Muncie M21 & Rear Gear Ratio Advice Needed !!!!!!

HiI was hoping to get some opinions from you all when it comes to Muncie transmissions and rear end gear ratios. I am building a 67 RS Camaro to take to cruise nights and drive around town on the weekends.
I am putting in a big block with a Muncie M21. I was told that the trans would not be a good street trans unless I went with steep gears in the rear. I know the M21 and M22 have the same gear ratios and the M20 has steeper gears. I was told that the M20 was better for the street cause of the steeper gears, but others told me it wasn't as strong a trans as the M21. My question is this..Can someone tell me if I use 3.90 gears in the posi rear with my M21, and a big block, is that a good combo? I will need to ride the car down to the Jersey shore which is about an hour away. Will the RPM's be killing me with 3.90's driving on the highway for about an hour (60mph)? Am I better off with 3.73's or are they going to be to whimpy for takeoff. I don't plan to race this car but want to be proud of its performance and kick some import with a big mufflers ass if needed :) Would I be better off with an M20 and 3.73's or what? Is the M20 just as strong as the M21? I know the M22 is the strongest of all. I'm just looking for the best combo for street racing and some highway crusin to get to a show. I am putting in a 454 that's going to be about 450hp and have good torque in the lower rpm range. Any advice from anyone who has experience with this setup would be deeply appreciated.!!!
Thanks Gary
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snipped-for-privacy@att.net says...

You should be fine. I have a 2.52 first M20 in my 71 T/A and it works just fine with the 455. If anything, first gear is a little steep. I usally don't use 1st gear for more than 5 seconds.
M21 and M22 typically have 2.20 first gears which work best on high torque big block Chebbies and large cube Pontiacs.
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I'm running M22 and 4.11 in my 73 'Vette with around 385-400 horses. I originally had an m20 and trashed it in about 3 months of owning the car. I then had it rebuilt, and trashed it again in about 2 months. Not from hard driving either, just lotsa torque. My reverse gear broke somehow and started to engage while going forward....you could imagine the problems with that!
Anyway, back to your question. My car is REAL fun on the street, very very fast light to light, but...on the freeway its a little overbearing. My RPMs around 65 are close to 4K and with headers and sidepipe, its loud! The other downside with the 4.11s is my top speed sucks, around 110.
I think you will be fine with the 3.90s, but expect some high rpm's on freeway, but at 60, it wont be bad. My opinion is if you have more than about 300hp, don't get the M20, it can't handle the toque, i think it is rated around 240 torque. Get M21 (400ish Torque) or M22 (600ish Torque)
Good Luck Casey

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Hey Casey, Thanks for the info. Hell it must have been hell having reverse engage while driving !! I have the M21 now and my motor will be putting out about 450hp. I think I am probably going to use 3.73 gears in the rear and if they are to light then I'll go steeper. I plan on learning to treardown and rebuild a muncie so when and if I do blow it out I can try to rebuild it myself. I dont plan on racing this car or beating on it, just want some great street performance.

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