Need opinions on gear ratio situation

[patmckinneyracing]

I have to drive my 80' malibu from san antonio to college station, tx (Texas A&M WHOOP!) which is about 3-3.5 hour drive. Well as I said in a couple other posts I swapped out my 86' 3.73 posi rear end for a 2.41 elki rear end in an attempt to get better gas mileage. The thing that sucks is that I have not noticed any change in my gas mileage from this swap.

It felt and looked like I was getting better gas mileage with the posi rear end than I was this dog 2.41 rear end. The only benefit from this swap that I've gotten is cruising at low rpm on the highway instead of 3400-4000rpm with the posi.

Round trip with the 2.41 rear end, I'm spending close to $80 in gas and thats cruising at 60-70mph the whole way (no speeding). So does anyone have an idea of what may be going on here? I'm thinking about just putting my posi back in...just want to get some insight. Just thought with a higher rear end I would notice a significant change in mpg.

Heres the engine set up:
-350 sbc
-2.02/1.60 cast iron heads
-flat top pistons with valve reliefs
-.442/.460 summit cam
-Edelbrock performer w/ Edelbrock 600 carb
-10.5mm dragon fire spark plug wires
-MSD HEI distributor
-350 transmission with B&M shift kit (automatic 3 speed)

Its not a radical 350 by most standards just has plenty of pep to it for a daily driver.

 

[TURNA]

The only way to see a noticable difference in gas mileage is to put in an overdrive trans.

 

[nycutlass]

what size tires are you running ? with a 26 inch tall tire you should be doing 2000 rpm with a th350 transmission at 65 mph with a 241 gear rear which is great !!!.........

 

[1evilregal]

if you're doing some stop and go driving in between, that's where your mileage is going....engine works harder to get the car moving...

if you're just figuring mileage on the freeway run, +1 on the overdrive... had a 73 plymouth with 2.72 gears an slightly modified 318 that got 11 mpg city, and 25mpg on the freeway cruising about 90 mph @ 2400 rpm... no overdrive though...

 

[79GP6.6L]

+1 on an overdrive transmission.

You could try running a 2bbl carb on long trips.

 

[pontiacgp]

it's impossible that putting in the taller gears didn't increase your gas milage on your 3 1/2 mile trip. I had 2:41 in my GP for a long time and switched it out to a 3:42 posi and the engine reved considerably higher on the highway which equals higher fuel consumption. I now have a 3:08 posi

 

[shotgun]

Missing a big piece of the puzzle, what convertor?

Also going too tall is as bad as too short on gears.

I agree 3.08 to 3.23 make a great all around ratio. Had 3.23z in my 70 LeMans.

I had a GP with 2.14( not a typo) gears. I tested a tank on gas leaving the shifter S instead of drive.

I got better MPG. The car was in it's powerband.

In D, it would shift into third really early and then you would have to give it extra gas to keep it moving or hit it hard enough to downshift.

It did love cruising at 75 mph+ but under that it was a dog with bad MPG.

 

[patmckinneyracing]

The converter is a 1900 or 2000 stall. The entire trip practically consists of +60mph except for two small towns. To me it just seems that it is taking more gas to get the car moving because it is such a high gear. The tires I have are old RS camaro rims (15x7) with a somewhat low pro tire. As far as the overdrive, yeah I'm kicking my *ss on that one wishing I went with an overdrive.

 

[Phoenyx]

Well for me, I swapped my 2. sumthin highway gears for my 3.73s. My car car does better on gas in town. As for the highway, I took a 2 hour trip. And it did as good on gas as my 98 Cavalier does. The only thing is that I was going a bit slower than the speed limit (took an extra 30-45 minutes) because I didn't feel safe with a tired 305 revving at 3000+ RPM.

 

[shotgun]

What size tire?