ring and pinion advice
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
ring and pinion advice
I have a 69 BB with a 4 spd M20
I have verified that the gear set is 3.90 to 1 and I don' like it. 3000 rpm at 58 MPH.
I'm thinking of going to a 3.36 to 1.
This car will not be going to the drag trip. I want the car to be driveable foe the street.
Advice will be appreciated
I have verified that the gear set is 3.90 to 1 and I don' like it. 3000 rpm at 58 MPH.
I'm thinking of going to a 3.36 to 1.
This car will not be going to the drag trip. I want the car to be driveable foe the street.
Advice will be appreciated
Tech Contributor
Joined: Aug 1999
Posts: 15,164
Likes: 3,966
From: Connecticut, USA
390 was offered long ago by GM as a performance gear, Richmond Gear also offered it. It was never a production gear ratio.
Your 427/390 HP M20 will work fine with a 336 gear. Some came with a 308 as well and the BB torque will drive 1st gear as well. I have built several of them and the owners were all drivers, no racing, and really liked the setup.
You will want to confirm the year of the diff though in case it was replaced. There are some variances in them from year to year, not with bolt in application but with strengths and weakness of the parts. Since you have a 390 it was built for some performance and most likely abuse so you will want to know there are no issues with it.
Your 427/390 HP M20 will work fine with a 336 gear. Some came with a 308 as well and the BB torque will drive 1st gear as well. I have built several of them and the owners were all drivers, no racing, and really liked the setup.
You will want to confirm the year of the diff though in case it was replaced. There are some variances in them from year to year, not with bolt in application but with strengths and weakness of the parts. Since you have a 390 it was built for some performance and most likely abuse so you will want to know there are no issues with it.
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
My 69 427/390 has an M20 and a 3.08 and I wouldn't want anything more for gearing. Who wants to be cruising at 3000 rpm just to do the speed limit? The thing is a torque monster anyway.
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
Race Director
Joined: Mar 2016
Posts: 14,348
Likes: 8,158
From: Napa Valley California
As part of the resto/mod to my 73 I'll be running a 496 with a TKO-600RR (.82 5th gear) and 3.08 rear end gears.
I'll be able to cruise at 2181 rpm at 70 mph in 5th.
With the 1.0 4th gear in the M20 you should be about 2660 rpm at 70 mph.
Nice!
I'll be able to cruise at 2181 rpm at 70 mph in 5th.
With the 1.0 4th gear in the M20 you should be about 2660 rpm at 70 mph.
Nice!
Last edited by OldCarBum; Dec 3, 2019 at 06:50 PM.
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Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
Are those numbers for the M20 with the 3.08 gear?
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
I'm with the consensus here. Go with a 3.08. I had a '69 a decade ago with ~525hp and 540tq (flywheel... I dyno'd it at the rear wheels, so I'm extrapolating the numbers for flywheel) and I had a Richmond 5-speed in it which has a 1:1 high gear, just like your M20. 3.08s were great on the highway at 70-80mph, which is what everyone runs here where I live, it seems. Granted, that transmission had much lower and closer 1st-3rd than yours has, but I think even with your M20, you will have plenty of low-end TQ. You'll probably be able to do 50-55mph in 1st gear, too... and that can have its advantages if you're not boiling the tires.
Le Mans Master
Joined: Feb 2005
Posts: 6,954
Likes: 0
From: New Jersey
running a 3:36 that Trac-Dog did 2 years ago and it is a pleasure on the street now with a new Auto-Gear wide ratio M-22, with the solid lifters it really winds up and has a wicked long 1st and 2nd gear
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
My 427 has been rebuilt 60 over with a Howards hydraulic roller cam now. Its a mild cam.
Basic rpm range 1600 to 5000 rpm
Lift in and exh .555
Intake Duration @ .050: 219
exhaust Duration @ .050: 227
lobe separation: 110 deg
good idle , performace street, great low to Mid range
Using the Rochester quadrajet which I'm very happy with..
The 3.90 gear is way to much gear because its not utilizing the rpm range where all the torque is.
The 3.08 might be the answer.
Basic rpm range 1600 to 5000 rpm
Lift in and exh .555
Intake Duration @ .050: 219
exhaust Duration @ .050: 227
lobe separation: 110 deg
good idle , performace street, great low to Mid range
Using the Rochester quadrajet which I'm very happy with..
The 3.90 gear is way to much gear because its not utilizing the rpm range where all the torque is.
The 3.08 might be the answer.
Race Director
Joined: Mar 2016
Posts: 14,348
Likes: 8,158
From: Napa Valley California
My gear ratio calculator shows with your M20 transmission you have a 1.0 4th gear ratio and with a 3.08 rear end gear you should be turning about 2660 rpm at 70 mph.
The calculation is using a standard 27" tall tire.
Your actual rpm at 70 mph may differ slightly depending on your actual tire diameter (26.5 diameter tire will bring the rpm's to about 2697 at 70 mph).
The calculation is using a standard 27" tall tire.
Your actual rpm at 70 mph may differ slightly depending on your actual tire diameter (26.5 diameter tire will bring the rpm's to about 2697 at 70 mph).
Pro
Joined: Mar 2014
Posts: 529
Likes: 113
From: Texas
Your best option would be this.
https://shiftsst.com/blog/post/1968-...ctfit-kit.html
But I agree with the rest 3.08 gears with your 4 speed and engine would work well.
https://shiftsst.com/blog/post/1968-...ctfit-kit.html
But I agree with the rest 3.08 gears with your 4 speed and engine would work well.
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
Your best option would be this.
https://shiftsst.com/blog/post/1968-...ctfit-kit.html
But I agree with the rest 3.08 gears with your 4 speed and engine would work well.
https://shiftsst.com/blog/post/1968-...ctfit-kit.html
But I agree with the rest 3.08 gears with your 4 speed and engine would work well.
Last edited by Z06CE; Dec 4, 2019 at 01:21 PM.
Race Director
Joined: Mar 2016
Posts: 14,348
Likes: 8,158
From: Napa Valley California
I would install the 3.08's and enjoy the improvement.
If you want to lower your highway rpm's even more in the future, save your pennies and pick up a Tremec 5 speed.
You could recover some of the cost by selling your rebuilt M20.
If you want to lower your highway rpm's even more in the future, save your pennies and pick up a Tremec 5 speed.
You could recover some of the cost by selling your rebuilt M20.
Last edited by OldCarBum; Dec 4, 2019 at 01:28 PM.
Racer
Joined: Jan 2002
Posts: 293
Likes: 2
From: Warrensburg, MO
Wanna Trade
Z06CE, I have a 3.08 HD differential with yokes, AW code that I’m trying to trade for a 4.11 or close (3.90 would work). It’s listed with pics in the C3 parts for sale/trade. I have the 3.08 gear in my 68 with the M20 and with my 27” tires, it turns 2400 at 60, 2600 at 70. Great cruising gear. Changing a pumpkin is a lot easier than changing a ring and pinion. I’m in Missouri.
Jimbo
Jimbo
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
Z06CE, I have a 3.08 HD differential with yokes, AW code that I’m trying to trade for a 4.11 or close (3.90 would work). It’s listed with pics in the C3 parts for sale/trade. I have the 3.08 gear in my 68 with the M20 and with my 27” tires, it turns 2400 at 60, 2600 at 70. Great cruising gear. Changing a pumpkin is a lot easier than changing a ring and pinion. I’m in Missouri.
Jimbo
Jimbo
My 390 is still in my vette.
I'm in Palm City, Florida
Racer
Joined: Jan 2002
Posts: 293
Likes: 2
From: Warrensburg, MO
Z06CE
No, this is a spare complete differential I bought a while back with the intention of putting a bigger gear in it for my '73 Vintage Race car to run on short tracks. It appears to be ready to "plug and play" after a wire brush and some black paint. I have family all over Florida (I grew up in Micanopy), but don't know of any trips upcoming. My email is: kjhawg@outlook.com
Jimbo
No, this is a spare complete differential I bought a while back with the intention of putting a bigger gear in it for my '73 Vintage Race car to run on short tracks. It appears to be ready to "plug and play" after a wire brush and some black paint. I have family all over Florida (I grew up in Micanopy), but don't know of any trips upcoming. My email is: kjhawg@outlook.com
Jimbo
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
Z06CE
No, this is a spare complete differential I bought a while back with the intention of putting a bigger gear in it for my '73 Vintage Race car to run on short tracks. It appears to be ready to "plug and play" after a wire brush and some black paint. I have family all over Florida (I grew up in Micanopy), but don't know of any trips upcoming. My email is: kjhawg@outlook.com
Jimbo
No, this is a spare complete differential I bought a while back with the intention of putting a bigger gear in it for my '73 Vintage Race car to run on short tracks. It appears to be ready to "plug and play" after a wire brush and some black paint. I have family all over Florida (I grew up in Micanopy), but don't know of any trips upcoming. My email is: kjhawg@outlook.com
Jimbo