If you want to get out on the open highways and put miles on, go with the 3.07's. I have those in my Strato Chief with a 15" tire to knock down the rpm a bit. With the stock size 14" tires even the 3.07's were borderline as far as I was concerned. Will 3.31 with an M20 work fine? Sure, it did way back when but that was in the days when 2500+ rpm on the highway was considered normal. Now anything over 2000 rpm on the highway is considered excessive.
Honestly, you're in an over 4000 pound car. If you want jaw dropping performance you bought the wrong car!
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
307 with a close ratio M21 ? whats your thoughts on using this Carl?
I suspect an M21 with 3.07 wouldn't be much fun at stop signs. The M20/3.07 combo is ok with a big block but I wouldn't want any less mechanical advantage.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
This is an interesting topic. My 70 LS6 Parisienne with wide ratio M20 has 3.07 rear gears. It's also running tall 15" tires (235/70R15). I'm using a 3 finger McLeod clutch which grabs pretty good. The 3.07's are ok around town, but I'm buzzing 3000 rpm at 80 mph on the highway.
I've purchased another 12 bolt diff from a 70 Impala with 2.73 gears, have removed that carrier and have put the 2.73 ring gear on a posi carrier. I'm yet to drop that carrier into that diff yet - maybe this spring. I'll experience more chatter around town with the 2.73's, but will drop my highway rpm's.
-- Edited by seventy2plus2 on Sunday 4th of February 2024 02:11:04 PM
-- Edited by DonSSDD on Sunday 4th of February 2024 05:37:08 AM
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic
Keep the 4:10's and do this. Only you would know that's not a Muncie under the car. That's my 2 pennies. You'll have the best of both worlds. No compromise.
I was talking to a guy at a show years ago with a nice Beaumont with a 396. He was running a Saginaw four speed with a 3:50 low gear with a 2:73 rear end ratio. He still had the original Muncie and rear end, 3:55 ratio I think. For going to cruise nights and shows the car was much more usable with the Saginaw and 2:73 gear.
That 3.50 first gear would sure make a difference.
Exactly, and how many of use really abuse our cars. The Saginaw trans although not as strong as a Muncie would be fine for the type of usage our cars would see today.
That 3.50 first gear would sure make a difference.
Exactly, and how many of use really abuse our cars. The Saginaw trans although not as strong as a Muncie would be fine for the type of usage our cars would see today.
Yes, the way I drive my car a Saginaw would never break. I only use a Muncie to make it correct, no other reason.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
What's that diff out of? It's missing the bracket to hold the brake line flex hose. That bracket is unique to 69-70 12 bolts, the 10 bolt bracket is different.
You've got 3.31s waiting? Run them! They are a great compromise between launch-ability & highway livability. That is what a 4-speed big block '69 Big car would have come with originally by default anyway.
The nice thing about 4.10s and a hot engine, at 60 mph you will be at your torque peak and can generate rubber at that speed. As I like to say, "tell it to the judge..."
3.07 gears with a close-ratio M21 makes no sense for stop-and-go driving, but it is great for slice & dice at speed on a course where the close ratios give a smaller rpm drop between gears. It is a pretty specialized combination. We used to have options, until Fleet Average Fuel Economy hijacked the option list & cancelled things.
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67 Chevelle Malibu Sport Coupe, Oshawa-built 250 PG never disturbed.
In garage, 296 cid inline six & TH350...
Cam, Toronto.
I don't judge a man by how far he's fallen, but by how far back he bounces - Patton
But I agree that the 3.31 is the best available compromise. I had 3.08's in my 65 with the M20 4 speed, a little soft off the line, but all round pretty happy for the most part.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
What's that diff out of? It's missing the bracket to hold the brake line flex hose. That bracket is unique to 69-70 12 bolts, the 10 bolt bracket is different.
This is the tough part of a car like this.
We know these guys did a lot of swapping 40 years ago.
Historic value was never a consideration.
They may not even had known how rare the car was.
I'm trying my best with what I have and what I can find
-- Edited by ABC123 on Sunday 4th of February 2024 04:59:09 PM
But I agree that the 3.31 is the best available compromise. I had 3.08's in my 65 with the M20 4 speed, a little soft off the line, but all round pretty happy for the most part.
When I think of your your choices I believe 3.31s is the way to go. If you want to go on the Highway take the white car with 273,s Auto and A/C . You have 2 cars and the best of city and highway cruisers
