Why am i not getting good MPG?

[Power Hungry]

One other thing to pay close attention to is the timing. At lower RPMs with even a modest load, timing can drop to almost zero which can seriously affect fuel economy. This is done in order to help prevent detonation under those types of load conditions. Larger tires compound the problem by dropping the RPM at certain speeds.

For example, my Expy with 3.31 gears gets better fuel economy at 80 than it does at 75 because of the load and RPM range. Oddly enough though, it also gets good economy at 65 which, despite the lower RPM and load range, I assume is due to the lower wind resistance at that speed.

One other thing to remember is that in order to help reduce droning from the CAI kits, we remove the modified Cam Timing curves and revert back to the stock ones. This has a slight economy hit as well.

Take care.

[Jackpine]

Originally Posted by Power Hungry

One other thing to pay close attention to is the timing. At lower RPMs with even a modest load, timing can drop to almost zero which can seriously affect fuel economy. This is done in order to help prevent detonation under those types of load conditions. Larger tires compound the problem by dropping the RPM at certain speeds.

For example, my Expy with 3.31 gears gets better fuel economy at 80 than it does at 75 because of the load and RPM range. Oddly enough though, it also gets good economy at 65 which, despite the lower RPM and load range, I assume is due to the lower wind resistance at that speed.

One other thing to remember is that in order to help reduce droning from the CAI kits, we remove the modified Cam Timing curves and revert back to the stock ones. This has a slight economy hit as well.

Take care.

Yipes! This also means my interpretation of the effect of combining a custom tune with a commercial CAI is somewhat wrong! The custom tune actually DOES reduce the effectiveness of the CAI a bit due to the reduced timing. (I guess we could call it an unfortunate interaction). Reduced timing means reduced power, and, a corresponding reduction in fuel economy.

I'm sure glad I'm using my homemade CAI!

And, larger tires will mean lower rpms at any cruise speed, so, the reduction in timing can be an additional hit on top of the increased moment of inertia of the larger rotating mass as well as larger frontal drag due to more surface area and the increased rolling resistance of the bigger tires.

- Jack

[Power Hungry]

Jack,

Keep in mind that I am referring to camshaft timing, not spark timing. The spark curves don't change when running a CAI.

[F150 Man 4Eva]

Wow, this is getting pretty technical. Is there any definitive answer to the question, is my K&N setup helping or hurting me? And after all of this, I am assuming that getting lower MPGs on my custom perf. based against the canned tow tune isnt alarming.?.? Thanks again

[Longshot270]

Originally Posted by F150 Man 4Eva

Wow, this is getting pretty technical. Is there any definitive answer to the question, is my K&N setup helping or hurting me? And after all of this, I am assuming that getting lower MPGs on my custom perf. based against the canned tow tune isnt alarming.?.? Thanks again

The K&N setup isn't exactly hurting you but to eliminate the CAI drone Bill has to go to a stock cam advance curve which isn't as good for performance. I would expect that the tow program would have modified cam curves for more performance while also having a richer fuel map to help on towing. With a CAI you usually have to use the richer tow program to keep from running a lean engine. The stock cam settings may be what are lowering mpg.

I also remember that you are running big tires. They are effecting the spark timing by effecting the RPMs.
As Bill said earlier when the RPM is low the engine load goes up resulting in the spark timing getting dropped to lower the chance of detonation. By lowering the timing you also lower both performance and efficiency. If the truck isn't regeared then your timing is getting thrown off because the RPM's aren't high enough. Also since you are slinging around more rubber the load goes even higher, dropping the spark timing even more.

[strokin'_tatsch]

Originally Posted by longshot270

The K&N setup isn't exactly hurting you but to eliminate the CAI drone Bill has to go to a stock cam advance curve which isn't as good for performance. I would expect that the tow program would have modified cam curves for more performance while also having a richer fuel map to help on towing. With a CAI you usually have to use the richer tow program to keep from running a lean engine. The stock cam settings may be what are lowering mpg.

I also remember that you are running big tires. They are effecting the spark timing by effecting the RPMs.
As Bill said earlier when the RPM is low the engine load goes up resulting in the spark timing getting dropped to lower the chance of detonation. By lowering the timing you also lower both performance and efficiency. If the truck isn't regeared then your timing is getting thrown off because the RPM's aren't high enough. Also since you are slinging around more rubber the load goes even higher, dropping the spark timing even more.

Well said Colby.. so to put it very basic, you want the drone of the CAI gone so Bill pulls it down to stock cam settings, thus lowering power and MPG. the timing drops at lower RPMs in order to prevent detonation during certain loads. now you have larger tires thus compounding the effect of those loads and helping to create your worse MPG.

Try playing around with different RPM levels and calculate your MPG on paper, not computer.

And colby, you don't have jack that is messing with your aerodynamics. your bumper might weight 100lbs and your antenna ain't jack. heck my antennas that i used were much more than yours is, yet no difference in any mileage or anything and my truck already has the aerodynamics of a brick... haha. then again, it is a diesel, not a 4.6. LoL

[Jackpine]

Originally Posted by Power Hungry

Jack,

Keep in mind that I am referring to camshaft timing, not spark timing. The spark curves don't change when running a CAI.

OK, so we're talking valve opening and closing times. Thanks for clarifying that, Bill. Forget EVERYTHING I posted in my last post, since I was thinking spark timing. I'm sure the valve timing has a somewhat similar effect, but nothing like what I was thinking.

- Jack

[Longshot270]

F150 Man 4Eva, if you want to try what tatsch said you can go in and adjust your 4th gear shift and lock points. Raising them will usually hurt your mileage and lowering them will do the same on performance until you get the RPMs back up, but every truck is different.

[F150 Man 4Eva]

Naa, I don't really want to go in and fool with anything right now. It isn't like it's a problem..just something to get used to I guess. My AVG on Gryphon says 13.6 right now and trucks comp. says 12.6. I am gonna give it some more time and see what happens. But I do tend to keep my eye on that INST ECON. and it isn't pretty. Oh well I guess. Let me ask this though. Does the drone sound indicate running lean or can they exist seperatly? I definitely want my truck running like it should, but at the same time...if taking away the loud sound is hurting my MPG...I would say bring the drone back. It never really bothered me anyway..I kindof like hearing the power when I hit the gas. But is that drone only there because the truck is running lean and/or not as it should?

[Longshot270]

Originally Posted by F150 Man 4Eva

Naa, I don't really want to go in and fool with anything right now. It isn't like it's a problem..just something to get used to I guess. My AVG on Gryphon says 13.6 right now and trucks comp. says 12.6. I am gonna give it some more time and see what happens. But I do tend to keep my eye on that INST ECON. and it isn't pretty. Oh well I guess. Let me ask this though. Does the drone sound indicate running lean or can they exist seperatly? I definitely want my truck running like it should, but at the same time...if taking away the loud sound is hurting my MPG...I would say bring the drone back. It never really bothered me anyway..I kindof like hearing the power when I hit the gas. But is that drone only there because the truck is running lean and/or not as it should?

The drone is only a harmonic vibration, like blowing across the top of a bottle. The big thing on the side of the stock intake is a resonator that takes that sound out for that particular setup. The reason Bill tunes out the drone is because after a while people get tired of it and then ask him to take it out.