rearend ratio?
Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
my 78 has 2.50:1 and does 80 - 85 mph at 2500 rpm
Highway use with a 3.50:1 would be fine just would be at a higher engine rpm to go with the flow of traffic unless you have an overdrive transmission.
Cargo Master
Joined: Apr 2007
Posts: 2,063
Likes: 38
From: Valley Center, California
Depends on your rear tire height and what sort of driving you do. There are all sorts of on-line calculators and charts that can help you estimate RPM. I ran 3:50s with a pretty tall tire (I don't recall the size) and it was great around town with occasional highway use. If you do a lot of highway driving I'd think that 460 would be happier with a 3:00. If you already have the 3:50 as a spooler, drive it as is for a while and see how it works for you. Just my two cents.....
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
Not to be contradictory, but I can tell you right now you aren't going to be happy with the 3.50 rear. Even if you are running 27 inch back tires. With a 460 you don't have to worry about pulling power but above 2500 rmp that motor is going to feel it's "screaming" at freeway speeds.
If you are running a back tire with a 27 inch diameter, you will hit 69 mph at 3000 rpm,
with a 3.50 gear ratio. With 3.00 it will run 67 mph at 2500 rpm.
Drop that to a 26 inch diameter tire and you will hit 66 MPH at 3000 rpm with the 3.50 With a 3.00 it will run 64.5 mph at 2500 rpm.
One more drop to 25 inch diameter tire and you will scream at 64 mph at 3000 rpm withthe 3.50 and 65 mph at 2750 rpm.
I have a 390 and running above 2400-2500 rpm gets feels a little high when I cruise the freeway - 3000 is way to high to be comfortable at cruise.
I have a 2.79 in my 9 3/8 rear. I have 26 inch rear tires and hit 65 mph at about 2600 I wouldn't go any higher than your 3.00 rear and might even look for a 2.80 with 26 inch or smaller diameter back tires. And I'm going to install a US Gear 20% overdrive as well.
Here's the gearing calculator I use and it is dead on!
Gear Ratio Calculator
If you are running a back tire with a 27 inch diameter, you will hit 69 mph at 3000 rpm,
with a 3.50 gear ratio. With 3.00 it will run 67 mph at 2500 rpm.
Drop that to a 26 inch diameter tire and you will hit 66 MPH at 3000 rpm with the 3.50 With a 3.00 it will run 64.5 mph at 2500 rpm.
One more drop to 25 inch diameter tire and you will scream at 64 mph at 3000 rpm withthe 3.50 and 65 mph at 2750 rpm.
I have a 390 and running above 2400-2500 rpm gets feels a little high when I cruise the freeway - 3000 is way to high to be comfortable at cruise.
I have a 2.79 in my 9 3/8 rear. I have 26 inch rear tires and hit 65 mph at about 2600 I wouldn't go any higher than your 3.00 rear and might even look for a 2.80 with 26 inch or smaller diameter back tires. And I'm going to install a US Gear 20% overdrive as well.
Here's the gearing calculator I use and it is dead on!
Gear Ratio Calculator
Junior User
Joined: Jan 2009
Posts: 67
Likes: 0
rear end ratio
my $.02.
As alluded to, you need more info.
Overdrive trans, or 1-1 final ratio?
Size of rear tires?
Where do you want to cruise at? - 70 MPH at 2400 RPM?
Personally, I have a th400 trans (1-1 final ratio) 265x70x15's on the rear
(over 29 inches tall) and run a 9" ford with 276 gears.
This is behind a high torque, low rev 500 Caddy. It'll chirp the tires in low,
pull trailers, and cruise at 70 around 2200 RPM's.
Acceleration isn't neck snapping, just smooth and strong.
If you want acceleration, you need to look at 1st and 2nd gear ratios also.
As alluded to, you need more info.
Overdrive trans, or 1-1 final ratio?
Size of rear tires?
Where do you want to cruise at? - 70 MPH at 2400 RPM?
Personally, I have a th400 trans (1-1 final ratio) 265x70x15's on the rear
(over 29 inches tall) and run a 9" ford with 276 gears.
This is behind a high torque, low rev 500 Caddy. It'll chirp the tires in low,
pull trailers, and cruise at 70 around 2200 RPM's.
Acceleration isn't neck snapping, just smooth and strong.
If you want acceleration, you need to look at 1st and 2nd gear ratios also.
Clean & Classy
Joined: Dec 2004
Posts: 1,656
Likes: 20
From: Riverside CA..
I'm running 3.0 with 26" tall tires. I have all the power and acceleration anyone could want. Not bad for freeway cruising, but when My ship comes in I am also going for the US Gear 20% overdrive also.
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I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
Likes: 110
From: Northshore, MN
FWIW, before putting in a Detroit locker or something, consider a gear change at the same time, since everything will be apart. As mentioned drive it first, and decide what gearing you want after, and do it all at once....less down time, and money payed just the same. My $.02
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