Remove Resonator for Intake Or Change Exhaust?
 

I'm yet to test but still thinking as restriction goes, the less the better.

DIY Intake

Do I remove the Resonator - Not necessarily Warm Air, just no resonator, on the intake, or do I focus on the exhaust options:
Resonator Drums down excess noise.
Muffler (straight through) Enhances sound!
Hi-flow cat converter Better flow than standard.
Extractors Improves power & efficiency!
Stainless Steel Muffler For a distinct sound & style.
2.25 inch system Improves overall performance!

The engine is lean burn, so I don't want to interfere with that if it relies on exhaust pressure (not too sure how exactly it works in terms of lean burn - or if it is, I thought it was from Wikipedia).

Of the exhaust options, I'm not sure headers would be helpful, however, freeing up the exhaust flow might help ?

Low end power is where I want to focus.

Perhaps:
- Remove Resonator On Intake to reduce one point of restriction.
- After Cat Converter, go to 2in exhaust with a resonator to reduce exhaust noise..

Would that make a not so noisy daily driver with some improvement in fuel economy? (assuming the exhaust changes don't matter to the lean burn ?)

It sounds like you have your mind made up already, it also sounds like you have not read any air intake or exhaust design books.
On my car I've had to replace both the intake resonator and switch the exhaust back from over sized to stock and saw a MPG increase with both of those.
Also, what is your current exhaust back pressure and what do you hope to reduce it to? (do you even know if you have exhaust back pressure?) you can have exhaust back pressure tested by a mechanic pretty easily but larger exhaust tends to increase the back pressure at lower revs because of loss of momentum of the exhaust gasses.
So please, before you spend any money make sure that you understand what you are doing, pretty much any book on exhaust design will give you the formula to size your exhaust for the engine speed that you want to run at and you just might find that your current exhaust piping is even larger then you really need if gas mileage really is your goal.

why would you run a 2.25 pipe?
is there a large (400 inch) V8 under the hood?

There are several calculators available for dtermining correct OD of exhaust pipe.
you need to use them.

The Honda Civic VX, a lean burn vehicle of superb mileage used a smaller diameter intake duct as well as a smaller diameter exhaust.

If you know more than Honda did when they built the VX then go for it, but as the previous two posters have alluded to, you may be making the wrong assumptions.

regards
Mech

What's the point of asking questions to determine if one is following a possible solution, if the response is go source books on the subject?
And who is to say the books are free of errors...

My question was based on the possibility that less restriction on the air intake will help the engine breathe freely, and with air more easily available to pump in, should require less time in higher RPMs to get to the desired speed. This combined with driving techniques, I thought might reduce fuel consumption.

The exhaust has a similar line of thinking, if the exhaust can be more freely flowing, perhaps it requires less energy lost in pistons forcing air out of the cylinder, as the back pressure is reduced. But I was reading somewhere that Lean Burn engines rely on exhaust back pressure. I can't recall where.

So I figured who better to ask then here! Many exhaust websites claim improved fuel economy is possible with aftermarket exhausts. I've got no problem with stock or aftermarket, was merely contemplating possible mods and hoping for feedback...

The resonator's purpose is noise reduction. How does removing that, reduce fuel economy? It'll remove a restriction on air intake - isn't that a good thing for fuel economy?

How is the resonator a restriction? Its simply a tube going to a chamber off the main pipe. At the rpms that ecodrivers drive at, this is not a restriction at all, neither is the filter or the intake plumbing.

Aftermarket intakes and exhausts are made for one reason, increased horsepower. Increasing horsepower means shifting torque to higher rpm ranges where it will produce more horsepower. This is what everything you have listed above does. Again, being an ecodriver means you don't use the engine in those upper rpm ranges and you now have less torque than you had before at lower rpm.

A tuned intake and exhaust may increase fuel economy, to figure this out you'd need to do a lot of testing. I have yet to see any soild testing on this (it would be a huge pain testing different diameters and lengths) but it can be done. If you wanted to mod your intake and exhaust you'd most likely go with a smaller intake and exhaust to shift the torque down to a lower rpm. This would result in less total horsepower and greater engine loads which also causes the engine to be used at lower BSFC rates which increases fuel economy.

You are right, there is nothing saying that those books are free of errors, but many of them do have formulas that have been tried, tested and proven over the years and as far as I know no one has proven those formulas to be wrong and I would link to an exhaust sizing calculator that I used to use but the last time I went to look at it the web site was gone, it did however use the same formula for figuring out exhaust size for a small engine running at low RPMs as it did for a large engine running at high RPMs because no matter the speed or engine size you want to size your exhaust to work with the engine, instead of fighting it.

Again, when you put a back pressure gauge on your exhaust (threads in to the O2 sensor bung) what is the pressure that you are seeing and how much do you hope to reduce it?

If you are running your car at high revs and seeing poor mileage it is most likely because your exhaust is not tuned for those high revs so at that point going with a larger exhaust will help slightly with mileage, will it help you get better mileage then if you were not pretending to be a pro-racer? no, will it help you get above EPA mileage? most likely not.

The intake resonator works kind of like a fly wheel, it helps store the pressure caused by pulses of incoming air between the pulses so that the flow of air coming in to the intake is steady and smooth, in other words it's quite, removing that resonator prevents the intake from storing the momentum and forces the engine to start from scratch pulling every fresh charge of air in to the combustion chamber.

You've posted 70+ times so your not a noob.
Try using the search botton.
There are amazingly informative posts on theis vary topic that you should read first.

Most of your 'comments' reflect what is posted on retail product sites and not sites like EM.

Beleive me, a lot of us came here with similar misconceptions. But this is one of the best non biased non product orreiented sites on the net. There is rarely a thread that you can't learn something from.

If you are after all out horsepower, you want the engine to breathe better.

if you want better mileage, you are going to probably be running at VERY little throttle opening, and trying to get the most power out of the least air and fuel.

For these reasons, changing your intake won't help for mileage.
Further, opening the exhaust won't give you better mileage. Your engine was designed to make 70 horsepower max, so it doesn't need very much exhaust or intake.

Your VX is a pretty cool car. You are going to have a tough time making the basic engine more efficient. I would look at ignition timing, check compression, and learn to drive it.

Sorry if 1) I can't read 2.) can't see 3) am stupid........

but........

Nothing anoys me more than a poster who
1.) assumes we know the car he is refering to
2.) doesnt state the car he is refering to.
3) presents multiple issues withuot refering to the specific car.

at this point, two responders say he has a honda, yet the diy link is a nissan and the op owns a sonata and a pulsar....

any clarification?

I think the others took "Lean Burn" to mean "Honda Civic".

"Ass U Me" is a good description.

The questions relate to the Pulsar, which is a Nissan, which uses the QG18DE engine. See this Wikipedia link on it: Nissan QG engine - Wikipedia, the free encyclopedia

Interesting from Wikipedia are:
HO2S - (4) Oxygen Sensors (2 before exhaust catalyst, 2 after) - note a series 2 1.8l has only 2 o2 sensors 1 pre and 1 post
TWC - Three Way Catalyst (2 in exhaust manifold, 1 under car)
Ignition Timing: 9 degrees BTDC (can be altered +/- 2 degrees using CONSULT-II handheld diagnostic tester, e.g. blaZt)
Knock Sensor - located on engine block; retards timing if pinging/detonation detected.
Heated Throttle Body - heated by engine coolant

I think mine has 2 O2 Sensors.
TWC - why not just one cat converter? More restriction ?
I have the ability to change Ignition Timing +/- 2 - which way is better for fuel economy?

Heated Throttle Body - isn't that the same as a WAI ? - since the air has to pass through it, and Coolant heating the TB would make the mixture heat ?

Now, some feedback to the responses (oh, and yes, it's the very reason that ecomodder is a non product oriented, non biased site, that I posed the question to the talented bunch here.. I do want better FE numbers, and results are results).

The resonator doesn't hold air - Resonator - Wikipedia, the free encyclopedia
It's a sound tool on the intake to reduce intake sound - that's what I took it to mean.

Now, I want to be using the very lowest air fuel mixture possible at the point the car spends the longest - neutral (coasting). When it's accellerating, it's at 2000 RPM tops before changing up (see, I do read and search - in fact, out of 70 posts, I've probably read many hundreds on here since joining looking for anything I can adapt with).

The exhaust was posed as a question for much the reason in the responses... the retail sites claim better performance and fuel economy, I wanted to see the response here.

Isn't more air a good thing (look at it this way: The faster the engine can get up to the desired speed, the more time it will spend idling).

I don't want to risk the battery etc, so I don't want to do Engine Off Coasting - yeh, I realise others do it, but the responses I saw said charging the battery.

I've looked through the mods list, I want more power low down, but don't know how a smaller intake will help that..? The science behind it needs to be explained. Google to the rescue maybe.. ?


http://ecomodder.com/forum/emgarage....&vehicleid=643
Resonators removed out of intake with K&N drop-in air filter.
- Shame he didn't put any FE numbers in.

I've wondered much the same things you have. Mainly about the exhaust (considered headers, low restriction cat, free flow exhaust for my metro) I'll be watching this thread with interest. After reading about reducing intake resistance on my Subaru I did a Resonator delete. Admittedly this was done for power purposes.

Just my .02 bits. my understanding is that EoC (Engine off Coasting) isn't terrible for the battery (Though I can't imagine it helps the battery). Rather, Alternator kills or deletes which prevent the Alternator from keeping the battery topped up and completely drain the battery, lead to their rapid demise.

While I have spent most of my life as a gear head, I'm a Ecomodding newbie and most definitely not an engineer so I could be wrong on the above. Just tossing in my thoughts/understanding.

I found this:
GasSavers.org - Helping You Save at the Pump Hypermiling and Fuel Efficiency Forum - View Single Post - intake resonator

And learnt a little ;).

Intake resonators are there to help charge more air in at certain RPM ranges. I wonder if that's why I feel my car kick and be better performing when I floor it past 2500 RPM?

Anyway, there are also bad types of resonators - purely for sound deadening.

Autospeed makes similar comments on their blog:
blog.autospeed.com/2003/11/30/those-funny-things-teed-into-intakes/

I still haven't finished getting the communications sorted so I can get some real time data from the car, and the tank is currently 3/4 full and it's just had an air filter change.

The tank will be due for a fill, and perhaps then I can arrange to take out the bottom resonator - leaving the top one on (I think that's the resonator that forces air in). Seal up the gap, and see how it performs.

In the mean time hopefully I can get some more definite answers on it's possible effect (or at least some way to clearly determine it's for noise).
Autospeed blog:
"Note that all of these devices are for noise reduction, rather than intake volumetric efficiency tuning. So if any of the volumes is likely to be causing a restriction to intake airflow (and that’s especially the case with a series expansion chamber), you can delete it without too much concern."

It should reduce pumping losses (suction to get air in)..

A turbo charger might be ideal then? Force more air in from the exhaust cycle, recycling the energy lost to exhaust.. ?

Else, removing the resonator would function like a WAI - though this does now question other WAI tests - where the stock tubing is removed, including resonator.

From link in OP:
I suspect it's not just books that can have errors...

This is very interesting. In my case I have an overpowered engine (160 HP V6) for the type of driving that I do. I can get the MAP up to 29"Hg using only about 1/3 throttle in some cases. Somehow I always figured that reducing intake diameter would simply be the same as operating with less throttle. My understanding is that the engine is going to try to fill the cylinders up to whatever the displacement is. Whether air is restricted by the valves (cams), throttle, or intake piping, anything that restricts that air is going to be... Well, a restriction. And I always thought that anything that restricted exhaust lowered output and, therefore, efficiency as well. Apparently my thinking is flawed if some are seeing better numbers by actually adding restrictions.

Would anybody care to elaborate a little further on intake and exhaust tuning?

a LOT of this is theory, with suspect application in in the real world.

The intake is as you describe - a restriction is a restriction, and the throttle plate works as good as anything else, so changing the intake for added MPG is probably not going to work.

On the exhaust, for mpg, the argument is you want to keep some exhaust gasses inside the engine for better mpg. the argument is there are pumping losses for a gasoline engine, and the exhaust gasses "fill the chamber" which is more efficient then a vacuum.
Variable cam timing does the same thing - at low speed keep the exhaust valve closed longer to get all the power out of the gasses and keep some of the gasses inside the cylinder.

These are subtle gains, but perhaps they can add some MPG.

Idling is the enemy. You don't want your engine to spend much time idling at all.

If you don't have huge electrical loads, EOC won't drain the battery.

Me thinks you need to do more searching here. It's all there; you just have to find it.

http://ecomodder.com/forum/showthrea...omy-12895.html

A similar question with respect to 'Restriction' was posed in the above thread. The theory there was that reducing pumping losses would improve efficiency. But then 'what kind of car' is probably more relevant.

I do know someone else with an older year pulsar and they've gone with a CAI in front of the car (big 50mm tubing). The engine is a 1.6L and they get near 600kM from a tank (not a good benchmark, but that got me thinking that some performance mods could be for fuel economy too).

Why are you taking this route with mods? You haven't even done any easy mods to the car yet. Start with a grill block, pump up the tires, and get a scangauge. Those few things right there plus a little driving technique will get you a 25% gain at least.

ditto!!!!!!

You also haven't said anything about testing your engine for back pressure to see if you really do have back pressure or what it is, that way if you do get a different exhaust you can again test the back pressure and see if it has changed.
The formulas that tend to be published in books on exhaust design tend to also be tested on real engines as well, they are also the same formulas that lead people to putting 2.5" exhaust pipes on their vehicles that they are using for racing with a 4 litter engine!
But the bottom line is, you want to keep your exhaust moving at around 240 feet per second and a larger exhaust pipe is not going to allow that to happen unless you have a much larger volume of exhaust as well, that larger pipe will end up with a much slower charge of exhaust moving down it so I have to wonder what good does that slower exhaust give you?
I really wish I could find an online calculator that did the math for you that allowed you to put in the engine size, RPM and get an ideal pipe size but Summit Racing has a crude version that you have to have to use a pen and paper to do your math.
How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

Ahh, but I have!
Tyres are at 40 psi, LRR tyres fitted, and I do a bit at getting good driving technique.
That's probably the 8%.

A Scangauge won't work in my car (No OBDII), but I spent my Christmas break busting out the Consult II protocol used in the car, and will be finishing integrating that into the OBDuino soon (it's probably more important now that I want to test different options).

I'm researching and looking into mods - is all, bouncing ideas around.

...a "tuned" intake uses acoustic(length)/mass(diameter) inertia to cram as much air INTO the cylinders as possible.

...a "tuned" exhaust uses acoustic(length)/mass(diameter) inertia to extract as much exhaust OUT of the cylinders as possible.

...working 'together' it's possible to achieve >100% volumetic efficiency...but, ONLY at the "tuned" engine speeds!

Well your garage doesn't say that. :p :)

I understand though, its fun to kick around ideas.

Reading this thread has really piqued my interest. So yesterday I taped my exhaust pipe up with aluminum foil tape down to about 1". I'd like to say that I noticed an increase in low-RPM torque, but I have no actual data to back that up. What I did notice, however, is that because the tape can flex a little bit over the open pipe, it tends to "flutter" during engine deceleration and actually suck in to the pipe. It also sucks in to the pipe when I shut the engine off too. I am guessing that this has something to do with the mass of air moving at a set velocity through the pipe, creating a low pressure in the pipe when the amount of air produced by the engine is suddenly reduced and the momentum of the moving air tends to continue out the end of the pipe at a set velocity.

This makes me wonder if putting a reduction near the end of the exhaust actually has any effect on the velocity of the exhaust gasses inside the pipe before the reduction, other than simply creating backpressure in the pipe. A stock exhaust system is going to have a series of reductions and expansions anyway (cat, resonator, muffler, tailpipe). The Corsica has a resonator just before the cat, which I'm guessing is probably the best point to terminate the pressure wave from the engine, depending on which RPM and throttle that resonator is designed for. My understanding is that anything after the resonator is simply piping and any change should have nothing to do with pressure wave tuning. That doesn't explain why adding restrictions near the end of the exhaust system would aid in low-end torque. I'm thinking about adding something like the adjustable butterfly valve setup. But WHERE to put it is really the question.

Wait wait wait! you are talking about using math, math is full of theories and we all know that theories are not real! don't you have some speculation and guesses that you can give us? maybe a few old wives tails.

and only at WOT and only when the exhaust temperature is "correct".

...and only with the same/proper fuel (methanol and gasoline different combustion waste temperatures).

...and, please NOTE - no digital or anlog numbers were harmed as they were being crunched through the obligatory mental equations of my brevit explanation above; thus, accordingly, the Numerical Nonsense Naysayers Society was not informed (wink,wink).

abogart: ya gotsta think of it not only as "flow" but as a series of pulses.

...an excellent analogy is a 'slinky' sliding through a clear piece of tubing:

The whole length of the slinky represents a "slug" of exhaust gas from one cylinder.

At the moment the slinky leaves the exhaust value, it is tightly compressed together, representing the sudden, high-pressure, explosive out-rush of exhaust gas out/past the exhaust valve into the 'freedom' of the exhaust manifold header pipe. As the slinky moves away from the exhaust valve, it's length expands quickly forward as it quickly moves forward, within our 'glass' pipe, away from the valve and toward the open-end of the exhaust system. The compressed slinky represents the compressed exhaust gas at high-pressure. But, when the slinky finally reaches the open-end of the exhaust pipe, it is no longer under as much pressure, as represented by slinkys' "stretched-out" length.

At the moment the slinky reaches the open end of the exhaust pipe and "pops-out", a "low-pressure" (rarefaction) wave is created/reflected which propogates BACK up the still exiting slinky length (the forward/backward compression of the individual slinky coils)...back toward the exhaust value. When timed correctly this low-pressure reflection arrives back at the just-closing exhaust value and literally "sucks" the last remaining vestages of exhaust gas out of the cylinder...and if there's sufficient valve timing "overlap" it also helps suck "in" the fresh Air/Fuel-mixture from the intake manifold, past the just opening intake valve, helping "suck" more A/F-mixture into the engine than it normally would ingest.

The above process is acoustic (length) tuning, since it's about pressure/rarefaction waves within an air medium (acoustics). Engine speed, exhaust gas temperature and exhaust/intake value timing are the major controllers here.

The physical movement of the gas slug (slinky) down the exhaust pipe is mass (diameter) tuning, since it is the front-to-back passage of the gas slug sliding within the confines of the exhaust pipe area. Engine speed and the squared-ratio of pipe diameter to piston diameter are the major controllers here. A maximum gas movement of ~ 300-350 fps (mach limiting) is optimum.

where can I pick up my diploma.......

I love you guys!!!!

...assuming you're complaining about me, I humbly refer you to the 'Auto Shop Series' article, "Header Science," in the November 1973-issue of HOT ROD Magazine, pages 114-118 (wink,wink).

...from the dust-bin: http://ecomodder.com/forum/163178-post22.html



...here's something recent from Prof. Richard Hathaway: http://www.google.com/url?sa=t&rct=j...qO7gvQTH9kfoWw

All of this works in theory on a single cylinder with a single pipe terminating into the atmosphere at a fixed point. With multiple cylinders exhausting into a common manifold, which later join a common collector pipe, I would think that the physics might get a little more complex. For example, an exhaust charge from one of the front cylinders on my transverse-mounted V6 would leave the cylinder into the manifold. The Pipe expands at the point where the other two pipes converge into a single pipe, which bolts to the crossover (and I don't even know how that flows into the rear manifold). From there, the pipe expands again where the rear manifold attaches to the collector pipe. Farther down the line there is a resonator, I think (big coffee-can-looking-thing before the cat), where the pipe expands greatly, then reduces again to 2". It then flows into the cat, expands again, and reduces again back to 2". Front there it moves into the muffler, where the pipe this time reduces slightly, expands inside the muffler, then reduces again to go out the tailpipe. That's a lot of "biggers and smallers" which I think pretty much get rid of any pressure wave charging effects beyond the resonator.

Back on the subject of tailpipe restriction, my thinking is that reducing the pipe diameter at the point that it terminates into the atmosphere increases the velocity of the exiting exhaust gases and reduces the amount of open area that atmospheric pressure can exert directly to the end of the pipe. If that is the case, then a butterfly valve would be ineffective to create this type of effect. Instead, one would want to simply reduce the tailpipe diameter. OR, perhaps a flapper or check valve with a fixed spring pressure which could effectively allow only enough open area to permit exhaust to flow out at a set velocity over a broad range of engine speeds.

Just my thinking out loud here, I might be totally wrong. ;)

...lookup "Helmholtz Resonator" and "quarter-wave shorted stubs" and you'll find that length tuning can also be used to ensure that exhaust pulses from one cyclinder do not interfere with exhaust pulses from another; it's all about timing and lengths; been proven over-and-over again with use of "Tri-Y" headers, first on WWI airplanes, then on cars.

...lookup "acoustic impedance" and "collectors for headers" for applied information about how/what happens as the hot, high-pressure, exhaust gas slug sudden encounters a change in media (ie: confines of pipe to open atmosphere).

Hmm.. Your car nearly has the aerodynamic properties of a golf ball.

...hopefully, without the weight of all that clay!



Used car salesman sez: "...That's not hail damage sir, that's automotive aero-dynamic dimpling!"

For those who are interested, here are the abbreviated, simplified, Intake and Exhaust "tuning" equations:

LENGTH...acoustic tuning:

• L(int) = [IOICº × Vs(int)]/RPM = (Xº × 1100)/RPM ± 3"

• L(exh) = [EOIOº × Vs(exh)]/RPM = (120º × 1800)/RPM ± 1"

...where:

L(int) = Length, atmosphere to intake valve, inches.
L(exh) = Length, exhaust valve to collector, inches.
IOICº = Camshaft Intake Open-to-Intake Close (see Xº below), degrees.
EOIOº = Camshaft Exhaust Open-to-Intake Open (120º typical), degrees.
RPM = Engine speed where acoustic "tuned."
Vs(int) = Velocity of sound at 85ºF (intake air temperature) is 1100 feet-per-second.
Vs(exh) = Velocity of sound at 1000ºF (mean exhaust gas temperature) is 1800 feet-per-second (gasoline), varies with type of fuel.
Xº = Intake camshaft timing: 90º (max.race); 85º (race); 77º (high-perf); 72º (stock), degrees.

DIAMETER (inside pipe)...mass tuning:

• dia(int) = B×SQRT[(RPM × S)/(360 × Vg)], inches

• dia(exh) = B×SQRT[(RPM × S)/(360 × Vg)], inches

...where:

dia(int) = Intake runner diameter, inches; same cross-sectional area as intake manifold opening.
dia(exh) = Exhaust pipe inside-diameter, inches.
RPM = Engine speed where mass "tuned."
B = Piston BORE diameter, inches.
S = Crankshaft STROKE, inches.
Vg = Velocity of gas slug (intake or exhaust): 300 (race); 260 (hp); 245 (street); 240 (stock), feet-per-second. Limiting criteria, Mach index Z ≤ 0.6 (Vg ≤ 300 fps).

Hehe, well if that's the case, maybe I should put a few more dents in it! :p

I love it when educated people post links to articles or post equations but ignore so many other obvious variables when it comes to a specific engine, driving style, altitude where the poster lives, etc etc etc. Just because something was demonstrated once given a certain set of conditions doesn't necessarily mean it's going to have the same results once nearly ALL of the conditions are different. That said, some of you also want to jump to tiny details while ignoring the general rules.

Le sigh.

OP, generally speaking: you probably won't see much of a difference on your particular vehicles with the modifications you're listing. I've installed 2.25" exhaust systems on 1.8L SOHC 8V engines and seen dyno verified gains across the entire rev range, so I'm hard pressed to think you'd see LESS power as someone suggested. That said, this was not done for economy. Another trap people get into is they tend to drive the car harder to hear the intake and exhaust, therefore canceling out any potential gains.

While the factory airbox and exhaust is restrictive by design (erring toward a quiet cabin and driver comfort), neither those engines you have nor the way you're driving them (ecomodding) are trying to pass more CFM of air through them than the factory parts can handle. I doubt you're hitting a point of restriction yet until you're at WOT bouncing off the rev limiter. But at 1,900 RPM cruising, you won't see significant gains from those parts...that's my educated guess. They can flow a certain amount of air for a given RPM, and I don't think you're asking them to flow anywhere near their limits yet. It's at THAT point where those parts become beneficial. I wouldn't waste the money on the exhaust, that's for sure...I wouldn't want the added drone in my daily driver. But for the low cost of a DIY intake system, I'm gonna do it for ****s and giggles to pass the time on a Sunday.

Note though, that many hypermilers are on factory intakes and exhausts getting double the EPA MPG's for their cars. There are bigger fish to fry.

But hey, I'm just a nut job with a 3" exhaust on a 2.3L. No, that's not the eco car. That's the corn-fed weekend car. :)

THIS is nailing the nail on the head and a clear explanation. as a hypermiler you keep your engine at lower RPM and throttle position and thus aren't flowing as much volume intake/exhaust. That's not to say that there ISN'T any benefit to modifying these parts, just that the return benefit is going to be less than one might expect. Unless your down to splitting hairs, there are better places to invest your time/money.

best of luck!