This is in referance to a 1969 Corvette 350/350 with the close ratio M-21 and 4:11 rear.

The standard rear gear with the M-21 was 3:70 with the 4:11 as the optional performance gear.

I'd really like to run a 3:55 as a happy medium but don't want to second guess the GM engineers as I assume 3:70 was standard for a reason.

The last thing i want to do is lean on the clutch heavy and or shudder at stop lights getting her rolling.

I also don't want to be winding out at 75MPH with very little punch left in her.

Anybody have any advice on gearing for the close ratio M21?

get a wide ratio gear set for it, and go with your 3.55's. or drop in a nash/richmond 5-speed and doo the 3.55's

I think you will be fine with 3.55s, 1st would be similar to an M20 wide ratio with 3.08 gears plus the corvette is lighter weight than a chevelle.

This is in referance to a 1969 Corvette 350/350 with the close ratio M-21 and 4:11 rear.

The standard rear gear with the M-21 was 3:70 with the 4:11 as the optional performance gear.

I'd really like to run a 3:55 as a happy medium but don't want to second guess the GM engineers as I assume 3:70 was standard for a reason.

Anybody have any advice on gearing for the close ratio M21?

In late '60s - early '70s chevelles/elcaminos, the 3.31 axle ratio was very common with M21/22 2.20 1st gear from the factory. I'm pretty sure 3.31 was the standard for several years. That combination works very well for around town and highway driving, I had several with that combination. They were in applications ranging from a '70 454/450 hp to '72 370/270 hp. The '72 performed very well even pulling a small trailer. If 3.55 is what you want you should have no problem. If it is to see more highway driving than city I wouldn't hessitate going with 3.31 myself.

My real preference would be to swap out the M21 for an M20 with 2.52 1st gear and go with the 3.55. With this combination the overall ratio in 1st gear would be the same as the M21 with the 4.11 - equal performance off the line while gaining the bennefit of the 3.55 at highway speeds.

I had a M22 in my camaro with 3.55's and it was a little too soft starting off in first. Next time I'll use a wide ratio with 3.55's.

Well, the 3:70 is standard with the L46/M-21, so I probably should trust the 1969 GM engineers.

In late '60s - early '70s chevelles/elcaminos, the 3.31 axle ratio was very common with M21/22 2.20 1st gear from the factory. I'm pretty sure 3.31 was the standard for several years. That combination works very well for around town and highway driving, I had several with that combination. They were in applications ranging from a '70 454/450 hp to '72 370/270 hp. The '72 performed very well even pulling a small trailer. If 3.55 is what you want you should have no problem. If it is to see more highway driving than city I wouldn't hessitate going with 3.31 myself.

My real preference would be to swap out the M21 for an M20 with 2.52 1st gear and go with the 3.55. With this combination the overall ratio in 1st gear would be the same as the M21 with the 4.11 - equal performance off the line while gaining the bennefit of the 3.55 at highway speeds.

The M20 (2.56 or 2.52 first) was typically standard with 3.31 gears, the M21/M22 (2.20 first) was typically standard with 3.73 gears. I don't think the close ratio transmissions were ever offered with 3.31 gears as standard, not sure they were even ever available together optionally.

Actually the 1970 LS6 M22 came with 3:31 standard and 4:10 optional.

Although after everything I've read here and on the Corvette board regarding the gearing of the close ratio M21/M21, I can't understand why.

Unless the shear brute torque of the LS6 overcame the handicap off the line.

The M20 (2.56 or 2.52 first) was typically standard with 3.31 gears, the M21/M22 (2.20 first) was typically standard with 3.73 gears. I don't think the close ratio transmissions were ever offered with 3.31 gears as standard, not sure they were even ever available together optionally.

My '71 454/M22 came with the standard 3.31 ratio. I'm pretty sure this was true in '70 too but my '70 454/M22 came with the optional 4.10 ratio. My '72 had the 350/270 M20 came with 3.31 standard. All references are Chevelle/Elcamino though, not Corvette.

I used to run the M20 with 4.10s....worked great on slicks!

I put in 3:55 with my 396/close ratio. I was going with 3:70, but was concerned about rpm on the highway. 3:70 would have been much better for stoplight driving, but the 3:55 is OK with all the torque I have. A wide ratio tans with 3:55 would have been perfect and if I run into a wide ratio trans in the future I will pick it up and do the switch some day.