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Discussion Starter · #1 ·
We bought a 76 hardtop as a cruiser for those times when the club goes on longer rides and in not so great weather (our other car is a 71 convertible). I'm tired of wobbling around corners with overall shitty performance so I ordered new rear trailing arms (upper & lower) along with new sway bars and performance shocks to start with the suspension. I'm also thinking about adding a Detroit Truetrac to the rear end and upgrading to a 200r4 4-speed automatic to help out with the highway gas milage and give me a little umpf off the line. Seems like a good choice since it will fit right in place of the 350 and is still a mechanical transmission. This will lead to eventually rebuilding the engine or dropping a crate motor under the hood. I am slightly confused about a proper rear end gear ratio for the stock 10 bolt under these parameters. I don't think I want to go any lower than a 3.23:1 or I run the chance of bogging the engine down at the lower rpm's at highway speed but some of what I have read suggests that a 3.23:1 would be way to aggressive for this type of driving and would suggest something like a 3.08:1. I still want some quickness coming off the line and am running stock size tires on 15 inch rims. Any advise from people who have been here and what your experience was would be most appreciated.
 

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1965 El camino. Originally regal red with a 283 and rear air ride suspension
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Are you planning on running this thing on the freeways or on the street mainly? Gearing is really dependent on what your going to be doing with the car. 3.08 would be good for highway speeds in a vehicle with over drive. Let's say a car with a 4.56 would not be a good choice for highway speeds. The engine would run higher rpms at highway speeds because of the ratio rotation. Taller gear ratio for highway speeds. Shorter gear ratio for acceleration speeds. I have a 283 with a th350 geared with a 3.08 ring and pinion in my 65 Elko. At 70 mph it's running approximately 3000 - 4000 rpm's. If I had overdrive, it would be no problem on the freeway for milage and rpm reasons.
 

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Its all about the intent and entire combo. No matter how high (low numerically) you go in a gear, it has to be matched with the entire drive train, tires to engine. A 2.73 isnt a bad gear for HWY if you have a 3spd auto, or a muncie if you have 650hp under the hood to cover it.

with a modest 350/383 (400/450 HP), a 200r4 and 3.23 isnt bad for the HWY. I actually think it to high and could get away with a 3.73 as well. I drive 60mi round trip HWY every day and I run a 3.00 with a TH350.

If I was doing this project and it was just to be a HWY cruiser, and I'm assuming you have an 8.5 10bolt, id go with a 3.42 rear gear and a 27" rear tire. Usually going with the 27 allows some fine tuning in the RPM / MPH adjustment from 26" to 28" when everything is said and done.

This gear will take advantage of the 2.74 first gear while not letting the .67 fourth lug you down in lower RPM. 1st gear shift not high/low. 80MPH @ 2500 RPM with enough room for higher cruising and or passing at 85-95mph at around 3000rpm. Perfect for Florida HWY driving.

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Mike
 

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I have a 3.73 with a GV overdrive which make it a 2.90. I would say that is on the edge of OK for todays highways in my area. I think a 2.50-2.60 final drive would be perfect (I have a 26.7 inch tall tire). If you had the 3.73 and the .67 gets you a 2.50 which is great. The 3.73 would give you some zip off the line.
 

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For street, cubes, low compression, th-400 with its massive amounts of torque multiplication and a rear end like the 2.73. is the way I like to go.. The Turbo 400 from a standing start has a first gear ratio around 5:1 with a big cubic inch engine like the 454. It may be more with a decent street camshaft that keeps the low end torque up. This is how you get away with running rear end ratios like the 2:73 with a direct 1:1 and have a very fast and enjoyable driving car..
 

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I think the general consensus is 3.42 to 3.73 with overdrive works well. The Monte SS from 86-88 had the 3.73 setup. I believe 84-85 were the 3.42 setup.
 

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Discussion Starter · #9 ·
Its all about the intent and entire combo. No matter how high (low numerically) you go in a gear, it has to be matched with the entire drive train, tires to engine. A 2.73 isnt a bad gear for HWY if you have a 3spd auto, or a muncie if you have 650hp under the hood to cover it.

with a modest 350/383 (400/450 HP), a 200r4 and 3.23 isnt bad for the HWY. I actually think it to high and could get away with a 3.73 as well. I drive 60mi round trip HWY every day and I run a 3.00 with a TH350.

If I was doing this project and it was just to be a HWY cruiser, and I'm assuming you have an 8.5 10bolt, id go with a 3.42 rear gear and a 27" rear tire. Usually going with the 27 allows some fine tuning in the RPM / MPH adjustment from 26" to 28" when everything is said and done.

This gear will take advantage of the 2.74 first gear while not letting the .67 fourth lug you down in lower RPM. 1st gear shift not high/low. 80MPH @ 2500 RPM with enough room for higher cruising and or passing at 85-95mph at around 3000rpm. Perfect for Florida HWY driving.

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Mike
Wow, thank you. The effect of that the 200r4 will have has been confusing. I think the result will give me the "best of both worlds" with a good jump off the line and decent highway milage over the current 350 configuration given the change in gearing. Thank you for breaking it down like this.
 
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