V6 to V8 Swap, Chevy Truck

Looking for answers for my 1994 Chevy C1500 2 Wheel Drive Pickup truck, with 4.3 V6 Vortec Motor, 4L60.E Transmission.

I have a 5.7 V8 350 Motor out of a 1989 GMC 4x4 truck.

Need to know all that has to be done for me to put the 350 motor in my truck.

taking out V6 and switching to V8 Power.

Need info about Wiring, Computer, Sensors, or more?

Plus, can I use my trucks Wiring harness, and just change my computer in my truck for V8 switch?

Thank you.

Are you in a state that has emissions testing?

If so, what you’re proposing can be a little bit tricky, from a legal standpoint

1 Like

Yeah, Nevada has smog checking

I’d search “4.3 to 350 tbi swap” and see what info I could get. The 4.3 was basically 3/4’s of a 350. And you’re swapping throttle body injection to throttle body injection. So it shouldn’t be crazy difficult. I believe the wiring harness will be the same.

I’m pretty sure you’ll need the V8 “chip”. You can use a V8 computer (or just install the chip into your computer) out of a 1994 or 1995 V8 truck. I’m fairly certain 1994 was the first (may have been 2nd) year the trans was computer controlled (4l60e). So I believe it’s imperative to use a 1994 or 1995 V8 chip.

I’m not certain the injectors or the throttle body bores are exactly the same size. Should be able to look up part numbers for those parts on each engine and see. Or if you have both throttle bodies, you could visually compare the bore size.

I think you may need new motor mounts or possibly have to relocate the motor mounts. The V6 is shorter and sits farther back in the engine bay, but I’m not sure if that’s due to motor mount differences or not.

That may be it…

As far as smog checks, I have no idea how that works, I do not have that in my state. But I thought antiques were smog exempt? Anything over 25 (in my state) is eligible for an antique tag…

1 Like

I think these mounts are the same for the V8. The front 2 cylinders were lopped off the V8 and the transmission face needs to be in the same spot so I think you are good to go.

Agree with other commentators. TBI to TBI swap, need the V8 chip OR a V8 ECU from 1994. Just make sure every sensor that is on the V6 is also on the V8. Don’t just swap them though. Buy new ones. The old ones have 25 years on them and it is far easier to swap them while the engine is out.

1 Like

I agree with @Scrapyard_John. Check Nevada’s smog check requirements for age. Your truck might be old enough that they won’t require checking. If they do, make sure an engine swap like this is legal as long as it passes. The truck uses OBD-1, and the test has to be tail pipe emissions, not an OBD-2 code check.

1 Like

I can’t speak to the legalities, procedures and regulations in Nevada . . .

But it might be best to contact the bar, and possibly a referee, and tell them what you’re proposing

In the end, it might be easiest to do the swap . . . whatever that entails . . . and plan on getting a bar referee label

The advantage of this is that it’s indisputably legal, and when you bring the truck to get smogged in the future, the inspector will simply refer to the label, versus trying to figure out what you have and if it’s even legal to perform the inspection

If you did the swap, and used a V8 radiator shroud from the same year truck with a sticker from the factory stating V8 epa info (I think they put it on the fan shroud on those trucks), I wonder if they’d even notice? Or do they check the VIN for the engine size or something? Sorry, my mind works like a criminal sometimes :grin:

I searched a bit just for funsies. The throttle body between the 4.3, 305, and 350 tbi trucks are all the same, except the injectors inside the TB are different for all 3 engines, so you will need 350 injectors.

1 Like

I’m not sure it’s tat simple . . .

For every smog you do enter the vin number

And I believe the vin does indicate what engine the truck is supposed to have

So once the inspector entered the vin, the smog program will be expecting a 4.3 liter V6 . . .

Hence . . . be legal, work with the bar, and get that bar referee label


I like the buying all new sensors idea if this is going to be a really nice truck. But if it’s just going to be a knockaround town truck, that might add quite a bit of cost. Depends on how nice this rig is intended to be!

After they catch you. :innocent:. Haha!

I’m sorry, you’re right, of course!

Leaving the smog issue aside, you will always run into a number of unforeseens with any swap… Always.

ECM for one. 700R4 on the 89 and 4l60E with electronic controls on the 94. I think there are some aftermarket modules to control shifting but they’re about 600 bucks.

I am planning this swap as well but mine is a 95 v6 w/ MT and donor is also 95 but w/ 4l60e i have both complete trucks. If i need to swap ecm the manual trans will throw codes wont it? Or swap chips? Is engine chip separate from trans?

3 years later…sorry didn’t see a year on the post it just said Aug

Yes the automatic ecu will throw codes with a manual trans. There are no replaceable chips in that era truck.

It might be able to be reprogrammed but it is a 27 year old ECU so finding someone with a Commodore 64 computer to program it might be hard… only slightly joking about the computer…

A V8 swap with non computer controlled distributor and a carburetor might be a better option.

1 Like

No experience w/this myself. But transferring both the v8 and the 4L60E trans might work if you are willing to live w/an automatic. The v8 w/the original manual trans configuration is the more desirable config imo, and is probably possible, but likely requires technical expertise from somebody who’s actually done it. Surf the web, maybe you can find that person. Another idea, Google “aftermarket ECM”, ask for advice at some of those companies. See what the folks at Summit Racing have to say as well. If you can live w/just basic functionality, like no cruise control, no need for emissions testing, you might could just put some black tape over the CEL.