Gmc 305 v6 mpg?

[thirdstreettito]

What kind of mileage does a GMC 305 V6 get?

[Corts60]

You can expect anywhere from 10-12 mpg. And just like any big block, they get that whether you are towing or empty. This past summer I got 12 mpg in my '60 suburban towing a 12 foot camp trailer and all stock with the one barrel holley and 4-speed.

[thirdstreettito]

Any way to get better mileage out of one?

[RockTonka]

Originally Posted by thirdstreettito

Any way to get better mileage out of one?

HEI conversion could help a bit...

[Iroc87]

Ever thought of stroken a 4.3L maybe get you closer to 15-17

[thirdstreettito]

I'm asking because there is a 65 GMC Longstep with a 305 V6 freshly rebuilt for $2000 a few miles from me.

[padresag]

change to higher gear ratio in the rear axle. o/d trans,
advance adaptors make a nice o/d unit to put in front of a sm420-365 4 speed. your looing at a few dollars though, but if you put on enough miles then it starts to pay for itself
ron

[awbrown]

I would change to a dual jet carb ,the primaries on the Rochesters got great milage.. You would have to make an adapter but I think it would be worth it ...

[MusicMan70]

I put a New Process MY6 NP440 A833 into my 1961 Suburban. I did it the way Classic Trucks article spelled out. I have a 305A with stock ignition, Holley 500 two barrel, K&N Filter and dual exhausts(2.5") wth an x-pipe and Hooker Aero Chamber Mufflers. My stock rearend has 3.92's. At 65mph my tach reads 1750-1800rpm's in overdrive.......

Mileage? Hmmnnn, I have not quite accurately figured out. A very rough estimate would be 14-16mpg...maybe higher. Again, I have just started to drive it. It had the SM420 and you can see the relocated position on the hump. I also liked how the engine does not seem to be straining at freeway speeds as it used to with the tranny.

[Surfdaddy]

I get 9-11 with the stock configuration, 305 4spd Hydra-Matic 410 gears and 28 inch tires. The only thing I canged was to Petronix ignition. The P.O documented every trip he took since new and it seems to have gotten about 10 with a 10ft cabover camper. Lately though my milage seems to have gone down a lot. Maybe time for a carb rebuild.

[chevy_man5]

Looking on Jolly's website, for performance, he recommends a Holley 500CFM (4412) and the HEI out of a 78-79 Buick 3.8 V6. He doesn't specify that it will help mileage, but the HEI shouldn't hurt, and ought to help in the reliability department.

Here is the link.

http://www.6066gmcguy.org/performance.htm

Hopefully that is OK to post!!

[HEI451]

"HEI conversion could help a bit... "

Actually...NO, it won't in most instances. There is only one case where an HEI would be better over a well set up set of points, that I can think of, and that is when the points are worn, retarding the timing, and/or, they have dirty contact faces, dropping the line voltage to the coil.

The best benefits ANY electronic ignition has over points are, no point degradation, which gives steady output, no rubbing block wear, which won't change the timing as the wear continues, and, once set correctly, no changes, greatly reduced maintenance.

What SHOULD help the engine to get better mileage would be to carefully re-curve ANY distributor type, points or electronic, to better work the engine.

And, YES, an HEI will increase spark plug firing voltage (drop-in type systems do not, they are NOT HEI), and a spark plug gap of .045 should be run with an HEI, but, IF the engine was right on with curve, jetting with a point distributor, don't expect much from any electronic system over the points. If the engine picks up with an HEI over points, find out what is wrong with the other factors in the engine, and fix 'em.

When I built the small body HEI for my 1964 1 ton Chevy flatbed 305E V6, what I saw that needed the most attention was the vacuum advance and mechanical advance curves. VERY utilitarian, and not very mileage friendly. Consider the engine usage, it was designed as an industrial engine, and adapted for vehicle use. Mileage isn't a large consideration on a large stationary water pump in a field.

In the mix for long term into the future modification for my 305E is a full tuned port Holley EFI. That should lift the mileage a couple of MPG< but, still, it ain't a 2.8 V6, it is a large bore fuel hog.

[Surfdaddy]

I would look at the truck and see what it's like, and get it if you like it. 2k for a truck with a rebuilt engine is not bad, depending on what the rest of the truck is like. These trucks were kind of hard on gas, but most of us don't drive them lots of miles all the time anyway. If the motor's been rebuilt you may never have to mess with it for the rest of the life of the truck. Very durable and not what's in everyone's truck. If the truck interests you then don't let the type of engine keep you from getting it. It's a very dependable powerplant.

[Surfdaddy]

On a side note. Wow, at least 3 60-61 GMC's responding, I have hood envy!!! Can't seem to find a decent 60 61 hood to save my life. Mine is so rusted that even though it's straight it's not worh fixing and all the one's I have looked at (3 of them) are just as bad only dented.

Sorry...I didn't mean to go off on a tangent or hijack the thread.

[T Herder]

HERE'S MY MILEAGE INFO FOR WHAT IT'S WORTH!
I completely rebuilt my 1965 305E with some major improvements. I'm running a Mallory Maglite distributor, 1988 GM Throttle Body Injection, SM420 with a married Gear Vendors OD, divorced NP 205 transfer case, 4.56 final drive gears, BFG All Terrain 35's, plus a few other things.
I LOVE IT!!! After sixteen years I still have not had to touch the timing or distributor, TBI, or controls.
I work this truck hard, sometimes very hard. I regularly tow a custom Sundowner 4 horse trailer with a GCVW of 18,000 lb. Log book verification shows the best mileage empty has been 18.61 MPG, worst, 7.2 MPG has been with a max load and pulling 21% grades in 4WD.
Average towing mileage runs 12.5-14 MPG, non-towing with a light load has been 14.8-16.4.
If you need some more info let me know.
Best regards,
Butch

[Corts60]

hey Butch,

Do you have any photos of your set-up? I would love to go with TBI on my V-6.

[T Herder]

Here's the only one I currently have, computer crash took the rest.
Best regards,
Butch