4.3 in 71 getting 19 MPG?!?!?

[iluvmy72]

OK....my friend put in a 1989 4.3 with a stock throttle body into his 71 LWB truck and he says he's now getting over 19 MPG on the HWY. Is he lying?! He said he also has great power. He also bolted over the 700r4 tranny as well. The engine is stock except for the headers. Has anyone else done this and has had good luck with gas milage? I'm thinking of putting in my 4.3 engine from my 88 astro into the truck. The engine and tranny were rebuilt just 3 years ago.

[farside847]

I guess anything is possible... Is the 4.3 a v6?

[70 shorty]

I don't doubt that for highway only mileage. I'd say to see how good the 4.3 in your Astro does and I would assume the truck would be about the same. I would say it probably has acceptable power especially if you're used to v8's but I wouldn't say it has great power. then again, why dont' you just ride or drive in your buddies truck and see for yourself.

[67ChevyRedneck]

There was a member here (scooter67) that had a newer fuel injected V6 in his 67 truck and he claimed to get 22-23 mpg highway, which is totally believable because new silverados with the 4.6 are listed at 16/21 for the automatic. You take away all the smog crap and catalytic converter and 23mpg is totally possible. With no fuel injection 19-20 seems about right.

[Ochre]

Also the ?92-93 - somewhere in there 4.3 motors were the beginning of the vortec technology later implimented in the 5.7's in '96, so if you get one from that year range they've got more HP/TQ than earlier years without much (if any) change in mileage.

[Palf70Step]

Originally Posted by Ochre

Also the ?92-93 - somewhere in there 4.3 motors were the beginning of the vortec technology later implimented in the 5.7's in '96, so if you get one from that year range they've got more HP/TQ than earlier years without much (if any) change in mileage.

92 was the change for the 4.3. I had a 92, 5 speed avearged 18-19 in town (AC always on in Mississippi)...Normally 22 on the road. What amazed me was when I was in Colorado springs, it would average about 24-25 in mixed driving. The truck loved the mountains and not the flatlands. Mine was a SWB regular cab. I towed occassionally with it, but the 5 speed/clutch combo behind the V6 won't take towing for long. To me it is a great daily driver combo, but also remeber with or without cats and polution controls, our year trucks are aerodynamic bricks, while the 88-98 years are much more air friendly and it does make a difference, especially at highway speeds.

A friend of mine around same time had one in an extended cab with automatic and loved it. But he most just haul a-- and what ever game he shot. If I was looking for a different daily driver I would look at a SWB with one. To me they are a great balance for everyday use and the occassional I need a big trunk or truck thing.

[joerocks]

believe it or not but i went to Miami over the weekend with my 04 Z71. I was getting average 23MPG @ around 65 or 70 no matter what gas i ran. I never really checked it before because usually my trips are between here and KY thru the mountains and i can't get a good reading there too much up and down to know for sure but i was really surprised-joe

[edmonton72]

My dad had a 97 extened cab shortbox with a 4.3 and a 5 speed that got like 26 on the high. I think the truck had 3:73 gears in it. It's even towed a 5000lb. 30 foot long trailer. He ended up selling the truck to my cousin who ruined it by putting more leafs in the back, taking offroading and damaging it, now he wants to put a locker diff in it. now the truck sits at my cousins place because he bought a cocge and doesn't use the chevy anymore. If he din't wreck it my dad would probably buy it back and I could drive it while my truck is being built, It was a good truck though.

[Mudder]

I have a ZR2 with a 4.3 auto. The very best it will do on the highway is about 17mpg.

[67ChevyRedneck]

Originally Posted by Mudder67

I have a ZR2 with a 4.3 auto. The very best it will do on the highway is about 17mpg.

I was seriously looking into buying a ZR2 last year (looked at about 5 of them and test drove 2) but I did some online research and found they get similar, sometimes worse fuel mileage than a fullsize. My Z71 (5.3L auto) conisistently gets 18 maybe a hair more hwy and 15 city. Being fuel mileage was no longer a factor I opted for a fullsize. I also have a friend with a 99 silverado 2wd reg cab short box 4.3L auto that gets 21 hwy with his and says he averages about 17. Pretty dang good. I'm sure it has a lot to do with 2wd vs 4x4. A stock 4 banger S10 (2wd) can only get 27hwy and an s10 with a V6 (the 4.3 2wd) should get about 23 hwy, I'd be very suspicious of a 26 mpg 97 fullsize, speedometer could be off. Could be somehow possible, but highly unlikely. sorry

[tomatocity]

IMO 4.3L engines get better gas mileage with manual transmissions vs automatics. I have one in a 1993 S10 4L60E and it gets 20-22 on the freeway with cruise control. Around town or mixed driving, the lock up TC seems to suck the gas mileage out of my truck. It trys locking up at 40 MPH which is a common driving speed. My 4.3L TBI is not big on low end power. Headers might help.

[redhead69]

My 98 zr2 is right around 17 too..

[Frank_Zeller]

I'm getting 18.5 highway mpg with this combo in a 69 SWB with AC on.
I do have a vacuum gauge that I try to keep above 10 mm hg

1800RPM at 70 mph

3.08's and 28 inch tire. 70 series tires.

Trans
700R4 with lockup converter

Engine specs.

1995 GM 305 crate motor with Edelbrock SP2P intake, 1976 800CFM BOP Q-jet with 2 inch 4 hole spacer, 1 5/8 full length headers, recurved HEI with MSD6A. Has thermo fan clutch. 195 F thermostat. Set up for lowend torque and to run on 89 octane.

Truck is lowered

[LUV2XCLR8]

Wife's 99 trailblazer gets 18 C / 21 H and it's a 4dr 4wd

[Jason915]

Originally Posted by Frank_Zeller

I'm getting 18.5 highway mpg with this combo in a 69 SWB with AC on.
I do have a vacuum gauge that I try to keep above 10 mm hg

1800RPM at 70 mph

3.08's and 28 inch tire. 70 series tires.

Trans
700R4 with lockup converter

Engine specs.

1995 GM 305 crate motor with Edelbrock SP2P intake, 1976 800CFM BOP Q-jet with 2 inch 4 hole spacer, 1 5/8 full length headers, recurved HEI with MSD6A. Has thermo fan clutch. 195 F thermostat. Set up for lowend torque and to run on 89 octane.

Truck is lowered

He has the right idea build a mild 305 it will get just as good mileage as the 4.3 and it will sound better!

[TP from Cntl PA]

You want awesome mileage drop a small Diesel in it.................It will blow the 4.3 away preformance wise and do alot better fuel mileage wise.

[68 Stepside]

My friend has a 96-ish swb ext cab C1500. It's got a 4.3/5spd, and he pulls down an honest 25 MPG all day long. Blew me away.

[68haywagon]

I think it depends on how you drive it. My dad's 93 4.3l 4l60E (which I think was the first year for the vortec, listed on the window sticker as vortec) is good on gas when you baby it. I drove it like I stole it and gas milage sucked. Highway if you push it over 65 forget about milage...pushing a brick with that engine over 65 makes it thirsty. I think it would be better on gas with the 5 speed.

Mike

[iluvmy72]

wow.....what great insite you guys have given me....and none of it negative!!!!.......I guess I know what I have to do.......She's going in!!!!!!.....After winter.

[jamesi20]

I've got a neighbor who is 87 yrs.young,really a pretty cool guy who has seen a lot and done a lot in his life and still doin neat stuff,called me tonite lookin for a hydraulic fitting for a log splitter he's making...anyway,he told me once and I never forgot it that "even the most honest people in the world will fib about two things,gas mileage and how long it takes them to get somewhere"

[chevybill]

I have a 7.3 turbo diesel international that will get 22 on a highway run as long as it is not loaded, just the truck and this is with 3.73 gears and a 6 speed manual with overdrive.

Actually, the 4.3 in that truck should top 20 mpg if driven right.

My 94 z 28 will get 25-27 on highway if driven like an economy car.

[iluvmy72]

now here is a funny question.....why doesn't GM have the 4.3 as an option for the Colorado?

[68haywagon]

I think they are trying to phase out that motor. The plan is probably to put the inlines in the new gen trucks. Thats just my guess.

Mike

[70rs/ss]

Originally Posted by 68haywagon

I think they are trying to phase out that motor. The plan is probably to put the inlines in the new gen trucks. Thats just my guess.

Mike

Yeah, the Coloradoes and trailblazers get either the in 6 or the small V8. I have an 05 Yukon XL (Suburban with the 5.3 and I pull 20-21 on the highway, so that kind of milage out of a V6 is believable. Do the swap you have all you need and it is easy as dropping in a V8. Let us know, the V6 is kinda like the plague at bone yards so they ought to be cheap!! I personally wouldn't put anything under a 350 in my truck, but a $3= a gallon a V6 is looking beteer and better.

[Yamaha74]

I had a 2003 ZR2 and it was consistently getting 16-17 miles to the gallon on the highway. Pulled a 2800 pound enclosed trailer once and got 9.5 mpg. The next week I traded it in for a 2003 GMC Sierra 5.3 litre 2wd and it is getting 18-19 on the highway and around 14 pulling the trailer. Yes I gave up 4x4 but I have a lot more power and room now with the full size. Plus with a 6 month old kid there is a lot more room in the extended cab of the full size then the ZR2.

My wifes 2004 trailblazer 4x4 is only getting 15-16 mpg in the city and have taken it on one small trip that was 75% highway and we only got 17 mpg. It is supposed to get 16 city and 21 highway. It has the 4.2 litre inline 6. I am not happy with the gas mileage at all.