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Old 12-31-2017, 03:24 PM   #1
robertsjm711
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High gear ratio w/ M20 & 5.3 Drivability

All,

I have searched and have not found a clear answer to my question. I have a '53 3100 with a S10 frame, 5.3l, Muncie M20 w/ 2.56 1st, 12 bolt passenger rear w/ 2.27 final & tire height ~27".

Will the 2.27 ratio that is in my rear cause harm to my truck? I plan to upgrade the rear to a lower gear w/ posi, maybe 3.73, but I'd rather spend my limited funds on getting it running, steering, stopping - can I drive it with this setup until I save for a new rear setup? Will the acceleration be so weak it will be undrivable?

As for RPMs, I live in Oregon so speed limits for cruising are fairly low, 55-65mph.
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Old 12-31-2017, 03:38 PM   #2
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Re: High gear ratio w/ M20 & 5.3 Drivability

2.27?
Where did you find that?
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Old 12-31-2017, 03:58 PM   #3
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Re: High gear ratio w/ M20 & 5.3 Drivability

Now that I think about it it is a 2.29 - but it came with the truck when I got it. It was a pile of parts with a passenger 12 bolt so I was pretty excited until I ran some numbers. I think it came out of a mid 60's Impala or Nova, maybe a 2 speed powerglide?
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Old 12-31-2017, 04:16 PM   #4
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Re: High gear ratio w/ M20 & 5.3 Drivability

What’s a couple decimal points between friends! Lol!
Run it.
You’ll be turning 2000 rpm at 70 mph.
Are you carbed or fuel injected?
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Old 12-31-2017, 04:19 PM   #5
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Re: High gear ratio w/ M20 & 5.3 Drivability

Stock fuel injected, ~250-280 hp (per Wikipedia). I know the top end will be better even with a 4 speed, but time will tell about off the line. Its just going to be a Sunday driver or parts truck, not any performance or racing.
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Old 12-31-2017, 04:40 PM   #6
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Re: High gear ratio w/ M20 & 5.3 Drivability

IMHO, you will not like the gearing.....there will be too much slipping the clutch in town traffic Based on a 27" tall tire, I feel that a 3.42 rear set would give the best of both worlds in a cruiser with the M-20.....3.73, if you want to rev it/play.... Longhorn
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Old 12-31-2017, 04:52 PM   #7
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Re: High gear ratio w/ M20 & 5.3 Drivability

The clutch was my main concern, and I'm sure I won't like it. I bet I will drive it some w/ the tall gears, been building for almost two years and once it can move on its own I don't think I could stop myself.
Spending a grand is a tall order (probably on the high side, Randy's R&P prices)- I'll have to start checking eBay & swap meets for deals.
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Old 12-31-2017, 05:00 PM   #8
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Re: High gear ratio w/ M20 & 5.3 Drivability

Take-off manners and acceleration won't be what they would with higher gears, but the 2,000 @ 70 is about how that engine would have been set up in a modern 1/2 ton Silverado. Just off the top of my head, 3.73's without an OD will put highway RPM's higher than necessary - 3.07 or 3.42's may be more to your liking. Either way, that's a really fast first to retain good manners over a broad speed range without an overdrive.
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Old 12-31-2017, 05:36 PM   #9
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Re: High gear ratio w/ M20 & 5.3 Drivability

Look around for a used differential....my brother sold a good 3.73, for a 100 doller bill! On that cruiser, you dont need to build a brand new diff.....Pick the one (proper ratio), with no lube dripping. You might do axle bearings & seals, just for pc of mind. But hear is the thing....if you are not racing the truck, you dont need a 9" Ford, or anything built (money) Best of fun....Longhorn
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Old 01-01-2018, 05:45 PM   #10
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Re: High gear ratio w/ M20 & 5.3 Drivability

Quote:
Originally Posted by crazy longhorn View Post
IMHO, you will not like the gearing.....there will be too much slipping the clutch in town traffic Based on a 27" tall tire, I feel that a 3.42 rear set would give the best of both worlds in a cruiser with the M-20.....3.73, if you want to rev it/play.... Longhorn
What he said. I just went through this in my BB C10 with 3.08 rearend with 27 inch tires. Had a spare M21 so put it in (no way) sold it bought an M20 thinking it would be enough ... barely useable... when I swapped in the DNE2 I saw the heat spots on my pressure plate from the little driving I was doing (probably total of 50 miles) This Doug Nash has a 3.27 1st and it is just right to get the weight moving and still have the 3.08 for what I want on the highway. I would say 3.42 minimum.

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Old 01-01-2018, 06:05 PM   #11
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Re: High gear ratio w/ M20 & 5.3 Drivability

Last car I built was a G-body with a 454 4-speed and at first 3.08s with 27" tall tire and loved it. Still had plenty to start out, and then could do 70-80 without the tach bouncing off the red peg. Then the ring gear took a couple teeth out and went with 3.42s and didn't like em. Take off was better, but highway sucked. Seemed like it pulled harder with the 3.08s over the 3.42s. But, this was a sorta lite car, so truck with less motor would struggle.
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Old 01-01-2018, 06:16 PM   #12
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Re: High gear ratio w/ M20 & 5.3 Drivability

In a truck I wouldn’t go lower than 4.10 or higher than 3.42
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Old 01-01-2018, 06:36 PM   #13
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Re: High gear ratio w/ M20 & 5.3 Drivability

This is all great stuff. I’m thinking a big factor is my weight, this truck is light - not much too it. I was pretty set on 3.73, but 3.42 May be the way to go.
I’ll have to keep it to test drives until I get those gears swapped.
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Old 01-01-2018, 08:23 PM   #14
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Re: High gear ratio w/ M20 & 5.3 Drivability

Try it and see how it is.
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Old 01-01-2018, 08:33 PM   #15
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Re: High gear ratio w/ M20 & 5.3 Drivability

Yes weight is a factor but so is the engine. A big block creates more torque at idle (I have a friend that accidentally shifted into 3rd at the stop light in a 427 Nova and it took off with just a little trouble) than a smaller engine which must 'wind up' more to move the weight. So, the gearing will be very important in the equation.
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Old 01-06-2018, 03:55 PM   #16
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Re: High gear ratio w/ M20 & 5.3 Drivability

You'll be fine.
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Old 01-06-2018, 10:43 PM   #17
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Re: High gear ratio w/ M20 & 5.3 Drivability

Have you tried using this http://www.5speedtransmissions.com/startlineratio.html
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