I see your point, and it makes sense. But I was thinking more in terms of accelerating at part throttle not just maintaining speed. Getting up to 55 mph from 0 is alot harder on your motor, and that is where you use most of your gas. Upon acceleration the reduced pumping loses mean more power going to the wheels, which means less power overall that needs to be generated, which means less fuel burned (however small that amount may be)

If you need 200 hp at the wheels to get up to speed, and 50 gets sucked up by drivetrain/friction/pumping loses, then you need to produce 250 hp at the motor. Now my pumping loses drop by 2 hp due to lower intake restriction, so I now only need to produce 248 hp instead of 250 hp to achieve the same acceleration.

Done correctly, an aftermarket intake can help performace and fuel efficiency. In most cases it is a very small improvement but the operation of IC engines prove it works.

Greg

 

I hope you were kidding, because that's not possible, TC locked up, without regearing, or an equivalent effective ratio change as in larger diameter tires.

The way to put it in the context of this discussion would be: "I can use xx% less throttle to maintain a steady-state 65 mph". A high octane tune will do that moreso than any intake change.

 

Well now...

You, in effect, just confirmed that a less restrictive intake will allow the use of less throttle for equivalent speed. That's an efficiency improvement - and the best way to improve mileage is to use as little TP opening as possible, to maintain your desired speed.

 

low TP but at a speed your tranny can at least be in OD. I see people here in town try to go even slower than I do for the sake of mpg. Slow speeds don't yield good mpg if the m part of mpg isnt high enough. Lotsa miles per very few gallons is the key.

As for the discussion here, if the driver has to let off the TP to maintain speed at 55 with the filter removed versus having to have more TP to maintain speed at 55 with the filter, then yes, you just have improved efficiency. One way to test might be to find a good exhaust cut-off but install it on the intake side with one inlet behind the filter and the other just free flowing and unfiltered, and with the MAF on the single outlet going into your intake tube. Hey, that might be a good mod! Make it out of lightweight plastic, exhaust cut-offs are metallic and heavy.

However, TP alone is not the whole input to the PCM for mpg. Knowing what your engine load sensor is saying also has bearing on efficiency. I know you can lighten up on TP, but if the engine load sensor goes up then it sort of offsets and mpg might actually go down depending on the balance. There are other factors as well.

 

Think about this for a bit;

If engine load requirements go up ( BTW - there is no Load sensor, Load is a calculated value), by necessity the TP% will go up as well , IF you try to maintain the same speed (as in going up a grade). And mileage goes in the toilet. TPS is one PCM input that detemines injector pulse width, and coupled with load (and a host of other things) also factors into how much ignition advance is appropriate.

Scangauge /Edge /Dashhawk /AutoTap /Xcal2 datalog will confirm this to be the case.

My example was @ stready-state cruise, relatively level, TC locked. Sorry if I wasn't clear.

bubba

 

The PCM will increase TPS as the load goes up due to your foot doing nothing, you can still lower TPS by letting off the gas more and more to counter. Road grades are one thing to increase the calculated load, A/C is another, spot lights, other high-current electronics, hard sharp turns at low speeds, etc. I called the engine load a sensor as it is coming off of the PCM, calculated or not, my bad. Maybe more appropriate to call it an output.

You were clear in your example. The word "maintain" was the key.

 

TPS is an input to the PCM, not an output from the PCM.

To my knowledge, in either an ETC ( see below) or normal mechanical throttled truck, the PCM cannot change it. Only your foot can. (Or your cruise contol actuator lol).

Actually, in an ETC, the PCM does contol the throttle electrically, but it's only in response to the TPS input to command a certain level of torque - it is still very much 'slaved' to your right foot, albeit a bit less directly.

Loose definition of Load = basically the amount of incoming air, ratioed against how much 1 cylinder can hold at standard pressure/density.

 

Well, you are right, but I was talking about the calculated load value, it comes off of the OBD II port for dynoing and diagnosing.

I must not have a fully mechanical throttled truck, it seems my TPS can rise without my foot moving, weird to me.

 

Yeah, I know what you are saying, and to be honest I added mine at the same time as other mods, so I can't say if the Intake itself added MPG or not, but I do have an increase in MPG. Overall though, I don't think it adds much for city, but probably at highway. I do know though that I added the K&N filter that replaces the stock before the kit, and I did get a small increase in MPG, like .5-1 MPG(this was over a year span as well, so I know it was working).

Is the cost savings over time worth it though? Especially if you plan on selling the truck in the next few years, who knows. For me it is, since I'm saving around +$700@$3/gal a year, and if gas prices go up, the savings go up as well. I also plan to keep the truck for as long as possible, so it works for me. I try to think of it as a performance enhancement that gives me a bonus of a little extra gas. I just don't think it'll give you the gains you are hoping it will though, 4 extra MPG and 300 less RPM's would be a dream purchase for me.

In the end, it's just trying the make the engine as efficient as possible.

 

On an '03? That is very wierd, as you certainly do have a directly attached mechanical throttle cable.

You are using what to monitor this?

Bubba

BTW - I just realized this thread went into the weeds - sorry about the Hijack, OP! LOL!

 

Scangauge II. Granted, if it seems to go up without me moving the pedal, it is minor, as if the cruise control was enabled and was adjusting the TPS, only not as much. I don't understand it fully either. If I was at 20 for TPS, and I went up a short grade, the TPS would go up to 21, 22, and maybe 23 yet I believe my foot didn't budge. Time to whip out the service manual dvd and see what is going on. I don't smoke or drink so cant blame that. Perhaps my PCM is doing to something to make it seem as if the throttle is being advanced if the TPS value is rising albeit slightly.

 

Hi & thanks for digging into this - it's intriguing.

I have an ETC truck and mine does vary a miniscule amount if I hold it steady, but it's single percentage points, + or - .

bubba

 

You will get there faster without the filter. Because the intake will take in more air because of a reduced restriction. But you'll burn more fuel doing it. See, when the engine senses the increased air flow, it will add fuel to compensate.

So, if you accelerate 1/4 a mile with the pedal exactly half down, and then accelerate for 1/4 a mile with the pedal 6/10 down, then you've done the same thing. See your gas pedal controls air ONLY! The computer adds the corresponding ammount of gas. Give the engine more air, and it adds more gas. It doesn't matter if you do it with the "gas" pedal or with an air filter.

Ok. Try to visualize your intake tract in your head... What comes after the air filter? A throttle body. It's a valve that controls how much air gets into your engine. So if you want your engine to get its air easier, you need to only open the throttle body. (eg. press the gas) At part throttle you're choking your own engine! How's a low restriction air filter going to help it?

Everybody is getting part throttle, and wide open throttle mixed up. It could help at wide open throttle, because your engine won't have as much intake restriction. But it CAN'T help at part throttle, because your engine is being choked by the throttle body!

A gasoline engine at part throttle is inneficient by design. You can't fix it by adding a low restriction air filter. Why do you think the 4.6 gets better fuel mileage? The main reason is that, you have to press the gas more to go the same speed as the 5.4, hence less intake restriction.

 

You don't really believe that do you? I can't begin to respond to any of your other thoughts if you think a 4.6 gets better mileage simply because you have to give it more throttle

It doesn't matter where in the intake track the filter is. If I want 100 cfm of air in the engine, it will require more work from the engine (hp) to suck it through a dense filter than it would a free flowing one. Its fluid dynamics, you can't change that.

 

Ok MGDfan, usually you're posts are mostly right, but this one is COMPLETELY wrong! The part I underlined is the root of all the misunderstandings. The best way to increase efficiency is to have the throttle body open as much as possible!!!!

Now, that is not practical at say 55mph. Because the engine would develop a lot of horsepower and take off. But if you could increase your gear ratio to a point where WOT would hold you steady at 55mph, then you would be at 100% efficiency with your intake, and a K&N would help. That's why a smaller engine in your truck will ALWAYS get better fuel economy. A 4.6L engine has to have the throttle body open MORE to maintain 55mph than a 5.4 does. A 4.2 (v6) has to have the throttle body open even MORE than the 4.6 at 55mph, so it gets better fuel efficiency, because of reduced intake restriction.

"fuel mileage wise" you are limited by the cubic inches of your engine, and the gear ratio of your rear axle. Those determine the ammount of air-per-time interval required to propel your truck 55mph. In theory, a 5.4 has the potential to be almost as efficient as a 4.2L. (it does produce more internal friction, but that is negligible compared to the "choking" effects of the throttle body)

Put it in context, your engine is a mass air engine. Meaning, if you give it more air, it burns more fuel. Idealy, an infinitely variable transmission would give you a situation where you would be driving down the road at 55mph with the engine at Wide Open Throttle at say 700rpm or so.... THAT would be a situation where you a large engine can nearly reach the efficiency of a smaller engine, and the air filter's restriction might start to come into play. But we don't have that with these "throttle bodied" engines.

The designers resort to choking the engine to regulate power output, rather than regulating RPM.

Now a diesel doesn't have a throttle body. It's power output is controled simply by the ammount of fuel you pour into it. But a gasoline has to maintain a constant air/fuel ratio, so you have to regulate the ammount of air it gets. And the fuel is injected in a set (more or less) ratio.

Conclusion... taking the air filter out would help "power output" at Wide Open Throttle, but it wouldn't help anything at part throttle, cause you could just stomp the "air pedal"