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Which will get better fuel mileage, a 6nz cat with a 13 speed…

Which will get better fuel...
Which will get better fuel mileage, a 550 hp 6nz cat with a 13 speed tranny,or a 475 hp c-15 cat with a 18 speed tranny? Thanks
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Answered in 3 minutes by:
5/6/2013
Technician: Jim, Technician replied 9 years ago
Jim
Jim, Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 116
Experience: U.S. Army Diesel tech. Owner of truck facility specializing in all diesel engines
Verified

Jim : Hello, Welcome to JA. My name is XXXXX XXXXX do not rate my answers until all of your questions have been answered, and you are happy.
Customer: Ok
Jim : The 6nz was a great motor, but the c-15's are more efficient, but you have to take into consideration tire size and gear ratio for the rears, do you happen to know what the ratios are?
Customer: No sir
Customer: 22.5 or 24.5 will give better mpg?
Jim : Ok, the way you have the question laid out, the c-15 will get better mileage with a 18 speed.
Jim : 24.5 will get better mpg
Customer: Ok thanks
Jim : Because with 24.5 you will be able to cruise at lower rpms.
Jim
Jim, Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 116
Experience: U.S. Army Diesel tech. Owner of truck facility specializing in all diesel engines
Verified
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Customer reply replied 9 years ago
If I have 445/50/22.5 in the back and 11r 24.5 in the front will i get better fuel mileage than if I 22.5's in the front?
Technician: Jim, Technician replied 9 years ago
No, that should not make a difference, are they super singles in the back?
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Jim
Jim, Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 116
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Experience: U.S. Army Diesel tech. Owner of truck facility specializing in all diesel engines

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