I have a 67 camaro with a stock 350 gm motor, 12 bolt posi and a close ration Muncie 4 speed, whats the best highway driving gear set ratio? mpg over preformance

 

3:31 gears will give you the best compromise .Other wise 3:08s,But it will be awfully doggie

 

There is no way to answer this. Like said above it is all about compromise. You could say 2.73 gear are better highway gears then 3.31. There are just too many variables, tire diameter, how is the engine built. What are we talking about highway speeds 55 or 80MPH. Depending on the cam you have the car could runs great at 1800 RPMs or it could run like crap under 2500 RPMS. Putting tall gears in serious race built engine my mean you have to run in 2nd gear at 45 MPH.

My 67 SS came with 3.55 from the factory which is fine running around town at 55-60 with the larger rear tires. But if I was going to hit the turnpike with its 75 MPH speed limit on the daily I would swap out the gears for something taller.

 

Get 3.73:1 ratio. You have a Camaro, not a Prius.
With 3.73 by stock GM design of the Camaro, stock 350 engine will be turning 3000 RPM at 60 MPH.
Otherwise, get a 3.31:1

 

I am considering getting a 12-Bolt Built to Order Rear End Package from Moser Engineering.
Car is a 68 with a 350, automatic transmission, 25.6" rear tires, doing 6.5sec. 0-60 with stock 3.08 rear end.
Now Moser offers 3.08 3.31 3.42 3.55 3.73 up to 6.00 !
Don't want to make it a dragster queen but would like to make it a bit "sporty". Is 3.31 or 3.42 going to make a difference in driving and acceleration? Tried different calculators but it's difficult to get an idea of where we are going. You can figure out the RPM at Highway speed but that's it.

 

go with a 3:55 or a 3:73 and a gear vendor overdrive unit ,or a 5 or 6 speed transmission. then you have the best of both worlds
with my 4 speed , 3;55 gears and a 26" tire i can run 80 mph and turn 2600 rpm in 4th over

 

Thank you. Not sure if you're replying to me but I don't plan a change in transmission.

 

3:42 should make a difference,if it's not a daily driver I'd go a little lower like 3:73 or 3:90 even.
3:31 won't make much difference from 3:08 in seat of the pants acceleration feel.
I ran 3:90s in my '69 with a big block and 4 speed,liked them a lot.

 

It all depends on what you want to do with the car .I have a 1979 Z-28 of which I change over from a Turbo 350 to a Super T-10 4 speed ..I kept the 3:42 gears even when rebuilt and upgraded the original 8.5 10 bolt rear end .And even with the supercharged small block .I still get fuel mileage in the 20`s MPG.

 

I realize I'm coming to this discussion a year late, but still, here are some sites and a procedure that might help people asking similar questions. To really understand the effect of ring to pinion ratios, you need to know up front what your transmission gear ratios are for each gear, the diameter of your rear tires, and ideally, the power curve of your engine. If you know those, you can visit this site: https://purperformance.com/p-29669-rpm-calculator.html and input the data to obtain RPMs at the crank. If you don't know the tire diameter, but know its designation (for instance, 245/60 R15) you can go to this site to obtain tire diameter: https://robrobinette.com/tire_diameter.htm Then, if you're handy with a spreadsheet like MS Excel, you can create something like this:

This particular chart is for a Muncie M20 wide-ratio 4-speed sitting behind a 396 making maybe 425 HP and appropriate torque, and landing in a 12-bolt rear end housing an Eaton Detroit TrueTrac limited slip differential and 3.42 new ring and pinion. Multiple charts were created for various rear gear ratios, and we ultimately chose 3.42 as our compromise between the world of a Camaro becoming multi-fueled (burning both gasoline and rubber) at one extreme, and the alternate world of turning a reasonable RPM on the freeways of today without holding up traffic. Hope this helps.