Fuel economy of 7.4L (454) powered 3/4 ton suburban

[oil pan 4]

The rear disc conversion has gone a little over budget.
3/4 ton 1997 4x4 front pads were only $50, that's not bad. The rotors, only $75pair.
And the real pricey item was calipers for the rear of a 1978 Cadillac Eldorado (obviously I eat the $60 core charge, bringing the price for them up to $250), they have mechanical emergency/parking brake provisions.
I could have gone with much cheaper and dug up some used 3/4 ton 1997 front 4x4 calipers, but I like stopping and then staying put.
And I still need to dig up some brake lines.

[oil pan 4]

Well the ARB air locker finely shipped, after about 3 weeks of backorder.
Wet grass will no longer be able to instantly immobilize me and soft or sandy soil will not so easily be able to trap me.

[kir_kenix]

Sounds like the build is coming along nicely! You are going to just about run out of stuff to get done before the diesel transplant.

As far as the $60 core, most parts stores don't really care what goes in the box, as long as they approximate whatever they sold you. Grab any old calipers and throw them in the box and get your core money back. Engine cores they might get a bit more picky about, but most things they really don't care too much about.

[2009Toyotoad]

I have not seen a Gear Vendors aux tranny suggested in this thread. The OD unit may be worth investigating for the 700R or original GM tranny. If they are built for motor homes they can certainly take whatever torque a 6.2 or 6.5 diesel can put out. Not sure how well it would hold up on a modified DMax.

[oil pan 4]

The gear vendor overdrive units are pretty cool, but they are really expensive, require a custom drive shaft and they seem to be fond of developing oil leaks.

[2009Toyotoad]

Originally Posted by oil pan 4

The gear vendor overdrive units are pretty cool, but they are really expensive, require a custom drive shaft and they seem to be fond of developing oil leaks.

Learned something new, I was now aware of a history of oil leaks for the units. Actually, I was thinking you should check into a used unit, from an RV salvage yard. Until Factory OD transmissions were standard on motor homes they were wildly popular with RVers. So they should be trickling into Salvage yards by now.
However, as you've alerted me to the oil leak problem I'll be doing a little more searching on the fix. I hope its an improved seal system or gasket when one rebuilds a unit, rather than a systemic design fault or uncorrectable casting error with limited possible corrections

[oil pan 4]

Hey a used one would be the way to go. I would not want to pay the new price for one of them that's all.
I am sure there is some way to find new seals and such for them.
I don't believe its a casting problem.
You also need a transmission with a tail housing for a transfer case.

[oil pan 4]

Now that I have the carb running the way I want I got fuel mileage up to around 8.5mpg and I discovered I had a small fuel leak at the carb. I don't know how long its been leaking or how much it leaked.
I got the leak fixed and refilled to test. I will be driving it for the next few days to get an idea what the MPGs will look like.
I am not burning through most of the 40 gallon tank. So sample sizes are kind of small, not looking for precise numbers, just trying to establish trends.

The engine has gone from running wildly rich qjet carb netting 6.5mpg to running correctly with a different carb. I don't know anything about the q-jet and don't care to learn or have to time to figure out a different fuel induction system when I already know the edelbrock 650cfm and have all the stuff to tune it.
I also bumped the base timing to 12 degrees of advance. The distributor is untouched beyond that.
Now at cruise I see 15:1 to 16:1 air fuel ratios. Lean idle barely registers on the gauge, showing OL and flashing high 17:1 numbers some times.
WOT air fuel ratio stays between high 12s and 14 to 1 most of the time.
No matter what I do to try and lower WOT air fuel ratio it always effects cruise air fuel ratio too, lowering it.
Its also on a cold air intake, for now. Not the best for fuel economy.
It runs like total crap when cold.
The engine runs better, except when I first start it and its still cold, it has more power since the engine is not being suffocated with fuel. In this quest for better fuel economy I have made this vehicle pull better and run stronger through its entire operating range.
Because I always hear people whine that if you want more fuel economy you have to give up power and you wont be able to tow as good. That is not always true.

I had an accelerator pump problem that I fixed. I thought the engine was not getting enough fuel from the accelerator pump because of the nozzle size turned out to be the accelerator pump not working or barely working at all. Having a non functional accelerator pump and it not effecting the operation all that much after the engine made it to operating temperature I may try switching back to a smaller nozzle or using less pump plunger stroke.
No accelerator pump really makes it run badly just after start up. A smaller accelerator pump or less pump plunger stroke may be sufficient for normal driving.

So any one can improve the MPG of their old out dated tow rig with a gas murdering motor. All you have to do is tune the carb, shouldn't matter if its a q-jet or edelbrock.
That is a 30% improvement, with a fuel leak on the side of the carb.
I am thinking max MPGs driving around town in a suburban with a 7.4L engine, non over drive, non lockup transmission and 4.11 gears has to max out at 9 or 10 MPG.

Now I have to figure out, am I going to put the 3.21 gears in now or after the diesel and its transmission get moved over?
(this will effect how strongly it pulls but who cares, its getting a completely different twin turbodiesel drive train here pretty soon, this will be just for fun)

EDIT: I just realized, I never changed the spark plugs after I got this rig. New plugs should help a little.

[oil pan 4]

Latest tank was 11.7 MPG.
Just using tuning and EOC. I could work the gas so I run around a 17:1 air fuel ratio while picking up speed, giving the engine about 1/3 throttle that is the most you can open the primaries before the fuel dump secondaries open. Its setup to run nice and lean until the primaries open up.
There is room for more EOC here and there. I am not going to EOC when driving to work, just incase it doesn't want to restart.

If I can get 12mpg in a suburban with 3 speed trans, no torque converter lock up and 4.11 gears, I wonder what it could do in a Camaro that weights a ton less, had some considerations towards aerodynamics, has an over drive transmission with lock up and has a rear that is close to 3:1.

Whom ever told me that a edelbrock 650 and edelbrock air gap intake manifold was a bad idea for improving fuel economy has some crow they need to eat, after they take their foot out of their mouth.

[ME_Andy]

%-wise that's an awesome improvvement, but still miserable compared to a modern suburban. lol