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Old 03-11-2012, 01:40 PM
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school me on pros/cons of gear swaps

I have a 06 f350 dually with a 8" lift and 37s. Right now i have 3.73s in and want to change to a 4.30 for better towing. So, what are the benefits? Right now i see about 7lbs of boost when cruising on the interstate, will it go up or down. Will gas mileage increase or decrease. Also i figured the motor and tranny wouldnt have to work as hard with more gear. So guys with lifts and large tires, please share your thoughts
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Old 03-11-2012, 02:16 PM
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Your gas mileage can only go down, not up if you install lower gears; unless you only drive in the city, then it may go up due to being able to accelerate easier. Nevertheless, your towing mileage may go up as it requires less engine pull with the larger tires but your hwy mileage will either stay the same or go down and the reason is if you step down to 4.30 gears your engine will have to run at a higher rpm thus using more fuel (in theory anyways) but you will gain considerable mechanical advantage for towing and load hauling. I would think instead of 7psi you would probably see 8-9psi for the same style of driving.
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Old 03-11-2012, 02:29 PM
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with 37s and 4.30s your gearing would come back down fairly close to 3.73s with stock tires. your boost isn't just dependent on RPM so it could easily stay the same if not go down a bit because your engine is under less load.
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Old 03-11-2012, 03:27 PM
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Quote:
Originally Posted by atvrider93 View Post
with 37s and 4.30s your gearing would come back down fairly close to 3.73s with stock tires. your boost isn't just dependent on RPM so it could easily stay the same if not go down a bit because your engine is under less load.
this is exactly as i see it.

if you are putting new lower gears in to compensate for the taller tire and are trying to get close to factory rpm/mph then i think you should see better fuel mileage. It most likely won't be close to stock but it should be better than what your getting right now. I don see your boost dropping because the engine isn't working as hard.

what you have right now is the same as putting 3.23 (guessing) gears in a truck with stock tires.

Im no expert in these trucks but I do know mustangs with turbos and this is the same theory except we put taller gears in to load the engine more and produce more boost! takes from mpg but makes it a lot more fun!!! lol
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Old 03-11-2012, 05:13 PM
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Tanks guys. I figured it would be like going back to stock. Also now the gears are doing more work so the motor/turbo dont have too. Im going to call and get a quote tomorrow for some 4.30s. Should feel like a whole new truck
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Old 03-11-2012, 05:17 PM
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I don't know about whole new truck, just closer to what it was like before the 37s
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Old 03-11-2012, 05:18 PM
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Meant to say "do see your boost dropping"

Yeah it will feel like a new truck!
Hope your doing the front and rear!!!
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Old 03-11-2012, 05:20 PM
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Originally Posted by atvrider93 View Post
I don't know about whole new truck, just closer to what it was like before the 37s
HAHA!
party pooper!
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Old 03-11-2012, 05:32 PM
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Ive never driven the truck without 37s. First it had 22.5s and now these. I know in the mustang world if you step up from 3.27s to 3.73s it makes a big difference. We shall see.
Anybody else have any thoughts or experience?
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Old 03-11-2012, 06:34 PM
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I did a gear change on my 97 from 3:55 to 4:10 lost 4 mpg so i could pull my 5er cost $1300 well still have my 97 but had to get my 06 to pull, it was way over the gross plus my 06 has 2x the pulling power.
2 stroker
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