Poor mpg

[Rusty Nail]

 

[82sbshortbed]

I'm fixin my gas mileage problem by swap in a BBC and setting my timing 10" After tdc so that it doesn't have to run as hard to move the truck therefore saving me gas.

What?

Yeah you heard me

Thanks to @Rusty Nail I've seen the light

Thanks dude

LMFAO

 

[shiftpro]

Edit- So I finally read through the rest of the thread, glad you straightened out your timing issue! This part still applies though:

You might actually want to try switching to shorter gears like 3.73s or 4.10s. I know having super tall gears is usually synonymous with good mileage, but unless it's all highway you're probably doing the opposite. With how tall the 700r4 is geared naturally you probably have to put your foot in it all the time just to move around, and I'm sure you rarely get out of 2nd gear. If you're going 90 on the highway for long periods of time at like 1800rpm I'm sure gas mileage is awesome, but does it EVER even shift into OD with those 3.08s under normal circumstances?

This^^^^^^^This^^^^^^^^This^^^^^^^This^^^^^^^^
One more time, THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

[Rusty Nail]

Certainly a smaller diameter tire is a viable option that will help immediately.

https://tiresize.com/calculator/

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https://www.morris4x4center.com/jee...n=cj&cjevent=4c991a88bc1411e98058020f0a1c0e0f

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I don't link a chart that reads 3.08 though, how funny is that?

Reckon i'd shop for a differential to swap real easy. That could be really really cheap too.
You could salvage yard.... It's only one or two hours shop labor for install...??

www.craigslist.com

 

[shiftpro]

It's only one or two hours shop labor for install...??

.

 

[Goldie Driver]

Certainly a smaller diameter tire is a viable option that will help immediately.

https://tiresize.com/calculator/

+

https://www.morris4x4center.com/jee...n=cj&cjevent=4c991a88bc1411e98058020f0a1c0e0f

=



I don't link a chart that reads 3.08 though, how funny is that?

Reckon i'd shop for a differential to swap real easy. That could be really really cheap too.
You could salvage yard.... It's only one or two hours shop labor for install...??

www.craigslist.com

Pretty cool !

Now, if they only made 3.91's for these rigs ...

You must be registered for see images attach

 

[Rusty Nail]

pretty sure 3.90 is thing.?

Its a good chart!

 

[Goldie Driver]

pretty sure 3.90 is thing.?

Its a good chart!

Oh, it probably is ( 3.90 ) , but I thought OE they did 3.73's & 4.10's with no in between.

Irrelevant as the labor charges to regear front & rear plus the parts costs probably come close to the cost of a more potent , non 100K motor.

 

[WFO]

pretty sure 3.90 is thing.?

Its a good chart!

Some Mopars have 3.90s in'em.
That's what my 70 440 Cuda had.

 

[Rusty Nail]

i'm really getting into the idea of an axle swap.
There's a guy in Craigslist, I don't want to resist him. BEST PLAN says go buy some 4.10 factory axles, sit em in the garage and rebuild em while still rollin on the 3.42s that there's nothing wrong with.
Wish ida found that chart sooner ida bought 28s instead of new 31s.

Actually I just had the axle seals replaced so they don't leak even and I feel stuck but what can ya do?

spend.money.

 

[80BrownK10]

First thing I noticed, long box's have 20 gallon tanks, short box's have 16 gallon tanks, but i have seen people use 16 gallon tanks on a long box, gives room between tank and front spring hanger for exhaust exit. Timing should be 10 BEFORE top dead center, check your mechanical advance and make sure it's working. Autolite 26 plugs gapped at 40. If no vacuum leaks and all other parts are in working order.....then I'd look at your carb closely.

I wouldn't use autolites and would gap closer than 40.

 

[80BrownK10]

Looking at that chart. I know I am not in the power band with my 3.08 gears and 33" tires but should I really believe that I will get best MPG reheating to 3.90s assuming they would exist. I always thought if I reheated I would go to 3.72s.

And I understand the whole power and of the motor and torque thing but while I am cruising down the highway at say 50-60mph I don't feel like I have no power or anything. To me it would seem like in the real world I would loose MPG going to 3.9 gears from 3.08s just from what available power I have at the speed while I cruise down the road.

 

[SquareRoot]

Looking at that chart. I know I am not in the power band with my 3.08 gears and 33" tires but should I really believe that I will get best MPG reheating to 3.90s assuming they would exist. I always thought if I reheated I would go to 3.72s.

And I understand the whole power and of the motor and torque thing but while I am cruising down the highway at say 50-60mph I don't feel like I have no power or anything. To me it would seem like in the real world I would loose MPG going to 3.9 gears from 3.08s just from what available power I have at the speed while I cruise down the road.

More importantly, what spark plugs would YOU use?

 

[80BrownK10]

Delco. There several that would work. Depends on heat range. 44 work and then heat range letters can go after them.

I have 44TS in mine. They fire off like they really all do. Color always looks good on them if I pull one

 

[Maxgforce]

I wouldn't use autolites and would gap closer than 40.

If you look in any repair manual, .35 gap is for 250 CID and anything that is running breaker points. With an HEI it reccomends .45, but after building dozens of engines and running them in Moab and the drag strip I've found out that .40 with an HEI works the best. I run autolite 24 at the track and 26 offroad......but hey, I tip my hat since you apparently have more experience than me.