Alright so I have a spare 4.3 out of a 95 Jimmy and looking to do a rebuild. I'm going to make it carbed first of all. Also going to get a master rebuild kit from RockAuto. I'd like to make it a bit beefier, nothing super fancy. Going to get the 96+ vortec heads for it as well as I know they have good flow. I'd like to get about 300hp out of it if thats not too much. With leaving the heads, crank, piston and rods stock, would this be possible? Whats a decent cam that could help? I know forged piston/rods/crank are a good choice but not really in the budget. Going to get it bored out .030 over as well. Any other ideas to help, or am I asking for too much?

 

I've been researching the topic a bit and found out that it would be hard to get over 300 hp out of the 4.3 but should be doable.
The cam would have to be at least a medium with lots of duration and lift. This will put the max power rpm way up the scale. In order for that engine to last you would have to rebuild a lot of stuff.

In a couple discussions with my engine shop we came up with these solutions. (For the 1994 with balance shaft - keeping all appearances original)
In your case you can go carburated which will make the build a lot easier.

Tear the complete engine apart. Clean and work all bores for water open to specs (get rid of casting ribs and stuff). Do your fancy on it for appearance if you like. Remove all ugly cast edges, smoothen edges and stuff. According to the rods you get you may want to work the block open eventually do this now in the first tear-down if you plan to enhance later on.

Crankshaft - for serious hp you either have it inspected for cracks or get a serious crank (could be difficult but there are some). Balance it to PERFECTION. (Static in this stage - later on with rods and pistons and flywheel dynamically - depends on your engine shop.) A stroker could add a bit but that has to be planned with the relative head. (Increase in compression.) And is weakening a crank if ground into an existing. Might just make things complicated - I would not go for that.

Bore - Boring over an engine with a 4" bore by .030 is a possibility. My engine shop guy meant that it would be better to go with the minimum bore-over required that gives you the option to bore it over again if need be. As you already have a 4.3 making it a 4.5 does not add much hp if the rest sucks. If you do a complete and nice build then this will be an addition.

Rods - Now it comes to spending money. If you want 300 hp spend it in rods in the crank and in the pistons. These are the parts that should never break in any build. If you blow head gaskets and such - not much money. If you break something in the block most probably you junk it afterwards.
Most V8 rods should work on the V6 as well. This is true for my 1994 not sure about the 1995/1996 thou. You have to check.

Pistons - We came up with a compression ratio of up to 8.5:1 eventually 9:1 for reasons of fuel. This should enable it to ride with a 95 ROZ fuel without additions eventually some Premium gas of 98 ROZ. (These are the most common fuels in Europe). Think "knock" when deciding about going fancy with the compression ratio. Lightweight is what I would look for and race pistons, forged or such for higher thermal and mechanical loads.

Cams - If I ever have time and money again for a build I'll put a mild cam into my spare engine. For the build you have in mind it may go to medium, depending on how aggressive it should become.

Heads - Not sure on what heads would fit the 95. You said you have the 96 Vortec heads. They should work. Again the grinder tools on the heads. Port them and match them. Don't forget to rework all water and oil passages. Valves - guides - springs - rockers etc. You choose how far you want to push it. Make sure the cams lift does not exceed what you can fit when going crazy with the rockers. Bigger valves? Roller rockers? Go figure it out with your engine shop.

Headers - This could add some hp. Don't go overly crazy on the exhaust side. Nice headers should do the job. Depending on the vehicle the engine gets put into you may have to change additional things. No catalytic converter? Street legality on emissions? Noise? I know that the 94 S10 Blazer does not neet ANY bigger thing after the headers. GM has put in the V8 exhaust and cat. So no need to fumble with things which need no fumbling. Have the headers fitted with access holes to all 6 cylinders exhaust portion for EGT and O2 measurements if possible.

Ignition - Get a good electronic ignition which is programmable. You will spend quite some time on the dyno for the carb and ignition. Check if it can be matched with a knock-sensor. Knock sensor calibration for the new engine needs to be figured if you want to be on the safe side.

Plenum/Spider - There are a couple workable things to match the heads to the carb or the carb to the heads. Edelbrock has some options but limited.

Additional thoughts
Lifters and studs are important too. Do you want to go all roller? Stiffer? Choose in accordance to what you will do to the heads (valve springs determine studs and such.)

The water pump should be rebuilt or new. You're not going to put junk stuff into a built engine. Think size and coolant flow depending on how crazy you go you have to get rid of the heat.

The oil pump is the same. A very vital part of any engine this one now has to cope with higher rpm, higher loads, eventually higher temps. Rebuild or get a new one. Depending on your budget think dry sumping the engine.
Oil spray cooling the pistons could be an addition as well. May help in the high hp ranges against knock as you can cool the pistons.

Oil cooling and oil quantity. At least get the towing kit with the oil-water heat exchanger core and external oil filter. Or plan for an external oil cooler and add at least 2 - 4 quarts in quantity to the meager 4 quarts of the original. You want to keep this cool and available in large quantities. Mind that my Alfa Romeo 2.0 has 7 quarts out of the factory but it outputs 130 hp at 2.0 litres displacement. (hmm - makes 122 cid).

Stripping - Stip the engine of all unnecessary stuff and make a plan on where to tap into the engines cooling for the heating.
Get rid of the A/C compressor.
Put a high capacity battery into the car this eases the load on the alternator.
Get rid of mechanical fans if equipped and convert to electrical fans. If possible add a two fan shroud to the radiator with staggered temperature switches or variable speed depending on coolant temp.

It might work out to put an electronic injection/ignition onto this engine. As it behaves as a V8 just missing 2 cylinders it could work out using a V8 map for the same kind of camshaft and flow numbers of the head. Edelbrock might work. The advantage would be tuning and knock control.
Electronic Fuel Injection - Introduction - Edelbrock, LLC.
Heat shields for the spark plugs and wiring.

Chevy 4.3L 262ci V-6 - Engine Build - Overview - Tech - Hot Rod Magazine

Performance & Brainstorming - Blazer Forum - Chevy Blazer Forums
https://blazerforum.com/forum/perfor...ot-gets-82914/

Just my 2cents worth of thoughts after 20 years of blazin. Hot rodding the 4.3 V6 could be done in all ways from 180 - 320 hp. Everything above 200 hp won't be for the faint hearted and those with small change only in their pockets.

 

Thanks for your input, I did some researching and found that going for 300hp is a bit out of my league. Maybe 250 then? I went on edlebrock and looked up the intake manifold compatable with the Vortec heads, it recommends the Performance Series 500 cfm carb and their Performer Plus 2112 camshaft. With proper tuning, the boring, a good exhaust, and a few other odds and ends, would 250hp be more possible? I might do a turbo down the road, but with that I would get all better stuff for the bottom end.

 

Is this vehicle still going to be street legal? If so you may run into some serious problems getting through emissions testing with everything your going to delete to go with a carb. If its for, off road only have at it.

 

Idk what I'm going to do with it. Anything from putting it into a truck, a car or buggy. Don't know if it will be street driven or what. Just seeing what I can do.

 

Ok, just asking. In Jersey where I'm at I know they would trow a fit if any or all the emissions controls or sensors where to be eliminated. Seems they forgot what Keep It Simple Stupid means.