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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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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. |
#5
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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 |
#6
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1965 Lemans (462 Butler, Duel Quads, Muncie M20 with 3.55s)
Is this the car? ...(from your signature) |
#7
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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) |
#8
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When I first bought my car, the M21 was paired with 3.31s in the rear. After I worked on the tune a bit, it ran great and - with the lousy tires on it - spun the tires in all 4 gears.
During restoration, I switched to 3.73s and good rubber - that REALLY woke it up.
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1965 Pontiac LeMans. M21, 3.73 in a 12 bolt, Kauffman 461. |
#9
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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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#10
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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 |
#11
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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) |
#12
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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 |
#13
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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 |
#14
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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) |
#15
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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 |
#16
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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. |
#17
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Quote:
Edelbrock intake Cam: Xtreme Energy XE274H 274/286, 230/236, .488/.491, 110 Hyd They have been tuned. Should be scary to drive, right!
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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) |
#18
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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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#19
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Quote:
Edelbrock intake Are those carbs way too small in your opinion?
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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) |
#20
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