4.3l vs. 5.7l in a commuter truck

[JCampbell]

Just thinking out loud, so to speak. I recently picked up an ’84 short bed to drive back and forth to work in (60 miles round trip). It currently has a carb’d 305 that runs like feces. Instead of screwing around with the computer controlled Quadrajet, I’ve decided to swap in a TBI engine from another truck. My default was to source a 350 from another donor truck, but I got to thinking about a 4.3l out of an Astro or S-10.

My question is two fold:

1. For those of you that have a 4.3, how do you like it? We had an Astro a few years back that got around pretty good, but I don’t really know how that would translate into a truck. I’m assuming the curb weight is about the same.

2. What kind of mileage could one expect form a 4.3l/700R4/10 bolt w/ 3.08s? How would it compare to a 350/700R4/10 bolt w/ 3.08s? I’ve read that while 20mpg (highway) is not unheard of with the 350, 14-15 is a more realistic figure.

What I’m looking for is a truck that has a reasonable amount of power (able to get out of it’s own way), gets reasonable fuel mileage (anywhere from 14-20+ mpg) and is relatively easy to maintain (TBI).

What I don’t want is a dragster that gets crap fuel mileage numbers (-12 mpg) that is a constant maintenance issue (carb).

It’s not a tow rig and it’s not a hot rod. For all intents and purposes, it’s a commuter vehicle with a trunk.

Converting to TBI is not the issue here. The issue is what displacement will yield the best results.

Any thoughts?

Frame of reference:

[foamypirate]

My honest opinion would be to do the 350. I just did a TBI 305 conversion on my 84' that has 3.08s. I would call it adequate for a truck that doesn't tow, but I would hate life with a 4.3L. The 305 has a hard enough time passing or overtaking as is. I don't think the mileage is that different between them either. I pulled down about 17.5mpg highway in my 87' with 3.08s (the truck the 305 in the 84' came out of) over about 300 miles. I can't see a 4.3L doing much better. You'd probably be waaaay under-geared.

[wyattglock]

I had a 2003 GMC Sierra 1/2 ton extended cab with the 4.3 and 4l60E. Granted it was a better injection system, but even with a 5000lb truck I got 22mpg with 3.42 gears. If you are running the 700r4 and have a well tuned engine, I don't see why you couldn't see similar numbers in your truck. It will be a dog off the line, but then if you are looking for reliable, daily driver traits, it will be hard to beat.

[foamypirate]

Originally Posted by wyattglock

I had a 2003 GMC Sierra 1/2 ton extended cab with the 4.3 and 4l60E. Granted it was a better injection system, but even with a 5000lb truck I got 22mpg with 3.42 gears. If you are running the 700r4 and have a well tuned engine, I don't see why you couldn't see similar numbers in your truck. It will be a dog off the line, but then if you are looking for reliable, daily driver traits, it will be hard to beat.

3.42 vs 3.08s will make a huge difference with that motor though. At 3.08s, the 4.3L is just waaaay out of its power band, especially the older TBI models.

[JCampbell]

That's easy enough to remedy. I can get a 3.73 rear off Craigslist right now if it will yield a substantial enough gain in performance.

http://inlandempire.craigslist.org/pts/3226487224.html

[mrhino]

My vote is for the 350. The v6 would only yield a very small difference in fuel mileage, (if any) however the 350 would out power the v6 and in theory not have to work as had to get up to speed especially with 3.08. Not to mention I believe a 350 would be cheaper to build than a 4.3. just my own thoughts

[Jonboy]

I bought a 2001 ECSB with a 5.3 in 2003, and my buddy bought a 2003 RCSB with a 4.3 at about the same time. My 5.3 truck had more power and got better mileage. I am pretty sure mine has 3.42's in it, not sure about his. This might be apples and oranges to your truck. I think I would go 350, especially if you already have it.

[JCampbell]

I get what you’re saying. Like if a 5.7l is working at 60% a 4.3l would need to work at 80% to do the same thing.

[Pyrotechnic]

Honestly, a 5.3L and 4L60E would be your best bet for mileage and it fits the description of what you want. With the lighter weight of the older trucks, you should be able to get at least what new trucks get if not a little better.

[mrhino]

Originally Posted by Pyrotechnic

Honestly, a 5.3L and 4L60E would be your best bet for mileage and it fits the description of what you want. With the lighter weight of the older trucks, you should be able to get at least what new trucks get if not a little better.

I put a stock 5.3l in my last project "Silver dollar" and it got 15 around town and 18 on the highway. pretty much what a stock 99-0? gets. Ill let you guys decide if thats good or not

[Vbjunker]

I have a commuter truck with a 4.3 liter and a 700R. Not sure what rear end. It is a 1987 GMC step side, bare bones work truck. I bought it for the classic look and the simplicity. My daily ride is 40 miles round trip. I get 16 to 20 mpg depending on traffic flow. 2 1/2" exhaust, full flow cat and thrush welded muffler.

When I bought the old gal a month or so ago, I figured I'd simply live with the 4.3 while building the perfect 5.7. That may happen one day. For now I am enjoying what I have. It merges and accelerates adequately, has a nice rumble, and cruises nicely at 60-70 mph. I'd have to say I am pleasantly surprised with the 4.3.

Do I still want to race? Yeah, but I have another car for that.
Posted via Mobile Device

[D13]

I had a 1990 W/T with the 4.3/700R4/3.08's, run 235/75R15's on it to keep it in its power band. Would not go over 100mph, but then again it's a truck (I was younger and stupider then). 18mpg mixed, 21-23 highway, 217,000 miles, had to replace the alternator and rebuilt the trans at 195,000. Had to sell it when the 2nd kid arrived. Guy who bought it used it to haul drywall for his house, was so impressed that he fixed it up and kept driving it.

I traded my 1990 454SS for it. Best move I ever made. Towed trailer with C20 around, loaded it, etc. Communted up to 200 miles a day with it. If you tow, slow down and run in D (4th clutch is weak on a 700R4). If you over load it slow down. But in the end it's a 350 wit 2 holes missing, and the power and mileage adjusted accordingly.

[Keith Seymore]

I'm happy with my 4.3. Gets about 20 mpg usually, 22 if I baby it. 4.3, manual overdrive trans (.73 or .70:1), 3.73 gears, P235 tires. I use it exactly as you have proposed; mostly back and forth to work, with some occasional light hauling or trailer towing.

It moves out ok, and will go as fast as traffic will allow.

The only downside I see is that it has a little bit of a vibration at idle - and - you don't get that V8 sound....

K

[LEEVON]

If you wanted to get radical about mileage swap in an NV3500 5 speed with the 4.3L. We had a '92 silverado with that combo that could get 20mpg. I remember a trip across the plains where every tank of gas lasted 500 miles!

[JCampbell]

Loving all this input. Thanks!

[manimal]

I would vote for the 4.3 as well. 350's are like buttholes,everyone has one. Besides,if later you want more power,you have PLENTY of room for a hairdryer!

[manimal]

"OR" if you want REALLY good mpg and NO SMOG EVER! get a 6.2 for your truck. In my '82 1t I got 19/21 mpg and it had 4.56's! No more spark plugs,cap,rotor,plug wires,etc....no more smog! will run on almost anything. The only thing you'd have to wire in would be a glow plug controller.,uses small chevy mounts and pretty much drops in.

[gchemist]

I drive a ZZ4 in my truck. 13-15 MPG in the city. 18.5 on the highway. The ZZ4 is a performance motor. It's about torque. Above 1500 RPMs, it makes 300+ ft/lbs of torque.

4.3 use a 96 or later with an updated FI. My 4 door Jimmy weighs as much as our trucks. 16-17 city, 21-23 highway, 20 MPG at 80 MPH!!

On a 350, I would swap a cam on a 96 and later Vortec with a carb. Great power and great milage.

[chebyshortbox65]

For what you want I'm for the 4.8 5.3 swap its easy cheap almost 300 hundred horse stock you can pick them up dirt cheap and get good mpg I'm running 5.3/700r4 in a 81 and get 20 plus running from palm springs to bloomington most everyday it hauls ass is a ball to drive sounds good what can get better I do these swaps for people full time and I have yet to have someone regret doing it oh and that 20 mpg is with the a/c blowing 40 and the cruise set at 80 just my .02
Posted via Mobile Device

[JCampbell]

How does that 700r hold up behind it?

This guy seems to have a pretty good thing going on:
http://www.pirate4x4.com/forum/showthread.php?t=1012735

[chebyshortbox65]

700 holds up good just run an 87 up or swap to the bigger pump and internals and your good as long as you don't hot rod it the stock 700 should be fine.
Posted via Mobile Device

[chebyshortbox65]

You can get a ls on craigslist for a under thousand there's all kinds on inland empire the harness is easy to modify ecm cost 75 bucks and your stock power steering lines fit the pump truck a/c compressor fits in the frame just run a express van compressor
Posted via Mobile Device

[legendman]

Originally Posted by manimal

"OR" if you want REALLY good mpg and NO SMOG EVER! get a 6.2 for your truck. In my '82 1t I got 19/21 mpg and it had 4.56's! No more spark plugs,cap,rotor,plug wires,etc....no more smog! will run on almost anything. The only thing you'd have to wire in would be a glow plug controller.,uses small chevy mounts and pretty much drops in.

Another vote for a 6.2, I have basically the same truck with a feeble 305 in it with a th350, hopefully to replaced with a 6.2, banks turbo and 700r4

[manimal]

With an LS you have to get it smogged to the year the engine came out of...OBD II...more crap than it's worth IMO.

[chebyshortbox65]

Not really there is less on my 05 5.3 in my 81 then factory it was easier to smog with the 05 then when I bought it you have charcoal canister,tank pressure sensor cats and o2 and other sensors no egr valve or anything its not everyone's cup of tea to do this and not everyone can do it but I wouldent knock it because its not your thing there is a lot to be said for hot ridding something the old school way and doing it your self without buying high tech parts and Making it all your self its hot rodding at its best and playing the game with the law and winning plus how much money does it take to build a 350 horse 350 and be able to get 20 miles a gallon and be dead reliable
Posted via Mobile Device