4R70W, 351W, 37" tires and 4:11 gears?

[kholding]

Here is what I am working with:

1. 4R70W transmission
2. 351W (basically stock other than gt40 intakes)
3. 35" or 37" tires (haven't totally decided yet)
4. 4:11 gears

Too many factors for me to know if this will be geared too high? Anyone with close to the same set-up or ideas on how this gearing will be? Thanks.

 

[needabronco]

I run an AOD, 4.88's, injected 302, and 35"s, and wish I had either gone with a 351 for more torque or 5.13's. At 70 MPH on the freeway, it runs at 2200 RPM's, which is a little low, at 75 MPH I'm at 2500 RPM's which is my engines sweet spot. With a 351 I would think 2200 RPM's would be perfect.

 

[NY-Bronco]

Id go 4.88 or above on the gears.

 

[Broncobowsher]

Geared way too high. The 4.11 might be good without an overdrive.

I was running 351, 4R70W, 4.88 and that was with only 33" tires. Worked out real nice, 4.56 OR 35's might have fine tuned it just a little nicer (the 351 was built and had a very strong torque to it). For what you are doing 4.88 or 5.13 would be my pick.

 

[bax]

When my AOD was alive I liked going 70 at around 2100 rpm. I had 37's and 4.88's and my 400 loved it. The 400 makes lots of torque at 2100 and had no problem pushing the square brick down the road. A 302 would have a hard time at this rpm and gear set up. Your 4.11's and 351 will have ha hard time with it too. I think a 4.56 is good for you.

 

[kholding]

Thanks everyone. Looking like new gearing options now! Anyone need 4:11 gears???

 

[kholding]

So the difference between the 35" and 37" tires really doesn't matter then, right?

 

[needabronco]

Well with 35"s I'd do either 4.88's or 5.13's, with 37"s I think I'd do 5.13's. If you were closer I'd let you drive mine and see for yourself.

 

[kholding]

I guess with the overdrive I would probably be safe going with the 5.13's then. Thanks.

 

[DanWheeler]

Do the math. Use a gear ratio chart and figure out your RPMs at cruise. Dont forget to factor in the overdrive.

There's no guess work involved. You will have a lockup torque converter so there will be no TC slop in the numbers.

Decide on what you want your RPMs to be at whatever speed you want to cruise at and gear appropriately according to the math.

 

[70_Steve]

Do the math. Use a gear ratio chart and figure out your RPMs at cruise. Dont forget to factor in the overdrive.

Here's the Gear Calculator I like to use. http://www.grimmjeeper.com/gears.html

 

[kholding]

Good advice. Thanks again everyone.

 

[barronj]

pm sent on your 4.11's.