Awful gas milage.

[Obwonkonobe]

Ive had my truck for a couple years now as a daily, and I’ve defiantly done a lot to it. Mostly for performance but always with Milage in mind too, but I can’t seem to get anything acceptable. My setup is a 78 single cab short bed, stock remanufactured bottom end with some completely rebuilt vortec heads, a hair over 9:1 compression, running on 87 octane with Doug thorley tri y headers, an Edelbrock dual plane air gap intake, an MSD Atomic efi throttle body unit, gm hei distributor with an msd street fire cdi. I’m running 14 initial and somewhere around 36 total with it all in by 3000, and cruising I see roughly 14.5:1 afr on the gauge. I have a stock 700r4 trans that I had rebuilt, open 3.08 gears and 30 inch tires. I don’t have lockup enabled because unfortunately my builder cut out all the wiring for it (I know, I’m pissed too), but I went for a 20 mile street cruise today and was light in the throttle and got 10mpg on the nose going 45-50mpg in stop and go traffic! Does anyone have any recommendations? I need to see better milage as this is my daily, otherwise I can’t justify this thing...

I’m tempted to lean the **** out of it, but scared to cause damage, what’s the leanest I should see at cruise?

 

[K201979]

Im no help here but somebody will be

 

[CSFJ]

You must be registered for see images attach

 

[legopnuematic]

700r4, 30 inch tires, and 3.08's don't really belong together.
All trucks that came equipped with a 700r4 (as far as I know) came with 3.42 or lower gears, as with 3.08's and 30 inch tires in 3rd (direct drive) is right around 1900rpm @55, and if I did the math right, less than 1400 @55 in OD, which IMO is way to low, that engine is lugging hard trying to push that weight at such a low rpm, it is way under the RPM band for most any engine.

I would try driving in Drive (3rd gear) and see how the economy improves compared to driving in OD. Also start and stop will kill any vehicles mileage.

 

[Big Chip]

What’s mialage?

 

[CSFJ]

What’s mialage?

Sounds french.

 

[Big Chip]

Sounds french.

Aka gay?

 

[Obwonkonobe]

I’ll have to give that a try, I’ve thought the same thing and have started getting quotes for an axle rebuild. I’m loosely saving to have a shop drop in some 3.73s and a tru trac, but 1100 dollars is gonna take me a couple months

 

[CSFJ]

Aka gay?

At least as pronounced by a cheese eating surrender monkey.

 

[Big Chip]

At least as pronounced by a cheese eating surrender monkey.

Right on, right on.

 

[Frankenchevy]

From my reading some can get away with leaner afrs but 14.7 maybe 15:1 at high vacuum cruise

 

[Obwonkonobe]

From my reading some can get away with leaner afrs but 14.7 maybe 15:1 at high vacuum cruise

I’ve got a stock cam and see as high as 25hg at idle, I’m sure it’s pretty well up there at cruise, I’ll defiantly play around with holding it in third and leaning out cruise a bit as well

 

[gotyourgoat]

Miles per gallon?
I thought it was smiles per gallon.

 

[Obwonkonobe]

Miles per gallon?
I thought it was smiles per gallon.

To the trucks credit, the 2.5 inch dual exhaust makes for plenty of those!

 

[gotyourgoat]

Well, your post actually saddens me. You're running what I wish I had. Would like the reliable street built 350 with efi and I already have the 700r4, unfortunately with an open rear as well. But my busted 305 gets the mileage you are getting.

Is your efi one that learns or is tunable?