L31 vs TBI 454 Swap

[NateButler]

Hi, new to the forum but a long time (unregistered) lurker. I have a mid 80's K2500 frankentruck that was cobbled together by a previous owner and I blew a head gasket a few weeks ago while plowing. The engine always felt tired so I'm evaluating options to replace rather than repair that particular 350. I've done some searching of the forum but didn't quite find specific opinions and advice so hopefully this isn't duplicating anything too much.

The truck currently has a 350 that may or may not be stock with the typical mechanical fuel pump and a quite new Edelbrock 4 barrel that I put on when I inherited the truck. It has the muncie SM465 transmission as well. It's always felt tired, though I will admit the carb and timing aren't fully dialed in. I see my options as follows:

Option 1: tear the heads off the engine, replace the gasket(s) and see how it does. Clearly the cheapest option but I do wonder whether I won't just have new or recurring issues and as I said, this engine has been a dog from day 1.

Option 2: I recently picked up a 98 3/4 ton suburban with a 5.7 in it to rob parts off for my 99 suburban (daily driver). I don't need that engine as my suburban has the 454/7400 vortec. I was told it runs but I haven't fired it up and it has 315k on the odometer so I'd probably want to rebuild it anyway. I could pull it, have it rebuilt and put that in my squarebody, probably with a new intake and convert to carb (yes, I know injection is better but carb will be faster/easier for me). I'd need to upgrade the fuel system to electric since the L31 wouldn't have a mechanical pump provision but flow and pressure could be moderate. I would think using my existing gauges would be simple enough. I'd have to come up with a flywheel and clutch since the suburban is an automatic - would the flywheel off my old 350 likely work on the newer 5.7? This would probably be higher cost but minimal work for me. I'm sure it would be a decent bump in performance as well but I'd love to hear anyone's real world experience.

Option 3: A good friend has offered me his '95 3500HD with a 454TBI set up for a manual transmission. It runs good and only has about 100k on it. "Free" and "Big Block" really have my attention but the internet experts often have nothing nice to say about this iteration of the 454 so I'm wondering if it's worth the hassle. I'd have to rework my exhaust, the fuel system would need a more serious overhaul to feed the injectors, and I'm not sure how to handle the gauges - any words of wisdom here? Is it less of a headache then I'm thinking? What's the seat of the pants dyno opinion on anyone who has done a 454TBI swap? Like I mentioned, the L19 454 gets a lot of hate in certain forums but by the numbers it's got a lot over the old 350 I had, even if it was running right and fresh. I have the vortec version in my suburban and I love it despite it's ability to dispose of fuel but I'd hate to go through the effort and have a dog. I'd love any advice or opinions from those who have done this swap.

I'm sure there are other options: LS Swap, 383, etc... but budget and shop time are limited, so I'm really just trying to get the old girl back on the road and back to work while making reasonable improvements based on what I have for opportunities.

Thanks in advance. Again, if this duplicates posts I apologize.

 

[bucket]

There's going to be a bunch of opinions here. So here's mine, lol.

The big block is free? As far as I'm concerned, that makes it the most cost-effective. Especially since it is lower miles and shouldn't need overhauled. Sure the TBI 454 is the "worst" 454, but it still makes a lot more useful power in a truck than a Vortec 350 does.

It can be done very simply too, if you don't mind sticking with a carburetor. Ditch the intake, put a 4bbl on it, stick an HEI distributor in it and then drop it in using the same mounts and brackets from the 350. You would also need a basic, low pressure external fuel pump to feed the carb since the '95 block likely doesn't have a mechanical pump provision. If you don't want to fiddle with fan shrouds, you can upgrade to electric fans. There are lots of factory-engineered fan setups available used that will work well.

 

[YakkoWarner]

Some extra food for thought: I discovered 2 weeks ago while changing my 454 throttle body that the 1989 454 actually has a Quadrajet style intake bolted to the heads, and then above that a wet adaptor plate (has coolant routed thru it for unknown reasons) with the throttle body bolted onto that adaptor. If the 1995 unit has a similar setup, configuring it to take a carb would not even require pulling the whole intake, just removing that adaptor and installing a standard HEI distributor (possibly needing a riser to get the carb linkages to clean the HEI?)

If you're doing plowing, you probably would get more use from the higher torque of the 454 even if the actually horsepower output is not impressive.

 

[bucket]

Some extra food for thought: I discovered 2 weeks ago while changing my 454 throttle body that the 1989 454 actually has a Quadrajet style intake bolted to the heads, and then above that a wet adaptor plate (has coolant routed thru it for unknown reasons) with the throttle body bolted onto that adaptor. If the 1995 unit has a similar setup, configuring it to take a carb would not even require pulling the whole intake, just removing that adaptor and installing a standard HEI distributor (possibly needing a riser to get the carb linkages to clean the HEI?)

If you're doing plowing, you probably would get more use from the higher torque of the 454 even if the actually horsepower output is not impressive.

Starting in '91 (gen V), the TBI 454 got a specific intake manifold for the throttle body.

 

[Catbox]

The heads of the GenV big blocks are what suck azz.
Swap it in and run it.
If you want more power later on, find a set of the Gen 6 heads and plop them on.
More power all around.

My son just installed a Gen6 into his Suburban and it sounds pretty good so far.
The internets have tested the Gen6 engine and found they routinely make around 375hp and 450-ish ftlbs with a simple carb / intake and headers.

 

[YakkoWarner]

Starting in '91 (gen V), the TBI 454 got a specific intake manifold for the throttle body.

Didn't know they made that change - good to be aware of!!!

 

[Vbb199]

Put the big block in the truck, the heads on it suck but thats only a junkyard swap away from being better

 

[75gmck25]

I would go with the TBI 454 because it’s in running condition and you can see and hear it run.

Swapping a 454 into a squarebody is a straightforward job, so all you need to figure out is what needs to be modified to adapt the old fuel system and electronics in your truck to the new. Since you have a complete donor truck I would probably drop it in as a complete TBI engine, including computer and other parts. Get it running well as is, use it this winter, and worry about upgrading later.

 

[Ricko1966]

Junkyard 4.8 and an Ebay turbo. They swap is almost free and it'll run 10s with 30 mpg.

 

[bucket]

Junkyard 4.8 and an Ebay turbo. They swap is almost free and it'll run 10s with 30 mpg.

Lol, yep. That's what the internet says. I wonder what AI has to say about the cost-effectiveness and efficiency of a 4.8 and cheap turbo swap...













...No, I ain't looking it up. But, I do wonder, lol.

 

[Catbox]

Lol, yep. That's what the internet says. I wonder what AI has to say about the cost-effectiveness and efficiency of a 4.8 and cheap turbo swap...

A VW club member was selling her late husbands crewcab dualie he used to haul race cars with.
It was fully decked out and had a mild built 454 in it.

Another member that likes to "know everything" told me he would yank that big block and put a LS6.0 into it as it would make more power.....

 

[bucket]

A VW club member was selling her late husbands crewcab dualie he used to haul race cars with.
It was fully decked out and had a mild built 454 in it.

Another member that likes to "know everything" told me he would yank that big block and put a LS6.0 into it as it would make more power.....

I don't understand where it all came from. Yeah, the LS platform is great for making power, but everyone acts like a stock 6.0 is king of the hill. My '00 6.0 pulls no better than my old and tired '78 454. Of course, my 6.0 is old and tired now too (almost 300k) but it wasn't when I used to pull with it, lol.

 

[Rustisbest]

From what I've been told the key to it all is the LS has to come from a junkyard.

 

[Catbox]

I don't understand where it all came from. Yeah, the LS platform is great for making power, but everyone acts like a stock 6.0 is king of the hill. My '00 6.0 pulls no better than my old and tired '78 454. Of course, my 6.0 is old and tired now too (almost 300k) but it wasn't when I used to pull with it, lol.

They all see the guys running the 6L in drag cars on the interwebs.
What they don't pay any attention too is the massive amount of money they put into that turbo system installed in the engine bay all run by the fancy EFI required to make it all happen.
Not to mention the dyno time and tuner time they have used to optimize the setup to run 7's in the 1/4.

On the internet it all looks easy.
So it must be in real life as well, right?

 

[Ricko1966]

They all see the guys running the 6L in drag cars on the interwebs.
What they don't pay any attention too is the massive amount of money they put into that turbo system installed in the engine bay all run by the fancy EFI required to make it all happen.
Not to mention the dyno time and tuner time they have used to optimize the setup to run 7's in the 1/4.

On the internet it all looks easy.
So it must be in real life as well, right?

Nope,that's not it.Its common knowledge, any high school kid can get a junkyard Ls put on a ebay turbo put it in a 4000 pound Chevy and run 10s all day long never break a thing and drive it home getting better milage than a new truck.