A Problem with CAI/SRIs and an Alternative (yes, finally)

[williaty]

Originally Posted by 06OutbackSport

We'll see about that. Unfortunately I don't have the facilities to test this, but I'm curious as to why the air box (& snorkus) make that much of a difference in the low ranges with the MAF. Because a cone filter is so close to the sensor in an SRI setup, I wonder if the variability in the velocity profile of the air at low engine speeds has anything to do with this (the car taking breaths of air instead of a relatively steady flow of air into the engine). If that's the case, putting a thicker filter or baffles should quiet the noise in the signal below 1,500 RPM. If I have some time later this week, I'll try to model a cone filter and the velocity profile at the sensor, but I wouldn't be surprised if that's over my head.

I think if I decide it's sound I'm going for, it's a better investment to make the intake end flow as good as possible, and concentrate on the exhaust for the sound.


Has anyone done a hybrid setup w/out the snorkus installed?

The MAF error is solely a resonant mode. The snorkus is a Helmholtz resonator that damps the resonance. Without the snorkus present and intact, the MAF is going to have problems.

Thickening the filter (which would kill airflow) won't help at all. In fact, you could even cover the inlet of the airbox with rubber and you'd STILL have a MAF error even though there wouldn't be any airflow.

* Registered users of the site do not see these ads.

[Syph3r_]

Williaty, thanks for the write up once again. It is good to see some technical data on intake system after so much hear say.

Question for you,

After seeing the problems associated with SRI/CAI/snorkus delete in terms of the sensor malfunctioning (due to resonance) and the "protection" that gets implemented via the ecu. What problems can you guess (as thats about all we can do at this point) might occur for people running without a resonator over a reasonable amount of time (again guessing here on the time frame).

Any insight would be helpful and greatly appreciated and thanks once again for your time writing this up.

[semaj]

Originally Posted by williaty

And yes, use Hump Couplers. I will be getting one to put between the MAF section and the metal pipe because it's about 5* off.

I didn't get a hump coupler for mine because the MAF section is 3" and the intake tube is 2.75", so I got a stepdown piece. Hindsight reveals that I should have gotten a 3" hump coupler, which should have been fine on a 2.75" tube?

[Jerry Xu]

Originally Posted by semaj

I didn't get a hump coupler for mine because the MAF section is 3" and the intake tube is 2.75", so I got a stepdown piece. Hindsight reveals that I should have gotten a 3" hump coupler, which should have been fine on a 2.75" tube?

Correct. You can always wrap a piece of rubber/silicon on the 2.75" hose before putting the hump coupler on, like what they do on some cone intake filters (3"/3.5" adjustable).

[williaty]

Originally Posted by Syph3r_

Williaty, thanks for the write up once again. It is good to see some technical data on intake system after so much hear say.

Question for you,

After seeing the problems associated with SRI/CAI/snorkus delete in terms of the sensor malfunctioning (due to resonance) and the "protection" that gets implemented via the ecu. What problems can you guess (as thats about all we can do at this point) might occur for people running without a resonator over a reasonable amount of time (again guessing here on the time frame).

Any insight would be helpful and greatly appreciated and thanks once again for your time writing this up.

I'm not entirely sure, but I can think out loud for a minute...


If you spent enough time in the trouble spot with the car in Closed Loop, the car would eventually react by setting negative values in AF Learning. This negative value would be applied through the rest of WOT, causing you to run lean on the top end. This would probably cause a lot of knock, which hopefully the ECU would learn away before you blew the engine though. Overall, it would lead to the car being less powerful than it should.

Running so very rich also runs the risk of bore wash, which is where fuel washes the protective coating of oil off the inside of the cylinder and metal-on-metal contact results. This is also a good way to lose an engine.


Obviously, neither of these must happen very quickly or we'd have a lot more 05+ RSes with blown engines posting on the forum. However, both are the kinds of things I'd expect to see if someone spent a reasonably large amount of time down there. I think that most of us wouldn't, but I've seen a number of drivers who are always 2 gears too high and bog the car like a mofo and think it's how they're supposed to drive.

[formula91]

I was just thinking a bit.

I realize that the airflow is like 2% lower than if we installed a regular SRI/CAI.

Maybe it's all the corners in the snorkus area, but I can't help but think that a CAI has more bends.

Could it be that the lower airflow is due to the restriction of that white cone thing that's in between the filter box and the snorkus?

The difference is small enough to account for a small piece like that.

[williaty]

No idea. It's plausible.

But I don't alter stock pieces just in case. I encourage someone else to try it though!

[Bluefoton]

Why arent the <04 models affected?

[williaty]

They use a MAP sensor, not a MAF sensor

[Bluefoton]

So the resonator's role is PURELY acoustic? Or does it actually also affect the airflow/g curve?

[williaty]

For a MAP based car, the snorkus is purely acoustic (AFAIK)

[Bluefoton]

So removing it has no benefits on the performance then... hm. another conclusion which would point towards cold air as the main source of improvement.
.. got to invent a hybrid intake for my 03 !

[fastenova]

This is wonderful info, williaty. I also read the data you collected on the TBS, and appreciate your objective stance - I know it's hard for most of us to be completely objective when we just dropped some cash for 'performance' parts.

I have been experimenting with the intake on my '97 LGT (also MAF) for about 5 years, on and off, mostly off , and thought I had the perfect design: Straight pipe to the stock airbox, custom piping into the fender with a cone filter for high airflow and cold air.

Seeing your data makes me want to try throwing the stock resonator in and see what happens.

Thanks for your hard work and excellent documentation!

[Soon2BturbodRS]

so, williaty, what manu was your sri before modding it for the hybrid setup?

[williaty]

It was DIY, but it had the same parts as the COSMO.

[zacks62fairlane]

I appreciate you doing this... now i can stop bugging you about it.

[XanRules]

Wait a minute...I just took out my snorkus on my n/a 2.2, does this mean my car is now going to be running super-rich and my engine is going to explode!?

[williaty]

The 2.2's are MAP based, aren't they?

[XanRules]

Originally Posted by williaty

The 2.2's are MAP based, aren't they?

Nope, it's a 97, MAF based...

[williaty]

Then I would suspect this would apply to you, though you have a different enough ECU and intake design, god only knows.

[XanRules]

My intake is the same, I believe. I just took out the snorkus in the fender well and left everything else, including the air filter and airbox, in place.

[williaty]

I thought the older cars had the air filter in a clamshell up near the TB?

[XanRules]

Nope, my air filter is just a panel filter in the airbox.

[williaty]

Weird. Sounds like it might be similar enough to have this problem then. Without logging, no real way to tell how good of a job the ECU is doing patching the problem if it exists.

[XanRules]

Talked to some technicians, turns out on the 97s or so the snorkus was PURELY acoustic.