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TH350 On a BBC


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I'm knee deep in an engine swap for my MC to a 454 bored .30 over with 10.5:1 compression with oval heads and moderate cam, cooled by a 4 core radiator. I was originally set on finding a TH400 to mate to the back, but I've seen some talk online of folks having good durability with a well built TH350. Is this feasible, or will it be better in the long run to find another transmission?

The TH350 that was in the car already needs gone through and along with the SBC taken out of the car is numbers matching, so it would be nice to use. It would also save the trouble of having the driveshaft shortened, dealing with electric kickdown, etc. However I don't really want to deal with frequent transmission problems if it's likely to be an issue.

I'm sure I'll be enjoying the HP and not babying it, but it will be a cruiser and for occasional car shows, unlikely that it'll ever see a strip. 

Thanks for the help!

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6 minutes ago, MC1of80 said:

400! A 350 will live behind a BBC for a little while. A 400 will live way longer. 

GM didn't put TH350s behind the big blocks for a reason...

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Depends on how strong (and how much you're willing to spend) you get your th350 built to.... 

If you're getting a complete hi torque/heavy duty re build and adding a good cooling system to the transmission, it could last a long time providing you don't abuse it. 

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Pull the original engine and transmission and store them. If you’re going to spend a buttload of money, spend it on one you know will take whatever you can throw at it. 

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Turbo 350 (built right) extra clutches, bigger drum, firm shift kit( valve body upgrades), it will handle a BBC .Better 1st gear ratio is the reason for it. Sure, you can spend more money buying the better 1st gear for the Turbo 400 (ask me I bought it), but like I said, a well built turbo 350 will live behind a BBC. I'd find someone who builds bracket car Automatics and tell them what you are thinking about doing. What rear gear ratio are you running? Here's a break down on a certain '70 Nova we built way back in the '80's.

1970 Nova 

468 BBC

Turbo 350

4:10 rear gear with 28" tire

Column shift with split bench seat

Would run 10.90's through mufflers (1/4 mile) The start of heads-up Super Street in NHRA 

Street car.... Drive to the track...race...go home... Rinse,repeat. Get down to finals... Split winnings

Old School.  

Edited by 420ponies
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Thanks for the help y'all. The car currently has the stock 2.73 rear end, planning on running it until things go south and then upgrade to a 12 bolt with a better ratio. Did that setup have a kickdown delete? With either transmission it would be tempting but I've seen some concerns about not getting a change in flow without the kickdown. 

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Yes it did have a kick down on the transmission. He also reworked the column shifter so he could bump it into each gear and not hit reverse with it. It only had a 2,400 stall converter.

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On 6/27/2022 at 7:38 PM, 420ponies said:

Turbo 350 (built right) extra clutches, bigger drum, firm shift kit( valve body upgrades), it will handle a BBC .Better 1st gear ratio is the reason for it. Sure, you can spend more money buying the better 1st gear for the Turbo 400 (ask me I bought it), but like I said, a well built turbo 350 will live behind a BBC. I'd find someone who builds bracket car Automatics and tell them what you are thinking about doing. What rear gear ratio are you running? Here's a break down on a certain '70 Nova we built way back in the '80's.

1970 Nova 

468 BBC

Turbo 350

4:10 rear gear with 28" tire

Column shift with split bench seat

Would run 10.90's through mufflers (1/4 mile) The start of heads-up Super Street in NHRA 

Street car.... Drive to the track...race...go home... Rinse,repeat. Get down to finals... Split winnings

Old School.  

This ratcheer! My TCI TH350 has been my 496 since 2006. And I am rarely nice to the car. Add to that dyno time and at least 500 trips down the 1/4 mile. 

 

177015_3853579032014_156019585_o.jpg

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  1. The car ran 12.40s when the 400 started slipping. The fastest way to get it back on the road was a TCI 350 that a local speed shop that had one in the box. It ran 12.0s and still does. With working a/c, power windows, and two twelves on the trunk. When it breaks I'll put the 400 I built ten years ago back in. 
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On 6/27/2022 at 3:52 PM, Dtret said:

Pull the original engine and transmission and store them. If you’re going to spend a buttload of money, spend it on one you know will take whatever you can throw at it. 

If anyone here knows how to tame a BBC, it’s Dennis. 

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2 hours ago, Glen said:

If anyone here knows how to tame a BBC, it’s Dennis. 

I can tame them alright. My theory, you can’t break them if you don’t ever drive them. lol. 

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Use what you like. Tci th350 behind a crate LS6 many years ago. This is what was left. 

PXL_20220708_205127821.jpg

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Was never impressed with TCI transmissions..... Montelishi had one when I bought her, sloppy and slipped.

Made the switch to a local custom rebuilt th200r4...... Bullet proofed to 750 hp. 

And just remember, a crate LS6 has a little bit more twist than a 454. ;)

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Remember an LS6 big block is a 454- 450hp. Have destroyed th350s behind small blocks. Anything can be destroyed! I always find the weak link, always! Lolol

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8 minutes ago, MC1of80 said:

Remember an LS6 big block is a 454- 450hp. Have destroyed th350s behind small blocks. Anything can be destroyed! I always find the weak link, always! Lolol

They always run great, right up to the very point they explode 😁

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2 hours ago, jft69z said:

They always run great, right up to the very point they explode 😁

Ain't that the truth! AMEN!!! LOLOL

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9 minutes ago, Scott S. said:

And when that happens.... No one's happy. :(

I am! Found the weak link! Build back BETTER, STRONGER, FASTER! 

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53 minutes ago, MC1of80 said:

I am! Found the weak link! Build back BETTER, STRONGER, FASTER! 

Were you the kind of kid that liked to break his toys ?? LOL !!!!

I find building better, stronger, faster the best place to start...... But then again, I wouldn't have had as much fun playing with Montelishi if the last owner had. :)

 

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1 hour ago, MC1of80 said:

I am! Found the weak link! Build back BETTER, STRONGER, FASTER! 

I have always said, If it breaks, it should not have been there to start with !!

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On 7/8/2022 at 8:07 PM, MC1of80 said:

Use what you like. Tci th350 behind a crate LS6 many years ago. This is what was left. 

PXL_20220708_205127821.jpg

Now that's a great trophy 👍

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  • 2 weeks later...

My thoughts…my 100K TH350 with factory converter, lasted behind my 465 hp, 467 for two years (best of 12.9 @ 109 mph), and about five low-to-mid 12-Second passes behind my 580 hp, 496. The original transmission stopped shifting 1-2 so I swapped in a TH350 which was rebuilt with good clutches, sprag, and shift kit back in the early 2000s.
 

The rebuilt transmission has seen a dozen mid-11-Second passes at 3800 lbs (406, on nitrous, in another car) and eight 11-Second passes in my 4115 lb Monte Carlo in addition to 10 low 12-Second passes at Midwest Drags and 5K miles (running on 7-Cylinders. Trust me, my 510 CID makes 680 ft-lbs at 4200 rpm, if the TH350 was an issue, I’d have found it. It sucks less power and weighs less - if you’re chasing ET, stick with the TH350. 

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  • 4 weeks later...

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