[Formulajones]

Originally Posted by thirtypointer

Yes still have the M20 and 3.55s. It was the duel carbs not tuned correctly.


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Yep that makes sense. I wouldn't have recommended switching to the M21 as it would have made that scenario worse.

[61-63]

2.52x3.55=8.9 and the ideal is 10.0 so you could go to a lower rear gear but 8.9 you shouldn't have to be feathering the clutch. A properly tuned quadrajet would be good but dual quad AFBs of any cfm should throw you in the back seat.

[unruhjonny]

Originally Posted by 61-63

2.52x3.55=8.9 and the ideal is 10.0 so you could go to a lower rear gear but 8.9 you shouldn't have to be feathering the clutch. A properly tuned quadrajet would be good but dual quad AFBs of any cfm should throw you in the back seat.

I think you're applying current logic, from the angle of best e/t's;
At the time when these cars were built, it wasn't uncommon for effective first gear ratios being well under 10;
According to current logic, no 1970 Firebird drivetrain combination would be acceptable:

2.73 x 2.52(M38) = 6.88 (common pairing)
3.07 x 2.48(M40) = 7.61 (common pairing)
3.08 x 2.52(M38) = 7.76 (common pairing)
3.31 x 2.52(M20) = 8.34 (common pairing)
3.55 x 2.52(M20) = 8.95 (common pairing)
3.73 x 2.2(M21) = 8.21 (common pairing)
3.73 x 2.52(M20) = 9.39 (very uncommon pairing)

For 1972 the "best" gearing you could get was 3.42 - it was split between M20 & M21;
3.42 x 2.52(M20) = 8.62
3.42 x 2.2(M22) = 7.52

[Formulajones]

A lot of those ratios suck LOL Sorry. And a lot of the really bad ones (first 3 listed) are automatics that don't have any bearing on the subject. Torque converter takes that out of the equation.

Speaking of 4 speeds with a clutch it's not from just a performance standpoint but from a drivability standpoint as well. I have some of those combos here. Not always the most pleasant to drive. Especially in traffic and some of the mountain grades we have.

I'm more in line with 61-63. I like my first gear start ratios right around 10. That's not even close to being optimal for drag racing either for many combos, but it sure is much more pleasant to drive. Once they start getting down around 9 that's about all I can stand. Below that and they start to be a real nuisance and I'll change around what ever I have to in order to make that more pleasurable.

[unruhjonny]

Originally Posted by Formulajones

A lot of those ratios suck LOL Sorry. And a lot of the really bad ones weren't "common" pairings.

Not from just a performance standpoint but from a drivability standpoint as well. I have some of those combos here. Not always the most pleasant to drive. Especially in traffic and some of the mountain grades we have.

I'm more in line with 61-63. I like my first gear start ratios right around 10. That's not even close to being optimal for drag racing either for many combos, but it sure is much more pleasant to drive. Once they start getting down around 9 that's about all I can stand. Below that and they start to be a real nuisance and I'll change around what ever I have to in order to make that more pleasurable.

I am not arguing the validity of '61-63', or yourself;
actually I was just trying to point out that current logic, isn't what has always been.
I'd suggest that those 'bad' pairings were in fact common - based on model and drivetrain.

[Formulajones]

I think the key point being missed are the cars with clutches. That's really what we are referring to. The autos have converters to multiply the torque so you can run a 2.29 gear behind one if you so please, doesn't hurt anything. Put that behind a 4 speed with a 2.20 first gear and life quickly becomes miserable and clutches expensive

With that said you'll notice GM didn't pair much less than 3.23's with the 2.52 Muncie, and I have never seen anything with that gear that would have had a 2.20 in it. Very common would be a 3.55 with the 2.52 Muncie, and few cars were built with 3.42's or 3.55's that had the 2.20. Was common to see that setup in the vettes in the mid 60's. But that's about as far as it would go. GM was well aware that pushing those numbers too low would increase warranty claims which is why they mandated or recommended certain packages together.

[The Champ]

One thing missing from the effective gear ratio calculations is the 25" tall tires on the original posters car. OE tires were over 27" tall, so his 3.55's are equivalent to about a 3.85 - 3.90.

3.85x2.52=9.7

Very close to that "10" that some people were looking for...

[unruhjonny]

@ Formulajones:

In the latter part of your last post, I understood what you're focusing on close ratio four speeds;
I agree that a close ratio four speed was uncommon to see with anything less than 3.73 (prior to 1971), but please permit me to point out that the list for 1970 Firebirds only has one combination with a close ratio four speed - and it is one of the "common" sets.

As far as original less than idea gear set, permit me to point out:
1971-1973 Trans Am
- standard gearing: 3.42:1
- standard manual transmission: M22 (71-72) / M21 (1973)

I have heard of, and seen many cars with gearing akin to 3.08:1 with an M20...

Prior to 1970 you could order cars with a drivetrain which had an effective first gear ration closer to 10:

2.2(M21) x 3.90 = 8.58
2.2(M21) x 4.33 = 9.53

I do not know if you could order (lets say) a GTO with 4.33's and an M20.

2.52(M20) x 4.33 = 10.911
2.52(M20) x 3.90 = 9.828

[lust4speed]

Yep, "current logic" in my case comes down to two words - Current Traffic. Getting stuck on the freeway in bumper to bumper traffic on the way home from a show and coping with crawl speeds are a big priority today. If I go to a show on the weekend down in Tom S's area I know I have 45 miles of stop and go crawling before traffic lightens up as I make my way home. It's like people know that I can have the clutch out and chug along at 14 MPH so traffic moves along at 8 MPH and I'm doing my best to minimize the clutch cycling. The 3.36 with the wide ratio trans works out to 8.47:1 and crawling along just isn't its forte.

There was a point where I retired the car from drag racing with the 4.11's and 400 auto trans where I was slowly converting back to street use. First was putting the 4-speed back in, and there was a period that I drove the car around with 4.11's and the wide ratio. It was a total blast to drive and even with the high compression big cammed motor it would handle extremely slow traffic speeds. Of course it also sucked big time at anything over 60 MPH so the 4.11 12-bolt was pulled and sold. But that 10.36 first gear drive ratio really worked good on the street, and I'm keeping that ratio in mind as I continue the search for a 5-speed overdrive trans.

Another thing to keep in mind from stock back-in-the-day to now is tire size. If you do the math on effective drive ratios my 3.36 rearend with the 2.75/60R15 tires will have the same engine RPM as a 3.23 and stock Redline Tire combo -- so the big tires are good for one drive ratio increase.

[unruhjonny]

/\ touche!

Tom's area has everything on where I reside - except for anything related to population density;
The worst traffic here pales in comparison to being stuck on an interstate in so-cal...

[Formulajones]

Originally Posted by unruhjonny

@ Formulajones:

In the latter part of your last post, I understood what you're focusing on close ratio four speeds;
I agree that a close ratio four speed was uncommon to see with anything less than 3.73 (prior to 1971), but please permit me to point out that the list for 1970 Firebirds only has one combination with a close ratio four speed - and it is one of the "common" sets.

As far as original less than idea gear set, permit me to point out:
1971-1973 Trans Am
- standard gearing: 3.42:1
- standard manual transmission: M22 (71-72) / M21 (1973)

I have heard of, and seen many cars with gearing akin to 3.08:1 with an M20...

Prior to 1970 you could order cars with a drivetrain which had an effective first gear ration closer to 10:

2.2(M21) x 3.90 = 8.58
2.2(M21) x 4.33 = 9.53

I do not know if you could order (lets say) a GTO with 4.33's and an M20.

2.52(M20) x 4.33 = 10.911
2.52(M20) x 3.90 = 9.828

exactly what I'm saying. I know there were 3.42's and 3.55's with the 2.20, but as I said before, that was the extent of it. You won't find 3.23's and 3.08's behind a 2.20. GM was not in favor of that. In the case of the original poster, he thought going to an M-21 would help his woes, when in fact it's much worse than his current M-20 setup for what he was complaining about. M-20 with a 3.55 is about the perfect all around street setup with a little fun mixed in and decent on the highway.
Lust4speed understands what I've been trying to explain. A lot of that 3.42 or 3.55 with a 2.20 trans just flat sucks these days if you really want to get out and actually "drive" the car. I have an M-21/3.55 car here. Trust me, it's not all that fun in Arizona, up hills, traffic, etc.... It's getting a set of 4.10's as soon as I get around to it, and when I get tired of that, I'll just stick a tremec in it.

[unruhjonny]

Originally Posted by Formulajones

... Lust4speed understands what I've been trying to explain. A lot of that 3.42 or 3.55 with a 2.20 trans just flat sucks these days if you really want to get out and actually "drive" the car. I have an M-21/3.55 car here. Trust me, it's not all that fun in Arizona, up hills, traffic, etc...

it was fine for me...
but hey, what would I know