I have a 1997 F150 4.2L V6, 109k miles, Manual with 3.55 gears. I've been wanting to increase the mpg and have been looking at going to 308's. Problem is that I can't find anywhere that sales them, along with with what's involved in changing them myself. Does anyone have any pointers involving this, I've heard it'd be easier to get a new pumpkin but not sure where to get that either.

 

Greetings fellow mileage seeker:

First, you have the 8.8 integral carrier diff. So, unlike us 9 inch boys, you can't just go down the the scrappy and find one. New gears and install: $400 if you're lucky. Gearsets are under $200, if you can do it yourself--

I found you some:

http://broncograveyard.com/products/cat/20/161

How tall is your 1st gear? Is it the low "granny gear", or is it a start out gear?

If you have a real low 1st, you can probably gear up a little.

But wait--do you really want to spend $400 to get maybe 1 or 2 mpg better?

Plus, with ultra high gearing, you will be down in 4th for most hills.

I have the six, and OD 4 speed and 31-10.50's. That is about as tall a set up as it will pull, give my 1st is not ultra low, and more than a gradual hill needs a downshift.

Serving suggestion: Borrow or buy a set of 30 or 31 inch tires and see how it runs with those.....
Good luck....

 

how would you know what size diff. you have. What does it take to change gears i just put some bigger 33" tires on and noticed some loss and probably only running about 1600 RPM at 60 i have 3.55 gears (dont have a tach so I am guessing at a chart that i say) i want to get that up to around 1800-1900 i was thinking around 3.90-4.10. I don't pull things very much when i do its about a 2000-2500lb trailer. Where i live in Nebraska there are a lot of hills that before the tire change it would down shift quite a bit. Want to know what you guys think. I also have a set of headers that i need to put on and a bigger Y pipe and a high flow cat. Will this be enough power increase to over come the tires and make it seem like it would run before the tire change.

How much would it cost to do so it is a 4x4 so i would have to do the front and rear.

 

Diff size: Ratio is on the door plate, poss. on a ratio tag on the diff, or jack it up and count, or take it apart and count.


What does it take to change gears: If you have drop out carriers, you pull them and swap out the gearsets. Approx $200 for gears, labor at 3 hours per axle, my guess. If you don't know how to do this, pay someone who does or your new gears will howl and grind themselves up. If you have integral carriers, add to the labor as they have to be done in the vehicle, may or may not add time to the job depending on the mechanic and if he has a lift or is going to be rollling in the mud to do the job.

If you think you have 3.55's and you went to 33 inch tires, that is probably a little tall.

You don't give other specifics, so I'll sign off here, other than to say I do not think headers will give you a power boost in the rpm range you are talking about here. Better minds may disagree, but I believe headers start helping at about 3000 to 3500 up on most engines. FE motors with the world's worst manifolds might be an exception, but I doubt there are any other motors that benefit at 1500 to 2000 rpm.

And since you have a 4x4, it will cost double..... Fold up $1000 and go have it done. You'll be able to buy a drink and a sandwich while you wait, and maybe a tank of gas for the drive home.....

 

All that money spent on changes and upgrades will buy a lot of gas and probably won't increase mileage more than 2-3 mpg.

 

i m not really looking at milage i want power to pull some hills with no downshifting and pull a small trailer. the question is should i go with? 3.90 or 4.10. what do you other guys think about a header and cat comb will do for the power

 

DHag, you haven't given enough info. What motor? We know 4x4, what truck, what tranny?

Generally speaking, if you gear it to pull hills pulling a trailer, you are going to run the whiz out if it on the flat.

Your exhaust mods are good for higher RPM.

You need to start your own question with all the specifics to get better answers.

 

it is a 92 F150, 302, E4OD, 3.55, 33" tires, 4" lift, K&N FIPK, 3" Cat back. What wouldbe the best gear selection for me to run about 1800 RPMs going 60-65mph. I tow a popup camper a few times a year a snowmobile and trailer and a few other things which usually doesn't weigh more then 3000 pounds. other wise most of my driving is in the city and the highway which is fairly hilly for nebraska. Hope this makes more sense.

 

3.73 or 4.10s, depending on how much you want it to rev.


Source:

http://www.4lo.com/4LoCalc.htm

Check that "Bronco Graveyard" link I posted above. It appears for 8.8's we go from 3.73s to 4.10s.

You used to be able to get a 3.91 in the 9 inch....

Check out these links too, or go to google and put in "e4od"

http://www.baumannengineering.com/e4odinf.htm

&

http://www.transmissioncenter.net/E4OD.htm


These might offer something that will allow your tranny to perform better and live longer.


Also, you had a header/exhaust question...again, I think those things give you top end, but you might look into shorty or mustang style manifolds....small diameter pipes that may actually function in your application.

Better minds may chime in...

 

hey thanks that was a big help. sorry for all the confusion and such but i do have one last question: How do you know what your trans. ratio and transcas ratio is? I have the E4OD transmission and 3.55 non LS i think i know the trans ratio .71? what is the transcas ratio?

 

You can probably get that info from Ford. Almost all the stuff I come up with here, and I pride myself as being a real know-it-all and helpful poster of links, I get through Google searchs.

Good luck....