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#1
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Muncie M20 Users: Love or Hate
Looking for advice from current/former M20 drivers. My car is street, monthly drags for fun. When I take off in first gear, it seems like more work than it ought to be. The low first gear (2.52) requires some feathering when letting out the clutch. I have 3.55s out back with just under 25 inch tires. Do you see anything wrong with my set up? I have a chance to switch to a M21 for a interim period as eventually I would like a overdrive tranny. Would that in your opinion make much of a difference? From what I have read, the big rpm fallout between 3rd and 4th would be better with the M21.
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1970 Tempest (428 Whitmore, Cliff Q-jet, Doug Nash Five Speed) slowly coming back to life 1965 Lemans (462 Butler, Cliff Q-Jet, Muncie M20 with 3.55s) |
#2
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If you think it's work now, switching to an M-21 is gonna be worse: The M-21 has a first gear of 2.20- way less multiplication than what you currently have.
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John IG: @crawdaddycustoms YouTube: https://www.youtube.com/channel/UCK9...Nc_lk1Q/videos |
#3
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What is the engine that is struggling with all that mechanical advantage. I’m thinking there is something wrong under the hood.
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
#4
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M-20 ratios 2.52, 1.88, 1.46, 1.00
M-21 ratios 2.20, 1.64, 1.28, 1.00 The drop from 1st to 2nd, then 2nd to 3rd, then 3rd to 4th M-20 .64, .42, .46 M-21 .56, .36, .28 If you had more gear behind an M-21, it'd perform pretty good... until you tached it up on the street. The M-20's drops allow that Pontiac torque to work it's magic- I had a 76 T/A w/ 3.55's, an M-21, and a 455 w/ H~O Racing HC-02, and BFG 265 50-15's. That thing ran pretty good, IF it would hook up. Your car is lighter, and has better gearing, so it should move pretty good.
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John IG: @crawdaddycustoms YouTube: https://www.youtube.com/channel/UCK9...Nc_lk1Q/videos |
#5
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1965 Lemans (462 Butler, Duel Quads, Muncie M20 with 3.55s)
Is this the car? ...(from your signature) |
#6
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What gear ratio in the back? M20 Muncies were in cars with a 3.55 & lower numerically. Cars with 3.70 & up would be M21-22. Won't matter how much power your motor has, it will be hard on the clutch. Your gear ratio determines which tranny to use.
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#7
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Are you sure you're running an M20 and not an M21 or M22?
I'm running an M20 with a 461, 3.42 gear and 28 inch tire which works well. I'd prefer a little more gear but don't want the extra RPMs at freeway speeds. It's all a compromise. With an M20, if anything on your combo with a 25" tire I'd think you would be looking for less gear. The 1st gear multiplication factor on my combo is 3.31 x 2.52 = 8.34 Yours with an M20 would be somewhere around 3.85 x 2.52 = 9.7 Yours with an M21/22 would be somewhere around 3.85 x 2.20 = 8.47. Still higher than mine
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1970 GTO-vert, 461, eheads, stump puller, m20, 3.42 |
#8
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*3.55, not 3.85- that's where the extra is coming from. I was thinking the exact same on the rest of your comments.
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John IG: @crawdaddycustoms YouTube: https://www.youtube.com/channel/UCK9...Nc_lk1Q/videos |
#9
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Looking for advice from current/former M20 drivers. My car is street, monthly drags for fun. When I take off in first gear, it seems like more work than it ought to be. The low first gear (2.52) requires some feathering when letting out the clutch. I have 3.55s out back with just under 25 inch tires.
Hey Thirty, I have a 66 gto, with a 455 and a M-20, 3.42 gears, 27 inch tires in back, im trying to figure out what you mean by feathering when you let out the clutch...…...unless im missing something, i have a CF duel clutch, don't really notice anything different while driving. Rich |
#10
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I have a street 455, 3.23, and M21........no problem at all getting going. With your 3.55, it should be easier than you are experiencing......especially with the 2.52 and 3.55 = 8.94 torque multiplication, I have 2.20 x 3.23 = 7.1 . Obviously tire size not in the equation here.
I skip 3rd usually and drive in 4th....still pulls when accelerating in 4th at 30 MPH. George
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"...out to my ol'55, I pulled away slowly, feeling so holy, god knows i was feeling alive"....written by Tom Wait from the Eagles' Live From The Forum |
#11
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Quote:
Yes that’s the one. Sent from my iPhone using Tapatalk
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1970 Tempest (428 Whitmore, Cliff Q-jet, Doug Nash Five Speed) slowly coming back to life 1965 Lemans (462 Butler, Cliff Q-Jet, Muncie M20 with 3.55s) |
#12
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Quote:
I meant when taking off/launching it around 3-3500 rpms. Not dumping it completely. I should have explained it better. Sent from my iPhone using Tapatalk
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1970 Tempest (428 Whitmore, Cliff Q-jet, Doug Nash Five Speed) slowly coming back to life 1965 Lemans (462 Butler, Cliff Q-Jet, Muncie M20 with 3.55s) |
#13
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Quote:
Yes to it being an M20. (3.55s rear gear) Sent from my iPhone using Tapatalk
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1970 Tempest (428 Whitmore, Cliff Q-jet, Doug Nash Five Speed) slowly coming back to life 1965 Lemans (462 Butler, Cliff Q-Jet, Muncie M20 with 3.55s) |
#14
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Muncie M20 Users: Love or Hate
Quote:
462 with duel eddys. A couple of guys who know their stuff have told me to go to a single q-jet. Sent from my iPhone using Tapatalk
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1970 Tempest (428 Whitmore, Cliff Q-jet, Doug Nash Five Speed) slowly coming back to life 1965 Lemans (462 Butler, Cliff Q-Jet, Muncie M20 with 3.55s) Last edited by thirtypointer; 07-17-2019 at 04:25 PM. |
#15
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What CFM carbs?
Are they calibrated to be run as a dual quad setup? Cam? Could/should be a monster..when tuned well, most DQ setups suffer from being way to rich just about everywhere. Unless something is way out of bounds hard to kill the torque of a big cube Pontiac @ 3K. |
#16
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What 2-4 intake?If a E intake,get a Offy.Remember a apair of 500s are not 1000!I would not run anything less than a a pair of 750s on your engine.I have been running 2-4s on pontiac since 1962.Both my 421 HO and my 421 SD have 2-4s.The HO has a a pair of 625s for 100% street driving,the SD has a a pair of 750s.The 428 RA V im building will have a pair of 750s.Tom
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#17
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Quote:
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#18
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A M21 with a 3.36 will be a dog and a clutch killer at the strip IMO,Tom
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#19
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I ran dual 650 AFB carbs non-progressive with 3.36's and the M20 with the Old Faithful cam in the 428. Car always left silky smooth with no effort.
I just solved a problem with the current combo which is a 462, Quadrajet, and a little larger cam that complained a lot on take off. I would have to feather the clutch on normal take offs while playing with the throttle. Problem ended up that I had leaned out the carb's low speed circuit too far and the engine didn't like it. I had decreased the primary jet size two sizes by following my AF meter. After ignoring the meter and going back up three sizes the drivability is now back to where it should be. Talking about wide ratio vs close, back in '67 when I ordered the car I settled on the 3.36 rear and wide ratio for two reasons. The first is I had to commute fairly large distances, and the second was looking at drive ratios. Ever notice that the first three gears with a wide ratio and 3.36 rear are almost the same as a 3.90 rear and close ratio trans? Yeah, healthy drop from 3rd to 4th, but I remember that being about 88 mph with the original tires. Most street races are over way before that, and torque does a pretty good job of pulling through the gap anyway. On the two fours - gas mileage was excellent but when I sold them and put on a 800cfm Quadrajet and Torker I manifold the car went a tenth and a half faster (and lost one MPG). The AFB's were silky smooth and never gave a problem, and I suspect the horsepower limitation was the Offy manifold. Still did okay on Harry K's chassis dyno producing 413 RWH at 5,160. Anyway getting back to the point, if your carb is off it will definitely screw up low speed drivability.
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Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress. |
#20
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Quote:
I also had (I switched to a TKO) one with the M20 and 3.55's out back. This was in a little Z/28 with a 302. Daily drove it like that for about 4 years. Was not that bad really. It's an 8.94 effective 1st gear ratio and I like to be in the 9's for comfortable driving, but it worked fine for years. Wife drives it daily and she never had a problem with it. Fast forward to now, I run a TKO600 in it with a 2.87 first gear. Much more fun, very easy take off, I can slip the clutch and it will take off on it's own without even touching the gas. Not bad for a 302 with a rowdy 254 @ .050 camshaft. 10.20 effective first gear is so much easier to drive around town, parades, traffic, etc... It'll basically idle on it's own at 3-4 mph without the need to keep working the clutch. As far as the 4th gear drop with the M20 it's not a big deal. I actually prefer the M20 over the M21 for both street and drag racing. By the time you hit 4th there is so much momentum the rpm drop with the M20 is really a non issue. What I like though is the M20 has a much better effective gear ratio through the first 3 gears, better than the M21, so the car will accelerate quicker if running the same rear gear. I had another car here I ran the M20 with 4.88's out back and it was a ball to drive. Think of it this way, the M20 ratios are close for the first 3 gears, the M21 is close for the last 3 gears. Typically with an M21 I don't like anything less than 3.73's minimum out back. |
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