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

[williaty]

Yes, there's quite a lot you're missing.

Think this one over harder. I'm sure you can figure out what the problem is if the MAF is supposed to be precisely metering the air entering the engine.

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[chazly413]

So you're pretty much saying there's a hole after the MAF, as in a leak for unmetered air?

[williaty]

Dude is effectively saying he wants air to move through the MAF (but how will it move it the engine isn't pumping it in?) and then be wasted into the engine bay. Then he wants a different, completely un-metered, amount of air to actually enter the engine.

Utter fail.

[99ForesterVA]

Originally Posted by williaty

Yes, there's quite a lot you're missing.

Think this one over harder. I'm sure you can figure out what the problem is if the MAF is supposed to be precisely metering the air entering the engine.

It has to be an exact amount of air coming into the intake, and no more or no less? So that means that ANY change in that would cause a disruption, no matter how small the disruption? So in theory, even a higher flow air filter would cause more air to get into the maf, causing problems? A crack in the snorkus, a loose clamp, anything would cause my engine to have problems? That kinda seems weird to me, because the hybrid setup you use alters the air flow also. Originally after the maf, there are a few bends, some flexible hose, and a large airbox to deal with. But your system removes all that turbulence, and makes it a smooth transition straight into the intake. So, in essence, your hybrid is all show and no go, but rather window dressing, right? I mean, if yours disrupts the air flow any, then you'll mess up your engine right? Does yours simply do the same thing as the stock, but in a prettier package, thereby taking absolutely no chance in harming your engine? Can you break it down more for this dummy here, because I'm not quite following?

[williaty]

Every molecule that passes the MAF must immediately enter the engine. Every molecule that enters the engine must have passed the MAF.

Air filters don't mess things up because the air that passes the MAF, and only the air that passes the MAF, enters the engine.

[williaty]

Every molecule that passes the MAF must immediately enter the engine. Every molecule that enters the engine must have passed the MAF.

Air filters don't mess things up because the air that passes the MAF, and only the air that passes the MAF, enters the engine.

[99ForesterVA]

Originally Posted by williaty

Dude is effectively saying he wants air to move through the MAF (but how will it move it the engine isn't pumping it in?) and then be wasted into the engine bay. Then he wants a different, completely un-metered, amount of air to actually enter the engine.

Utter fail.

Ahhhh...that's the unanswered question. Does the engine have its own vacuum? It seems if it did, wouldn't it still suck in the same amount of air as it did with the original setup? Or does the original setup decrease the flow of air on purpose? Thanks for your responses.

[Zefy]

Originally Posted by 99ForesterVA

It has to be an exact amount of air coming into the intake, and no more or no less? So that means that ANY change in that would cause a disruption, no matter how small the disruption? So in theory, even a higher flow air filter would cause more air to get into the maf, causing problems? A crack in the snorkus, a loose clamp, anything would cause my engine to have problems? That kinda seems weird to me, because the hybrid setup you use alters the air flow also. Originally after the maf, there are a few bends, some flexible hose, and a large airbox to deal with. But your system removes all that turbulence, and makes it a smooth transition straight into the intake. So, in essence, your hybrid is all show and no go, but rather window dressing, right? I mean, if yours disrupts the air flow any, then you'll mess up your engine right? Does yours simply do the same thing as the stock, but in a prettier package, thereby taking absolutely no chance in harming your engine? Can you break it down more for this dummy here, because I'm not quite following?

what you are proposing is like having an air conditioning unit installed in your house but then you go and open all the windows thinking, "if open windows make it cooler AND the AC makes it cooler, then it should be SUPER cool in my house!"

If you find the above statement completely correct, then please don't touch your car. ever.

If you think, "hey, that's crazy. AC works best with the windows all closed," then you're on the right track.

So pretend the AC unit is your MAF, the house is the engine. If you remove the maf from the flow into the engine you're engine won't know how much air it is receiving. Think if the car was idling at a stop. No airflow would go through the maf but air would still be going into the engine. (back to my metaphor, you'd have all your windows open with the AC unit sitting on the front lawn... doesn't work)

You can move the maf anywhere you want as long as everything AFTER the maf goes right into the engine with no leaks. If you mess around with things (like what a SRI or CAI does) the sensor won't work properly. The hybrid is a nice middle ground where everything still works with a little bit better flow.

[99ForesterVA]

Originally Posted by Zefy

what you are proposing is like having an air conditioning unit installed in your house but then you go and open all the windows thinking, "if open windows make it cooler AND the AC makes it cooler, then it should be SUPER cool in my house!"

If you find the above statement completely correct, then please don't touch your car. ever.

If you think, "hey, that's crazy. AC works best with the windows all closed," then you're on the right track.

So pretend the AC unit is your MAF, the house is the engine. If you remove the maf from the flow into the engine you're engine won't know how much air it is receiving. Think if the car was idling at a stop. No airflow would go through the maf but air would still be going into the engine. (back to my metaphor, you'd have all your windows open with the AC unit sitting on the front lawn... doesn't work)

You can move the maf anywhere you want as long as everything AFTER the maf goes right into the engine with no leaks. If you mess around with things (like what a SRI or CAI does) the sensor won't work properly. The hybrid is a nice middle ground where everything still works with a little bit better flow.

Okay, thanks. I see what your saying. My only point is this: if the engine sucks its own air, then I don't understand where it matters where its coming from. The maf does not alter the flow correct? It only measures it, correct? Does the original setup decrease or increase the flow in some way? If not, and its sucking air willy nilly into the engine, what does it matter where it comes from, so long as the maf is reading what's coming through the snorkus?

[99ForesterVA]

Originally Posted by williaty

Dude is effectively saying he wants air to move through the MAF (but how will it move it the engine isn't pumping it in?) and then be wasted into the engine bay. Then he wants a different, completely un-metered, amount of air to actually enter the engine.

Utter fail.

I very much appreciate your answers. What I'm trying understand is, does the snorkus cause a decrease or increase in the air flow, which is what makes it the perfect amount of air to be the most efficient? Or does the engine take in the amount it needs based on the amount of throttle given?

[renyo]

Since you're typing like you've at least seen an English textbook, I'll try to explain.

To burn gas properly and create usable combustion without breaking the engine, there is a specific ratio of air to fuel you have to have (it's more a range of ratios, but not the point). For example, if an engine sucks in 14.7 pounds of air, I have to spray 1 pound of fuel into the engine for a good combustion event.

The engine uses the MAF sensor to determine how much air is going into the engine. The MAF sensor can only measure air that has gone through it.

The problem with your ideas is the engine doesn't give a **** where the air comes from, be it the intake through the MAF sensor, a vacuum leak, or a cone filter stuck to the side of the intake pipe after the MAF sensor.

The problem arises when (with made up numbers) 14.7 pounds of air flows through the MAF sensor, then an additional (once again, made up number) 3 pounds of air flows through the leak/hole in the intake pipe after the MAF sensor. Since this did not come through the MAF sensor, the engine thinks only 14.7 pounds of air is in the engine, so it injects 1 pound of fuel.

Unfortunately, instead of a nice 14.7:1 air to fuel ratio, you now have a 17.7:1 air to fuel ratio and your engine just exploded.

Now, to answer a couple of your questions.

Yes, the MAF sensor affects the air flow. It has to because of how it measures it. That said, it's a negligible amount.

Intakes (ideally) increase the amount of air you can flow to your engine by creating less of a restriction for the incoming air (having a lower pressure drop across them). The accordion pipe that's behind the MAF sensor in stock intakes doesn't help air flow smoothly. Replacing it with a smoother pipe (i.e. Williaty's hybrid intake) lets the air flow, well, smoother. Sort of how single file lines can get more people into a building faster than people mobbing for the door.

[williaty]

You must have an unbroken, non-leaky, air-tight pathway directly from the MAF to the engine. Yes, engines pull a near-perfect vacuum.

[99ForesterVA]

Originally Posted by renyo

Since you're typing like you've at least seen an English textbook, I'll try to explain.

To burn gas properly and create usable combustion without breaking the engine, there is a specific ratio of air to fuel you have to have (it's more a range of ratios, but not the point). For example, if an engine sucks in 14.7 pounds of air, I have to spray 1 pound of fuel into the engine for a good combustion event.

The engine uses the MAF sensor to determine how much air is going into the engine. The MAF sensor can only measure air that has gone through it.

The problem with your ideas is the engine doesn't give a **** where the air comes from, be it the intake through the MAF sensor, a vacuum leak, or a cone filter stuck to the side of the intake pipe after the MAF sensor.

The problem arises when (with made up numbers) 14.7 pounds of air flows through the MAF sensor, then an additional (once again, made up number) 3 pounds of air flows through the leak/hole in the intake pipe after the MAF sensor. Since this did not come through the MAF sensor, the engine thinks only 14.7 pounds of air is in the engine, so it injects 1 pound of fuel.

Unfortunately, instead of a nice 14.7:1 air to fuel ratio, you now have a 17.7:1 air to fuel ratio and your engine just exploded.

Now, to answer a couple of your questions.

Yes, the MAF sensor affects the air flow. It has to because of how it measures it. That said, it's a negligible amount.

Intakes (ideally) increase the amount of air you can flow to your engine by creating less of a restriction for the incoming air (having a lower pressure drop across them). The accordion pipe that's behind the MAF sensor in stock intakes doesn't help air flow smoothly. Replacing it with a smoother pipe (i.e. Williaty's hybrid intake) lets the air flow, well, smoother. Sort of how single file lines can get more people into a building faster than people mobbing for the door.

Thanks for that response. That was what I was looking for. My main issue is understanding exactly how the snorkus works, and what the purpose of the MAF is. I know from williaty's responses that the MAF meters the air. What is the main purpose of the snorkus though? Is it to allow a certain amount of air into the intake?

By the way, I will using williaty's hybrid intake template for mine. I was 99.9% sure before, but I wanted to test some other theories too that sounded good. I saw a picture of a short cowl induction on another forum, and thought about trying it.

Just to make sure you understood what I was talking about, let me repeat my idea, adding the info I've learned here.

1. Since the engine sucks it's own vacuum of air, I thought about a cowl induction system where (a) either I would leave the rear airbox in its original place, and run a 90* elbow out of the side and through a hole in the firewall, drawing air through the cowl area, or (b) running a pipe straight from the intake into a hole in the firewall, and deleting the rear airbox and adding a filter inside the area where the windshield wipers are located or in the pipe area between the intake and firewall. As I understand it, there is plenty of air pressure at the base of the windshield to be sufficient for the intake. The only issue would be rain or snow accumulation in that area, and risk of hydrolock if some were to get in the motor.

2. As for the MAF, I was considering leaving the original snorkus and airbox and MAF section as is, and placing an air filter right after the MAF section. Since it has been established that the engine is what draws the air through the MAF, that idea is out the door. I thought that if the air going past the MAF did not have the vacuum from the engine, then my solution to the MAF causing the car to run lean would be brilliant. But it seems like, if anything, if I was going to be hard-headed like some people are, I'd be better off taking the whole shebang out and there'd be less issue than if it was getting a false reading from not enough air with my set up. I have no intention of doing that however.

[williaty]

The snorkus, aka the big jug inside the fender, is there to control a resonance in the intake tract that would otherwise cause the MAF to give false readings. That is explained in the first post.

[chazly413]

You can do whatever you want with the intake before the MAF, it doesn't make a damned difference (besides having a resonance or not). You cannot cannot cannot change anything after the MAF in the sense that more air enters the engine. Cannot cannot cannot. The MAF tells the engine the current flow rate of air into the engine so the engine can fuel accordingly. As renyo explained earlier, if you have air entering after the MAF, the MAF has not been affected by this airflow, and as such, has no idea this air is entering the engine. This will promote lean conditions, detonation, and possibly engine death.

You can change details of the intake post-MAF, such as piping diameter, but this requires a tune. The MAF is set up to work with the current intake's diameter, as a given pressure N over a given cross-sectional area has a unique mass flow rate. Increase the diameter by 33% and you're flowing almost 50% more air at the previously mentioned pressure N.

[williaty]

Not quite true. The helmholtz resonator is before the MAF and it's absolute critical.

[chazly413]

Originally Posted by williaty

Not quite true. The helmholtz resonator is before the MAF and it's absolute critical.

I know it's absolutely critical to eliminate the resonance but you don't necessarily need it to run the car.

[williaty]

Take it off, put the car in open loop, step on gas, watch car stall.

Yeah, it's kind of necessary.

[chazly413]

What about the dingbats who remove their snorkus via SRI or CAI?

[williaty]

Their cars usually aren't in open loop in the spots where the problem happens. It turns it from a stall into a bog.

[chazly413]

Ah, fair enough. Thanks for the clarification.

[renyo]

Originally Posted by 99ForesterVA

Thanks for that response. That was what I was looking for. My main issue is understanding exactly how the snorkus works, and what the purpose of the MAF is. I know from williaty's responses that the MAF meters the air. What is the main purpose of the snorkus though? Is it to allow a certain amount of air into the intake?

As williaty said, the snorkus is there to control a resonance issue with the MAF. As a byproduct, it reduces air flow slightly.

By the way, I will using williaty's hybrid intake template for mine. I was 99.9% sure before, but I wanted to test some other theories too that sounded good. I saw a picture of a short cowl induction on another forum, and thought about trying it.

If I understand you correctly, it's known as a gravelsports intake. You can't do it with a MAF.

Just to make sure you understood what I was talking about, let me repeat my idea, adding the info I've learned here.

1. Since the engine sucks it's own vacuum of air, I thought about a cowl induction system where (a) either I would leave the rear airbox in its original place, and run a 90* elbow out of the side and through a hole in the firewall, drawing air through the cowl area, or (b) running a pipe straight from the intake into a hole in the firewall, and deleting the rear airbox and adding a filter inside the area where the windshield wipers are located or in the pipe area between the intake and firewall. As I understand it, there is plenty of air pressure at the base of the windshield to be sufficient for the intake. The only issue would be rain or snow accumulation in that area, and risk of hydrolock if some were to get in the motor.

If you have any kind of hole or membrane permeable enough for air to flow through it after the MAF, you're going to have problems.

2. As for the MAF, I was considering leaving the original snorkus and airbox and MAF section as is, and placing an air filter right after the MAF section. Since it has been established that the engine is what draws the air through the MAF, that idea is out the door.

I think the idea you're missing is that if it doesn't go through the MAF, there's an issue. It doesn't matter why it doesn't. If it doesn't, you're going to have a problem.

I thought that if the air going past the MAF did not have the vacuum from the engine, then my solution to the MAF causing the car to run lean would be brilliant. But it seems like, if anything, if I was going to be hard-headed like some people are, I'd be better off taking the whole shebang out and there'd be less issue than if it was getting a false reading from not enough air with my set up. I have no intention of doing that however.

A MAF is like any other scientific instrument. Aside from the occasional mechanical or electrical problem, it doesn't make the car do anything. Basically, the MAF isn't a problem that needs a solution. The engine expects the MAF to tell it how much air is coming into the engine. If you prevent the MAF from doing it's job, you prevent the ECU from doing its job. When the ECU doesn't do it's job properly, you have engine problems.

• all the air, and only the air, entering the engine must pass through and be recorded by the MAF
• all the air, and only the air, passing through, and being recorded by the MAF must enter the engine.

If either of those two rules are violated, you're going to have issues.

The snorkus is there to make sure that all the air recorded by the MAF is actually entering the engine.

It's bedtime, forgive grammar issues.

[jonclarke]

So if I do the hybrid on an 07i from stock... Will I have to do some kind of retune? Is it even worth it for the cost?

[jonclarke]

Anyone?

[williaty]

Tuning for the hybrid is desirable but not required.

If you are using the stock tune now, a well-done tune will substantially improve the car.