Seventh Gear!

[Big Dave]

OK. Numbahs.

First tankful: 548.8 miles 19.293 gallons 28.44 MPG
Second tankful: 510.6 miles 18.272 gallons 27.91 MPG

Overall: 28.2 MPG

This is over my usual circuit (one-third each urban/suburban, two-lane state roads, Interstate). Flat terrain Hot & humid (low air density)

Urban/suburban - run along with traffic
Two lanes - 60 MPH = 1125 RPM
Interstate - 70 MPH = 1310 RPM

At all fillups I eye-droppered in the last drop she'd take.
My speedo is perfectly adjusted for relatively new 235-85x16E tires @ 100 psi

I baselined (no GV) at 26.4 MPG. Base MPG down because I cut down the air dam & removed the side skirts. Even I could not stand the things.

The difference in the tanks (about a half-MPG) may be an answer to the old question about windows down- no A/C vs windows up with A/C. First was run driver's side window down and very little A/C. Second tank was windows up and A/C on recirc.

On both tanks, I was on my hypermiling game.

[slowmover]

You ought to be able to hear us from waaay down here, yeehaw!

As before, hope you'll run some video/audio some day. What kind of man press/pyro temps on a run like that?

[Big Dave]

At 60 MPH in seventh, 500 degrees EGT Zero boost

At 70 MPH on seventh, 575 degrees EGT 1-3 psi boost

[Big Dave]

OK. The GV gained me 1.5 MPG over baseline, but I'm greedy.

I noticed my EGTs were up, so I thought maybe I've gone past the optimum.

So I experimented by putting my 225-75x16s on the drive axle and the 235-85x16s on the front.

EGTs went down but so did MPG: 26.5 MPG.

Rats!

Engine speeds.
@60 MPH - 1200 RPM
@70 MPH - 1400 RPM.

Yes, I corrected my odo by 7% which is the difference in tire OD.

OK, unless this next tankful shows a huge improvement (telling meI have experimental error) I'll swap 'em back.

That's why you experiment: to separate truth from BS.

[Big Dave]

slowmover:
A 4BT3.9 and a T-56 in a F-150 should give outstanding results. They are much lighter than Super Duties. If it were a long bed with a aeroshell, even better. I've been thinking about a 4x4 Expedition with a 4BT and a T-56 for a winter vehicle.

comptiger:
You are right. T-56s can be adapted to transfer cases.

nubbzcummins:
With smaller (like 235-85x16) tires and 3.31 gears you could get awesome MPG. Those big-diameter tires exact a huge price in rotational moment of inertia. You have four gynormous "flywheels" to pour energy into everytime you accelerate away from a light. You have to accelerate those "flywheels" rotationally before you accelerate the truck laterally.

[Phantom]

With regards to the EGT it could help to go one step colder and or adjust the gap. The gap might not be able to be made much bigger under boost before it blows the spark out.

[comptiger5000]

Phantom - He's working with a diesel. No spark plugs.

[Phantom]

Oops I was thinking he had the Triton V10 but I guess he would be running at a lower MPG if so.

[DieselFan]

Big Dave,
Does that mean that you are getting only a 6.8% fuel efficiency gain with the overdrive Gear Vendor?