I have a 85 Monte Carlo fuel injected 4.3/v6 I am looking to swap the engine and tranny for a 383 stroker and th400 tranny. I have never done a engine swap before. I am really confused as to the ecu and wiring harness were do I get the ecu or wiring harness from a ss? Please help!!!

 

Unless you are required to I'd just do away with the engine harness and ecu, toss a vac advanced distributer and non computer controlled carb good to go

 

If I was to get rid of ecu completely and wiring harness what all would i have to wire back up to work? Tail lights, radio , headlights, etc ? Is it as easy as removing the ecu and harness and dropping the engine in and go?

 

If you are serious about doing this you will need

New engine, mounts, transmission, tranny mounts, wiring harness, ecu, rad, possibly new rear end to handle the upgraded power, new front suspension (meaning shocks and such as the new motor will be heavier and your current suspension may not handle it), but the time the dust settles you would be further ahead to sell your car and buy a car with a v8 already in it.

Anything the V6 bolts to, and anything that bolts to the V6, will be different than the V8. Only possible exceptions are AC compressor (but the hoses and brackets will be different), alternator (early V6's were different, and again the brackets & wiring are different anyway), and power steering pump (guess what - the brackets & hoses are different).

Forget about using any of the factory-type V6 exhaust on the V8. This is a perfect opportunity to upgrade to headers and high flow cat on back. Otherwise, use the donor car pieces.

If you are doing a computer-controlled swap (which is the only emissions-legal way), the engine control module (ECM) from the V6 won't work without modification. Use a V8 ECM, change the PROM, or have the computer reprogrammed.

The V6 tachometer has a different resistance than the V8 tach. You can change the resistor, but it's typically easier to just get a V8 tach.

If your car has auto tranny and AC, and is intended to be driven on the street, use V8 front springs and sway bar. Otherwise, you'll be bottoming out the suspension regularly.

Most likely the V6 power steering gear will be fine. Just remove the pressure & return hoses from the gear and attach the V8 parts to it. There are some performance steering gears out there that the V6 probably doesn't have, but your donor car probably doesn't have it, either

If the V6 is fuel injected and you are putting in a carbed V8, the fuel pressure will need to be lowered using a 3-port (with return) adjustable fuel pressure regulator. Or, drop the fuel tank and remove the in-tank electric fuel pump. If you keep the electric pump, an oil pressure switch can be used to power the pump. Depending upon the V6, you may have to rewire the in-tank pump when the ECM is disabled. Also, if you eliminate ECM control and have an overdrive auto tranny, you will have to make provision for the torque converter clutch lock-up.

For the amount of work involved, it is easier to just buy a new car with the v8 already in it, plus for what you would pay in finding all parts required, as most donor cars aren't in the best condition to begin with or you would be putting it on the road.

 

Ok thank you for the very detailed post there. I'm not looking to run power steering! I have all hotchkins suspension set up for front and back. Looking to run a ford 9" rear end in the near future before i buy the engine. I just bought a digital gauge set up from Dakota will that work for the tac? This engine is a turn key 383 I'm looking to buy . You said if i wanted it to be emissions legal i would need the computer what if i don't care about the emissions how would i install the engine that route ? Without the ECM?

 

the 4.3 is the same thing as a 350 but just 2 cyl. missing. same brackets. same tranny even same exh.

 

It wouldn't be a hard swap. My 84's got a 305 (same casting, different machining) as long as you've got the clearance (or can make clearance) in front, it should be easy. The mounts may be different. As far as the ECU, You're talking about a 1985, it just controls the engine. if you go with a hei distributor and a carb (I would) your key will turn the ignition coil on/off and bump the starter. Also hook up your oil and temp gauges. A stock tach (on a V6?) would probably read +33% until you corrected it. I think the engine swap would be fairly simple. if the stock exhaust is small, you might upgrade.
The original transmission would bolt up, I'm not so sure about holding up though if that 383's built. as long as the TH400 will fit, it will work. you may need to have a driveshaft customized if you cant find one the right length with the right yokes. you also may need to slide the crossmember back or forward. As said before you would need a lockup kit with most overdrive (should be a latch that also is broken if the brakes are pressed) but you said TH400 which isn't overdrive.
My two cents. If you found a 383 from a competent builder, and you feel like going fast, go for it.