Unusually Poor Mileage

[Step'67]

Originally Posted by GASoline71

So if I read this correctly you have only 29 degrees total timing in by 2,800 RPM's? It should probably be close to 32 degrees or 35 degrees. A few more degrees of total timing should make a difference.

Gary

No, 14* initial, 19* mechanical, 10* vaccuum

14+19=33 w/o vacuum at 2800rpm

Also, on a side note, climbed under the truck, fully warmed up, and traced the fuel line from tank to carb. Bone dry the whole length, as well as around the fuel pump. Doesn't look like any leaks to speak of...

[GASoline71]

I'm a math whiz! LOL...

Gary

[Step'67]

Originally Posted by GASoline71

I'm a math whiz! LOL...

Gary

Haha, no worries. I'm in AP Calculus and still can't add right in my head most days...

So what are we thinking guys? No leaks to be found... Get a lighter converter?

[Rufton]

Originally Posted by Step'67

Haha, no worries. I'm in AP Calculus and still can't add right in my head most days...

So what are we thinking guys? No leaks to be found... Get a lighter converter?

How many hwy mileage readings did you take?
Was cam timing double checked when chain installed?
The acceleration feels right?

[Step'67]

This has all been city mileage, since I don't really need to drive the freeway too often. For several weeks now I've been checking the mileage, and it's always right in that range. Yes, we did check the cam timing during assembly. Acceleration is nice and strong. Under light pedal pressure, accelerating away from a dead stop until some momentum is built, the truck does feel a tad heavy. But then again, it is. I wouldn't at all call it abnormally heavy, I'm sure its just due to the taller 1st gear in the 4l80e.

[SCHRUMGMC]

Only thing I'd think of is Bad Oil

not sure though

[Step'67]

As for oil, running Amsoil (dad's a dealer) high-zinc full synthetic 10w-40. Trans running Dex 6.

[Rufton]

City mileage has many variables.
Suppose you don't have time for a road trip
If you do that would be a good data point.

[piecesparts]

Did I miss what you may be running for tires on the truck? The diameter is important in what your tranny can do. What tranny gear ratios did you have in it prior to the 4L80E install? You mentioned that the take-off was not what you liked, due to the higher first gear in the tranny. How many miles on the engine since the rebuild? The miles and break in is an impact to your MPG ratings. How cold is your winter in the area that you live, cold air and gas mileage do not relate well.

You really need to check the mileage on a longer trip on a highway and verify that you get the same on the way back. If you can do it without a lot of hills, then that would be best.

The truck in my avatar has a stroker engine with many of the things that you have in your truck, but I have a 700 R4, not a 4L80E. I am getting 15 MPG.

[Step'67]

Yah I had the tire size posted a couple back, 275/60/r15. I agree that I need to just take it out and drive a tank through it. I've been driving on this combo for a while (several months), my daily driver, it is definitely broken in. I didn't start checking mileage till winter hit, this has been the coldest winter in a couple decades, so I figured the -4*F temps were what was killing me. But now, a couple months into the 60-70* weather, mileage hasn't hardly fluctuated, even with me retuning for the warmer weather.

The thing that gets me is I was getting 13mpg, driving while burning oil, and a worn out wide as hell ratio truck granny-gear 4 speed behind it. Now I get 9 driving the exact same route, and much easier since I don't have to wind out each gear just to catch the next.

I'll admit you're making me envious with the 15mpg stroker, should've just gone that route like I wanted

[Longhorn 70]

When this motor loosens up a bit there will be less friction and better mileage. My old worn out Olds big block gets 15mpg in my 3/4 ton. When I first put it together 25+ years ago, I only got 11. I went through a few tranny changes, always recalibrated speedo, but the mileage has been doing better.

Let it break in well and see what goes....