Does anyone know how much it would cost to change my v6 4.3L to a v8 350 or 454?

 

Depends on the cost of the motor and how much of it you are going to do yourself. Also what condition is your transmission in along with your rear diff. Adding more power your going to find worn parts and weak links quickly.

Are you planning on getting a motor and rebuilding/having it rebuilt or buying a motor ready to drop in and run? Figure out your budget, what you wanna/can do yourself and what you have to sub out. Once all that is figured out, leave yourself a buffer in your budget for extras. It never fails doing a project like this that you run into costs that you didnt think you would have. Whether it be a part you have to upgrade or replace. Or broken something or other. That buffer allows you to have that extra cash and not be at a standstill.

 

Mossy Oak is very correct! Make sure to plan on spending money you didn't think you would have to spend because regardless of the project, you're going to run into unexpected costs. I live in West Virginia, so our used parts are probably a little cheaper. For example, I bought a used 91 chevy Silverado for 300 bucks that was wrecked, but you could still drive it. It had a 350 so I pulled the motor and changed it over to carbureted by using a 87 model quadrajet intake that came on my car stock(it had a 305). This is what you have to watch because small block chevys changed in 1987. They have different valve covers and the center two bolts on the intake are straight up and down, where 86 and back have the intake bolts all at the same angle. So, I changed the 350 I had to carbureted, but if you were to use the same engine I did, you would have been able to leave it fuel inj. since a 4.3 is basically a 350 with two cylinders cut off the front. As long as you put a TBI fuel inj. motor in, it should hook up the same as your v6 did. All the 350 truck engines are the same (as far as bolting up some are 2 bolt main some are 4 bolt main but they bolt up and wire up the same way)from 1987-1995. If you could find one of these trucks cheap make sure it says 5.7 liter on the block. I don't care what ANYBODY says, if you swap to a 305 you'll wish you'd left the v6 in it. So, to give you a simple answer to your simple question that I've blown all out of proportion, you'd be best to use a 5.7 either out of 1987 thru 1995 chevy trucks, or if you're lucky, 1987 thru 1992 TBI 5.7 car engines. It could cost you anywhere from 500 dollars to 5000 dollars, you won't know until it's finished. At least the car already looks good and don't need a bunch of body work like mine does. Unexpected things will come up throughout the whole project, so it's impossible to come up with a good estimate. I've got close to 4000 bucks tied up in my car, and it's nowhere near finished. It's a labor of love. I can tell you a new 350 starts at about 1500 bucks, but this is a brand new motor without an intake, distributor, etc. A turn-key drop in carbed motor starts at about 2500. These are pre-86 style engines, but if you are willing to change to carbed this won't matter. A carburetor stays at a set setting, where with fuel injection, the computer changes air/fuel ratios many times each second with input from various sensors to keep optimum performance in any weather or elevation. I'd suggest trying to keep it fuel injected since you already have a efi car and live in such a high elevation.
The good thing about a Chevy V8 car motor is that from 87-92 they come factory with roller cams. Roller cams have more valve lift, last a lot longer, and make your engine run more efficiently and in turn the engine lasts a lot longer. 93 and up car motors are LT1 motors and are completely different. The trucks never got roller cams till 1996, when they changed to vortec. Vortec fuel inj won't hook right up to your car, so most ppl change vortecs to carbureted (you can buy a carbureted vortec intake) when they use them in a Monte. Most, not all, I'm sure somebody's got a efi vortec in a Monte, but I'd say that's a costly and tedious thing to do. Also, this is very important! If you use a 350 out of a 4-wheel-drive truck(87-95), you will have to change the piece your oil filter screws onto. It's got two 7/16 bolts holding it on. You'll have to use the oil filter adapter off of a two-wheel-drive truck or a car. Hell the one off your 4.3 might work. If it goes on your block, it's ok. It'll look way different but it'll be ok. You just have to remember to get oil filters for the engine you took the adapter off of. If you get an engine that the oil filter sticks straight down from the engine, that'll work. If you get an engine out of a 4-wheel-drive, the oil filter may be sticking out to the side, this is how mine was, it won't fit in the car that way. I wish you all the luck in the world, it's a crazy struggle but it's so awesome when you fire it up and say, wow, I did all that? Don't give up either. You'll get frustrated with it. Take a break for a day or so when that happens. DO NOT try to get in a hurry. I've seen that ruin some badass projects. This is everything I know about what you're trying to do so I hope it helps you.