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Transmission & Driveline Transmissions and Differentials

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  #1  
Old Jun 22nd, 11, 10:07 AM
airtime airtime is offline
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Default will my m21 hold up behind a 550hp bbc?

building a camaro with a 496 stroker, hp in the middle to upper 500. this will be a street/strip car and i plan to lean on it kinda hard every once in a while. i already have a built m-21. i have to buy a bell housin, shifter and clutch so i still have alot of money to get it going. my question is should i just get a different transmission that will hold up better or do you think the muncie will handle it? not concerned with highway cruisin, i will run at least a 3.73 rear gear. full interior, most likely install a 8 point cage.

thanks, airtime
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  #2  
Old Jun 22nd, 11, 10:38 AM
jjgrizz73 jjgrizz73 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Most likely if you beat on it often it won't hold up (however I'm sure people have done it, I just wouldn't feel 100% comfortable). Would have a good shot with a M22 but with the price of one you might be better off going with a 5spd tremec or richmond if you want to keep it a manual.

However I do have a close ratio M22 sitting on the shelf haha.
Also a Lakewood bellhousing and Hurst Comp shifter
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  #3  
Old Jun 22nd, 11, 10:52 AM
airtime airtime is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

u wanna trade for a rebuilt m21??? lol

is the tremec or t56 any stronger? i know the tko 500/600 are rated higher but i was thinking the t56 is rated around 400 to 450 hp
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  #4  
Old Jun 22nd, 11, 11:00 AM
jjgrizz73 jjgrizz73 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Haha, no thanks, just sold one and 2 M-20's

I haven't really done much looking into a T56 honestly, only the TKO's, Muncies, and ST10. I would also look at what kind of gearing you are looking for. What rear are you running? 3.73?
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  #5  
Old Jun 22nd, 11, 11:06 AM
airtime airtime is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

this is new build, so everything is in the planning stage. i will use 3.73 most likely. since this car will be street/strip i am not concerned with an over drive. strength is major concern. i know a t 400 would be best but i wanna bang some gears. i have several old cars so i don't drive any of them much. all the others are autos .
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  #6  
Old Jun 22nd, 11, 11:13 AM
jjgrizz73 jjgrizz73 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Well Im sure you've heard that your best launch comes with a #9 by multiplying your rear ratio x 1st gear ratio. If you go with a TKO you will have your choice of 1st so keep that in mind. Your M21 1st gear should be 2.20 if it was a stock rebuild. This only puts you at around a 8.2. The Muncie 2.2 first was really designed around a 4.11 rear gear set (gives you a 9.0). You can however change the gears in your M21 to the Wide set and have a 2.52 first but I think that will be defeating the purpose of using the tranny you already have.
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  #7  
Old Jun 22nd, 11, 11:40 AM
JodysTransmissions JodysTransmissions is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

If your plans are for a Muncie 4 speed and a 3.73:1 differential, your driveline would be better suited for an M22W with the 2.56:1 first gear. The M22W and 3.73:1 differential would give you a 4.34:1 first gear take off feel compared to an M21 and the 3.73:1 differential. The M22W has been proven to survive 600+hp.

My formula:

2.56 x 3.73 / 2.20 = 4.34:1
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  #8  
Old Jun 22nd, 11, 11:43 AM
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bcm66 bcm66 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Quote:
Originally Posted by airtime View Post
building a camaro with a 496 stroker, hp in the middle to upper 500. this will be a street/strip car and i plan to lean on it kinda hard every once in a while. i already have a built m-21. i have to buy a bell housin, shifter and clutch so i still have alot of money to get it going. my question is should i just get a different transmission that will hold up better or do you think the muncie will handle it? not concerned with highway cruisin, i will run at least a 3.73 rear gear. full interior, most likely install a 8 point cage.

thanks, airtime
What was all done when the M21 was rebuilt? Did you have a bushing installed in the front for the cluster shaft? Did you use a cast iron midplate?

Just from what I can tell from what you posted, you would probably be on the edge of what an M21 can handle without the upgrades mentioned in last paragraph. Doubtful even then if you plan to use sticky tires and launch really hard.
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Last edited by bcm66; Jun 22nd, 11 at 12:16 PM.
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  #9  
Old Jun 22nd, 11, 12:01 PM
jjgrizz73 jjgrizz73 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Agreed, we are running the W gearset in my fathers 68 with 3.70's and the Z gearset (2.98 first) in my 67 running 3.31's. The regular 2.2 with 3.73 will not be ideal in any way.
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  #10  
Old Jun 22nd, 11, 04:00 PM
airtime airtime is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

it was rebuilt about 5 years ago and the guy has since past away. so i am thinking just a regular rebuild and replaced what was worn. so i should go with the 4:11 with the 2.20 1st gear. thar sucker will be wound out in the quarter mile. lol trying to keep it old school on the build/ looks department. i always liked the tall first gears, those granny low m 20's always felt like it was a wasted gear. or course they should of been matched to the 3.34/ 3.55 rearend gear i guess.
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  #11  
Old Jun 22nd, 11, 04:07 PM
airtime airtime is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

i will have to check my current rearend and see if the gears are any good and the ratio. it makes a grinding, popping, ratcheting, banging, pinging, rattling type of noise currently. lol this is a different car than the one in my signature. lol the rearend has ears on top of it like it came from a puck up or other large body car. i bought it from bubba's uncle budro.
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  #12  
Old Jun 22nd, 11, 04:14 PM
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Andrew69 Andrew69 is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

Your big block should have pretty good torque so the 2.20 first and 3.73 gear will not bother you as much as mine would have. With Jody's help I rebuilt my M22 with the "W" gearset and enjoy the 2.56 first gear and 3.73 rear gear combo which equals overall 9.55 first ratio.
I wouldn't recommend anything lower than the 3.73 for your big block unless you are only going down the 1/4 mile strip.
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Last edited by Andrew69; Jun 22nd, 11 at 04:27 PM.
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  #13  
Old Jun 22nd, 11, 04:20 PM
airtime airtime is offline
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Default Re: will my m21 hold up behind a 550hp bbc?

thanks for info guys. sounds like i will be ok with muncie for awhile. transmission is the cheap part, it's the flywheel, clutch, pressure plate, shifter, bell housing that makes it expensive
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  #14  
Old Jun 22nd, 11, 04:24 PM
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Default Re: will my m21 hold up behind a 550hp bbc?

I recommend a scattershield rather than a bellhousing for your setup.
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  #15  
Old Jun 22nd, 11, 04:28 PM
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Default Re: will my m21 hold up behind a 550hp bbc?

Quote:
Originally Posted by bcm66 View Post
I recommend a scattershield rather than a bellhousing for your setup.
Ditto to that.
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