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Better mpg?

3K views 15 replies 6 participants last post by  kujata 
#1 ·
I need better mpg.. I avg 13 highway which is shit lol i have an 4.7L v8 2005.. Anything i can do?


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#2 ·
Things I've been told and have been doing.

Intake, TB, Exhaust, Tuner, lighter foot, and possibly look into replacing o2 sensors and plugs if you think you are having lower than normal mpg.

Just realized you said 13mpg highway...check your plugs and sensors. Clean your TB and IAC. Better airflow and a better fuel/air mix should help it some.
 
#3 · (Edited)
Most of the above. An aftermarket intake won't do that much for you, and you can modify the stock setup to be as good as any aftermarket CAI. With that poor mileage, I'd for sure be looking at the O2's, MAP Sensor, and spark plugs. The biggest weak spot on any of the WK's is the exhaust system. With my mods. (see signature), my Hemi routinely gets over 20 mpg highway....usually ~21-23, with a best of 24.4 mpg.

I just got back from a 1786.6 mile trip and overall average for the whole trip was 20.65 mpg......86.48 gallons of fuel. It would have been better if I had driven my normal 65 mph in 4th gear instead of 65-80 mph in 4th and 5th. That included almost all mountain driving, head winds, two climbs to over 6500 ft. and one to 7800 ft., and about 40 miles of city driving. Altitudes ranged from ~500-7800 ft. elevation. I use 91 fuel at lower altitudes and climbing, and 85-87 at higher altitudes. I find that using Standard/Chevron fuel works the best and if I can't get it, I add about 6-8 oz. of Techron. The very best fuel I've found is a Commerical Fueling Network (CFN) station in Wells, Nevada. It's a "no name" fuel, but all of my best mileage has come from the same pumps at this station. I use their 85 fuel, as the elevation there is 5500+ ft.

The bottom line goal to improving fuel economy is to improve the Volumetric Efficiency (VE) of the engine, without going too far overboard. IMO, your first order of business (aside from making sure all engine tune items are working properly) is to fix the exhaust. Again, IMO, headers and a low restriction header back exhaust system is the most important thing you can do. I had to have my headers custom built about 3 1/2 years ago, and they've easily paid for themselves. Next, you may want to consider advancing the stock cams by about 5-10 degrees. I have advanced aftermarket cams in both my Hemi vehicles, with a 6* advance on the WK and a 10* advance on my LX. It gets 27-29 mpg highway with about the same mods. as the WK. A Superchips Tuner with the Advanced Transmission Tuning Application (ATT) will allow you to set your shift schedules to keep your engine RPM in a range that is closer to your torque curve. That's why I drive mine, most of the time, in 4th gear....usually 65 mph in 4th gear, ~2400 RPM. If I could up the RPM to ~2600-2700 RPM, I am sure the mileage would go up a little more. Other things you can do is to cut weight (hard to do), and try to improve the aerodynamics a little. I added an SRT body kit (drag coefficient of .39 vs. the stock Cd of .41) and lower it a little which further reduces the Cd. I also use Airtab Vortex Generators on both my vehicles. The weight of mine, loaded for travel, a full tank of gas and the wife and I in it, runs right at 5500 lbs.

Other little things you can do (after the above) that make slight differences (improvements may be slight, but cumulatively they all add up) are add an underdrive crank pulley, higher voltage coils, improved, modified stock intake (two air inlets into airbox and low restriction air filter), slightly larger throttle body, and a resistor in line with the IAT Sensor to fool the PCM into thinking intake air is cooler than it really is. I haven't done this to my WK yet, but I have an adjustable setup on my LX which may help a little. Theory is that cooler intake temp. will allow the PCM to add a little more timing advance.

A few other obvious things are front end alignment (I have mine aligned with the wife and I sitting in the vehicle), proper tire pressures (go on the high side), making sure the wear patterns encompass the full tread width. Too high pressure wears center only, too low wears outer edges only. Also, much above 65 mph your fuel economy starts tanking. If I drive 75-80 mph, I'll lose 1-2 mpg. I also use cruise control as much as possible which, along with the Superchips ATT App., maximizes the MDS "on" time of the Hemi.

Good luck, and have fun tinkering. For me, fuel economy improvement is a game. It's fun to see what works and what doesn't. My goal for the WK is a fairly consistent 24-25 mpg. I've got a few more ideas I'll have to try though.
 
#5 ·
I found that by using the recommended mid grade fuel instead of regular that I picked up an additional 1.5 miles per gallon on my hemi. The additional cost was off set by the increase in mileage. The recommendations are there for a reason. I've run in to too many people running regular in their hemi's and complaining about mileage.

Just my $.02 worth.
 
#6 ·
Jeff, the thing that made the biggest difference in mileage and performance on the LX was the 10* advanced Sidewinder cam. I've gotten a little over 30 mpg before on it, but most of my driving is at altitudes of 3000 ft. and above. That's also why I can get away with running 85/87 fuels. I also continuously monitor Knock Retard so I know if the fuel octane is wrong for the driving conditions. My WK is modded almost exactly like the LX, and I do the same with it. The LX is about 500-600 lbs. lighter and has a drag coefficient of .35 vs. the WK's (with the SRT body kit) .39. Gearing and the 4WD drivetrain load also makes a little difference in fuel economy.

Your mileage increase with the headers is even a little better than mine were when I added the headers. I think I've said before, I'd really like to "tinker" with a 3.7 like you're doing, just to see much I could get out of it. Headers/catbacks and cam(s) make the biggest difference though.
 
#7 ·
I really need to get home and take a more indebth look at my cams. Last time i looked at them, right cam specifically, the cam tone ring and sprocket are aligned with a key on the cam itself. I really want to advance them but if they are locked like i think they are then i cant do it. Now if there is no key, i can rotate the cam separately on each head so i can shift the powerband to a little lower rpm
 
#8 · (Edited)
I am not familiar with the 3.7 but it shouldn't be a problem. The tone ring on the 5.7 is part of the gear too. Just count the teeth on the cam gears and divide by 360 to see how many degrees advancing one tooth will be....probably ~5-10 degrees. On the Hemi gear it is just under 7*. You'll be moving the whole gear/cam assemblies.
 
#10 ·
I don't think that should be a problem. Just move them both ahead by one tooth. I am sure it'll be a little more work though. Just be sure to mark everything and make sure you keep the chain from coming off the crank pulley.....maybe wire it so it can't move, or ???
 
#15 ·
It was burning up the coolant constantly, flushed it when I changed the oil. Probably a combination of both

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That makes no sense. If its eating the coolant its still doing it. A coolant flush wont fix that. Was your coolant low? What temps was it running at? Can you smell coolant? And what color was the oil/coolant when it was done?
 
#16 ·
I hadn't checked it in a few weeks but I must have gotten to it just in time as the reservoir was near empty. I didn't notice any increase in temps but in the 2 years I've had the thing I hadn't done a coolant flush. It could have just been reaally old to be burning up so quickly.

Idk if that had any affect on the oil and it was like all the other changes I've done.

No idea if it helped or not but my highway Mpg is now sitting at 23 when I'm cruising


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