Chevy 1994 V6 to V8 swap

Howdy,

Im trying to get some info for my dad on a engine swap hes doing, so im trying to post on forums in hopes to get him some help. 

Heres what he Wrote,

"I have a 1994 Chevy Truck, 2WD, with 4.3 Vortec V6 Motor. I am pulling the V6 out, and putting a V8, 5.7, 350, motor in.

I just need to know if I can use the same Harness, and just change the computer, or will I have to re-chip it.

All information is appreciated."

v6 to v8, gonna need more injector plugs at least. So no you can't use the same harness, and almost definitely for a hundred other reasons as well

Are both engines TBI? If they are, you should be able to use the factory harness with either a modded v6 computer or the v8 one.  If they are not both TBI, then you will need a v8 harness and computer. That is if my memory is correct, it has been a while since I helped a friend with this.

Chesterfield said:

Are both engines TBI? If they are, you should be able to use the factory harness with either a modded v6 computer or the v8 one.  If they are not both TBI, then you will need a v8 harness and computer. That is if my memory is correct, it has been a while since I helped a friend with this.

^ This.  Most swaps i've seen just ditch the TBI for a carburetor.  1994 should be TBI for both the 4.3 and the 5.7, so just mod the computer or swap for a V8 one and you should be ok. 

Harness works, will need chip or computer for 94 350 with correct transmission.  It's almost plug and play.  Have done it more times than i care to remember 

In reply to Patrick :

Really? wow, guess I shouldnt have talked when I know nothin bout American cars 

Most V8 wiring harnesses from GM in this era were completely different than other engine choices.

If he's going that route and still has access to a usable donor car, it might actually be MORE work to remove the TBI for a carburetor. 

Clarification.  TBI 4.3 to TBI 350 is simple.  The mounts need changed to the v8 mounts and it will bolt in and play.  The computer from a 94 350 TBI truck or van, provided you stick with the same transmission, will run it like it was always there.  If for some reason he has an older engine where the TPS plug was the wide flat one and not the little round one, the throttle body will interchange all you need is to pull the injector pod off the v8 unit.  They are the same cfm/bore.  The accessory brackets will work, the accessories work, the power steering lines work but the v8 ones are slightly shorter.  The AC line to the compressor may need changed.  

I have done 4.3 to 305, 350, and 454 tbi swaps and never changed a harness.  The 454 needed the oil pressure sending unit wires lengthened because it was at the front and the sbc/4.3 are over the oil filter.  

Howdy,

All the responses have been very helpful, The engine is in, and it seems to be getting hooked up slowly, ive just been asked to post for some more help. Ive basically typed out his letter and copy and pasted it here.

"

Good Day folks, I am attempting to fix my 1994 Chevy Truck 2 Wheel Drive - 350 motor - 4l60E Transmission . I want to switch out the TPI System for a carburetor and Regular Intake setup , What Fuel Issues will I run in to as well as Electrical as far as Distributor? Another Question regarding my truck; my truck had a 4.3 V6 Vortec Motor , I put a 1990 5.7 350 V8  Motor in my truck , If i put new Intake and Carburetor in my truck -plus change Fuel Setup ,  CAN I still Run Same ECM computer from my Vortec V6 Motor in my Truck  

Answers are appreciated

Thanks The Outside World  

The Soss

"

Going to need a transmission controller and an older distributor.

So I have a 93' 1500 with a 4.3l and a manual tranny, I'm trying to put a 396 (402) into it and it seems to not fit correctly. What do I need to do to the frame or what do I need in general to make it work? 

In reply to ralph_jr26 :

You need to remove the V6 engine mount pedestals from the front crossmember. They're just bolted on. Then bolt the V8 mounts into the existing holes in the crossmember. No drilling or modifications needed. 

Cousin_Eddie (Forum Supporter) said:

In reply to ralph_jr26 :

You need to remove the V6 engine mount pedestals from the front crossmember. They're just bolted on. Then bolt the V8 mounts into the existing holes in the crossmember. No drilling or modifications needed. 

Yeah this. Motor mounts on the frame side, bolt it in. If you don't want headers get new manifolds and Y pipe for a 90 454SS. Same for the motor mounts. 

Gmt400 are like legos. 
 

assuming carb, take the lines that went to the throttle body and cut them at the firewall or reroute to the inner fender and install a return style fuel pressure regulator and feed the carb.