm currently building and will hold together the longest. From others experience, what works and holds together behind a strong 455?
Thanks you for reading.
I'm wondering what everyone with Modified big block Olds motors are running for transmissions. I purchased a very solid 1970 Cutlass Supreme about 6 months ago that I take to the track for the club clashes. It's basically bracket raced once a month and I do drive it on the street just for fun. I'm replacing the original 350 with a 455. Without going into a lot of details... I had a good standard bore 455 F block. The crank was bad from a spun bearing so the short block is now a 455, .030 over with a stroker crank (488 ci) with forged rods and pistons. Basically and Eagle after market rotating assem. kit. The top end will be Edelbrock heads, 10:01 compression, performer RPM intake and headers. In fact, might just purchase the Edlebrock power package including the cam and lifters. So I'm guessing the motor will make somewhere around 450 HP and 540 torque.
My question is... what are people running for transmissions behind modified 455s? I think I have 3 options.
1. Find a shop that can build my existing TH-350 to match the performance of the motor. Although I think there is a reason GM used the TH 400 on most of their Big block cars.
2. Purchase a TH 350 already built for performance. I have been looking on the performance parts web sites and see TH-350's by differernet brands that claim to hold up to 550 HP, but they never give torque specs.
3. Purchage a TH 400 already built for performance. Again I see HP rating but no Torque ratings (?).
The car will run a 3000 speed stall convertor and someone already swapped in a chevy (not and BOP) 12 bolt rear end with 3:55 gears.
Again just looking to get some advice. I've been reading the forum and see guy's saying a TH350 is fine if it's built right. The TH350 is lighter, takes less power to turn and will be fine if modified. Some are saying don't buy one, use the one you have and have it built by a local shop. I don't know of any good local shops that do that type of work. Others are saying junk the TH350 and find a TH400. GM already knew the TH350 would not hold the power of a Big Block, don't second guess the GM engineers and just go to a TH400. Some saying this brand of Transmission is OK and this brand is bad... I also read where one person is stating you need to buy the BOP to Chevy adaptor and run a Chevy bolt pattern trans if you plan on buying either a TH350 or TH400 that has been built to live with 500 Plus torque. I'm just looking for whatever works behind the motor I'm currently building and will hold together the longest. From others experience, what works and holds together behind a strong 455?
Thanks you for reading.
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