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Discussion Starter · #1 ·

It is easily one of the most discussed issues out there as far as performance, and just about everyone will tell you that they know the real deal when it comes to intakes and WRXs.

There are basically two theories out there. The first is that the best intake that you can get for the WRX happens to be the one that comes with the car. This is nice because everyone all ready has it. Of course, you can add a high-flow filter to help it flow a little better, but otherwise, just leave it alone.

The second is that an intake of some kind, ideally a cold air intake, will free up a lot of hp, make your turbo spool up sooner, give you improved throttle response…maybe even better gas mileage. These range in price widely, and there are few different types to choose from, and it seems like for every story about one of these delivering great results, there is a story about one that didn’t work at all.

Now, as you have noticed from all the previous installments of this Blog, I have subscribe to the Stock Air Box theory. In fact, this is my second WRX, and on both cars, I put in a high-flow filter, and never though another thing about it. But there have been a few new intakes that have come out recently that have made me ask a fateful question…

Is there horsepower out there that I am missing out on?

Well, I have had my suspicions for a while, but they were just that. Suspicions. There have been a couple intakes that have come out lately, namely one made by Subaru Performance Tuning (SPT) that made me wonder if I was still holding fast to a concept that has gone the way of OBDI. Then there is the fact that for virtually every other tuner car out there, an intake is the first power mod that people do, and with good results. Clearly it was time to do some experimentation.

With a dyno secured, all that was left to do was to pick an intake, and set up a testing criterion.

As far as what filters to use, well, the baseline was clearly going to be the stock air intake system, with a Subaru filter. Next, I have been running a Perrin Foam Panel filter for the last couple thousand miles, so that was a natural second filter. The Foam filter is at least as free flowing as a cotton gauze filter, if not even better, so it should give a reasonable result for a panel filter.

Then came the hard choice. What kind of intake to test.

If you decide to put an intake on your car, the most important piece of information that you need to know is if it is designed to work with the stock Mass Air-Flow Sensor (or MAF). If there is something that separates Subaru’s from other cars when it comes to intakes it is the fact that their MAF sensors are much more sensitive. If an intake isn’t designed to work with the stock MAF, it can create turbulence that cause the MAF to read out of range. This will throw a Check Engine Light (CEL), and it means that there is air getting past the MAF that isn’t being metered, causing you to run lean. This is a real problem. In my opinion, if you have an intake that is throwing a CEL, it needs to come off immediately, or get your car tuned to re-calibrate the MAF signal. Those stories about an intake blowing up the engine if your Brother’s Cousin’s former room-mate’s WRX could very well be true. I have seen it happen a couple of times, and I just don’t think it is worth the risk.

So first we need an intake. There are a few out there to choose from, and we decided to go with the SPT intake for two reasons. First, it bolts on easily, and it almost looks like a factory part, which isn’t surprising as Subaru made it. Second, this is the intake that got me curious. It was a pretty widely held belief that the stock intake was best, so for Subaru to come out with one… I also have to confess that I had the opportunity to talk to one of the people that helped develop this intake at Subaru, and he assured me that they had spent a lot of time developing this intake to work properly, and to make power. But I had to see the numbers for myself.

Now on to the testing. What we decided to do was to take out as many variables as we could so that we knew that any gains that we saw on the dyno would be clearly attributed to the changes we made, and nothing else. We wanted to perform the testing in a short amount of time so the atmospheric conditions would be the same for all the tests. We also decided that we would re-set the ECU with the Access Port after installing each filter so that they would all be starting from the same learning point. We would then do between 7 and 10 pulls to allow the ECU to adapt to the new system. Then we let the car cool off for 20 minutes, after which, we let the car come back up to normal operating temperature, and did a few more pulls to make sure that we were getting consistent numbers, and that would be our result. One more key testing point was that we performed all the tests with the hood closed to try to better simulate actual driving conditions.

So here is what we found. On this graph, run number 46 is the car with a brand new Subaru filter, 49 is the car with the Perrin filter, and run 58 is the SPT intake. All of there are of course on our Project Car, with the Cobb Stage 2 Protune that you can read about in our previous installment. I will tell you what run number 68 was in a moment.

From looking at this graph, you can see that we gained about 4 ft/lbs of torque over the stock filter with the Perrin between 3,500 rpm to 5,500 rpm, and gained about the same over the Perrin with the SPT over the stock range. All in all, the panel filter is definitely a great modification for the cost, but the SPT definitely out performs it. Now, we did measure the intake temperature for all the tests, and it was pretty consistent at 90 deg. Fahrenheit no matter what system we were using, so I believe that the heat shield on the SPT intake definitely does its job. We did get a temperature spike once with the SPT intake, but we let the car idle for a minute with the fan still on, and the intake temperature immediately dropped.

Now, what was really interesting was what the Ignition Advance Multiplier did. First, the Subaru ECU is dynamic. It is always looking at the information it gets from its sensors and trying to make more power. This is what people often refer to as “learning”. One way to gauge how well this is going is with the Ignition Advance Multiplier, or IAM. This is a measure of how much more timing the ECU feels it can run with out putting the engine in jeopardy. The higher this number, the more power you are getting just by your ECU being a little more aggressive.

When we re-set the ECU before each test, the IAM goes back to its starting point of 12. With each of the panel filters the IAM would stay up for a run or two, and then go to zero, and once it did, we couldn’t get it to come back. (One possible explanation for this is that the car was tuned with this set up, and was pushed pretty much to the max, so there wasn’t much room if any for the ECU to change anything). However, with the SPT intake, the IAM would stay at 12 no matter if we heat soaked the intercooler, or engine by doing successive pulls. Basically, the engine was telling us that it was happier with this intake than with either of the panel filters.

This leads me to run number 68. Kris had the feeling that with the SPT intake there was some more room for tuning, so he spent literally 10 minutes, and tinkered with a couple load sites and the result is that run. This is easily the best result, and notice that we never drop below 200 whp after about 5,000 rpm. He definitely felt that there was more power potential there, but it was too late to really explore that.

I have now been driving around with the car for a little over a week, and I can say that it does feel like there is a little more power, but more than that, it seems like the turbo is a lot quicker to spool between shifts. I also think that it feels like the car is pulling harder in the higher rpm range than before, as the dyno chart shows. Over all, I am very happy with the results, and am now sorry that it took me a few years to warm up to the idea of an intake on my WRX.

I have to say that these are by no means the ultimate power numbers that these intake systems will produce. It is entirely likely that if the car had more time to learn between testing that it may have been able to deliver higher results for each intake. The problem there is that the more time goes by between each test, especially if we are talking days or weeks, there is a greater chance of outside conditions skewing the results. Also, what we were looking at here was the merits of each system, given as close to identical conditions as possible. By keeping the tests close together, and not letting the ECU learn too much, what we are looking at is a more accurate assessment of the individual merits of each system.

I bet at this point you are wondering why we didn’t test a whole bunch of other intakes at the same time to see which one was the absolute best. First, time was something of an issue. The longest brake between testing was when we had to install the SPT intake, and if we were installing a few cold air intakes, that would have made the testing take a lot longer. Also, that wasn’t what we were trying to find out; we wanted to know first if there was a gain to be had by going with an aftermarket intake. Now that we know that there is, we will more than likely do another test between a few different styles of intakes to see if there is a difference there, and what the best design is. In other words, this is just the first installment of this test…
 

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Okay...........this not only has been posted a ton of times with other tests but this topic has been discused a millon times as well.Tons of info if you search.That test was probably one of the worst ones out there..........
 

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Ya that test is pretty old man. Also, its not that SRIs or CAIs are bad. Its that they are bad w/o tuning. When tuned for there can be gains, especially with a higher horsepower wrx/sti.

Personally, I have a Cobb Intake w/heatsheild. But, I got is as a gift. Also, I installed it just b4 my custom open source tune, so it is tuned for. As for specific gains the Cobb gave, I have no idea because that tune was for my hybrid build w/18G. But, it does sound nice.
 

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I think this was a good test. I see nothing wrong with it; it was an apples to apples test. I've read a lot of these threads and most of the testing I've seen wasn't done correctly or it was done correctly and the conclusions weren't supported by the data results.

Maybe it's the majority of people I've seen posting (and not a true representation of the majority of the Subie community) but it seems like most people still feel there's no advantage with an AEM intake unless you tune for it and even then, gains, if any, are minimal. From this test, it seems like our cars run better with the SPT compared to stock or even with an upgraded filter, without any tune. Just because there isn't a HP or TQ gain, doesn't mean there's not an imporvement on effeciency of airflow. Is it always expected to se HP/TQ gains with an improvemnet in efficiency? I thought Cobb officially released that adding an intake (and I thought they used the examples of the K&N Typhoon and the SPT) doesn't have any negative even without tuning...

Can you guys please explain why you think this was a bad test? I don't understand why you think that...

Similar tests have been done, but what year was used? Hasn't there been changes from 02/03 to 04/05 to 06 to 07 to 08 to 09 in the way the ECU handles engine input? If it has changed, wouldn't that merrit new tests such as this one (even though this was an 02)? Would this same exact test and test conditions done on another year (aside from 03) have the same outcome? What surprises me is that an 02 was used and produced these results....does this mean previous intakes used in prior tests didn't perform as well as the SPT?

Clarification please? I now seem to be confused about this...
 

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I am not gonna argue whether the test was valid or not, b/c I don't have the technical knowledge (intake, MAF, airflow), data, nor am I a tuner.

The only thing I will say is that some (not all intakes) w/o a tune throw the MAF and AFR off, which in turn is not good for the engine. I feel its just best to be tuned for any intake (that is not a panel filter), but then I like to play it on the safe side.
 

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I would agree about an intake that throws a CEL would not be good to use without a tune, but it has been verified that the SPT does not suffer that problem. It would seem that the thoroughness of this test seperates it from the majority of the others I have seen.

I understand being safe rather than taking chances, I just didn't understand why this post met with resistance. I guess my questions were directed more towards Donkey since he didn't seem to like it and felt it's been done too many times...
 
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Discussion Starter · #7 ·
Okay...........this not only has been posted a ton of times with other tests but this topic has been discused a millon times as well.Tons of info if you search.That test was probably one of the worst ones out there..........
Of course it's been discussed a million times. Did you even read all of this? I thought it was a well laid out test, complete with dyno charts, graphs, etc. Especially for the complete novice. So what if I contributed to an endless stream of "intake tests"? If this one was "one of the worst ones out there", please refer me to one that's better.
And yes, I do know how to use the SEARCH function.
 
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Discussion Starter · #8 ·
Ya that test is pretty old man. Also, its not that SRIs or CAIs are bad. Its that they are bad w/o tuning. When tuned for there can be gains, especially with a higher horsepower wrx/sti.

Personally, I have a Cobb Intake w/heatsheild. But, I got is as a gift. Also, I installed it just b4 my custom open source tune, so it is tuned for. As for specific gains the Cobb gave, I have no idea because that tune was for my hybrid build w/18G. But, it does sound nice.
Of course there can be gains when tuned properly. Didn't you read it all bro? Lol... they tested the SPT intake, which seems to work very well as Subaru designed it for our cars...and they have a COBB stage 2 tuned for the SPT intake. Check out the graphs/dyno bro.
 
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Discussion Starter · #9 ·
I think this was a good test. I see nothing wrong with it; it was an apples to apples test. I've read a lot of these threads and most of the testing I've seen wasn't done correctly or it was done correctly and the conclusions weren't supported by the data results.

Maybe it's the majority of people I've seen posting (and not a true representation of the majority of the Subie community) but it seems like most people still feel there's no advantage with an AEM intake unless you tune for it and even then, gains, if any, are minimal. From this test, it seems like our cars run better with the SPT compared to stock or even with an upgraded filter, without any tune. Just because there isn't a HP or TQ gain, doesn't mean there's not an imporvement on effeciency of airflow. Is it always expected to se HP/TQ gains with an improvemnet in efficiency? I thought Cobb officially released that adding an intake (and I thought they used the examples of the K&N Typhoon and the SPT) doesn't have any negative even without tuning...

Can you guys please explain why you think this was a bad test? I don't understand why you think that...

Similar tests have been done, but what year was used? Hasn't there been changes from 02/03 to 04/05 to 06 to 07 to 08 to 09 in the way the ECU handles engine input? If it has changed, wouldn't that merrit new tests such as this one (even though this was an 02)? Would this same exact test and test conditions done on another year (aside from 03) have the same outcome? What surprises me is that an 02 was used and produced these results....does this mean previous intakes used in prior tests didn't perform as well as the SPT?

Clarification please? I now seem to be confused about this...
Thanks Vez. I too thought this was a decent test and relative still today. That's why I posted it, even though I seem to be getting some flack from it.
The test was pretty inclusive and detailed, I think. The SPT intake is king, IMHO. The dyno charts and graphs and raw data they used was solid, I think. Not to mention, like you said, they made good hp and tq numbers with the SPT intake and their COBB tune.
 

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I don't think this was a waste of our time. However, the problem is that you were comparing them all on a single tune, except for the SPT. Obviously they were mostly not working well with that tune. The better comparison would be to completely retune the same car to see how much HP etc. when they are each optimized. Then to add reps, do the same with another car and a different tuner, and repeat.
 
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Discussion Starter · #11 ·
I don't think this was a waste of our time. However, the problem is that you were comparing them all on a single tune, except for the SPT. Obviously they were mostly not working well with that tune. The better comparison would be to completely retune the same car to see how much HP etc. when they are each optimized. Then to add reps, do the same with another car and a different tuner, and repeat.
I agree. Only, this wasn't meant to be a science project of comparing multiple intakes and multiple cars and multiple tune's data and getting some sort of final data/conclusion. Just a simple "project car" test on the SPT intake from a local well respected tuning shop in my area.

I feel like I opened a can of worms...
 

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I agree. Only, this wasn't meant to be a science project of comparing multiple intakes and multiple cars and multiple tune's data and getting some sort of final data/conclusion. Just a simple "project car" test on the SPT intake from a local well respected tuning shop in my area.

I feel like I opened a can of worms...
Not to me. I honestly wonder if there is anything to it.
 

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Just because there isn't a HP or TQ gain, doesn't mean there's not an imporvement on effeciency of airflow. Is it always expected to se HP/TQ gains with an improvemnet in efficiency?
Yes if your paying money for it.;)

Can you guys please explain why you think this was a bad test? I don't understand why you think that...
[/quote]
1)"Now, what was really interesting was what the Ignition Advance Multiplier did. First, the Subaru ECU is dynamic. It is always looking at the information it gets from its sensors and trying to make more power. This is what people often refer to as “learning”. One way to gauge how well this is going is with the Ignition Advance Multiplier, or IAM. This is a measure of how much more timing the ECU feels it can run with out putting the engine in jeopardy. The higher this number, the more power you are getting just by your ECU being a little more aggressive.

When we re-set the ECU before each test, the IAM goes back to its starting point of 12. With each of the panel filters the IAM would stay up for a run or two, and then go to zero, and once it did, we couldn’t get it to come back. (One possible explanation for this is that the car was tuned with this set up, and was pushed pretty much to the max, so there wasn’t much room if any for the ECU to change anything). However, with the SPT intake, the IAM would stay at 12 no matter if we heat soaked the intercooler, or engine by doing successive pulls. Basically, the engine was telling us that it was happier with this intake than with either of the panel filters." This to me (in bold) is suspect.If you understand what it takes for the ECU's IAM to go to zero and why the ECU does this it would be hard pressed for you to belive a panel filter alone would cause this,or better yet,nearly impossible.My guess would be an incorrect installation,oil on the MAF or the knock sensor picking up false knock.Since the MAF housing has not changed nothing else should either.

2)Most intakes make power by leaning out the AFR mechanically (different size MAF housing).I can get the same gains with the stock airbox in place by leaning out the AFR's in the fuel maps.I would like to seeing what the dyno would have looked like after the fuel trim corrections stabilized (50-200 miles of driving).I am susprised no wideband data or boost level plots were available data for the test.Also The resonator/snorkus is probably the biggest restriction in the stock air induction system.Removing it is free.I bet if a comparison was done between a stock airbox with the resonator removed and an intake there would be zero gains seen on a stage 2 WRX.

3)Cobb's test on the SPT is an intersting read.

Not saying intakes can't/won't help make power,just not on a stage 2 WRX.Especially a 2.0L.



 
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