Hey I have a 1987 F-150 XLT Lariat with a 351w and a C6 auto with 3.08 gears it has headders and 1 7/8" duals with the factory holley carb(list 50264-1). The truck is getting around 13mpg hiway and 14 citity. Is this normal? Also the transmisson shifts at 4000 rpm on full throtle, is that normal, and would a shift kit change that?

 

I wish i got 14 in the city... I'm lucky if i can get 9 on the highway.

 

It's odd that you get lower milage on the highway than in the city, what speed do you typcically drive?
A basic shift kit won't change the upshift point but some kits can do it. Also consider the stock tack probably isn't real accurate, it may be off a couple hundred rpm.

 

Sounds like pretty typical mpg for the 351w w/Holley 4bbl, but those figures should be reversed......never heard of better city than hi-way mpg.

 

I thought it was odd to that i was getting better on the hiway to. I usuall set the cruise to 105 kmh (62mph?). would putting an edelbrock carb say a 650 help out the mpgs? and what cfm is that carb? (list 50264-1) thannks for the help.

 

You get better mileage in the city with that truck because of the lack of overdrive in the C6. You are turning much higher RPM for a sustained period which is not good for mileage at all. The faster you drive, the worse it will get. An overdrive gear or much slower highway driving is the key to getting better highway mileage. New Corvettes have over 400hp, run 12's in the 1/4 mile and are capable of 30mpg on the highway because both 5th and 6th gears are less than a 1:1 ratio, 6th being less than 0.6:1. Overdrive is an amazing thing.

Is your issue with the trans shifting that it shifts at too high or too low of an RPM? A shift kit would allow gears to be held longer, but if you are looking for lower shift points the only way to control that is to lessen the pressure on the loud pedal as applied by your right foot.

My 95 F150 351w with an E4OD and idk what gears gets about 15.5 on the highway.

 

4180 holley/motorcraft 4bbl stock carb is 600 cfm.....Properly tuned it will give you better mpgs than a edlebrock 650...........If you have the C-6, it will limit your hi-way mpgs.

 

I got the transmisson fixed. With an adujustable moudlatour valve. shift points at full throutle went from 3900 to 4500 rpm. the fuel milage isent a big deal. just curious.

 

Glad to hear that you got it fixed!