ok i have a 99 ford f150 xlt supercab 4.2 l engine and have been making some mods to it. i replaced the OEM spark plugs with some with some e3 spark plugs and i replaced the spark plug wires with some aftermarket wires. i put a k and n air filter kit on the truck. i also put a body kit and some 20 inch rims with 275/45/20 tires. i realize that the diameter is close to the same as the factor rims and tires but it still feels slow. is this because of the weight of the rims? do i need to go up in gear ratio and if so what should i go up to? if the diameter is the same, what will happen if i increase the gear ratio? what other mods can i make to the 4.2l engine? and last but not least where can i possibly take my truck to find out what kind of increase in HP and torque i have made with my mods on my truck? anyone with any advice what so ever please help! not very savvy with all of this but doing as much research as can be aloud. i am in the military so i dont have all the time in the world. thanks

 

A set of lower gears would help a lot. What is your gear ratio now?

 

ok i have 3.55 gears in there now. is this the cause of it being harder to get moving? also if i do drop to the 4.10's will it still be good for long distance travel or are the lower gears mostly for towing and hauling? i am just concerned about the heat index of the differential. i have read other posts wear upgrading the gears without a significant reason will just cause more heat output in the differential.

 

That is the first I've ever heard of that. A 3.55 is a pretty tall gear for a V6.

 

well thats what it said on the pumpkin so should i go sith 410's or what should i go with? should i even increase at ll. the 355 were factory with the truck

 

I think 4.10's would be a good choice.

 

I think 4.10's will be a good choice too. I have heard of the heat problem but not on 4.10's it in when you deside to go 4.88 or higher you have some heat build up. that is why some guys buy aluminum covers for the differential to disipate the heat. If I was to buy 4.56 I would probably get one of those aluminum covors just to be safe but you should have no problems with the 4.10's. those aluminum covers are not cheap they run between $150 and $250. as far as it hearting you gas milage. your highway gas milage will probaply drop 2 to 3 mpg's and your city gas milage will probably go up 1 to 2 mpg. so if you do most of your driving in town as I do you can probably count on better gas milage. hope this helps

 

i also recomend 4.10 gears