Hey Guys I need a few pointers. I am looking to swap out me open diff for a trac-lok and changing gears on my 99 f150 4.6 auto. I think I either have 3.08's, or 3.27's in a 8.8.

The question is do I swap to 3.55, 3.73, or 4.10's? I would like to keep the revs under 2500 rpm at 70 mph. I do mostly city driving, but do occationally hit the hwy.

Thanks in advance,

-braupe

 

What gears do you have? Check the axle code on the door sticker. What tire size are you running?

 

Axle code is 19.

Tire size is 255/70/16

 

I just went from 3.55's and 33's to 4.10's and 33's and didn't notice a huge difference. If I was you I would go with the 4.10's. With 33's I am at 2200 rpm's at 70mph.

 

Good advise, thanks. At the least I will go with 4.10's. Should I consider 4.30's?

 

You are running stock tires, which I think are around 29". You have 3.55's.

RPM's at 70 in OD are the following:

3.55: 2015
3.73: 2117
4.10: 2327
4.30: 2441

 

Wow that is great info. Thank you so much.

I think I will go with 4.10's.... its not a race truck, im just wanting a little more umph.

 

i wouldnt go over 3.73 if i was not gonna go bigger than those stock tires. 4.10 and 33 would even put you higher than your stock gearing. maybe 4.10 and 31