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Old 04-11-2009, 07:52 PM   #1
Back Road Runner
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Default Intake Measurements - Effect of the stock box and piping

Ok, I've been looking into some intake setup options. One main one is a simple cone filter on the throttle body (MAP based car). However, I wanted to compare the stock box and if it did anything useful and if the stock intake plumbing had any useful effect. I ran a series of road dyno runs to compare.

For the comparison, I disconnected the battery and reset the ECU. Then I drove a short distance (few miles) to a test section of road. I proceeded to run 4 back to back pulls with the particular intake measuring some parameters like intake temp, air/fuel ratio, and so on. For each intake the ECU was reset and the same 4 runs were done. This is a direct comparison on equal grounds. Besides graphing out some data I also used Data Log Lab to plot torque and horse power. Everything was SAE corrected to current outside conditions with the exception of intake temps set at what the ECU measured for the intake. I figure this would give a less biased impression of each design's capability in the sense if I could pull the same temp for each.

The three designs tested were the cone filter on the throttle body, the stock box with no piping attached, and the stock box with stock piping attached. Cone filter to box shows the influence the box has and box to box with intake piping shows what tuning Subaru put into the intake tract or I should say at the very least what benefit a length of pipe has, tuned or not. I did not test with a length of pipe without all the resonator stuff. I simply don't have any laying around.

I'll note the pic is big at 1920x1080. I'll leave it as a link to keep this thread more readable. Simply click on in and view it in a different tab/window.

http://www.gigafiles.co.uk/files/185...asurements.jpg

The first set is the cone filter on throttle body. What should be noticeable in the TQ/HP graph is the low midrange dip in power. The data plots show that the intake temp is a bit lower then stock and that the air/fuel ratio is pretty messy. This seems to correlate towards the less then even resulting power band (not noticeable with heavy smoothing I'm using). This might be able to be tuned out or a small resonator could be added to compensate like the stock airbox.

The second is the torque box alone. Notable things are the improved upper midrange response in the TQ/HP graph but still lower low range power. The air/fuel ratio is ruler flat, and the intake temps are rather high. Note outside temp is 58F, so quite a jump. It's interesting that the cone is somehow better in this regard, partially specific to where the air is pulled from I guess.

The third is the full stock intake, piping, and all its resonator glory. Notable things would be the still high temps despite pulling from near the headlight (and maybe other places), the great low and midrange power, and again the flat air/fuel curve. There are definitely specific gains to be had by both the box and intake piping. You can also see that timing seems to be a little bit higher too with the stock intake parts.

That air/fuel spike at 5500 rpm, I have no clue what it's doing. It repeats on all setups and all runs. On an actual dyno, this never shows up with whatever they're using to measure air/fuel. I can't say what it is.



I will make a couple notes. First, this is run with an I-Speed SRS-10 flash. This was designed specific for the stock setup. It is possible that the cone filter on TB setup could be simply retuned to run a ruler flat air/fuel curve too. The stock intake manifold design does run a very small plenum volume. This would make the intake manifold and MAP more sensitive to the intake parts then normal. With a larger plenum volume, it's very well possible air/fuel numbers would be far more consistent. I resonator before the throttle body would probably cause the same benefits. The rest of the car consists of a full exhaust and intake and manifold spacers.

I would like to eventually grab some piping and test also a short ram intake with the cone filter and a cold air intake design both with the cone filter and with the stock box. If I'm compelled and can find an adequate part, I would like to run a helmholtz resonator inline in the intake piping of the cold air intake setup. I have a feeling that the stock box or the resonators in the stock piping may attribute to the improved low and midrange response through making use and reflecting back those resonances. These resonators act as spring boards for the pressure wave pulses, aiding in airflow. I'd be curious to see if there is something useful there beyond just simply a tuned pipe of some length.

One final note is the high end power band. It should be noted that all of the intake designs, even the aftermarket exhaust did very little with the top end power band of the car. This is all cam work here as was stated by williaty in his own thread. I'll note that the intake may show different gains when the engine is actually tuned for high rpm use.
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Last edited by Back Road Runner; 04-11-2009 at 08:46 PM.
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Old 04-11-2009, 08:52 PM   #2
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excellent post. another omgmysrigivesme10hp mythbuster... now le'ts just wait for Williaty to chime in

As a side-note, if you have a 02 NA forester: shouldnt your stock air intake go straight from the funnel above the rad into the resonator, with no routing through the inner fender? that's as cold air as stock can get...
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Old 04-11-2009, 09:13 PM   #3
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No funnel. It's a cluster of chambers piled in the corner behind the headlight. There is simply an opening that pulls air in right behind the headlight area. There is a scoop funnel thing on some of the newer cars. Mine also completely ignores the gaping hole in the fender.

The common DIY intake is to use the stock box and simply run a 3" pipe from the box to the hole in the fender or eliminate the box and run a pipe from the TB to the fender hole with a cone filter on the end inside the fender area. The cone filter could be in the engine bay but is generally accompanied by a shroud of some sort to block out heat and promote cold air draw from the fender area.

I intend to run a CF scooped hood. I want the weight reduction and on the older Foresters, this is the only option available. If the scoop is going to be there, I figure I should use it. I've been contemplating simply using the stock box but plugging the side pipe and cutting slits or holes along the back top as the inlet. A shroud could be built and the air pulled from the scoop to the back side of the stock box, through the filter, and into the TB. A secondary option is to use the cone filter but with a short section of pipe and an inline resonator for tuning.

At some point I want cold air in and some form of tune method to make use of pressure waves. One issue that has come up as of now is simply the air/fuel ratio and what is needed to keep that flat and consistent. The stock box does this. I'm not sure why. A simple section of pipe or resonator or pipe plus resonator could achieve the same goal. The stock box alone only appears to be a partial fix, fixes the air/fuel, but it doesn't fix the bottom end. That seems to be a factor of the resonators built into the intake piping. I know this has been mentioned in the past too. There is a thread around here somewhere specifically discussing some low rpm peak that the main resonator takes care of and mild secondary peak that the long tube fixes. These are things that are supposed to be addressed with the MAF setup. With MAP, I see it more as a tuning issues, taking advantage of pressure waves to improve low and midrange volumetric efficiency. I just need to figure out what I need to do to end up with better results then stock. There are discusions and equations on the stuff, so there are some paper results, but there really should be real tuning as well and testing various pipe lengths and resonator sizes to determine the best option.

http://www.team-integra.net/forum/di...g+Common+Topic

http://www.team-integra.net/sections...?ArticleID=466

It's interesting how much tech info that website has.
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Old 04-11-2009, 09:55 PM   #4
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Hm, interesting. We should have the exact very same stock setup. What I did, after trying the in-fender sucker, or a home depot flex aluminum tube CAI, is a "better" stock version - which I saw on an Outback NA. The only difference is the foremost piece - my orginal one was drawing air from behind the headlight, whereas my new one is a huge, WRX-ish type funnel which draws the air from above the rad and below the hood. That alone resulted in a nice >10F drop of air temperature as per the scangauge - and flooring it at 70mph makes the intake temp to be barely a few degrees above the outside air temp.

This is the OEM piece I talk about (ignore the custom straight piping after)
http://forums.nasioc.com/forums/show....php?t=1465686
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Old 04-12-2009, 12:13 AM   #5
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Yep, I'm aware what it is. It seems to be one of the better methods. The downside is that our cars aren't really meant to suck air in there. It depends on if there's much restriction. Basically straight to the fender area or use the WRX funnel are the two good options. With a top scoop like the older sedans or with an aftermarket hood, a secondary location opens up. The question then is how to effectively use it and still build a proper intake.

Last edited by Back Road Runner; 04-12-2009 at 12:24 AM.
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Old 04-12-2009, 02:37 AM   #6
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It would be very interesting to see what you think of a completely stock intake setup (since that preformed best for you) coupled with a WRX intake trumpet. The trumpet is the only thing I've ever done that's had a meaningful effect on IATs.
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Old 04-12-2009, 02:43 AM   #7
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Oh, and RE: your comments on the top end being limited by cams. I am not as impressed as I had hoped to be:
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Old 04-12-2009, 04:19 AM   #8
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On my 05 RS.. which was MAF based, I had tried a few different setups as well for intakes along with a STi hood and scoop. The 05 STi scoop had some serious design flaws for evenly dispersing air over the intercooler.. BUT, it worked quite well for forcing large amounts of cool air into the engine bay and acted as a vent when the car was sitting still.. keeping the temps down considerably for short rams. All in all, I'd have to say the setup I liked most ended up being the stock one, with a high flow drop in filter. I also had a cone attached to the stock system via MAF adapter which worked fairly well.. Eliminating the resonator section and filter box.. and also a Injen short ram.
For Daily driving, the car felt better with the air plume on and strongest with the stock system.
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Old 04-12-2009, 12:04 PM   #9
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There are a lot of variations here between setup and years too.

williaty, what was your other upgrades with that setup and how was it plotted? I would expect to see better gains. I'm curious if it's just a byproduct of the logging and if you would see something different on the dyno. I know my data logging doesn't properly show the very top or bottom end. Maybe there's simply another restriction or tuning issue. I sort of lean back to this:
http://forums.nasioc.com/forums/show....php?t=1682242
I would expect to see more with a more aggressive cam. Where springs upgraded?


Audi20Tdriver, the 05 was significantly changed from the older cars. It ran a MAF, had a new intake manifold and even new exhaust. When things get changed on that car, there will be different effects resulting. This is unfortunately part of the challenge when simply discussing Subarus. Subaru kind of made a bunch of changes in the recent years and end gains or the ability to improve changes. For example, the 05 intake manifold is one of the better designs compared to the older ones. The stock exhaust manifold is equal length and does not show gains like with the older crappy version. You'll toss on a Borla UEL and lose power over stock. With the MAF on the intake, you need to be more careful with good, consistent flow. It measures flow by the air blowing over the wires. Air blowing over the heated wires equals a temp loss and equates to X flow volume. You mess up the calibration by switching to a different pipe size or introduce turbulent air or even reverse air (pulses/oscillation of air back and forth), you mess up the results. With the older MAP based ones, all you had was the MAP sensor in the intake manifold. It simply measured absolute pressure and equated that to X volume flow. The downside is the plenum is small, and I have a feeling it makes the MAP less accurate when you start messing with the intake improperly.

Intercooler?
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Old 04-12-2009, 12:26 PM   #10
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Quote:
Originally Posted by Back Road Runner View Post
williaty, what was your other upgrades with that setup and how was it plotted?
Intake, TBS, EL headers, cat delete.

That's a direct plot of engine loading, so it shows the true change in airflow into the engine.

Quote:
I would expect to see better gains
Yeah, so did I.
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Old 04-12-2009, 01:26 PM   #11
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For you MAF guys, you might consider one of these in FRONT of your MAF sensor, behind the airfilter. Even of your airfilter has this funnel shape, you should be good to go. Make sure the neck ultimately matches the MAF. A velocity stack funnel in front of the MAF smooths the airflow and doesn't disrupt the signal by beating up the sensor. If you just threw on a filter in front of your MAF and got wacky AF readings, it's the lack of a VS that is doing it on that setup. This is a piece with one of those "effects" that can throw off your results when it isn't used.
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Old 04-12-2009, 02:05 PM   #12
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yeah, Blox makes a nice filter setup. It's not just that. The velocity stack helps linearize flow, but you still have resonances from the engine side that Subaru uses helmholtz resonators for. That I feel still needs to be included to keep flow consistent over the MAF. For the MAP setup and the small plenum, it may also partially be the case, i.e. the effect the stock torque box has.

Digging through some old threads trying to find specific information on this:
http://forums.nasioc.com/forums/showthread.php?t=30366
Quote:
Originally Posted by Boostup! View Post
No, you will not blow your MAF sensor without the Helmholtz resonator. It is there purely for noise purposes only. My company (Roush Anatrol) has build many many of these resonators for automotive intake systems.
People blow their MAF sensors because they hard mount the sensors to the chassis after an intake mod.
http://forums.nasioc.com/forums/showthread.php?t=413598
Quote:
Originally Posted by subawang View Post
FYI, I believe the stupid tube that hangs off the intake is either a 1/4 wave resonator or helmholtz resonator. Their purpose is to basically reduce sound pressure waves in the intake.
http://forums.nasioc.com/forums/showthread.php?t=783827
Quote:
Originally Posted by Section 8 View Post
Its a Helmholtz resonator.

http://www.mecc.unipd.it/~cos/DINAMO...suonatore.html

A tube with d diameter and L length with resonate at a specific frequency with varying intensity relative to the speed of the air traveling through it. This phenomonon is known (other than resonance) as an Aeolian Harp. See also the Tacoma Narrow bridge.

The resonator dampens this sound in the intake at the resonance of the tube diameter and length. It is essentially an air spring that attunates the waves produced, that can wreak havoc with flow inside of the tube under the right circumstances.

Weather or not you can actually reach the right (wrong) circumstances to generate flow problems is debateable, and the addition of a high flow air filter introduces more intake engine noise into the intake which is likely beyond the attuneating ability of the resonator anyway.

It is going to have very very little effect on the flow of the air through the tube weather it is there or not. Leave it alone until you remove the entire intake as the likely hoood of making flow worse by messing around with the interfacing area between the two parts is pretty good. Aside from that, it is possible that it reduces some dips in the output of your engine. If you aren't replacing your intake, screwing around with the stock intake by cutting off pieces isn't going to improve flow.
I still didn't find specifically what I was looking for. There was a post...somewhere...that someone actually did clearly state specific rpms or frequencies that the resonators targeted and improved. Knowing the exact frequencies, one could pick the correct resonator size and mimic the stock setup. One should also be able to simply measure the volume of the stock parts or simply reuse the stock parts attached to an aftermarket intake setup.

I'm curious if one should match a resonator between the intake and exhaust sides.
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Old 04-12-2009, 02:38 PM   #13
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Roadrunner, You are correct about the intake manifold and MAF; however, the 05 was still UEL OE exhaust manifold. The power output and exhaust system was the same as 02 but the car did have better potential for breathing mods because of the intake manifold if the car was properly tuned after being modified. I still felt my 05 felt best for DD with the stock intake system. I also had borla UEL headers which since I was UEL stock, actually gave the car a bit of of midrange grunt, due to slightly larger piping and a stromung cat back.

what I mentioned about the intercooler was what led to the 06 STi having the same size scoop as the WRX.. The 05 Sucked for even passing air over the intercooler but worked very well for cooling the engine bay with no intercooler.

Hamfist,

that is the exact setup I had for a while.. there is definitely something to be said about the Helmholtz resonator at least for the power band used in a DD.

do you still have that car you supercharged a while ago?
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Old 04-12-2009, 03:13 PM   #14
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It's the same car I've always owned . Gasoline, supercharged, and now on E85 while n/a.

I've actually done well over 50 different combinations on this car mostly on a whim or creative idea that I think would work better. It's never been turboed, but I've worked on plenty of others that were. I learned a good bit on this car, but far from "everything there is to know." I swear by stock parts largely because of all of that bolt-on experimentation. All of my best results have been from modified stock parts.
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Old 04-12-2009, 03:22 PM   #15
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right on man! I used to dream of doing that to my RS while reading your thread, then I'd sign off the net and be like, leave the nice little new car alone. I had a lot of boltons on the RS and I too have found the stock parts to be quite well engineered for the most part.. more so then other manufactures.
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Old 04-12-2009, 09:45 PM   #16
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Well most things are done with purpose. The aspects that interfere with power are the ones done for emissions or longevity or cost savings. The exhaust manifold is a good example of cost savings. Cams are a matter of emissions and longevity as well as standard drivability. The intake is generally well done but it is done with specific intent. If that intent is changed, the ideal design is changed. Because it is ideal for stock only indicates it is ideal for stock. When the engine is designed for some other use, that becomes less then ideal.

I'm going to measure the resonators of the stock intake and see what I get for numbers. I'm curious what their specific tunes are. There's a small chamber and a large chamber resonator and that tube thing that I'm not quite sure how to measure. A normal resonator is a chamber of X volume connected via a tube of length Y and cross sectional area Z. These parameters along with the speed of sound define the tune frequency of the resonating chamber. A simple closed off tube doesn't fall into that design since it is all chamber.

More resonator info, weee...
http://www.dinamoto.it/DINAMOTO/on-l...suonatore.html

http://blog.autospeed.com/2003/11/30...-into-intakes/
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