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Jayvee53
03-21-2019, 11:41 AM
Hello! A new member here, asking about a 56 Bel Air I found a few states away with limited info to share. I am told this car was originally a three speed manual. Today it has a 383 stroker and a Muncie 4 speed. Don't know anything more about the engine or the Muncie (M20 or M21???) and the guy selling it doesn't have answers either. He says it has a "highway gear". Is it safe to assume it came with a 3.70 seeing as it was born a three speed manual? If so what should I expect as far as performance at highway speeds? I am looking for a good all round driver, something I can use daily and get reasonable gas mileage and not have the engine screaming down the interstate. Is there enough info here to deliver a verdict? Thanks in advance for your help!!!!!

John
markm
03-21-2019, 11:59 AM
No 56 came with a highway gear they were not invented until 1959 when the 3.08 came out. A 3.55 was the std gear for a 56 with pg trans. You are mosy likely correct about the 3.70s probably in the 3500 rpm range at 70.
Jayvee53
03-21-2019, 12:29 PM
No 56 came with a highway gear they were not invented until 1959 when the 3.08 came out. A 3.55 was the std gear for a 56 with pg trans. You are mosy likely correct about the 3.70s probably in the 3500 rpm range at 70.

And 3500 rpm is going to be a bit busy, you agree?
markm
03-21-2019, 12:45 PM
And 3500 rpm is going to be a bit busy, you agree?

Yes, especially since today we have 75 mph on highway and all have OD in our daily beaters.
55 Rescue Dog
03-21-2019, 04:28 PM
3000 rpm at 60 mph use to be pretty much normal. Now, it is like 1650 rpm at 60. It can be resolved.
Rick_L
03-21-2019, 07:53 PM
It's all in your expectations. I used to run a 4.11 gear and drive 75 mph, back around 1970. Maybe that's why I'm hard of hearing now, LOL. Expectations change, especially when you have more choices.
busterwivell
03-22-2019, 04:51 AM
Just got back from Good Guys in Scottsdale. I drove my 56 210. It has 350/700R4 and 3:42 rear on 29 inch tall tires. My son in law went too, in his 67 Chevelle (his first road trip). He has a 327/TH 350 and 3:36 gears on the same size tire. I got 19 mpg, and the car LOVES to run 80/85 at about 2100 rpm. My son in law got a little better than 10 mpg, was buzzing the motor the whole trip, and his 700R4 is being built as we speak. He'll go from about 3000 rpm to about 2100 with this change.
chevynut
03-22-2019, 05:59 AM
Hello! A new member here, asking about a 56 Bel Air I found a few states away with limited info to share. I am told this car was originally a three speed manual. Today it has a 383 stroker and a Muncie 4 speed. Don't know anything more about the engine or the Muncie (M20 or M21???) and the guy selling it doesn't have answers either. He says it has a "highway gear". Is it safe to assume it came with a 3.70 seeing as it was born a three speed manual? If so what should I expect as far as performance at highway speeds? I am looking for a good all round driver, something I can use daily and get reasonable gas mileage and not have the engine screaming down the interstate. Is there enough info here to deliver a verdict? Thanks in advance for your help!!!!!

John

It's hard to say what gear ratio is in the rearend because it could have been changed out to just about anything available. If it's still the stock ratio that came with a non-OD 3-speed it's a 3.70 ratio. If the 3-speed had OD it was a 4.11 ratio.

Changing out the gears is not a big deal, but it will always be a compromise with a non-OD transmission. A 3.55 or 3.70 gear would give you good street performance but non-optimal highway performance. A 3.08 gear would be opposite. I think every car and truck sold today has an overdrive transmission, and there's a good reason for that.

Here's a good calculator https://www.richmondgear.com/wp-content/uploads/calculator/street-performance-calculator.html

A 3.70 gear with a 1:1 final drive and 28" tires gives 3330 RPM at 75 MPH. A 3.55 drops that to 3195 and a 3.08 to 2772. All of these RPMs are too high if you plan to do much highway cruising, imo.

My Nomad has a T56 with double overdrive, .75 5th and .5 6th gears and 4.10 rear gears. At 75 MPH with my 26" rear tires it should be turning 1987 RPM in 6th.