Gear swap question
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Senior User
Joined: Aug 2009
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From: Brazoria, Texas
Gear swap question
I have a 89 f150 4x4 with a i6 and it has 31'' tires. I have 3.18 gears in it right now and I am thinking about switching over to 3.55s. I get 13mpg and sometimes 14mpg on a good day. How would switching the gears affect my gas mileage? What about the power? How would it affect the truck going 65 or 70 down the highway?
Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
It will barely affect gas mileage at all. You might see an extra 1 or maybe 2 MPGs out of it. Power will be better, and RPMs going down the highway will be higher but not unreasonable. If you have the gears laying around and can do it for cheap then go for it, but I wouldn't spend any real money on it. Don't forget you have to change front and rear to match.
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FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
+1.. 3.55's are right in the sweet spot for that engine and tire size and will put 70mph cruising rpms at about 2000rpm. The reason this should improve milage is because it won't take as much throttle to maintain speed... lighter engine load equals less fuel injected, and because the increased mechanical advantage will allow the computer to stay in closed loop more. BTW.. your truck should now have 3.08 gears, there was no 3.18 option.
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Thread Starter
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Senior User
Joined: Aug 2009
Posts: 252
Likes: 0
From: Brazoria, Texas
It will barely affect gas mileage at all. You might see an extra 1 or maybe 2 MPGs out of it. Power will be better, and RPMs going down the highway will be higher but not unreasonable. If you have the gears laying around and can do it for cheap then go for it, but I wouldn't spend any real money on it. Don't forget you have to change front and rear to match.
Thread Starter
|
Senior User
Joined: Aug 2009
Posts: 252
Likes: 0
From: Brazoria, Texas
+1.. 3.55's are right in the sweet spot for that engine and tire size and will put 70mph cruising rpms at about 2000rpm. The reason this should improve milage is because it won't take as much throttle to maintain speed... lighter engine load equals less fuel injected, and because the increased mechanical advantage will allow the computer to stay in closed loop more. BTW.. your truck should now have 3.08 gears, there was no 3.18 option.
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