I have a 2004 FX4 Supercrew with the 5.4 engine and 325/60 R18 tires. The tires are approximately 33" tall. Stock gears are 3.73. I am considering going to 4.30 gears and wanted to know how much of an RPM increase I should expect. Anybody have any experience with this combo of tire size and gear ratio?

 

It's purely mathematical: 4.30/3.73=1.153 so the engine will have to turn 15.3% faster to get the same wheel rpm.

 

Sorry to say but you will not find any 4.30 reverse cut gears. I don't think anyone makes them. This is what i have found to be true!
You would have to go with a 4.10 or 4.56 or stay with your 3.73s

 

phil6608 is right, 4.10 and 4.56 are available for the 9.75 rear end, I have not seen anywhere where 4.30 is available.

As for your RPM question, you could use this calculator:

http://www.ring-pinion.com/Calc_RPM.aspx

or

http://www.ring-pinion.com/Calc_GR.aspx

 

Your are right phil6608. I made a couple phone calls after I made my original post and found out the same info. I guess I should have done my homework before posting a question. In my opinion changing from 3.73 to 4.10 is not really worth the money and going to 4.56 is a bit to low of a ratio with my tire size for highway use. Thanks for the help guys.

 

Thats what the sire is here for. Posting here is doing your homework.

I think you just need larger tires so that the 4.56s aren't bad.

 

They make them now...
http://www.jawsgear.com/store/catalo...roducts_id=165

 

I don't know why everyone always says: They don't make them. They been making them for a while now, and it is a good thing, b/c 4.10 just isn't enough, and 4.56 is almost to much.

The thing I'm unsure about is the front. I've seen at least 2 trucks that supsoedly had 4.30 gears. I haven't personally seen the company that makes that ring and pinon for the front, but I know they make it for the rear.

The money you'd spend on the gear change almost isn't worth it.
IF you had 3.55s and 35" tires, I'd highly suggest some 4.30s or 4.56s.

But with only 33s and 3.73s....... The $1,500 just isn't worth it.

 

I had some 285s and I forget the height on them but they were huge on the stock Expy rims. I really didn't notice any performance with those before or after. It still seemed to be a faster truck than my other '98 Expedition (tranny is going out though).

I now have 4.30s in my truck (stock) and the first gear is very rev happy. Since it's a 6 speed, it turns about 2K at 75 mph.

To continue with what I was saying earlier, I'd say, if you don't need the extra performance, it's probably better just to keep stock and make up that power with some pipes and intake. If you want to keep the low end power, stay with close to stock size pipes making sure you never go from larger to smaller and stay with single exhaust tip. If you want some high end, dual exhaust is the way to go. I chose dual because I love the way it looks. An intake would help quite a bit with letting that exhaust/engine breathe.

-rockstate

 

285s are just shy of 33s.

Dual exhaust can be done to improve low end torque, you just need to know what your doing.

 

4.10's will make a big difference, but not enough to justify the price tag. 4.30's will make you snap your neck off the line. try some 4.56's and 35" or 37" tires

your best bet is just stay stock or get the performance elsewhere.