BUICK 454/th400 swap

Aug 19, 2022
4
3
I have a very clean 81 lesabre (it’s basically just a big g body 😁) that currently hosts a 350 that smokes like a diesel and a 700r4 that has a lack of 3rd and 4th gear. This winter I’m hoping to swap in a 454/th400 getting the motor and trans mounted is not my concerns, the wireing aspect worries me, I was thinking I could find a beat up 81 c30 with my desired motor and trans and just use a modified version of the engine harness to hook it up but at not sure if this is the right way to go or not, any info helps, thanks
 

78Delta88

Master Mechanic
Supporting Member
May 23, 2022
381
43
SW Arizona
What is it you are actually needing? Are you keeping the C3 system and carb etc...? I have a 89 B Body Wagon and 86 Cutlass. Not keeping wire loom of the 89 or 86.

Currently building 2x looms for TBI to Carb conversion. If you Are just going 454 Carb; the loom is very simple. The TH400 only concern is kickdown, there is no lockup or ECU controls until 4L80E. Speedometer is still analog.

Not knowing where you are... If your close to SW I could rebuild the 700R and / or the 350, for you, they are getting harder to find.
 

B_ROCK42690

n00b
Thread starter
Aug 19, 2022
4
3
What is it you are actually needing? Are you keeping the C3 system and carb etc...? I have a 89 B Body Wagon and 86 Cutlass. Not keeping wire loom of the 89 or 86.

Currently building 2x looms for TBI to Carb conversion. If you Are just going 454 Carb; the loom is very simple. The TH400 only concern is kickdown, there is no lockup or ECU controls until 4L80E. Speedometer is still analog.

Not knowing where you are... If your close to SW I could rebuild the 700R and / or the 350, for you, they are getting harder to find.
I’m up in the Midwest, so that’s probally out of the question, this car is an 81 so I believe it never ha
What is it you are actually needing? Are you keeping the C3 system and carb etc...? I have a 89 B Body Wagon and 86 Cutlass. Not keeping wire loom of the 89 or 86.

Currently building 2x looms for TBI to Carb conversion. If you Are just going 454 Carb; the loom is very simple. The TH400 only concern is kickdown, there is no lockup or ECU controls until 4L80E. Speedometer is still analog.

Not knowing where you are... If your close to SW I could rebuild the 700R and / or the 350, for you, they are getting harder to find.
My plan is carb on the 454, not sure what you mean by c3 system , I’m in wisconsin so that’s probally out of the question, I was wondering what I should use for engine management, as in harness and ecm and whatnot, I’m guessing just a modified early 80s 454 harness they are similar from what I’ve seen, when you say there would be a problem with the kickdown do you mean routing it? Or just adjusting it, currently going through problems with the kickdown on the 700r and am not liking it lol
 

78Delta88

Master Mechanic
Supporting Member
May 23, 2022
381
43
SW Arizona
Yep, bit of a drive. I used to work out of Chicago area. So familiar with Beloit and Baraboo, but long time ago.

700R has a TV cable not a kick down. If not setup correctly it will burn out all the clutches.

C3 is also known as the "CCC" system. When changing to Carb you don't need the ECU, only hookup there is electric choke.

Main issue is get a pre 1981 HEI distributor with vacuum advance or you will have ignition and spark issues.

If you go with 4L80E Transmission you will need the stand alone controller, which is about $800 through Summit Racing. If you keep with TH400, you won't need any type of controller.
 

Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
961
93
Anglemont, BC
I used the factory 305 wiring for my 454 in my 81 Malibu. Basically all the same, except electronic kickdown, which I am not currently running at all. I did have to relocate the oil pressure sender as the big block i think was behind the distributor...? Either way, it wasn't behind the power steering pump, but there is a port there for it.

Of course, if this is a BOP 350, that may not work as well. But I'm willing to bet it wouldn't be TOO much different. You'll want to keep the factory senders for the car and swap them over, rather than use the ones on the 454, because they are specific to your gauges.

TH400 BARELY fits under the Malibu, but Monte's must have a different tunnel because they fit much nicer. You'll likely have no issue with that being a full size car.
 
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stew86MCSS396

Apprentice
Aug 1, 2022
81
18
(808)
The 396 in my MCSS used the same wiring as mentioned^^^.

What I'd like to talk about but may not apply since the OP has a '81 (availability era)...is there's been some mention on the internet that the B-body 700r4 used a different tailhousing that placed the crossmember mount in the same location as a TH-2004-r. Coincidentally TH-400 (short tail) and TH-2004-r share the same mounting location +-1/16". Well if that's not the case, perhaps a later b-body crossmember might make it a bolt in. Anyone who's in the know, please share...???
 

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