3.91 gears for shorter 60 mph trips

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Richie

Richie

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Hi everybody.


Yes 3.91 gears with a 340 with 370 to 400 hp and a 727. The tires would be on 14 inch rims with stockish diameter so 27 inches I'm guessing about. Would it be to low geared for say going into town witch is at the most 20 miles.
 
I've got 3.91 gears in my daily '73. But I also have an overdrive transmission in the car.

For actual 'in town' driving it might be 'ok'.
The moment you get onto longer straight road or roundtrips, the rpm's can get old pretty fast.

Personally I would not want to drive 20 miles to a town with 3.91 gears in the rearaxle with a non-overdrive car.
 
Well 27" and 3.91's are going to run close to 3K at 60, which for me would get pretty old pretty fast

I currently run a 28.3" tire with 3.7x Ford gear, and that's still a tad over 3K at 70. I would not want much higher RPM on the highway

Your gear, 27" and 3.91, from here:

http://www.wallaceracing.com/gear-speed.php
 

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What converter?
In the 3.70's would be my choice,
and you still won't get any mileage.
 
When looking at gear calculators keep torque converter slip in mind, it could take more rpms to reach a certain speed than what the chart says. Unless you do a lot of racing, an alternative would be to go for a more highway friendly gear, such as 3.55, and then run a shorter tire (24") at the strip to make up the difference.
 
I drive mostly around town on 3.25 and 25 1/2" tires and the rpms get old. To me it stops feeling like crusing and makes me feel like I'm working the car all the time. I think we are so used to overdrives anything over 2000 rpm is for accelerating.
 
Hersbird said:
I think we are so used to overdrives anything over 2000 rpm is for accelerating.
Click to expand...

I agree X2. Back in the 1970s my big block Mopar used to cruise at 65 - 70 mph with the tach showing 2200 - 2500 rpm while in 4th gear. The sound of the engine with its headers and glass packs was pleasing. Of course, if I wanted to listen to the radio, I had to crank the volume up to eleven!
 
I cruise at 3 grand @ 65mph with the 3.91's and 50mph with the 4.88's. both on a 28" tall tire.
 
Hersbird said:
I drive mostly around town on 3.25 and 25 1/2" tires and the rpms get old. To me it stops feeling like crusing and makes me feel like I'm working the car all the time. I think we are so used to overdrives anything over 2000 rpm is for accelerating.
Click to expand...

That's about what I have 3000 rpm is around 69 mph 3500 80 mph . I'm thinking hard about an 0/D where 2400 will be good for 70 mph , even with 3.55 or 3.73 70 mph would be 2600 - 2700
 
It all depends what kind of stall you get too for the car doesn't it? If you get a lumpy cam you need a higher rpm stall so if you're going down the HYW at say 2500 at 60 mph and you have a 2500 stall that's no good right?
 
Too Low for me:
I have a 340 6pk 4spd 73 cuda with 3:90's 29" tire. It is fun to drive, but I wouldn't leave town and evade freeways as much as possible.
My wife has a 71 Dart with 360 2500 Hughes converter, 28" tire, and 3:55's it is just as bad. Everybody was right on with the 3000 RPM's @ 60 MPH.Her car has solid lifters, and it's very noisy even with quite mufflers.
 
I've always considered around 4.1 to 4.11 ok although I have run much lower ratios on the street with big blocks I don't recommend it unless you are rich. I get along good with 3.23's. If I wanted more acceleration I would just try to get it out of the engine instead of the gears.
 
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