305 to 454 Engine Swap?

[Velder]

So here’s the deal;

I have an 85 C10 truck with a 305 small block engine, 4 speed automatic transmission, and 2.73 rear gear ratio. Seems the general take on towing with it is, that it will work, but that it is not what that setup was designed for.

My dad has a 96 GMC Suburban, with a Vortec 7400 L29 454 in it. The burb has well over 200k miles on it, but the engine was replaced about 70k ago, truck itself is in really poor shape, and he is intending to get rid of it.

How about swapping the 305 for the Vortec 454? Our auto parts guy said it would be a drop in fit, would be real easy to convert the engine to a carburetor, and that we could keep the old four speed mechanical transmission. I would obviously replace the 2.73 rear gears to something more appropriate to the new engine. Really like the Idea of going from a 5 liter to a 7.4

I would really like to get everybody here’s opinion on this idea. It is definitely well above my ability level, but I am willing to learn as I go, and seek help where needed.

Please be free with any advice, I will try to answer any questions or give more info if needed.

Thank you all for your help,

Christian

 

[bucket]

It is indeed a direct swap, with the exception of the exhaust and the fan shroud. It's also correct that it can be converted to carb rather easily.

The hang up is the transmission. That stock 700r4 won't live long behind it, especially with towing.

 

[Velder]

@bucket, thank you for the response, is there anything I can do for the transmission? The one in the 96 burb is the original, with 230k miles on it, so I don't really want to put that in the truck.
Can anyone recommend a good aftermarket transmission that wouldn't brake the bank?

 

[Sgt Gus]

What trans is in the burb? Any purchase of a rebuilt gonna be pricey. I'd probably install the trans with 454. Rebuild trans when the time comes or take to good shop and do it now. They'll rebuild what's necessary. But, then you're still looking at cost of rebuilt trans...

 

[squaredeal91]

Sounds like a sweet swap. That's the best generation of 454 imo, I'm probably wrong but I thought 97 was first year for vortec 454?

 

[Velder]

@Sgt Gus, I am not sure what the trans is in the burb, only it is the original, but the parts guy said it was an electronic trans, while the one in my truck is a mechanical, not really sure what the implications of that are?
@squaredeal91 I certainly wouldn't know, but according to this article the 96 was the first year for the Vortec 454. so you think it would be worth while to do the swap? what would you recommend for the transmission?

 

[vr1967]

The cams in the Vortec 7.4s are a “lazy” design, but to swap it, you really need to go to adjustable rockers.
They are good engines, good flowing heads, and the intake system makes good torque. Plus it has individual injectors, unlike the Vortec small blocks/4.3, if you want to keep the fuel injection.
Not sure what your goal is, or level of mechanics, but if you keep the injection, I’d get rid of the black box computer and go to the 98-02 0411 pcm, for a better processor and tuning ability.

 

[Sgt Gus]

@vr1967, interesting on pcm...does his have old ecm and chip? And you're suggesting replacing with newer processor?

 

[Sgt Gus]

@Velder , mine has TH400, no overdrive but it is a 3/4 ton. Read 6L80e would have the overdrive. So something to look at besides 700r.

 

[Craig Nedrow]

I believe they come with a 4l80e, an excellent, strong OD trans. I have done this swap and documented it here: https://www.gmsquarebody.com/threads/1973-k20-350-to-454-swap.29840/. Also US shift makes one of the best standalone controllers on the market. Here is the quote to me from them for my carbed 454:
Quick 4 controller - $585
Main harness w/loom - $150
TPS Adapter for carb - $175
Not cheap, Here is the web site: https://www.usshift.com/

 

[Craig Nedrow]

The Mark VI blocks are great, Richard Holdner loves them, HOWEVER, all aftermarket blocks are designed after the Mark IV which has the round hole for cooling, unlike the VI that had the round hole and an oblong cutout. Supposedly makes the cylinders weaker. IV was also two bolt main VS the four bolt main, which is stronger. Mark IV mains can be upgraded, but then will need to be line honed.

 

[Sgt Gus]

I believe they come with a 4l80e, an excellent, strong OD trans. I have done this swap and documented it here: https://www.gmsquarebody.com/threads/1973-k20-350-to-454-swap.29840/. Also US shift makes one of the best standalone controllers on the market. Here is the quote to me from them for my carbed 454:
Quick 4 controller - $585
Main harness w/loom - $150
TPS Adapter for carb - $175
Not cheap, Here is the web site: https://www.usshift.com/

Meant 4L80e thumbs up

 

[84c10Tony]

Seems the general take on towing with it is, that it will work, but that it is not what that setup was designed for.

True, hmm, instead of doing all that work, then fix trans, brakes, computers, fuel delivery, on n on etc... how about keeping both for what they are built for?...no need to mess with the engineer's design. Maybe a slight upgrade or improvement.

Drop a set of 3.73 or 3.91's in the C10 for all around daily, really wakes up a small block...3.73's an a Trutrac amazed me. Gas mileage went up, not down, go figure.
More fun too.

Keep the big boy as is, repair as needed, use it for what it was designed for.
Drive one, work on the other, a spare is great to have.

People generally won't park next to, or mess with a raspy lookin' vehicle.
Tow or cruise light with the little truck, and big with the big truck, cool beans Maynard.
If you do that, you might thank the idea and wallet when your 50 or 60 lol.

 

[vr1967]

@vr1967, interesting on pcm...does his have old ecm and chip? And you're suggesting replacing with newer processor?

No, there is no chip like the older tbi ecms. And yes, the 0411 is a better, more tunable ecm than the old black box ones.

 

[Bextreme04]

Honestly... just pull the entire harness, ecu, and engine/trans together. 2wd to 2wd is a super easy swap. Just put the entire L29/4L80e into the C10.

You would need to either put a normal EFI saddle tank in with an 87 truck sending unit or convert to a rear mounted 31 gallon blazer EFI tank and sending unit. Then use a vortec EP 381 fuel pump and you are off to the races.

I am putting a 97 K2500 Suburban 454/4L80 into my 1980 K25 pickup. I've rebuilt the engine and trans and fixed most of the Gotcha's and common points of failure on the L29. New Bosch D3 injectors, reground the cam for more performance, Comp adjustable valvetrain kit, relocated an adjustable FPR, got rid of the vortec distributor cap and converted to 24x reluctor for LS coil near plug ignition, converted to 0411 ECU for tunability, etc...