going from a 350 to the 454

[Dheater]

Good evening all,

Need some help...

It has been awhile, and as the title says. Turning big tires and the 350 are not agreeing with one another. I have the chance to buy a 1978 3/4 ton 2 wheel drive truck with the 454 and it runs.
I know the small blocks can be "built", but not for $700 bucks. So I'm getting everything that goes with the motor with the truck. This is what I'm going from, or currently have.
350 motor a little tired.
TH350 - yes I know this will need to get changed, but it was just rebuilt
dana 60 front with 4:56 PSC power assist crossover
14 bolt rear with 4:56
NP 203---going doubler real soon

To help this along a little and it needed it anyhow. I was going to swap in the ORD engine cross member and their comp mounts.
So here is the help part,
What I'm I missing? is it really straight forward
Any good headers that fit? seems like it is a toss up hooker or hedman
Ideas...

Thanks,

David

 

[COCHEV]

Getting a complete rig is the way to go. You'll score all the little parts that are a pain to track down at the junk yard. Plus you'll get the bigger radiator and maybe hydroboost

 

[ColoradoChevyK5]

It is a straight forward swap. Except...you will need to use the 454 flexplate (I'm assuming its an auto) which has a different bolt pattern for the torque converter - the th400 and th350 are slightly different. When I did this swap years ago, I was mostly done with the install when I figured this out. In my case, I clamped the flexplates for both motors together (as a template) and drilled holes in the 454 flexplate in order to mate to the th350 torque converter. The 454 is an externally balanced motor and the 350 flexplate can't simply be swapped over. Other than that, the distributor, carb, ps pump, alternator, ac compressor, starter, etc. can all be re-used with the 454. Even motor mounts can be reused, although if I recall the 454 mounts used a more solid rubber compound. Exhaust mods are in order of course but chevy did a great job of making so many things interchangeable. The th350 can live behind a 454 if you're not too hamfisted. Mine survived 3 years of off roading and pulling light trailers before I sold the blaze back in '94. Someone correct me if I'm wrong on anything, but that's all I recall from my swap 350-454 swap in 1991.

 

[Dheater]

It is a straight forward swap. Except...you will need to use the 454 flexplate (I'm assuming its an auto) which has a different bolt pattern for the torque converter - the th400 and th350 are slightly different. When I did this swap years ago, I was mostly done with the install when I figured this out. In my case, I clamped the flexplates for both motors together (as a template) and drilled holes in the 454 flexplate in order to mate to the th350 torque converter. The 454 is an externally balanced motor and the 350 flexplate can't simply be swapped over. Other than that, the distributor, carb, ps pump, alternator, ac compressor, starter, etc. can all be re-used with the 454. Even motor mounts can be reused, although if I recall the 454 mounts used a more solid rubber compound. Exhaust mods are in order of course but chevy did a great job of making so many things interchangeable. The th350 can live behind a 454 if you're not too hamfisted. Mine survived 3 years of off roading and pulling light trailers before I sold the blaze back in '94. Someone correct me if I'm wrong on anything, but that's all I recall from my swap 350-454 swap in 1991.

Great info on the flex plate, I would have figured the flex plate would have been the same.
I learned a long time ago, hammering on the go pedal ended up costing more money in the end. Funny I heard it run (454) and it has cherry bombs on it now, good god might as well run straight pipes..that and I'm older now..

 

[454Sub]

Just a thought, but with a doubler, you would be able to turn them tires with a 4.3L 6 popper.

But, the TH350 will survive if its been decently built with a nice cooler. My headers didnt fit worth crap, I ran Hedman Elites, I had to grind the framerails out a bit. I honestly believe the motor mount pads on the frame may be slightly different between the SB and BB. And possibly the crossmember as well. I can not remove my oil pan the way it sits now, with brand new motor mounts. So I too plan on the ORD crossmember and mounts. I also need this to stiffen the frame up as crossover is twisting mine up pretty good.

I would get some Windstar fans as well, it will be a tight fit with a mechanical fan, and I for one am not a fan of the mechanical fan, seen to many come out of the hood to say hello.

The converter will stall funny compared to the 350 as the added torque will change its stall characteristics.

 

[ColoradoChevyK5]

I've got a line on a 454 that was rebuilt 10 years ago, never fired, and is currently in storage. If I can get it, I will pull it apart and check everything out and hopefully do this exact same swap in the next few months. So this stuff has been on my mind. But like you, I'm out of the loud-exhaust stage as well.

 

[454Sub]

Its going to need at the least rings and a hone job if it hasnt been rotated over manually. Thats the suck part about buying engines that have never been started, they dont have much for lube on anything and they rust up and sieze.

 

[Dheater]

Just a thought, but with a doubler, you would be able to turn them tires with a 4.3L 6 popper.

I agree with the above problem for me is, I still have to drive it to get to the trails. And in Colorado that means going up the mountain roads. I had a broncos with 300 to 1 low range, nothing like idling up a trail
I will look into the fans and the cooler for the tranny. Good idea this is my first auto, getting older and for what ever reason I wanted an auto this time around.

 

[80' 427]

I didn't read everything cause I am lazy but my buddy has a th350 lasting behind a 454 running 10s and it is just a solid rebuild. I wouldn't worry till it is time to worry. I have summit cheap headers and they fit good except against the driveshaft. You won't miss the 350.

 

[diesel4me]

I ran a TH350 behind a 454 in two of my trucks with no issues,and they weren't babied ,they held up good...I wouldn't be afraid of using one,nothing wrong with running what you already have...they are beefier than a 700r4 at least..

When I swapped the 454's into my trucks,the 454 flex plate on both of them (one was a '73 Impala and the other a '74 Chevelle),they both had the dual bolt patterns for a TH350 or TH400,so that saved me some mods...ditto for the SB400 I swapped into one truck from a '78 Burb,it also had both bolt patterns on its flex plate...

I re-used the original motor mount brackets and mounts off the 350 ,and the exhaust even bolted up on one truck,the other 454 had a larger 3 bolt flange on the exhaust manifolds than the small block one was so I had to cut off the front pipes and use an exhaust adapter to get it to bolt up...pipes were 2-1/2" vs 2" I.D. on those manifolds...

 

[shreddercowboy]

Nice Im just new on here and Im a welder that likes to tinker on trucks Ive got 2 454 motors sitting in my garage at the moment and have been thinking about doing the swap in my 1979 Jimmy