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Old 04-09-2008, 03:30 PM   #126
angel2167882
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Well you said that so... it let me think the problem at the really first is the MAF
Quote:
What's the basic problem

The MAF sensor is vulnerable to a nasty resonance in the intake tract between 1,000RM about about 1,800RPM at WOT.
I mean this would affect EVERY CARS with MAF if you install a CAI/SRI so?
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Old 04-09-2008, 03:58 PM   #127
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The resonance is due to the intake tract and valves. That resonance is what screws with the MAF, not the other way around. Other cars can have the same kind of resonance but at different frequencies/amplitudes that may not effect the MAF.
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Old 04-09-2008, 05:44 PM   #128
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^^^^^
bingo.
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Old 04-10-2008, 12:27 PM   #129
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Ok I see... I'll try to log my fuel trim and knock from OBD-II and see myself too but I guess your O2 was a wideband and way more precise than the stock ones.

Thank you again for all this info!
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Old 04-10-2008, 01:28 PM   #130
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OBD-II is going to be too slow to see this. You need to be logging MAF sensor voltage directly via SSM.
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Old 04-10-2008, 05:34 PM   #131
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Mmm did you use any kind of bracket for support on your intake?

I currently have no support and it wiggles a little but not enough to make me worry.
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Old 04-10-2008, 07:12 PM   #132
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Nope, just the silicone couplers on each end.
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Old 04-10-2008, 07:21 PM   #133
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Question Basic...

Hey,

Great post about the CAI/SRI and the related problems!

However...

I've been looking into installing SRI for my impreza but I'm not convinced of the logic used regrading the Helmholtz resonator.

Quote:
What's the basic problem
The MAF sensor is vulnerable to a nasty resonance in the intake tract between 1,000RM about about 1,800RPM at WOT. Inside the passenger's side fender is a large Helmholtz resonator, the so-called snorkus, tuned to damp out this resonance. Removing the resonator (snorkus) either as a snorkus-delete or as a consequence of putting in a CAI/SRI causes the MAF sensor to massively over-estimate the air entering the engine and cause the car to run very, very rich.
Quote:
This leads to each "chunk" of air being cooling the MAF multiple times as it vibrates back and forth before migrating downstream and into the engine.
I came up with this diagram to explain my problem:



So effectively, the Helmholtz resonator doesn't prevent air from moving back and forth in the MAF... If it was to prevent that back and forth motion, it would have to be placed between the engine and the MAF.

Only the air between the MAF and engine is used as a "cushion" as it compresses.

I don't know, maybe I got this all wrong, but I don't see how this resonator helps the MAF at all. Can anyone enlighten me?

Thanks,

-S
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Old 04-10-2008, 07:38 PM   #134
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Quote:
Originally Posted by damnstraight View Post
Hey,

So effectively, the Helmholtz resonator doesn't prevent air from moving back and forth in the MAF... If it was to prevent that back and forth motion, it would have to be placed between the engine and the MAF.
wouldn't the one resonator on the flex pipe between the airbox and the "torque box" accomplish this?
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Old 04-10-2008, 07:44 PM   #135
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Quote:
Originally Posted by RS Guy1513 View Post
wouldn't the one resonator on the flex pipe between the airbox and the "torque box" accomplish this?

That's what I thought, but the "hybrid" design doesn't include this and still achieves similar results to that of the stock intake.

So... maybe it's more about flow restriction in the reverse air flow direction rather than resonance absorption.
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Old 04-10-2008, 07:44 PM   #136
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Quote:
Originally Posted by damnstraight View Post
So effectively, the Helmholtz resonator doesn't prevent air from moving back and forth in the MAF... If it was to prevent that back and forth motion, it would have to be placed between the engine and the MAF.
You are right that it's not as effective as placing it between the MAF and the engine. However, if you destroy the resonance anywhere within the tract, you have a sharp decrease in resonance EVERYWHERE within the intake tract.
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Old 04-10-2008, 07:45 PM   #137
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Quote:
Originally Posted by RS Guy1513 View Post
wouldn't the one resonator on the flex pipe between the airbox and the "torque box" accomplish this?
The one up there (which is a quarter wave resonator) damps a much less severe resonant mode much higher in the RPM range that is totally tunable.
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Old 04-10-2008, 09:05 PM   #138
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Quote:
Originally Posted by williaty View Post
You are right that it's not as effective as placing it between the MAF and the engine. However, if you destroy the resonance anywhere within the tract, you have a sharp decrease in resonance EVERYWHERE within the intake tract.

hehe ok I'll take your word for it! Thanks for the good info.

If I sums things up...

1. The hybrid design removes the major resonance issue while providing a small but noticeable performance increase.

2. On the downside, there is still a potential problem:

Quote:
Switching from a stock intake tract to a SRI/CAI reduces the volume between the MAF sensor and the cylinders. This leads to the stock tip-in being WAY too large. On any positive throttle movement, the car will rich spike badly for a few hundred milliseconds.
But not as badly as when the Helmholtz resonator isn't used... Would it be fairly simple to tune the ECU to overcome this problem with the hybrid air intake? I've never ventured into tuning the ECU...

Thanks
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Old 04-10-2008, 10:27 PM   #139
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so my ebay intake (same as is pictured on page 1) finally arrived today. not sure when i'll get a chance to put it in, and i want to install the TBS and IMS at the same time. will post pics when it all goes down. anyone in north pittsburgh wanna join in on the fun?
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Old 04-10-2008, 11:10 PM   #140
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Quote:
Originally Posted by damnstraight View Post
Would it be fairly simple to tune the ECU to overcome this problem with the hybrid air intake? I've never ventured into tuning the ECU...
Tip-in is going to become a problem any time you make ANY CHANGE AT ALL between the MAF and the valves. It can be tuned with RomRaider, however. It's not a simple matter as tip in happens so fast as to be un-loggable, so you basically have to kind of intuitively get it right.
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Old 04-11-2008, 12:19 AM   #141
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Quote:
Originally Posted by williaty View Post
Tip-in is going to become a problem any time you make ANY CHANGE AT ALL between the MAF and the valves. It can be tuned with RomRaider, however. It's not a simple matter as tip in happens so fast as to be un-loggable, so you basically have to kind of intuitively get it right.
How sensitive is it to changes? Would it be any easier to tune if the length and volume of the new intake was close that of the stock one?
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Old 04-11-2008, 12:21 AM   #142
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Not sure, haven't gotten mine dialed in yet.

Tuning the car right now is a process of learning about an issue, learning how to fix the issue, the finding out that fixing the most obvious problem has uncovered another problem, leaning about the new problem........
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Old 04-11-2008, 12:53 PM   #143
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Quote:
Originally Posted by williaty View Post
OBD-II is going to be too slow to see this. You need to be logging MAF sensor voltage directly via SSM.
You might be right yes, OBD-II is indeed not really fast (~500ms per refresh)... still I might try it and let you know.


Oh and last thing... if this thing only occur between 1000-1800RPM @ WOT, well why not be gentle on the throttle up to 2000RPM and then floor it if needed???

That would "workaround" the problem no?
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Old 04-11-2008, 01:04 PM   #144
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That's what I was doing, and it seemed to work for my application. But, as soon as I put the snorkus back on, I was flooring it down in that range again.

It probably is a good idea not to floor it under 2k rpm anyway.
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Old 04-11-2008, 02:37 PM   #145
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While WOT under 2k isn't something you're likely to do, if you do accidently need it, you DON'T want to be having a problem.

The way most people end up down there is to be idling along in stop and go traffic and then see a hole in another lane and try to dive out into it. Or to flub a launch and end up bogged down there when you thought you could jump out in front of that stone truck. Or to grab 5th on a hill when they meant 3rd. None of that is very likely to happen, but when it does, you DON'T want the car to give up and take a nap.
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Old 04-12-2008, 12:34 AM   #146
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^^I agree^^

Why not have it all for relatively little work, and almost no loss in top-end power?
I don't have time nor the means to data log until summer, but the 2% loss in power (which is minimal anyway) I theorize (BIG EMPHASIS ON THEORIZE) is the conical white thing right after the snorkus that helps connect it to the air filter box. The problem is that it's too long, causing a slight restriction. Enough to make a small and unnoticeable/nonsignificant difference.

Because as will's previous data as proposed, the snorkus has no restriction on stock setup airflow. Although technically, it might have been the torque box creating the higher restriction bottleneck. Now that the torque box is gone, the snorkus may be causing the 2% restriction.

Whatever it was I made slight modifications in an attempt to get rid of that 2%. Just because I wanted to.

But that two percent can be anything from the actual panel filter itself to the way the intake was made. The way I hacked that pipe together wasn't great, and there are nice big gaps only to be joined by coupler. It's a tight fit for sure, but it's certainly not perfect. Yet, I want to find the source.

I'll put up pics next post of my variation of the will-setup.
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Old 04-12-2008, 01:24 AM   #147
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The setup was basically the same except I did a few extra things.

Difference 1:


This part wasn't really for stopping restriction really. I just wanted to grab a bit of cold air from the fender instead of going back into the engine bay. Although from what I understand, IAT values don't seem to change. Maybe some insulation will change that.

Because I literally cut off one of the supporting structures for the snorkus, the thing moved around A LOT. Too much for my comfort. So here's what I did to secure it.

Zip tied the neck part to a hole in the fender.
There was a hook that came around to the fender hole, and therefore prevented me from putting on the fender plug. I simply removed part of the fender plug clip, and used duct tape to secure the part that was without the clip. I love using duct tape and I'm not afraid to use it. Also you can see here that I used duct tape to cover up the hole below the fender plug, because hot air can get in that way too.


The 2nd tie down was using an old shoelace to secure the neck part just above the resonator area to the front bumper behind the foglight covers. This won't work if those holes are being used. I use foglight covers so there's nothing there.

Difference 2:


I cut off the while cone thing. I comes straight out of the snorkus, and extends into the air filter box. This seems to be a small restriction as instead of flowing freely into the airbox to be filtered, it juts out straight at the filter. That can't be good. It's prevents the air from easily accessing the full area of the filter. The rubber section also causes a restriction, but I actually pushed that back so it would simply be a connector to the snorkus and the airbox. So that problem was solved.

You can sort of see the cone thing installed in the above picture where I'm trying to show the zip tie.

Holy crap, the duct tape looks way ugly in picture. It doesn't look that bad in person. Really. It matches with the silver. lol.

Cheers. I'm in a good mood since I did a catch can right after. =3
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Old 04-12-2008, 03:07 PM   #148
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I like your sterile field there
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Old 04-13-2008, 03:12 AM   #149
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lol, my mom is a nurse so she has a bunch of these supplies lying around. It's really quite useful for the car. You can use a huge wash pan as a drain pan and the sterile fields are great mats to sit on while under the car and stuff. I just have a bunch of them lying around.

Plus the cotton towels. Those are great for general stuff
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Old 04-13-2008, 03:30 AM   #150
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Quote:
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my mom is a nurse
So am I
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