You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums.
D.L. Kansas City, KS
Q: My trusty 1936 Plymouth 4-door has a .060-inch over, 350 Chevy with an RV cam and a Holley 4-barrel. I’m also running a Powerglide transmission and a stock 1980 Cutlass 10-bolt rear end. Should I change the rear gear ratio to get the best possible highway mileage or would I be better off with the stock ratio?
A: There’s nothing like cruising down the highway in a classic hot rod! However, it’s difficult to recommend a new ratio without knowing your current gear ratio (GM 10-bolts came with 2.21-3.42:1 ratios) and the rpm you’re turning on the highway. From what you’ve told us, you might want to leave the ratio as is and upgrade to an overdrive transmission like a 700-R4 and lockup converter. The 700-R4 is an easy swap and it doesn’t require a computer.
I exchanged my GM. 350 with a 700R4. And went from 20 mpg at 70 mph to 40 mpg! In my 84 el Camino 305.