Texrange

Have an 02 with 4.6 and 3.55 gears and 32" tires need more towing power but not sure how far to go, considering 4.56 but still want it daily driveable, any suggestions?

smokeywren

I had an '03 F-150 with 4.6 2V engine and 3.55 ratio. It was a dg when towing. I gave up on it after one trip to Phoenix dragging 5,000 pounds cargo trailer. Until that trip I never realized how many steep grades there are between El Paso and Phoenix.


For gear ratio changes, think in terms of percentage.


3.55 to 3.73 is 5% change. Your corrected speed at 65 MPH with 3.55 will be 61.75. Speed back up to 65 and your engine RPM will increase 5%, getting you a bit higher up on the HP curve. But probably not worth the cost for that little bit of change.


3.55 to 4.10 is a 15% change. So if you're cruising at 2,000 RPM now, you'll have to cruise at 2300 to obtain the same speed. That gets you a lot higher on the HP curve, and might be worthwhile.


Next practical and available is 4.30, then 4.56. 3.55 to 4.56 is a 28% change. That's a bunch! If you're cruising at 2,000 RPM now, you be doing 2560 RPM at the same speed with the 4.56 gears. If that won't get you high enough up on the power curve, then your only choice left is to do what I did - trade for a newer truck that has an EcoBoost.

jkenprice1

I have 3.55s and i'm going to 4.10s. A couple of reasons. I can use Ford gears. 4.10 is the lowest they make for a 9.75 rear end. I think I'll have more power with the same or even better gas mileage. I don't plan on bigger tires. If I were, i might have gone with 3.56s. I had 2 4.6s with 3.55s and know they're dogs towing, especially in summer. I wish I'd changed gears but I never did. I'm also putting a detroit trutrac in the back diff. I'm tired of one wheel spinning when taking off on wet roads.

PerryB

If you intend to stay with 32" tires I think you'll find the 4.10 ratio to be the best compromise. For tires in the 34-37" range, 4.56 is the better choice in my opinion. In your case I think the 4.10's will give the truck a noticeble improvement in effective pulling power with very little impact on fuel economy. Your empty MPG will likely diminish a little but towing mileage will probably improve somewhat.

Z7What

Im a big fan of having a little extra gear but 4.56s with 32s is a little much.

I had a 03 Supercrew lifted on 38's with 4.56s. Since the shop that did my front end alignments couldn't do it with the big tires on it I would have to put stock tires on it. Let me just tell you. 4.56s, Stock Tires, and 12# of boost was a freaking blast to drive! The RPMS were way high when on the highway though.

If you are going to stay with 32"s I would go 4.10s

Wayne
Wayne

PerryB

That's what you call a tire fryer.

Z7What

Oh yeah, the truck dynoed 331RWHP/411RWTQ with the 38"s. With the 31"s it would be much more. Rolling at 40-45mph and mashing it would get the truck sideways!

Wayne