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He would have to have a set of really short tires....like 16" in diameter total lol
What is a good "all purpose" gear ratio?
- Thread starter 69redrunner
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howiedodat
Well-Known Member
Not to beat it to death, but I would think the brother would be able to tell 3k from 5k rpms in a big block by the sound. Just trying to address the bad tach question. That motors howlin pretty good at 5 k.
69redrunner
Well-Known Member
Running 235/60 15's all the way around.
I jacked the car up, marked the yolk, 1 rev of the tire = roughly 3 1/2 turns of the yolk..perhaps 3 3/4.
Is that telling me I have a 3:55 or 3:91 or something in between?
Perhaps I need to invest in an inexpensive tach to verify...but it sure seems like the motor rpms are higher than 3k on the highway.
I jacked the car up, marked the yolk, 1 rev of the tire = roughly 3 1/2 turns of the yolk..perhaps 3 3/4.
Is that telling me I have a 3:55 or 3:91 or something in between?
Perhaps I need to invest in an inexpensive tach to verify...but it sure seems like the motor rpms are higher than 3k on the highway.
john.thompson068
Well-Known Member
With 3.91, 4000 stall convertor, and 29" tall tires my motor spins 3500 rpm at 75 mph and probably gets 9 mpg. With 2.76, my same combination spins 2600 rpm at 80 mph and I actually recorded 10 mpg on that cross country trip. My motor is a 440 with 543 hp and 560 ft lbs of tq and over 500 ft lbs of tq from about 3000 or 3500 to 5700 rpm so it has a lot of torque (the dyno pull started at 3800 and it had a flat torque curve beginning at 535 ft lbs of tq at 3800 rpm).
I think the 3.91s are perfect for where I drive the car which is around town with a little interstate action. If I had to get another sure grip for my chunk I would opt for 3:55s because it wouldn't make it noticeable slower, especially because I have so much torque, and freeway cruising would be much better at 3100 rpm at 75 mph.
I can just tell by looking at the rpms at 75 mph that I would not like a 3:23 on the street. The engine would always be loafing just above idle around town even in first and second, and third would be like overdrive. It would be to much like the 2.76s.
You have to remember that I have a 29" tall tire and you likely have a 26" tall tire. With a 26" tall tire, 3:55's will behave like a 3:91 with a 29" tall tire.
So, if I were to select a rear end ratio that I feel you would enjoy, and assuming your car has a 26" tall tire, I would install a 3.08. That will give you the ability to cruise at 75mph at 3100 rpm. Anything higher than this will leave your motor loafing around town which I find annoying. Anything lower than this will leave your motor spinning too fast on the freeway which does not solve your issue. If you ran a 3.08 with a 26" tall tire it would be the same as me running a 3:55 with a 29" tall tire. If you didn't like it, getting it swapped is not very expensive. You could pick up some used gears and then pay about 150 bucks for setup plus another 50 bucks for a gasket, oil, and additive.
Something else to consider is this. Hot Rod Magazine once ran a test using a 12 second Nova. They ran the car using every ratio between 4.56 and 3.08. The difference between the 4.56 and the 3.08 was less than one second slower ET, and the mph went up progressively with the higher gears. You could probably locate that article on the Internet if you had the time, even though this test was done about decade ago. So if I switched from a 3.91 to a 3.55 my car would probably lose 2 tenths in the quarter mile which is negligible on the street, but make cruising to the next car show or whatever much more enjoyable.
Also consider this. While 3100 or 3200 rpm may seem excessive, I don't worry about it wearing out my motor. When I was going to Afghanistan, the diesel generators on the bases I went through run at those same rpms, 24 hours a day, 365 days a year, year after year. At night, their manifolds would glow orange. Some generators were turbo inline 6s, but many of the generators were twin turbo V12s. I recently drove my car for over 3 hours on the freeway at 3500 rpm and while I wish I had overdrive, it really is not that bad once you get used to it.
So, in conclusion, with a 26" tall tire I would recommend a 3.08, and for a 29" tall tire I would recommend a 3:55 for a general purpose gear ratio. Go to Randy's Ring and Pinion and play around with the rpm calculator and decide what rpms you are willing to tolerate on the freeway at your desired cruising speed and height of your tire. Obviously, the best solution for me would be a 700 R4. Somewhere out there is a place that can build them to withstand as much as 1600 hp. Take a look at SD Concept Engineering's orange 68 Dodge Charger on their website.
I think the 3.91s are perfect for where I drive the car which is around town with a little interstate action. If I had to get another sure grip for my chunk I would opt for 3:55s because it wouldn't make it noticeable slower, especially because I have so much torque, and freeway cruising would be much better at 3100 rpm at 75 mph.
I can just tell by looking at the rpms at 75 mph that I would not like a 3:23 on the street. The engine would always be loafing just above idle around town even in first and second, and third would be like overdrive. It would be to much like the 2.76s.
You have to remember that I have a 29" tall tire and you likely have a 26" tall tire. With a 26" tall tire, 3:55's will behave like a 3:91 with a 29" tall tire.
So, if I were to select a rear end ratio that I feel you would enjoy, and assuming your car has a 26" tall tire, I would install a 3.08. That will give you the ability to cruise at 75mph at 3100 rpm. Anything higher than this will leave your motor loafing around town which I find annoying. Anything lower than this will leave your motor spinning too fast on the freeway which does not solve your issue. If you ran a 3.08 with a 26" tall tire it would be the same as me running a 3:55 with a 29" tall tire. If you didn't like it, getting it swapped is not very expensive. You could pick up some used gears and then pay about 150 bucks for setup plus another 50 bucks for a gasket, oil, and additive.
Something else to consider is this. Hot Rod Magazine once ran a test using a 12 second Nova. They ran the car using every ratio between 4.56 and 3.08. The difference between the 4.56 and the 3.08 was less than one second slower ET, and the mph went up progressively with the higher gears. You could probably locate that article on the Internet if you had the time, even though this test was done about decade ago. So if I switched from a 3.91 to a 3.55 my car would probably lose 2 tenths in the quarter mile which is negligible on the street, but make cruising to the next car show or whatever much more enjoyable.
Also consider this. While 3100 or 3200 rpm may seem excessive, I don't worry about it wearing out my motor. When I was going to Afghanistan, the diesel generators on the bases I went through run at those same rpms, 24 hours a day, 365 days a year, year after year. At night, their manifolds would glow orange. Some generators were turbo inline 6s, but many of the generators were twin turbo V12s. I recently drove my car for over 3 hours on the freeway at 3500 rpm and while I wish I had overdrive, it really is not that bad once you get used to it.
So, in conclusion, with a 26" tall tire I would recommend a 3.08, and for a 29" tall tire I would recommend a 3:55 for a general purpose gear ratio. Go to Randy's Ring and Pinion and play around with the rpm calculator and decide what rpms you are willing to tolerate on the freeway at your desired cruising speed and height of your tire. Obviously, the best solution for me would be a 700 R4. Somewhere out there is a place that can build them to withstand as much as 1600 hp. Take a look at SD Concept Engineering's orange 68 Dodge Charger on their website.
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I know the question was asking what a good all around ratio is, but just a consideration depending on your budget: An overdrive transmission. This way you get both the acceleration as well as the highway manners.
There are two ways to do this: (1) Replace the transmission or (2) add a Gear Vendors overdrive to your existing transmission.
I think the Gear Vendors overdrive is about $2000. I plan to add this to my 70 Roadrunner (with 3.55) after it is restored.
While $2000 sounds like a lot, how much will you spend goofing around with different gear ratios to find one you think is OK? How often will you want to swap out one vs. the other for performance vs. highway driving?
Just a thought for your consideration.
To answer your original question, my 73 Roadrunner (which I have had for almost 30 years) has always had 3.55s. In my opinion, this is the best all around compromise between acceleration and tolerable highway manners.
Hope this helps,
I know the question was asking what a good all around ratio is, but just a consideration depending on your budget: An overdrive transmission. This way you get both the acceleration as well as the highway manners.
There are two ways to do this: (1) Replace the transmission or (2) add a Gear Vendors overdrive to your existing transmission.
I think the Gear Vendors overdrive is about $2000. I plan to add this to my 70 Roadrunner (with 3.55) after it is restored.
While $2000 sounds like a lot, how much will you spend goofing around with different gear ratios to find one you think is OK? How often will you want to swap out one vs. the other for performance vs. highway driving?
Just a thought for your consideration.
To answer your original question, my 73 Roadrunner (which I have had for almost 30 years) has always had 3.55s. In my opinion, this is the best all around compromise between acceleration and tolerable highway manners.
Hope this helps,
SUPERSTOCKRACER
Well-Known Member
69clone
Well-Known Member
If i am right that would be between 3.50-3.75 ratio, i'd say 3.55 since i don't think there is anything else. It's simple math, and it doesn't add up. I'm guessing your ether not in 4th or your tach is wrong.
Anyways i have 2.73 in my 69', Runs good on the highway and believe it or not i run low 14's with the 318 in it. (best of 14.12 i think) bad tune..
shag766
Well-Known Member
me of course- i had forgot that trick
john.thompson068
Well-Known Member
Gear Vendors only has .80 overdrive which is not that great. Plus I heard it takes a second or so for it to kick in so it will not be shifting snappy like it should. Just some things to investigate while thinking about GV.
wingcarenvy
Well-Known Member
I love my 3.91s. 4.56s are a bit much, but 3.91s are perfect. Your only talking like 300 rpm difference at 60 than a set of 3.23s. At 3k rpm a few hundred more RPM isn't much difference. My daily driver has 4.56s in it and its great. You get used to the RPM after a while and then its no big deal.
hemistix66
Well-Known Member
I ran 3.23's in my Fury,mild 440/727.I likeed it cause did alot of 300-500 mile weekend trips with wife when I first finished it.I was looking at 3.55's before I sold it.Didn't want any higher for traveling alot,IMO.My new project will be 5spd,4.11's if I can find the money for a Passon 5 in a 4spd case.
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