2.8 to 3.4 mpg

S

sandblaster

NAXJA Forum User

Location

shelby n.c.

• Mar 11, 2008

• #1

i'm swapping my 2.8 to a 3.4 in my 86 chief that has 4.11 gears. do i need to change to overdrive also or will the mileage be ok with the 3 speed 904. i'm building a daily driver and need as good mpg as possible.

 

J

Jess

NAXJA Forum User

Location

Tennessee

• Mar 11, 2008

• #2

This is a very open-ended question and you have given very little information.

 

W

WB9YZU

NAXJA Forum User

Location

Madison, WI

• Mar 11, 2008

• #3

All in all, I don't believe changing the transmission isn't going to help because the two engines have similar power curves.

Ron

 

S

sandblaster

NAXJA Forum User

Location

shelby n.c.

• Mar 11, 2008

• #4

the 2.8 is locked and i have not driven it so i don't know what to expect.
2.8 tf904 np207 stock with 235/75-15

 

pabloconrad

NAXJA Forum User

Location

In the NW hunting Sasquatch

• Mar 11, 2008

• #5

When I did my 2.8 - 3.4 swap, my mileage went up about 2 mpg. After I tossed in a new Weber 38DGES carb, it went up another 2.

 

S

sandblaster

NAXJA Forum User

Location

shelby n.c.

• Mar 11, 2008

• #6

what did that make the mileage all together

 

RichP

NAXJA Forum User

Location

Effort, Pa

• Mar 11, 2008

• #7

I had a 2.8/4 speed in an 82 S10, that got 25mpg on the hiway whether I had the tonneu cover on, off with tail gate open or closed. I think that had 2:92 gears if memory serves me right.

 

W

WB9YZU

NAXJA Forum User

Location

Madison, WI

• Mar 11, 2008

• #8

Jeep Cherokee to Jeep Cherokee then.

My 85' and 86' got about 20-21mpg @ 65 with 3.73s, and 31's, but it was a pooch. When I went to 4.56s, it dropped to 19-20mpg @ 65, but the available power skyrocketed.

When towing a camper (1,200lb popup) I could never get better than 12mpg with either gearing.

Like I mentioned, I don't think you'll gain anything by putting in an OD gear because it takes the engine out of the power band and into the pooch band. You may gain 1 or possibly 2 mpgs, but because of the aerodynamics of the vehicle, or lack of, the power will suck at highway speed.

Ron