What sort of MPG would you think the following combo would provide :

70 B body, 360LA, stock rebuild with a slight bump in compression (trying to be E58), Edelbrook 4bbl carb, factory (think its 24-2600RPM stall speed) convertor and 727 with 8.75 rear end with 3.23 sure grip, 235/60/15 tires all around . . . . just finished 1,540 mile round trip . . . 70-80mph, cruise control, ac . . . avg of 16mpg . . .

Not really sure if that is good or bad for this car . . . . fires right up no problem, no pinging, plugs seem about right color . . .

My last 360 car, was my Duster360 with the original E58 in it, 727, BUT, 2.45:1 rear end . . . and that was giving 22mpg all day long . . .

Would be nice to bump the Satellite up to 20mpg . . . so do I need to rethink my rear gear ?? Any thoughts are appreciated . . . .

Oh, and cause of elevation here, (3500ft), it is jetted for altitude and not running at sea level (trip was to west coast and back) . . .

I'd expect mid 14s in mixed driving, the way I drive.

Have you ever thought about joining the ThermoSquad ?

Way higher than I’d expect.
Double check your odometer.......

I’m only getting 16-17 with stockish 340, 373 gears and 518 OD

Both of the small block mopars I've had that got 25 hwy mpg, had 2. something hwy gears , 2 bbl and single plane stock intakes.

What size carb?

Years ago I had Diplomat I put a 4bbl atop, with a 650 Edelbrock carb I could get 25ish mpg highway. With the 750 I got maybe 20. 2.94 gears, A833 trans (no OD) similar weight and aerodynamics.

I later put a mild 360 in, similar mileage if I kept out of it.

Uhh, think it is 650 ??? I have lots of TQ's that I could build up for this (I like TQ carbs - that was on my Duster360) . . . but things run so well, I really don't want to mess with it too darn much . . .

Hi Mark,

What fuel mileage did you get from my old Feather Duster (360/600AFB/A833OD/3.55)?

Since an a body is smaller and lighter than a b, no surprise it gets better mileage.

For reference, many years ago I took a long road trip in my 69 rr, 383 od833, 323 gears and 235, 75,15 tires. Got 16 on the freeway. But, I was dealing with a few problems like, a cracked intake causing a vacuum leak, a worn out and badly tuned carb, and the overall gearing and tire size didn't help.
On the gearing, the I couldn't keep the engine in its sweet spot, either revving higher in 3rd or lugging it in 4th. Since I've resolved the carb and intake problem, the car is able to cruise in od nicely. Enough so I might put in 276 gears. I have no idea what my current mileage is.

I say all that to point out I think you can do better. Setting up vacuum advance, perhaps adding egr and some carb tuning should get you closer to 20. After that you'll be looking at aero and gearing.

I wish I could get egr on my 383.

70-80MPH, B-body, maybe no headers. Yeah that's about right.

400's came with EGR.

400 intakes fit 383's.

If you really want it you could got that route. I'd use ported vacuum and a thermal switch so taht you only get EGR above idle and warmed up.

Hi Cass . . . uhhh, if I recall, I think that was around 18-20 . . . course, that car was may more fun to drive - full throttle, heh heh heh, so mileage wasn't the concern

I got 14.2mpg. 4600lbs, 526 stroker, 727, 3.73’s 275/60/15 on the 3 hour drive to Carlisle.

This is when it had an 850 Holley and a performer rpm. It now has a 1000cfm quick fuel, M1 intake, and 3.23’s.
I’ll find out how much that changed, going to Carlisle

I'm always surprised when anyone gets mileage out of a 360. I've owned 4 stock ones and they all sucked gas. I actually swapped in a (stock) 440 to replace the original 360 in a Club Cab I owned thinking mileage couldn't get much worse, and it actually got better. What the 440 gave me in day to day, the 360 barely got, on the hwy, downhill, with a tailwind.

EGR and a leaner Air to Fuel ratio do the same general thing:
they both cause the throttle to have to open more to continue to make the same horsepower
which raises the intake manifold pressure
which pushes down on the pistons a bit more on the intake stroke
which relieves the pistons on the power strokes from having to make that extra horsepower.

Lean air to fuel ratio is better than EGR
because EGR flows above 10% begin causing more spark plug miss-fires
whereas lean miss-fires generally do not start until about 30% leaner.

Going to a rear diff ratio of 2.76 also causes the throttle to open more to create the same horsepower
because you need more torque at the lower rpm to make the same horsepower.
The lower engine rpm also lowers piston ring rubbing friction.
You can lower piston ring friction more to going to lower viscosity oil
or by installing thinner rings.

If you want better MPG
Install diff gears like 2.76,
add overdrive,
go leaner AFR,
consider doing some cheap aerodynamic tricks:
chin spoiler, tire spads, vortex generators at rear of vehicle to reduce wakes,
and go to lower rolling resistance tires
(look for tire Crr of less than 1%, many new designs are less than 0.8%)

If you have your cam specs
find out your dynamic compression ratio

http://www.wallaceracing.com/dynamic-cr.php

Dynamic compression ratio affects MPG more than static.

I am a fan of 360s but they do have bigger bearings that cause just a bit more friction,
and they are about 60 lbs heavier than other makes “small blocks”.
Perhaps 408 stroker kits have shown us what the block should have been configured as by Chrysler as a truck engine from its beginning.
Similarly 318s should have been 340s.