4.9L mod help
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Senior User
Joined: May 2009
Posts: 294
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From: Ponchatoula, LA
4.9L mod help
<TABLE width="100%" border=0 itxtvisited="1"><TBODY itxtvisited="1"><TR itxtvisited="1"><TD vAlign=top width="100%" itxtvisited="1">i have a 1995 f150 manual inline 6. i am currently stationed in ramstein air base germany and i am looking to upgrade my truck. here are my plans so far:
-4" lift
-bushwacker <A href="https://www.ford-trucks.com/rx98192zju/kwldirect.php?kwid=379" target=_top rel=nofollow>fender flares
</A itxtvisited="1">-33 or 35" tires (havent decided yet)
-split headman headers, true dual pipes
- k&n intake (already installed)
-cams, lifters etc, typical engine mods
here is my problem:
i have heard that lifting a truck and getting larger tires can cause drivetrain problems due to axel ratio. is this true? if so what axle ratio should i go with? any help is greatly appreciated.
thanks,
kevin </TD></TR></TBODY></TABLE>
-4" lift
-bushwacker <A href="https://www.ford-trucks.com/rx98192zju/kwldirect.php?kwid=379" target=_top rel=nofollow>fender flares
</A itxtvisited="1">-33 or 35" tires (havent decided yet)
-split headman headers, true dual pipes
- k&n intake (already installed)
-cams, lifters etc, typical engine mods
here is my problem:
i have heard that lifting a truck and getting larger tires can cause drivetrain problems due to axel ratio. is this true? if so what axle ratio should i go with? any help is greatly appreciated.
thanks,
kevin </TD></TR></TBODY></TABLE>
Posting Guru
Joined: Jan 2005
Posts: 1,299
Likes: 2
From: The Vieux Ford, Kansas
When you go to larger tires the truck will move farther each time the tire goes around because they are bigger, this will make your gearing higher. To correct this problem you can install new ring and pinion gears in the axles you currently have to bring the gearing back to stock, you don't have to swap the whole axle. The lift will have no effect on gearing. What do you want to do with the truck has a lot to do with what gears you end up going with. I would much rather have a truck that is geared a little to low than to high, and you should as consider that the M5OD 5spd used in most of these trucks really has too high a 1st gear with stock sized tires.
-Johnboy
-Johnboy
Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
Here's the formula for calculating what gear ratio you want:
Gear Ratio = (Desired RPMs * Tire Diameter in inches) / (Speed * Final Drive * 336)
So, if you want to cruise at 2000 RPMs at 65 mph with 35 inch tires and have an overdrive of 0.75 (which I believe the M50D does)...
Gear Ratio = (2000 * 35) / (65 * 0.75 * 336)
Gear Ratio = 70000 / 16380
Gear Ratio = 4.27
The closest they make to that is a 4.11, which would be pretty good for getting 35s moving. Pick and mix the numbers as you like.
FYI: 336 is simply a number that removes all of the conversions, like feet into inches, diameter into circumference, minutes into hours, etc, and sums it all up into one easy number. If you're curious, it's 5280(ft per mile) * 12(in. per ft.) / 60(minutes per hour) / pi
Gear Ratio = (Desired RPMs * Tire Diameter in inches) / (Speed * Final Drive * 336)
So, if you want to cruise at 2000 RPMs at 65 mph with 35 inch tires and have an overdrive of 0.75 (which I believe the M50D does)...
Gear Ratio = (2000 * 35) / (65 * 0.75 * 336)
Gear Ratio = 70000 / 16380
Gear Ratio = 4.27
The closest they make to that is a 4.11, which would be pretty good for getting 35s moving. Pick and mix the numbers as you like.
FYI: 336 is simply a number that removes all of the conversions, like feet into inches, diameter into circumference, minutes into hours, etc, and sums it all up into one easy number. If you're curious, it's 5280(ft per mile) * 12(in. per ft.) / 60(minutes per hour) / pi
