We have a 64 300hp with a 3.36 non posi rear and would like to upgrade to a posi 3.55 or 3.70 rear. 98% of our driving is in town and the 3.36 is a bit sluggish and 4th gear is like using overdrive. Any suggestions? Thanks!
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Re: 64 Rear Ratio Change
The 300 HP engine has lots of low end torque and the wide ratio gearbox with a 3.36 axle was the shortest gear combination available.
Because the WR box has a big 3-4 step, fourth is not too usuable below 30 MPH but it's a pretty good highway cruising gear.
A shorter gear will make the car more responsive and allow fourth gear to be used more around town, but it will drone more at freeway speeds.
You might want to compare your engine with another known to be stock 300 HP. A lot of these engines have had cam changes which often kill a lot of low end torque and throttle response. A stock 300 HP engine should idle butter smooth at 500 RPM. If it has a lumpy idle, it's probably had a cam change.
My SWC has a 340 HP engine CR gearbox with a 3.08 gear. The SHP engine definitely has less torque below about 3000 than the 300 HP engine. It will pull from about 30 MPH at about 1200 revs, but the 3-4 shift is best left to 35 MPH or above. With a 75 MPH first gear, off the line performance is not condusive to serious drag racing, but 80 MPH freeway cruising is only 3100 revs and the top speed is over 150.
With only four relatively closely spaced gears, Corvette transmission are like five speeds with out first or fifth depending on the axle ratio.
Duke
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