I am building a blowen 460 Chevelle with a 671 supercharger and can get an M21 for cheep will it hold up to this motor?

Yes, as long as you only run 195/78r14 tires on it! :D If you ever get it to hook, your car will get free rust proofing underneath it.

So I would be best with a th400 then I guess. How are the th400s with trans brakes do they last very long?

If built with your application in mind, and not just a stock rebuild. Yes, very reliable. A trans brake doesn't make the trans stronger though.

Yes I know the brake doesn't make them stronger, I'm just saying that when you let go of the brake at a high rpm with a set of slicks it must be hard on the tranny.

I am building a blowen 460 Chevelle with a 671 supercharger and can get an M21 for cheep will it hold up to this motor?

At least look for an M22 if you want a manual box but, even that may not survive. It all depends on your driving habits and if your car has wheel hop.

You could use a Saginaw 4 speed behind the blown 460. Just don't side step the clutch, flat shift, or shock the driveline! Doesn't sound too fun! If you go over the top with an engine, you will have to do the same for everything in the driveline. Beef it up!

Yes I know the brake doesn't make them stronger, I'm just saying that when you let go of the brake at a high rpm with a set of slicks it must be hard on the tranny.

Its harder on U-joints and rearends, what are your intentions for the car when its done? Put something like that in front of the stock driveline, you'll find the weak spots quickly :thumbsup:

Its harder on U-joints and rearends, what are your intentions for the car when its done? Put something like that in front of the stock driveline, you'll find the weak spots quickly :thumbsup:

It’s just going to be a street/strip car. As for the rear end it has a built 12 bolt with 4.10 gears.

I've blown up 2 m-21s in my 69z-28 with a 350 horse 350. Both were profesionally rebuilt with an iron midplate. They just don't like being slammed into 3rd. Good Luck