Thoughts On A Gear Ratio For My Rear End - Chevelle Tech
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post #1 of 23 (permalink) Old Sep 3rd, 19, 10:37 PM Thread Starter
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Thoughts On A Gear Ratio For My Rear End

I'm running a 454 power plant and 700R4 Tranny and I'm wondering what would be a good gear ratio? I'm running the stock (Real Close) 15" tire size. This is a street car and I'm not racing it (Not saying it will never end up on a track). I want it to take off like a 4:10 but hit the freeway with a low RPM like around 2000-2200. Thoughts?

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post #2 of 23 (permalink) Old Sep 3rd, 19, 11:40 PM
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Re: Thoughts On A Gear Ratio For My Rear End

With 3.73's, you'll be doing roughly 70 mph in overdrive (.696:1). That's about 2200 RPM with a 28" tire.
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post #3 of 23 (permalink) Old Sep 3rd, 19, 11:52 PM
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Re: Thoughts On A Gear Ratio For My Rear End

Since you know what RPM you want to cruise on the highway, thatís the place to start. Find a gear ratio calculator and crunch some numbers.

By the way, 700R4ís have a steep 1st gear (3.06), itís not necessarily a good idea to run a high numerical rear end gear. 3.06 x 4.10 = 12.546 overall first gear ratio.

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Last edited by Steve R; Sep 4th, 19 at 12:12 AM. Reason: X
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post #4 of 23 (permalink) Old Sep 4th, 19, 12:07 AM
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Re: Thoughts On A Gear Ratio For My Rear End

Spicers gear calculator...


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post #5 of 23 (permalink) Old Sep 4th, 19, 7:42 AM
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Re: Thoughts On A Gear Ratio For My Rear End

Given the steep first gear and you have a 454 I think a 3.73 would be good when you factor in the OD it is like having a 2.60 rear which is good. I have a GV OD in mine and I am at a 2.90 final drive with OD rear and I wish I had 10% more so a 2.60 would be right there.
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post #6 of 23 (permalink) Old Sep 4th, 19, 7:43 AM
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Re: Thoughts On A Gear Ratio For My Rear End

A 3.42 or 3.55 would work well with the 3.06 first gear and overdrive. Your tires are probably about 26 inches tall if they are stock size. It would help if you gave your tire size and what RPM you want to run and what speed.


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post #7 of 23 (permalink) Old Sep 4th, 19, 8:28 AM
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Re: Thoughts On A Gear Ratio For My Rear End

I have a 454 with a 700 and 3.31 gears and 26.5Ē tires. First gear goes away very quickly. There is such a wide split, I canít imagine using a deeper rear gear than a 3.55.
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post #8 of 23 (permalink) Old Sep 4th, 19, 11:49 AM
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Re: Thoughts On A Gear Ratio For My Rear End

Here is what I have. 1970 Nomad Sta. Wgn. 4380 Lbs. I built it to look like a SS 454, Its a very nice FRAUD.
My engine is a mild ( like the LS-5, 468)---Transmission- 700R4---Rear end---Chevelle 12 bolt with 3:07 gear, WHY a 3:07 gear?
My 700R has a 3:06 first gear ( Kinda like low range in a 4WD.). Mash on it from a dead stop and the Prius beside you will drive away while you are burning your tires down. While burning the tire it may or will go to second. ( burning tire and shifting under these conditions is not a smart thing to do with a 700.)
Why a 3:07 rear gear? G.M., Chevrolet used a lot of 3:08s with the 700R4 transmissions. So, Before I went to a 3:07 -12 bolt, I ran the 10-bolt 3:08 for a year just to see the results. I was a Happy Camper. So I built a 12 bolt with a 3:07. Here are some numbers. My 700 has a bit over 40.000 miles on it. first wagon engine 396 then a 454 now a 468. AND NO, I do not race it or mash on it a lot. WHY? My pea brain says, G.M.s 700R4 transmission were built for V-6s and small " TORQUE " V-8 engines.
Since I have GEESER statis,,, I know Dam well BIG TORQUE engines will find the " WEAK " link in the chain.
At 75 MPH in Electronic cruise. B.B. spins 1975 RPMs. & 18-19 MPG.----- W-A/C= 16--17.
At 65 MPH in " " " " B.B. spins 18?? RPMs & 20 MPG. W-----A/C=18--19
My tires a 225 X 70R X 14".
Not real good fuel mileage in traffic or going to a cruise,,, Its in first & second a lot. Fuel delivery= 1970 Q-Jet built for this engine.

Bob
If you want to beat on it? I would go with a T-400 or a 727.
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post #9 of 23 (permalink) Old Sep 4th, 19, 12:23 PM
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Re: Thoughts On A Gear Ratio For My Rear End

This is a Post Script to my Station Wagons, 700R4s 40.000 mile life span. After building a 12 bolt posi with ( Catholic ) axels " Moses "...
I did a hole shot or two. 70 Station Wagons have a bit of weight over the 12 bolt, They HOOK UP VERY,,VERY well...
My Alligator mouth said to my Canary Azz, This may bring your 700R4 to the eve of destruction, So I pulled the posi and now its a peg leg.
So, Now I drive it everywhere, Just like Grandpaw!!!!! Also, No parts are landing on the asphalt.
Remember.... "We get to soon old and to late smart."
Bob


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post #10 of 23 (permalink) Old Sep 4th, 19, 11:11 PM Thread Starter
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Re: Thoughts On A Gear Ratio For My Rear End

Nice info Bob!

I'm going to run the stock size of tires 225-75R x 15 and I would be happy with around 2200 on the freeway at 70. I'm going to have some work done on the 700r4 but I could still go another route. I have the original TH400 but I was wanting to add over drive.

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post #11 of 23 (permalink) Old Sep 5th, 19, 8:31 AM
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Re: Thoughts On A Gear Ratio For My Rear End

I'd go with 3.42's. Give you some good take off power but still maintain a good gas mileage on the highway.

I'd go with Richmond Gears.

https://www.jegs.com/c/Transmission-...29731&sbv=true
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post #12 of 23 (permalink) Old Sep 5th, 19, 9:18 AM
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Re: Thoughts On A Gear Ratio For My Rear End

When I had a big block 454 and 700R4 I ran 3.36 in my 12 bolt rear.

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post #13 of 23 (permalink) Old Sep 5th, 19, 10:52 AM
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Re: Thoughts On A Gear Ratio For My Rear End

I run a 4l60e(700r4 electronic version) with a 3.73 rear and 26.9 tall tire and see 2450 rpms at 70 mph. A 3.55 with a 26 inch tall tire would put you near 2250 rpm at 70 mph.This is calculated with the converter locked in fourth gear. Add another 200rpm if not locking the converter

Last edited by modern malibu; Sep 5th, 19 at 11:13 AM. Reason: wrong tire size
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post #14 of 23 (permalink) Old Sep 5th, 19, 10:59 AM
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Re: Thoughts On A Gear Ratio For My Rear End

If you get TOOOooooo deep with the rear gear, You will be is second gear in the blink of a eye. A muncie first is 2:20 / 2:54. First gear in a 700R4 is "" 3:06 "", Thats DEEP!
My gear set up works fine because I have a Motor Home cam. My cam is in at around 900 RPMs. Did you ever notice the giant gas powered motor home with a gas engine leave a red light pretty quick. Cams in a 900 and dies at around 42 / 4400. Good mileage and tons of power with a big cube & big torque engine.
I built my wagon to go on very long cruises and trips. When I stomp on it at 75 MPH, I drops into third and goes into fourth around,,, 102--105 MPH.
I only did that once or twice, WHY? I just do not have the LARGE MALE parts to do that anymore....
My driveline is like a modern class 8 Diesel road tractor. #1 Big cubes & Torque--- #2 Get it in the highest gear quick--- #3 keep the RPMs low.
Bob
P.S. My driveline will " NOT " work with a small block??? A small block with the same set up you will be in THIRD most of the time. Mine is set up for a big CUBE and a BIG torque engine. I do not want to be in my Sta. Wgn. on a flat road when the tach. says " 4000 " RPMs....


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post #15 of 23 (permalink) Old Sep 5th, 19, 3:12 PM
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Re: Thoughts On A Gear Ratio For My Rear End

I've got a 2.73 with the T700R4 and can spin the tires in first with no problem. I can't imagine driving with a 3.73. I plan at some point to change gears, but with 1st as it is (as Robinls5 said) low to mid 3 series is as high as you would want to go. I run 2,000 rpm at 80 mph (1,500 rpm at 60 mph!) with my tires, so the 3.07 would bring this to 2,250 rpm and 3.42 would be 2,500 rpm at 80 mph.

And 1st gear total ratios (rule of thumb aim for 10) with the T700R4 for various rear gears:
2.73 x 3.06 = 8.35
3.08 x 3.06 = 9.39
3.31 x 3.06 = 10.13
3.42 x 3.06 = 10.47
3.55 x 3.06 = 10.86
3.73 x 3.06 = 11.41

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