Most common gear in a 60s era car was a 3.08. Takes a lot of zot to launch a 3.08 gear. For general driving around unless I am running a mill that wants to be revved I like a 3.26-3.55:1 gear. Gets you across the intersection and still runs well on the highway.
And you will have another mechanical device to buy , install , provide controls for & maintain ! As a means to what end ? Earplugs would be far cheaper !
Selling the hotrod and buying a corolla would be cheaper [that would be no fun] The AOD is a bolt in swap for the C4 [except rear mount position], Same length .same yoke etc etc AND it is mechanical [it does need a TV cable] AND he can sell the C4 to recover some costs The OP quoted The answer to that is a "bigger engine." [more $$$$]
Yeah the overdrives and hiway gears became popular during the 80's street machine, street rod Era. They were parade ground, show circuit cruisers, not really made to perform but just look good at the car shows. Pro street put the performance back into the "hot rod" style cars to a point with the blown motors and low gears. Before that there were hot rods where performance was king and gas mileage and cruising rpms were never considered or talked about.... ...
It’s funny what people get accustomed to. Almost all vehicles made in the last 30 years or so have some kind of overdrive. That conditions us to low, 2000 or so RPM, freeway engine speeds. I occasionally drive my O/T F-100 to work in St. Louis and it’s 40 miles one way with about 50/50 freeway and state highway. I was on I-55 south out of downtown, keeping up with traffic and happened to notice the tach. Yikes! 3000 RPM, and I backed off and changed lanes. My F-100 has a 302/M5OD and 3.73 TracLok with the stock P235 tires. Then, I got to thinking, 302, 3” stroke, came out in 1968 with very few overdrive transmissions around, 70 mph speed limits back then, and it occurred to me, shoot, 3000 RPM freeway running ain’t going to hurt this thing. I hammered down and haven’t thought about it since, until I read this thread.
My normal suggestion is to get on a long road and put your car in second gear. Then drive a few miles with the engine at different rpms that would be comparable to the rpms you want when in high gear. Your actual speed during this test is irrelevant. What you want to decide is what rpm are you comfortable with if you were making a long drive in high gear. There are a lot of cars that don't get driven much because the rpms of the engine become annoying or worrying during long drives. Then decide what ratio will keep you at an acceptable rpm and noise level with the trans you have. OR............put an AOD trans in it along with a 3.25/3.50 rear gear and enjoy way more performance as well as better gas mileage and even lower noise levels on long trips. Thats the best choice. Edit: My 2000 Chevy with a 4.8 liter V8 and od automatic has 3.73 gears. Thats smaller than your 302 by about 12 cubic inches. Don't remember tire size, but they are stock wheels so not anything special. It will cruise at 75/80 mph and about 2250 rpms. I tow with it as well and it does pretty well. To me the thing to think about with 3000 rpms is noise level and engine wear. If an engine is turning almost 1 1/2 times the rpms , its gonna wear out a lot faster. Probably no initial problems when driving, just long term wear. Then I ask myself.......what benefit do I get from turning 3000 rpms instead of 2250 rpms at 75/80 mph ? I honestly don't see a benefit unless someone just likes the sound of loud mufflers for hours on end. Having busted both ear drums when I was younger, I can tell you that its irritating as hell when your most used word is "what ?" .
Just remember , any self respecting hot rodder in our alleged target time was just dying to get ahold of an O.D. !! Whats that ? they weren't ? Imagine that ?
You might need all those gears if the engine doesn't make a whole lot of torque. But the lower gears are kind of useless if you have 600 ft lb or so.
MPH x Rear Gear Ratio x 336 / Tire Height x Overdrive = Cruise RPM Your C4 has no overdrive, so just cut that from the formula. https://www.jalopyjournal.com/forum/threads/calculating-optimal-highway-cruising-rpm.312099/
The stock tire size on your 2000 Chevy is 31.6" tall. Modern trucks have a lot taller tires than we think they do because the vehicles are proportionally larger.
From what I remember (selectively) was that most of us were happy just to have a car, any car. If we tore a trans out, an overdrive trans was nice to have but were not very common. Gas was also 29 cents a gallon. Most of us didn't have A/C either......but tht don't mean we would not have liked it. Highways have changed and so have speed limits. I somewhat agree that lots of torque makes driveability much better when you have fewer gears but a 302 can benefit from more gears. In the end though, 3000 rpms is 3000 rpms no matter how much torque either engine is making. So either engine is going to wear more at a higher rpm. Didn't you put a gear vendors overdrive in one of your cars a while back? Didn't know what my tires actually are, so I got up off my chair in the air conditioned basement next to my computer and as I looked out the window in the kitchen I saw the thermometer at 100 degrees............but I was already upstairs and heading to the garage. The tires are on factory stock wheels and are Michelin 255/70/16. The actual diameter was either 29 or 29 1/2 depending on how I looked at it. Basically when my speedo says I'm going 80 the tach says 2200-maybe 2350 at most unless its a BIG hill, and I'm usually passing people while occasionally moving over to let someone(s) go by. The highway says 70 mph..........but thats apparently only a reccomendation. I haven't ever taken the time to calculate my actual speed, but I keep up with the traffic. I will say that when I go visit my son just below Etown, there is a big long grade with an extra slow lane for semis with problems. When I hit that grade, it downshifts about a third of the way up and the engine goes to 2300/2500rpms..........and the noise level is noticably higher inside the cab.....with stock exhaust. So, for me I find the lower rpm noise level to be better. Edit: OK a little semi-quick calculation. So if I did it right.......... If I have a 3.73 rear gear and a .696 OD, thats like having a 2.59 ratio. AND 31.658 diameter tire gives me 80mph at 2200 rpms my estimate is that a 29" tire with the same gearing would be about 2400 rpms. I'd say a 3.50 rear gear with overdrive and a 29" tire should be a very good choice.
I have it in a couple of them. One was free, the other was heavily discounted. 2500 rpm on the highway with OD. Very few of us drive our old cars enough to wear out engines. I don't, and I drive a lot.
[I just played with a calculator plugging in the possible specs for my 48 that I am putting the 292 chebby six in. 292 six, Novak adapter, AX-15 5 speed (with 51 granny shift handle) and a nine inch with 3.55 gears. Comparing 215-75-15 tires that are 27.7 inchs tall and 225-75-15 that are 28.3. With 1 to 1 trans ration and .79 to one trans ratio. All at 70. Using : Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio (purperformance.com) Tire comparison calculator Tire Size Comparison Bias letter tire size diameters for 50/60 and 70 series Tire Sizes and Dimensions (plain text version) (pontiacserver.com) Don't beat up on me for odd numbers in the calculations. View attachment 5824567 View attachment 5824568
There are far more effective ways to limit engine wear than rear end ratio choice. If you were to tow your rod around on a trailer, you would almost eliminate it entirely............
One other thing to consider is that older non-OD transmissions often don't have a "lock up" feature to prevent torque converter slippage. That would be a drivetrain loss that isn't figured into any of our calculations. Apparently the OEMs thought it was worthy of some attention for gas mileage but still, someone using a transmission without a lockup feature is probably going to turn somewhat higher rpms than what they calculate. I'm thinking ballpark 150/200 rpms additional.
The lockup feature is used when the gearing is such that the engine is running at really low RPM on the highway. They started it about they time they went to really long gears in the mid 70s, to boost mileage...when you have 2.29 rear end gears and a 55 mph speed limit, the converter will be slipping in high gear on the freeway. So they added lock up. Then when they went to overdrive automatics, with the same RPM situation, they continued using lockup in the new transmission designs. If you put a lockup converter 3 speed auto in a car with 3.0 or steeper gears, you're not gonna gain anything from the lockup.
Might be odd, but when I had the 3.9? factory posi in my ‘59. (Speedometer didn’t work) but I was always in the slow lane a 3k RPMs. Found a 3.55? out of a GMC, was still in the slow lane at 3k RPMs. That 235 was happy
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