Poor fuel mileage - 86 K10

[Orion88]

I'm fully aware that nothing with the aerodynamic properties of a brick will get great fuel mileage, but with the setup I have I think I should be averaging more than 9-10mpg.

86 K10 long bed with a camper shell, stock height, 31" BFG tires, stock 3.08 gears, 350 with world products S/R heads, edelbrock performer intake and 600cfm carb, recently rebuilt 700r4 transmission, stock exhaust, has a small cam but no idea on the specs, daily driver.

Part of the problem is the quality of the fuel in Indiana. Highway driving through Kentucky last year I got up to 15mpg, which is around where I think it should be.

If all I cared about was mileage I'd just castrate myself and drive a Prius, but poor mileage in my eyes signifies something isn't performing like it should or parts are improperly matched. Knowing my cam specs would help I know. Are my 3.08 gears too high and I'm wasting all my fuel getting my truck moving? Any other thoughts/suggestions appreciated.

[rich weyand]

Yeah, I'm getting 10 around town with 3.73 gears and a TH350, with everything else the same. And I'm also in Indiana, so same gas. With 3.08 and 700R4 you should be doing closer to 15.

The Edelbrock is running rich. They ship them that way, to keep people from burning up engines by running too lean. You should probably get an A/FR meter to set it up properly. But our setups are so much the same, you can probably just copy my tune.

Crack the Edelbrock open and adjust the floats. They'll be wrong. Use #1499 gasket to put it back together.

Oh, while you have it apart, put in .092 primary jets (#1425).

Once back together, put 065/052 rods in it (#1460) and change out the step-up springs for 8" springs (from kit #1464).

Move the accelerator pump actuator to the shortest of the three positions (most actuation) on the lever.

Make sure the vacuum advance is on manifold vacuum (drivers side of the 1406).

Change the vacuum advance can to an AR23/VC1853. Pollution -era vac advance cans have too much advance and it comes in wrong.

Time it properly: http://67-72chevytrucks.com/vboard/s...d.php?t=689321

You do have a thermal gasket under the Edelbrock, right? They don't like to be overheated.

You should also use the original thermac air cleaner. No carb likes to be cold.

[1redbowtie3]

Originally Posted by rich weyand

Change the vacuum advance can to an AR23/VC1853.

I can't find this anywhere ...

[1redbowtie3]

And yes you have an issue, I get 14 with 4.10's .

[rich weyand]

Originally Posted by 1redbowtie3

I can't find this anywhere ...

These are all listed as interchange parts. You can find them around.

AIRTEX 4V1054
CARQUEST 57-7563
WELLS DV1853
GM 19138053
GM 1973482
ACDelco D1321A
STANDARD MOTOR PRODUCTS VC-236
BWD V444
ECHLIN VC1853

[1redbowtie3]

Thanks, that helps ...

[1redbowtie3]

Rock Auto has VC-236

[Orion88]

I have an aftermarket HEI distributor so I assume that doesn't apply to my application?

[rich weyand]

Originally Posted by Orion88

I have an aftermarket HEI distributor so I assume that doesn't apply to my application?

The aftermarket HEI distributor should take standard HEI vac cans. No one is going to want to make their own rather than just accommodate the ones out there.

[Orion88]

Bowite, I bet you guys get some of the best quality fuel down there in Texas. I imagine that has something to do with it

[Orion88]

So I should or should not replace the vacuum canister?

[Tom]

Your revving too low in overdrive and lugging the engine. My 79 c10 had a vortec 350 with rpm intake, 600cfm eddy carb, msd hei components and adjustable vaccum advance. It had a 200-4R and 3.08 rears. One time the lockup stopped working which ment the trans couldn't be run in overdrive without hurting it. I got 4mpg better running around at 3000rpm vs the 2000rpm I normally was at with overdrive.

That said your also a 4wd. Best I ever got with my old combo was 15mpg. 11mpg is pretty good for your setup.

[rich weyand]

Look down between the actual vacuum can and the distributor cap. You should see numbers stamped on the vacuum canister arm. What are those?

http://hbassociates.us/HEI_VacuumAdvance1asm.jpg

[MikeB]

Which Edelbrock carb? The 1405 and 1406 have internal differences other than jets and rods, and each has its own calibration chart.

[Orion88]

1405 - manual choke 600cfm. I installed a manual choke but it actually made the truck more difficult to start on cold days. A few pumps of the gas pedal was usually enough to get her going. She would die once or twice but I never really needed the choke, which probly means it is running rich.

[rich weyand]

Originally Posted by Orion88

1405 - manual choke 600cfm. I installed a manual choke but it actually made the truck more difficult to start on cold days. A few pumps of the gas pedal was usually enough to get her going. She would die once or twice but I never really needed the choke, which probly means it is running rich.

Yeah, the 1405 and 1406 are a little different internally -- different venturis and such -- which means you can't just copy my tune above.

My suggestion is to pop 300 on a good wideband AF/R meter and set it up right. It's worth it. Mileage goes up and performance is night and day.

You still need to connect the vac advance can to drivers side manifold vacuum and get the right vac advance can on there.

Also tune the timing properly. You are probably retarded. Uh, that's a reference to timing settings....

[MikeB]

Originally Posted by Orion88

1405 - manual choke 600cfm.

I don't know if a properly jetted 1405 will ever get gas mileage as high as a 1406. Just look at the jetting charts.

And although the 3.08 is definitely way too tall for a 700R4 and 31" tires, I'm not sure a 3.73 would gain you 4 mpg like Tom saw with no OD. But you are definitely lugging the engine in OD. And 3.73s would make a huge difference in how well the truck performs.

Also, the unknown cam you have could be contributing to the problem. Increased valve overlap, which helps mid-high RPM power, will cause some of the incoming fuel to blow out the exhaust port at lower RPMs. Also, even 10 degrees more intake duration than stock will close the intake valve later, reducing cylinder pressure, efficiency, and torque at low-mid RPM. What is your manifold vacuum at idle?

[Orion88]

A/F meter won't do me much good til I replace my rusty exhaust. I'll double check timing but I think I'm at 12 initial. My vac advance is hooked up properly. I'll look into switching out the canister. Thanks.

[rich weyand]

See which numbers are on the existing canister.

16* BTDC is probably closer to where you want to be, assuming the right vac cam.

I don't think rusty exhaust would change A/FR meter readings considerably, not considering how far off tune you are right now, because you're WAY rich.

[Orion88]

When I get home I will check out the canister #, as well as post a spark plug picture. If she's really that rich a spark plug should be able to tell me.

[rich weyand]

Yeah, they'll be black.

What plugs are you running, and what gap? Should be something like ACDelco R45TS or Autolite 24, with .045" gaps for HEI. Umm, with aftermarket heads, could be different plugs, though.

[Orion88]

Should be the ACDelcos but I'll double check everything tonight

[Orion88]

Spark plugs are R45TS gapped to .040. After looking at them I'd say the engine is right where it needs to be, not rich or lean. Vacuum advance canister has no serial number. Got the HEI distributor off eBay. Not necessarily a name brand unit but it works perfectly fine. All vacuum lines look good. Now I'm out of ideas. Might just have to live with 10mpg.

I have a line on a set of 3.73 axles. I was looking for 3.42 thinking it would be a good middle ground. Would the 3.73s work better or worse than the 3.42s?

[Orion88]

Was pretty surprised at how good the plugs looked.

[68post]

You'll like the 3.73's with OD.