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thirtypointer · 07-17-2019, 02:49 PM

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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JC455 · 07-17-2019, 02:56 PM

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.

74Grandville · 07-17-2019, 03:03 PM

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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thirtypointer · 04:25 PM

Quote:

Originally Posted by 74Grandville

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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462 with duel eddys. A couple of guys who know their stuff have told me to go to a single q-jet.

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JC455 · 07-17-2019, 03:03 PM

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.

STEELCITYFIREBIRD · 07-17-2019, 03:25 PM

1965 Lemans (462 Butler, Duel Quads, Muncie M20 with 3.55s)

Is this the car? ...(from your signature)

thirtypointer · 07-17-2019, 04:12 PM

Quote:

Originally Posted by STEELCITYFIREBIRD

1965 Lemans (462 Butler, Duel Quads, Muncie M20 with 3.55s)

Is this the car? ...(from your signature)

Yes that’s the one.

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Chris65LeMans · 07-19-2019, 03:49 PM

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.

Steve Shively · 07-17-2019, 03:28 PM

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.

MrWrestlingII · 07-17-2019, 03:29 PM

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

thirtypointer · 07-17-2019, 04:16 PM

Quote:

Originally Posted by MrWrestlingII

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

Yes to it being an M20. (3.55s rear gear)

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JC455 · 07-17-2019, 03:41 PM

*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.

gtorich · 07-17-2019, 03:44 PM

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

thirtypointer · 07-17-2019, 04:14 PM

Quote:

Originally Posted by gtorich

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

I meant when taking off/launching it around 3-3500 rpms. Not dumping it completely. I should have explained it better.

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george kujanski · 07-17-2019, 03:50 PM

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

STEELCITYFIREBIRD · 07-17-2019, 04:56 PM

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.

thirtypointer · 07-17-2019, 06:45 PM

Quote:

Originally Posted by STEELCITYFIREBIRD

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.

Edlebrocks 1404s (500 cfm)
Edelbrock intake
Cam: Xtreme Energy XE274H 274/286, 230/236, .488/.491, 110 Hyd

They have been tuned. Should be scary to drive, right!

tom s · 07-17-2019, 05:14 PM

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

thirtypointer · 07-17-2019, 06:47 PM

Quote:

Originally Posted by tom s

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

Edlebrocks 1404s (500 cfm)
Edelbrock intake

Are those carbs way too small in your opinion?

TAQuest · 07-17-2019, 05:46 PM

Quote:

Originally Posted by thirtypointer

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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M21 with 3:36. No problem at all. Would like a 5 speed. Until the Muncie breaks it's staying in there.

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