[daleb]

I am building a 65 GTO Convertible. The engine is a built 455, tri-power, M-21 close ratio tranny and a 3:55 posi rear end. A friend told me I would not like that tranny with that engine and 3:55 rear end. I have a Doug Nash 5-speed but to use it I would have to change out my new Centerforce clutch (10 spline) and put a new end on my driveline. Anyone have a combo like this and if so do you like it? Or, any comments about this combo. Thanks, DaleB

[Grusome Goat]

This setup will work fine especially with the 455.

[302 Z28]

Can't understand what you would not like about it. I agree, it will work fine. That is what Pontiac had in them

Vince

[Grusome Goat]

Also with a Nash 5-speed you would need to go to a 3.23 gear as the 3.55 is to steep for the first gear in a Nash. By all means stay with what you have as the 455 has plenty of torque and that will mor than make up for the gearing of the 21.

[k-star]

I also agree you will love that set-up,, just stick with what you have..

Keith

[daleb]

Thanks guys for the input. I feel better about the Muncie setup now.

[35chev/302gmc]

How tall are the rear tires you plan on using?

[wendy goode]

hay Ive tried a400 with a m-21 to411 posi and felt that tork off the line but it wasnt practical for street at all and fuel use was crazy , Ive gone to 323s and Im really happy with that combo. on the street and at the drags.

[daleb]

I have 255/60/15's for the rear, on an 8 inch rim.

[Ozz1967]

Dude, they used Muncie's for years in cars like yours! lol I've got a M21 in my 67 Camaro with 3.42 gears and 255 50R15 wheels on the back. I'm running 3000 RPM at 70 mph but I get up and go! I think you will be very happy with your 4-speed set up.