I have a 2005 F-150 5.4L 3V. My truck weighs ~5,300-5,500 lbs no driver or passengers, unloaded, depending on what truck scale it is on.

I have 3.55:1 gears on 30" tires. I have a custom 2-1/2" dual inlet into 3" single outlet y-pipe and a Magniflow muffler.

I have a Hypertech tuner on permium tune. It pulls harder than stock and needs 89 octane minimum to run detonation/ping free.

Unloaded it has decent passing power and I can go 100 mph up a grade/mountian pass easy and still get 15/16 mpg if I drive over 100 miles without stopping. I get 10.5mpg normally with all my short trips.

I installed a vacuum gauge and I am pulling 0-5 inchs of vacuum most of the time. If I lock it out into a lower gear so I am revving 3,000 rpm in cruse control on flat ground I start to see 20" of vacuum. I have gotten 15 mpg driving locked out in third gear for over 100 miles non stop. I even did a long trip locked in third gear at 55/60mph and still got 15 mpg.

My truck doesn't have the grunt of my old '82 F-150 351W 2V with 4.10:1 gears and 29" tires. I need that grund in my new truck. Its not like I am going to outrun anything in a truck so I am not concerned about total horsepower here. Should I put long tube headers on? I can't make up my mind on lower like 4.88:1 or higher like 4.10:1 gears. 95% of my driving is short trips so I don't see how having higher gears would help me. I dont' want my city fuel economy to fall below 10 mpg.

 

My 5.4L 3V pulls hard around 4,000 rpm where my 351W really hit hard around 2,000 rpm and continued pulling hard higher into the rpms but it only got 6-7 mpg in a lighter 5,000 lb truck.

 

Long tube headers would be helpful.

but you need a tunner that can take in account your tire and exhaust & gear changes

But you really need to consider that gear ratio change.... the 4:10 would be fine, & comparable to your old f150...maybe consider 3:73 if your not towing heavy

might want to look into vacuum leaks.

your butt dyno is showing the difference in gears and cams, hence the noted RPM differences...not really a fair comparison between your 82' and 05'

really doubt that you can pull 15MPGs doing 100MPH for any length of time??

It is still a truck get 15-16mpgs is pretty normal....the 10.5mpg in town is getting on the low side

 

My Hypertech tuner ask for wheter I have modified the transmission valve body, what tire diameter and gear ratio I have.

I regularly drive 75/85 mph on the freeway and get 15 mpg when traveling a long trip ~100 miles. When I drove east from El Cajon, Ca on I-8 through Alpine, Ca and out in the desert to Plaster City and back I was traveling as fast as 90 mph on one or two long vast stretches. Most of the trip I was going ~80 mph and did so going up hill. I topped my gas tank off before and after the trip, all in the same day. I averaged 16-mpg. So I did not get very good gas mileage hauling *** up a grade but I drove ~100 miles each way in the desert, out to Plaster City and back again which propped up my gas mileage.

If I travel as much as 30 miles at a steady state I can get 11.5 mpg. When I double i I get 13.5mph and If I were to drive to Temecula, Ca or Big Bear, Ca I get about 15 mpg averaging 80 mph.

At 70 mph in third gear I am pulling ~20 of vacuum, 2,783 rpm.

I am on my third set of spark plugs and second set of coils. I know that it shouldn't need them but it really seemed to run better with new ignition system parts. A couple of times it got to running really
s*&ty. One time my TPS had broken off of my throttle body. I JB welded the bolt hole and put the screw in holding the un damaged sensor in place. The gas mileage was ~9 mpg for that tank and always is when it breaks down. The other time it was ~9mpg I replaced the spark plugs and coils and it came backup to 10.5 mpg.

Should I get my camshafts re-ground for more bottome end torque? What are the cam specs anyway?

I found some Pacesetter headers for ~$200-$300 on Summit Racing. They were for Ford Modular engines. On mustang with my truck's engine they often move the catalytic converters back and sacrafice the rear ones since ther just is no room.

 

Regear that pig. 4.30s outta take care of it.

 

I lost the link but on "Project 460 gas mileage", that Centurian got best fuel economy at 2,200 rpm-2.500 rpm. It must because peak torque is down low on the 460 but my peak torque is at 3,750 rpm on my 5.4L.

That Centurian got 9 MPG city at 7,000 lbs. I get 10.5 mpg at 5,300 lbs. I bet that 460 could pull 10 mpg in a lighter truck.

I really think I need new camshafts, aside from that I really like my truck.

 

I dont understand why you think that holding it in 3 with 20in of vac will get you better mpg you will be running that motor way above its volumetric efficiency. If you are indeed getting better mpg in 3 without towing you really need a gear swap I have 3.73s and my truck tows great(not like my 7.3 or 6.0 stroke but it does what it was designed for with out a problem.

Volumetric efficiency - Wikipedia, the free encyclopedia

 

I have done back to back high way fuel economy tests and I am getting 15 with OD locked out or running in OD. One time I got 16 mpg because I traveled hundreds of miles.

So I should seriously swap in 3.73:1 gears if not as low as 4.30:1. How low can I go on gearing before my city fuel economy goes down, 4.88:1 with 30" tires?


"I dont understand why you think that holding it in 3 with 20in of vac will get you better mpg you will be running that motor way above its volumetric efficiency."

I thought that volumetric efficiency was higher at peak torque. I make peak torque at 3,750 rpm. Where is my volumetric efficinecy highest?

 

Efficiency goes down as rpm go up. You just need to spin a high enough rpm to get the toque required to move the load without lugging its a balancing act. A 4cyl Honda probably makes peak torque at 5-7000 but that's not where volumetric efficiency peaks that's for sure. Looking at vacuum is good but not the end all be all. I can spin a 460 at 3500rpm cruiseing in a #3300 car and get good vacation but I would get better MPG at say 1500rpm because all of that torque is being wasted. I say go 3.73 or 4.10 you will be limited by what is available.

 

Imo, it would be pointless to do 3.73s. Give the 4.30s a shot. You could always put a little bigger tire if you have the steeper gears.