Quote:
Originally Posted by gobrdgo
Hi everybody. Just picked up a m21 for my 69 firebird. It is a 69 350 2 barrel turbo 350 model. I was wondering if you could share any error traps or shortcuts to make this as painless as possible. Is buying a complete conversion kit the best option? Will the turbo 350 driveshaft work? It came with the yoke for trans and a crossmember which I’m not sure is the same. Happy hot rodding!
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You may not be happy with the M21, in part, due to its 1st gear ratio. The wide ratio M-20 is a better choice because of the better first gear in getting the car rolling.
The wide ratio trans typically used a 3.23 rear gear for the most part, but of course other gears like 3.36, 3.55 were a good choice. The close ratio M21 is better with the 3.90 rear gear.
You did not say what gears you have or if you plan on changing them, but if you have 3.08 or any 2 series rear gears you are not going to like the M21. It can be done, but you can also eat up clutches real fast because you will find yourself slipping the disc a lot more to get the car rolling. If you have taller tires other than the stock 26" tall tires, this will only add to a more difficult start as this can drop the rear gear ratio down to the next lowest set, ie 3.23's down to closer like 3.08's. Your choice of clutch disc material could be important as well as rated clamping force to keep the disc from slipping if you have 3.08's or any of the 2 series gears. More clamping force from the pressure plate may mean a daily trip to the gym to keep your left leg muscles built up - unless you go with a hydraulic throw-out bearing set-up.
I am not a Firebird guy, but you may also want to think about stiffer leaf springs ( believe you have a mono-leaf and may want multi-leaf) and/or traction bars. If I recall correctly, the HO version had a factory type traction bar AND I think the floors had an additional metal plate to add stiffness to the body - but the Firebird guys should be able to confirm this.