Against my better judgment, I’ll contribute to this (hopefully) dead, if not dying, thread.
This is true, to a point, and requires a rather long explanation (apologies in advance), addressing three issues - power, throttle response, and fuel economy. (BTW, I am NOT a physicist or an automotive engineer, but I have built and tuned engines [NA and supercharged], done a lot of research on EFI systems, and built my first engine 20 years before most of you young guys were born - and back then understood very little about how engines make power - just throw on bigger this or that. If it makes it louder, it must be faster! If only I knew back then what I know now, or is it the other way around? I'm certainly no expert now, and this is a simplistic explanation, but . . . )
Power:
An internal combustion engine is, as a first approximation, an air/fuel 'pump'. The more air/fuel the engine is able to flow (and burn) the more power it can make. There are many things that limit the amount of air/fuel an engine can flow, such as heads, exhaust, intake manifold, air intake system (throttle body, air intake/MAF/air filter), and cam design. The limiting factor in a normally aspirated engine is ultimately the displacement. The other factors (exhaust, intake, heads, cams, etc) contribute to its volumetric efficiency (how close to the maximum amount of air/fuel a normally aspirated engine of a given displacement can flow at a given RPM - at 100% volumetric efficiency, the engine is completely filling all cylinders and burning all the fuel it can burn with that amount of air [though in NA race engines it is actually possible to exceed 100% VE]). Volumetric efficiency of production engines is typically around 80% (on high-performance engines, such as the 5.0 in the Mustang it is higher, due to improved flowing exhaust, intake, cams, heads, etc, designed to make high-RPM power). Forced induction is able to increase the volumetric efficiency past 100% - typically ranging from 150-200% (200% effectively doubles the displacement @ ~15 PSI). Anything that restricts the airflow limits volumetric efficiency, and power, so it is true that better intake and exhaust will help an engine make more power (and perhaps exhaust will increase mileage some), but only to a point, and this is that point!
If a normally aspirated engine is running at 100% volumetric efficiency (or up to about 110% for full-on race engines), then anything other than forced induction WILL NOT increase its power (assuming the tune is ideal) - because the cylinders are being completely filled at the peak power RPM and burning all the fuel possible in an engine of that size. Thus,
improving the intake or exhaust will not have any effect on the power since it is already at 100% volumetric efficiency (i.e. it simply cannot make any more power or flow any more air without increasing the displacement - simple physics). This is the point at which better intake or exhaust no longer have any effect on performance.
Likewise, if the engine's volumetric efficiency is less than 100% (say, ~80% - which is probably typical for our 3.4L motors), anything that increases the airflow (volumetric efficiency) will increase power, also up to a point. But, the volumetric efficiency will be limited by the most restrictive component in the system - head design, cam design, intake manifold, exhaust system, or intake system. Thus, if the limiting factor is the cam and intake manifold design (which it is in our trucks), assuming all the other components flow enough air to meet the airflow requirements of the design parameters, increasing the amount of air available on the intake side won't make any more power since the amount of air the engine can flow (or can use, or 'needs') is not limited by the intake system, but by the cam and intake manifold design. (I think this is where the problem in understanding these things lies - air intake mods do not 'push' more air through the engine. They simply make more air available if the engine can use it, or needs it. Adding a fancy intake is not going to make any more air flow through the engine when cruising at 70 MPH than the stock intake will. The amount of air flowing is not determined by the intake but by your foot on the gas pedal!)
Side Note:
Our 3.4L engines are not designed for peak horsepower, but for maximum torque over as broad a range as possible. If they were designed for high horsepower, the peak HP would occur at 6000+ RPM. Since this engine is moving a two-ton truck it needs torque, and that is what it produces, at mid-range RPMs, which is where it produces it. The cams and intake manifold (long runner design), in particular, are tuned so that this engine produces peak torque and horsepower in the mid-range band. The peak HP (183) occurs at 4800 RPM (which is low), with peak torque (217) @ 3600 RPM. Toyota engineers designed the engine this way, not as a compromise, but to meet the power and fuel economy needs of a truck. As an example of this, the 4.6L in the Lexus GS460 makes 347 HP @ 6400 RPM, while the 4.6L in the GX460 makes 304 HP @ 5500 RPM - the cams (or cam timing) and likely the intake manifold are different to produce power in a different RPM range (moving a lighter, quicker car versus moving a lumbering luxury SUV). At high RPMs, where horsepower is created, the cam and intake manifold design of our 3.4L truck engines is simply not designed to allow enough airflow to make any more power (short of forced induction). Thus, the horsepower limiters in our engines are the cam and intake manifold design. Shorter intake runners and longer-duration cams will move the peak HP RPM up, making more power, but they are the ONLY thing that will do that (except forced induction). Thus, the volumetric efficiency is limited, not by the air filter or intake tube or Helmholtz resonator, so modifying these things (or replacing them with aftermarket parts) will not change much, if anything.
Let me illustrate this with an analogy. Given that, as a first approximation, an engine is an air pump, we can use a water pump as an analogy (since it's simpler for most people to understand - and I do realize it's not a perfect analogy since water is not compressible and air is, and fluid dynamics might be a little different, but it's close enough for an illustration). If a given fictional water pump is designed to flow 20 gallons per hour at a given pressure (the limitation is due to the displacement of the pump, the RPM of the motor driving it, etc), then at its design parameters it is capable of flowing 20 GPH - and no more. On the intake side it needs a pipe or hose coming from a water supply of some sort (say, a pond or flooded basement) that is capable of flowing 20 GPH. If the hose is too small to supply 20 GPH, the pump will not be able to flow 20 GPH because the intake piping is limiting the system. Likewise if the output piping is too small it won't be able to flow at its designed volumetric efficiency. But, once the intake (and output) piping is able to flow 20 GPH, increasing the size of the piping beyond that WILL NOT increase the amount of water the pump will flow. If an intake pipe of 4" diameter will flow 20 GPH (I don't know if it can - this is just an analogy), then increasing that pipe to 24" (or 48" or 96") will not increase the flow at all - since the limiting factor is NOT the intake pipe, it is the design of the pump itself (once the input and output piping is large enough to flow 20 GPH) - it will never flow more than 20 GPH, no matter how large the intake (or output) piping is.
Now, if we look at the factory intake system on our NA 3.4L engines, the question to ask is if it is able to flow enough air to meet the airflow NEEDS of our engines (whether the volumetric efficiency is 100% or 80% or any other value). If the intake system is able to supply enough air to meet the airflow needs (as determined by the most restrictive component in the engine 'system' - in our case, the cam and intake manifold design) then an intake system modification - deckplate mod, ISR (if either of these really increase airflow), or an aftermarket intake system, will not have any effect on the power output (or the mileage). So does the factory intake system flow enough to meet the airflow needs of our engines? Yes. In fact, it exceeds them by at least 40%. Toyota uses the same intake system (including the Helmholtz resonator ['silencer']) with the TRD supercharger kits, which increase engine output by 40% (from 183 to ~260 HP - 75 HP increase). Now, a better intake on a supercharged 3.4 MIGHT make more power (assuming more fuel and a tune) but that is not the point. If the factory air intake is capable of supplying enough air to make 260 HP on a supercharged 3.4, it is more than capable of supplying all the air a normally aspirated 3.4 will ever need (even with better exhaust, short-runner intake manifold, new cams, ported heads, or fancy spark plugs - none of these will increase power like a supercharger) - in fact, it is able to supply far more than our engines need. And the fact that a supercharger is 'sucking' more air through the filter is really irrelevant. The airflow requirements of an engine making 260 HP are the same, whether it is supercharged or not. Thus, our intake system is capable of supplying more air than a NA 3.4L will ever need (or can use). (BTW, the Wix air filter for the 3rd gen has the same CFM rating as the 4.7L in my GX470, which makes 263 HP - 40% more than our engines, so that cheap Wix filter will supply all the air a NA 3.4L will ever need, or can use.)
Throttle Response:
As for throttle response, that is not likely to be affected either (at least not positively). Throttle response is a part-throttle 'thing'. If the intake can support 260 HP it can certainly flow enough air when you hit the throttle a bit at mid-RPM range. In fact, mid-range power (or 'seat of the pants', which is really torque) is typically enhanced with smaller air intakes since smaller intakes increase airflow velocity, which makes for better mid-range power and throttle response (though this is more applicable beyond the throttle body). Putting an intake manifold with shorter/larger diameter runners on an engine will kill low- and mid-range power (torque) and turn a stop-light racer into a slug (though it might do well launching on slicks at 7500 RPM at the drag strip - the classic bigger-is-better mistake of 'old school' hot rodders. I once stuck dual quads on a short-runner Offy intake on a 283 in a Chevelle. That thing wouldn't do squat until it hit 5000 RPMs. It did well enough with 5.57 gears, and looked very very cool, but it was a classic mismatch. Ahh, to be 19 again!). A higher-flowing air intake may not decrease throttle response, but it certainly won't increase it.
The 'intake silencer' is called a Helmholtz resonator. Its purpose it to tune out pulses in the intake airflow caused by the opening and closing of the intake valves as the engine runs. This is not really an issue at WOT, but it affects mileage, emissions, and throttle response at normal driving speeds (and it makes the engine quieter at WOT). The pulses can confuse the MAF and cause it to read the amount of airflow inaccurately, which increases emissions, and reduces fuel economy. The resonator is tuned to cancel out these pulses at a particular RPM range (typically at cruising speeds - mid-range RPM). If it is removed, the MAF may not read the airflow correctly and the ECM cannot supply the proper amount of fuel to make peak torque when you press the gas pedal while running down the road ('throttle response'). Thus, removing the resonator can not only affect mileage and emissions, but might even reduce throttle response (since the ECM is confused about how much fuel to supply and where to set the spark timing when you punch the pedal).
Fuel Economy.
This is where the aftermarket intake makers take people to the cleaners. They tell you that your engine is sucking air through a straw and with their magic intake it will not have to work so hard to breathe, as though your engine is using horsepower to suck that air through the straw. Well, first of all, the engine doesn't have to do much work to suck air into the cylinders, certainly not enough to cost you 2 or 3 MPG (10-15%). Second, the amount of restriction an air filter causes (or an air intake system) is negligible. Here's a link where a guy tested (using instruments) the difference in airflow restrictions with different filters.
Air Filter Flow Testing for Napa Gold, Amsoil two stage foam, Jackson Racing foam, Baldwin, Mazda and K&N
The difference between the K&N and the Napa paper filter was .018 psi (or about .00012 ATM if my math is correct - in other words, it ain't much!). And, if Toyota designed into the intake system 40% more flow capacity than needed, that difference is less than negligible. Since mileage is based on cruising speed, and it probably takes about 35 HP to maintain 70 MPH going down the highway in a 3rd gen, the amount of airflow needed is about 14% of what we know the stock intake system can supply. It doesn't sound to me like the engine is sucking air through a straw; it sounds more like it is sucking air through a 24" culvert.
Third, removing the Helmholtz resonator might actually decrease fuel economy (at some point) if the MAF is misreading the amount of airflow. Now the ECM will compensate using feedback from the O2 sensors (after a while - the long-term fuel trims will adjust accordingly), but it certainly won't increase fuel economy.
And finally, the amount of fuel burned in an EFI engine is determined by the amount of airflow through the engine. The ECM calculates (and constantly adjusts) the air-to-fuel ratio based on load, RPM, etc. It meters the air through the MAF, and measures the amount of oxygen in the exhaust and adjusts the mixture and timing for best fuel economy or power, as needed. The amount of air
available through the intake system has almost no effect on fuel economy, since the MAF measures how much air is
actually flowing based on the amount of power the engine makes or needs to make and the O2 sensor feedback allows the ECM to adjust the mixture. As long as the intake can flow enough air to make the required amount of power at any given moment it is happy. More air availability will not increase mileage (though more airflow will decrease mileage, as more fuel is required, but the amount of airflow is determined by the gas pedal, not the intake). If there is not enough air available to make the power needed, the ECM will reduce the amount of fuel and the power output will be reduced. But the airflow restriction (if such a thing exists) will not decrease mileage. In fact, a government study on fuel economy concluded that running a clogged air filter made almost no difference in fuel economy.
Here's the link:
https://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf)
And here's the conclusion:
"The goal of this study was to explore the effects of a clogged air filter on the fuel economy of vehicles
operating over prescribed test cycles. Three newer vehicles (a 2007 Buick Lucerne, a 2006 Dodge
Charger, and a 2003 Toyota Camry) and an older carbureted vehicle were tested. Results show that clogging the air filter has no significant effect on the fuel economy of the newer vehicles (all fuel injected with closed-loop control and one equipped with MDS). The engine control systems were able to maintain the desired AFR regardless of intake restrictions, and therefore fuel consumption was not increased. . . . Acceleration performance on all vehicles was improved with a clean air filter. . . .
Closed-loop control in modern fuel injected vehicle applications is sophisticated enough to keep a
clogged air filter from affecting the vehicle fuel economy."
If a clogged air filter won't decrease your mileage, a fancy 'high flow' filter isn't going to increase it either.
Conclusion:
As long as the intake system can supply enough air to meet the maximum requirements of the engine, increasing the amount of air an intake system can supply has no effect on power, may hurt throttle response, and has negligible effect on mileage. Putting a 96" intake pipe on a 20 GPH water pump won't make it pump 40 GPH. It can only pump 20 GPH, no matter how big the intake (or outlet) piping is. I realize there are other factors in making power, such as intake air temp (run that dyno on the deckplate mod with the hood DOWN when it's 95 degrees out and see what happens to the power!) and fuel octane (higher octane, more ignition timing and more power), but we're talking about air intakes and airflow.
I'm always sorry when I get sucked into these discussions (no pun intended, and no offense intended to anyone either), but I hate seeing people spend good money for products that promise a lot, but simply defy the laws of physics and play on the fact that most people don't know how engines work (e.g. how many thousands of those 'Tornado' things have been sold, and everyone who buys them is sure they get much better mileage). Sure Toyota makes compromises in their intake designs, but the compromise here is that they
only designed in 40% more capacity than a NA 3.4 needs! I guess they figured that would be enough, but apparently some don't (the aftermarket guys who want your hard-earned money).
If your mileage increased, it's probably due to the exhaust rather than the intake mod (but I've written enough and don't want to go into exhaust theory).
