Looking for a recommendation on a good cruising 65-70 mph highway rear gear for a 51 coupes I am working on. Has a mild Ford 302 with an AOD .What would be s good highway gear with that combination?
I have a 3:55 behind a T-400 in my Olds, nice fit for around town and light highway use (<70). I have a 3:70 in the 41 PU behind a RE46 OD trans and it is a pleasure both in town and freeway speeds.
If it’s in your avatar…I installed a 2.74 rear gear in our 56 and it’s perfect for hyway and street with no OD trans. I don’t know what the ratio is for your AOD or what rear you have and what’s available. Mine is an 8.8 from a Ford Explorer with F-150 drum brakes.
All of the US (muscle cars, if you can call them that) had legs like that under them because they needed fuel economy, not for power or fun. Most of the late 70's Trans Ams I owned all had those gears, dogs on the street! Embarr***ingly so. Couldn't get out of their own way. They are cheap though, every wrecking yard has a host of 2 series carriers in them. I guess it depends on what the OP wants out of his ride. To each their own. Not every car needs to be quick. I get lousy gas mileage, but I make it from station to station in a hurry.
Another vote for 3.70's That's the ratio I sold most of when I built a customer ch***is with an OD trans.
Tire diameter is going to be a big factor but given the general range of tire that would be common on a shoebox 3:70 sounds about right. There are plenty of free calculators online if you have a certain rpm at x speed you are wanting to aim for.
The answers given work for the people giving the advice. But you need more info to make a proper decision. Tire size, power and torque curve of the engine and all 4 gear ratios for the trans. And most importantly how you plan to drive it. There are numerous rpm calculators online. Once you have the above, figure out where you want it to cruise at the speed you desire. Also figure out what it looks like in each of the gears. If you accelerate you want to be somewhere in the power band and you want it to shift before you are out the top of that band. But you don’t want it to fall through the bottom when you hit the next gear. OD is usually a lock up gear so what does it take to lock it up?. Is 3rd a lock up also? Small blocks usually cruise at more rpm than a big block but with rpm comes exhaust noise. What is comfortable is also a consideration.
What type rearend are you running or have? That may help the gear ratio choice some. Also good point on tire diameter. I think around 3.55 will be good starting point for evaluation.
I've got a 327 engine rpm 2900/ TH350/3:55 rear/28.9 dia. tire = 70.26 mph I wish I had around a 2.73 rear A good site to figure out what you have or what you need to get better results. Transmission Ratio RPM Calculator | ****er Parts
65-70 will allow you run a little more gear. I like to gauge "left lane" speed, so I try to gauge my gear on an 80 mph cruising speed. I have a stock 3.08 rear with a 700R4 and a 27.7" tire, and it could really use a numerically higher gear. A 3.64 or 3.42 would probably be ideal, since right now 80 mph is 2000 rpm and sort of below the powerband.
Something that starts with a 3. I have 3.45 gears in the ‘54 with a Yblock and AOD and it is a perfect cruiser with 205/65r15 tires. My mustang has a 302 and t5 with 373 gears and 235/60r15 tires. It’s also a great combo. It previously had 308 gears and that wasn’t enough, and 410’s temporarily but that was no good on the highway.
27 inch tall wheel, stockish sbc, 200-4r trans w lockup, and 3:73 rear gear. Perfect for a 1951 Merc.
my OT car with OG 28" tall tires has a 3.42 gear. I do 2000 RPM's at 65 MPH. I don't see any reason to want a higher cruising RPM than that. the only time it downshifts is up a hill or when I hit the go pedal hard.
I had an old hot-rodder (now I fit that bill) tell me years ago when I asked that question- 3.25 to 3.50 for non-OD transmissions, 3.55-3.90 for OD transmissions, and torquey engines such as Nailheads and straight 6s high 2s or low 3s
My chevy with a tired sbc 267 with a 350 trans runs suprisingsly good with a 3.30 gear. But the most optimal choice is a high torque engine with a 2.73 gear, youll get there fast and cheap
An AOD has a .67 overdrive so take any ratio you had with non-OD and divide by .67. So if you liked 2.73s for cruising with a 1:1 transmission, with an AOD you could have a 4.1 to have the same RPM at highway speed. 3.73 is a common gear for an 8.8 or 9-inch as is 4.10. I would lean towards 3.73.
Get your tire size and use the calculator someone listed above to see what puts you at 80 mph and 2200/2300 rpms in overdrive. That is what it takes to be able to cruise with most traffic in my truck. I imagine my rear tires are probably slightly larger than what you will have. It came with 3.73 rear gears. What you don't want is to have to be at 2500 rpms+ when in the speed lane and just staying generally with the traffic. Try getting on an Xway and driving about 30 miles at 70 mph in your DD and see if you aren't constantly looking in your rear view mirror at the approaching traffic behind you........especially semis.
Plan on using a 3:70 in the wife’s car with an auto OD I have a 3:92 in the car I’m building with a 3 speed OD I cruise around 55 I’m my beater. Never an issue on the interstate
I was a pretty serious 5.0 Moostang guy (still am), and the hot ticket with an AOD in one of those was the 3.73 for best performance and fuel economy, and 4.10s if you were more worried about performance but still wanted to be able to drive it down the highway. If you were running a T-5, we went with 3.55 or 3.73s. This is with engines in the stock 225 hp to mild built 300 hp jobs. 2.73, 3.08, and 3.27 that they came with was WAAAAY too high, and you'd get worse fuel mileage than a 3.55 rear diff with any of those ratios. Worst thing for one of the AOD transmissions is it constantly up and down shifting between drive and overdrive: you need a ratio that keeps it in overdrive until you're climbing a hill or giving it the beans for p***ing, and in countless personal experiences with cars with a Windsor type Ford powerplant and an AOD transmission, that ratio is a 3.73 if you're running an 8.8 inch rear diff, or a 3.70 if it's an 8 or 9 inch.
This is a simple to use calculator that you put in speed, tire size, rear gear rato and trans ratio and it will give you the RPM. It's the simplest to use with overdrive as you don't have to multiply the rear gear rato by the overdrive ratio to get final drive ratio. Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio This shows that at 70 with a 26.5 tall tire 3.73 gears and a .67 overdrive you would be running along at 2218 rpms If you are thinking radial or know the bias to radial tire size comparison this comparison chart lets you see the difference in tire sizes side by side. It will let you see how big and littles stack up too. Tire Size Comparison
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