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Old 03-01-2013, 03:55 AM   #251
J_Baker
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Quote:
Originally Posted by thelloyd View Post
I work as a mechanic at a honda dealer, and am forever feeling sad/frustrated at all these cars coming in with aftermarket intakes. More often then not you can tell even at idle that it is a bit off. Anyways, Unibombers intake FAQ brought up interesting info about air turbulence throwing off the MAF reading.
You know those fuel saver little turbine things you put in your intake? I am wondering if one of those would help get rid of this air turbulence.
When going through school at UTI I had got a chance to play with a dyno and various verhicles/engines. A fellow student had one of these "fuel savers". So we put a stock 350 on the dyno, then followed up with a couple runs. Put the fuel saver on there, and retested. No gains in HP as the box had claimed. Not so sure about actual fuel saving though. I have never been a fan personally of these types of things. Consider them to be a hoax. But it would be interesting to see if it can help reduce air turbulence since it is kind of "guiding" the air flow.
I like the way you think. I'm an Aeronautical Engineering undergrad and owner of a hawkeye STI, and you're sortof onto a basic understanding of fluid dynamics. Basically, I'm not sure if the right terms are being used here-- laminar and turbulent. What these refer to is whether the airflow is nice and smooth or all "jostly". Regardless of the internal dynamics, when the opening of the intake is given the same pressure, free-stream velocity, temperature, and density of air, the amount of air will depend purely on the dimensions of the pipe-- for incompressible flows below M0.3, at least. A simple A1V1 =A2V2 analysis can be used, where A is the cross-section of the pipe at any point where the flow is purely perpendicular to the cross section. V is the flow velocity. Contrary to what you might think, air is actually basically (~5%) an incompressible flow up to velocities of 0.3 the speed of sound in that specific air mass.

What's this mean? Well. What goes in must go out. While restrictions within will speed up and slow down the air in varying methods, geometry throughout the intake really isn't as important as you might think. It's not going to cause some sort of "backup" and keep air from entering the inlet.

So onto laminar and turbulent. Going off the Air is a liquid analogy, air is a sticky liquid. It likes to stick to itself and surfaces it passes over, forming interesting things like boundary layers-- regions of varying flow velocity near a surface. So, from an engineering standpoint, you want to design your intake to provide an optimally distributed flow across the turbo inlet. From an inviscid view, flow will always be uniform at a crossection where velocity is perpendicular, if it went in that way. From a viscous view, this isn't the case at all, as boundary layers cause regions of high and low velocity, and cause some interesting phenomena at corners-- stuff that even now is nearly impossible to accurately model or predict perfectly. But considering specifically your turbine example. What you're basically doing is "normalizing" the air flow, very similar to what's done before and after wind tunnels in closed-return type systems. You're equalizing the flow across the cross section, chopping it up into tiny little bits and, through rapid velocity change of going through the turbine, forcing these chunks to have roughly equal velocities.

So. Turbine. In theory? It'd help. In practice? It'd be interesting to see what it'd do.

Corollary. This is why open compressor housing breathes so damned well. The airflow before the turbines is basically uniform and still, and thus air pulled in is incredibly uniform, meaning equal mass of air rotating and balanced turbine rotation (the weight of the quantities between blades of air even being equal), and just a good life.
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Old 03-01-2013, 09:48 AM   #252
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Quote:
Originally Posted by thelloyd View Post
Unibombers intake FAQ brought up interesting info about air turbulence throwing off the MAF reading.
Which is misleading, IMO. The MAF errors you see with aftermarket intakes are very rarely due to turbulence. As Cobb points out in their article, turbulence is untunable:
http://www.cobbtuning.com/Technical-...es-s/70677.htm

Sometimes an intake that has turbulence problems will pop up, usually it's the cheap eBay parts with zero R&D invested. The name brand parts do NOT have turbulence problems, otherwise they too would be untunable. Any AFR problem that is fixable with tuning, is therefore not being caused by turbulence...pretty simple.

I've seen a turbulent intake before, it behaves VERY differently than anything people will see with normal aftermarket intakes. The owner of the car went through THREE different tuners, and none of them could even get the car to run without stalling. It wasn't until he welded in a new MAF flange farther down the intake pipe (farther away from the filter and bends) that the problem went away and he had it idling and running well in a matter of minutes.

So would shoving one of those aluminum cans shaped like a propeller from the movie Twister into the intake solve a turbulence problem? Maybe, but doubtful (if anything it would probably make it more turbulent). Whether it does or not doesn't really matter though, because for the price of the POS turbulent intake and the propeller you could have just bought a decent intake that had a shred of R&D invested and avoid the problem entirely. You'll still need to get a tune, but that is not because of turbulence, it's because of pipe diameter and flow distribution.

Last edited by the suicidal eggroll; 03-01-2013 at 10:20 AM.
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Old 03-10-2013, 11:24 PM   #253
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Thanks for the useful information! I have a stock 07 WRX and I'm currently debating on going with AEM, which I've had a great past with or try something else. Everything here helped me a lot.
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Old 03-16-2013, 07:11 PM   #254
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If I'm running cobb AP stage 1 with a catback and nothing else, can I run a K&N intake with that stage 1 tune..? Cobb has a tune for a Cobb sf intake so if I ran that will it be ok to run the K&N and not the Cobb?
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Old 03-16-2013, 07:47 PM   #255
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Quote:
Originally Posted by Kantnerner View Post
If I'm running cobb AP stage 1 with a catback and nothing else, can I run a K&N intake with that stage 1 tune..?
No

Quote:
Originally Posted by Kantnerner View Post
Cobb has a tune for a Cobb sf intake so if I ran that will it be ok to run the K&N and not the Cobb?
No

If you want to know why, please do some searching, because this has been covered at length hundreds of times.
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Old 03-20-2013, 01:15 AM   #256
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Thanks a bunch! Super helpful!
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Old 03-20-2013, 03:14 PM   #257
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Do you need a tune if you add Cobb post maf hose?
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Old 03-20-2013, 08:44 PM   #258
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does a drop in filter need a tune? looking at the aem dryflow
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Old 03-20-2013, 08:57 PM   #259
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Quote:
Originally Posted by BigRob74 View Post
does a drop in filter need a tune? looking at the aem dryflow
No, but you won't see any real benefit from it (with or without a tune).
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Old 03-20-2013, 09:19 PM   #260
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Originally Posted by sc00by4life View Post
No, but you won't see any real benefit from it (with or without a tune).
this is my 1st car without an intake, i dont even know what the interval is to change the oem...lol guess i gotta look in the book
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Old 03-20-2013, 09:24 PM   #261
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Originally Posted by BigRob74 View Post
does a drop in filter need a tune? looking at the aem dryflow
Depends on the car and the filter, but often times, yes. I've seen more than one reputable tuner post results showing the definite need for a tune after swapping in a drop in filter. A year or so ago somebody even posted back to back logs of the AFR from a wideband with the stock filter and an aftermarket filter. He went back and forth a few times, and the aftermarket filter was consistently ~.5 AFR richer than the stock filter at WOT.

Our cars are incredibly sensitive to changes in the flow pattern across the MAF.
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Old 03-20-2013, 09:25 PM   #262
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Quote:
Originally Posted by WaitTheresMore View Post
Do you need a tune if you add Cobb post maf hose?

Seriously? It's a hose bro.
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Old 03-20-2013, 09:27 PM   #263
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Originally Posted by minorc View Post
Seriously? It's a hose bro.
I understand but these cars are so sensitive with intakes and intake parts.
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Old 03-20-2013, 09:27 PM   #264
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Quote:
Originally Posted by WaitTheresMore View Post
I understand but these cars are so sensitive with intakes and intake parts.

Alright sorry, No you don't need a tune for the afta-maf hose because its after the maf.
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Old 03-20-2013, 09:34 PM   #265
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Alright sorry, No you don't need a tune for the afta-maf hose because its after the maf.
Don't be so sure...anything that alters the air flow pattern around the MAF will alter the MAF scaling. Yes the afta-maf hose comes after the MAF, but that doesn't mean it doesn't alter the flow pattern ahead of it (especially since it's located IMMEDIATELY after the MAF). If you think the air flow pattern through a ribbed tube is the same as a smooth tube, you should go back to fluid dynamics, and probably re-think why companies would offer this tube in the first place if it doesn't change anything. If you agree that the air flow pattern is altered with the afta-maf hose, then why wouldn't the air flow pattern 3 inches in front of it be altered as well?

I'm not saying an afta-maf hose certainly needs a MAF scaling adjustment, but I wouldn't be surprised in the slightest if it did. Hell, if a different panel filter needs an adjustment to the MAF scaling, and if an air/oil separator needs an adjustment to the MAF scaling (due to the change in flow dynamics in the turbo inlet, ask Clark Turner if you want to know more), then why wouldn't swapping from a ribbed after-maf hose to a smooth after-maf hose need an adjustment?

That said, while the car might benefit from an adjustment, it would probably still run alright without one. Having never actually tested it (or seen the results from any tests), I can't say for sure.
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Old 04-17-2013, 07:49 PM   #266
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11 pages of helpful stuff! Cobb SF it is
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Old 04-17-2013, 08:43 PM   #267
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Originally Posted by bjudd31 View Post
11 pages of helpful stuff! Cobb SF it is
well, i bit the bullet and put this on last weekend. its loud, just like everyone said. i know butt dynos dont mean crap, but the car is def faster. in looking at my DP only log, and my DP + cobb sf log, i am def making more boost at a higher rpm than with just the stock intake. still peaking at 19
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Old 04-17-2013, 10:06 PM   #268
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This is an awesome, informative write-up. It may be answer to something that's been puzzling me. I recently bought my 2002 WRX, and it's been running rich, and I couldn't figure out why. The intake has been replaced with an aftermarket intake, and I wouldn't be surprised to find out that the lack of a tune after the swap is causing the problem.
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Old 04-18-2013, 04:26 PM   #269
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Originally Posted by Unabomber View Post
Until proven otherwise, it's crap.

Is this still true, or have the Injen CAI's changed since this was written 9 years ago?
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Old 05-13-2013, 01:05 PM   #270
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Quote:
Originally Posted by J_Baker View Post
I like the way you think. I'm an Aeronautical Engineering undergrad and owner of a hawkeye STI, and you're sortof onto a basic understanding of fluid dynamics. Basically, I'm not sure if the right terms are being used here-- laminar and turbulent. What these refer to is whether the airflow is nice and smooth or all "jostly". Regardless of the internal dynamics, when the opening of the intake is given the same pressure, free-stream velocity, temperature, and density of air, the amount of air will depend purely on the dimensions of the pipe-- for incompressible flows below M0.3, at least. A simple A1V1 =A2V2 analysis can be used, where A is the cross-section of the pipe at any point where the flow is purely perpendicular to the cross section. V is the flow velocity. Contrary to what you might think, air is actually basically (~5%) an incompressible flow up to velocities of 0.3 the speed of sound in that specific air mass.

What's this mean? Well. What goes in must go out. While restrictions within will speed up and slow down the air in varying methods, geometry throughout the intake really isn't as important as you might think. It's not going to cause some sort of "backup" and keep air from entering the inlet.

So onto laminar and turbulent. Going off the Air is a liquid analogy, air is a sticky liquid. It likes to stick to itself and surfaces it passes over, forming interesting things like boundary layers-- regions of varying flow velocity near a surface. So, from an engineering standpoint, you want to design your intake to provide an optimally distributed flow across the turbo inlet. From an inviscid view, flow will always be uniform at a crossection where velocity is perpendicular, if it went in that way. From a viscous view, this isn't the case at all, as boundary layers cause regions of high and low velocity, and cause some interesting phenomena at corners-- stuff that even now is nearly impossible to accurately model or predict perfectly. But considering specifically your turbine example. What you're basically doing is "normalizing" the air flow, very similar to what's done before and after wind tunnels in closed-return type systems. You're equalizing the flow across the cross section, chopping it up into tiny little bits and, through rapid velocity change of going through the turbine, forcing these chunks to have roughly equal velocities.

So. Turbine. In theory? It'd help. In practice? It'd be interesting to see what it'd do.

Corollary. This is why open compressor housing breathes so damned well. The airflow before the turbines is basically uniform and still, and thus air pulled in is incredibly uniform, meaning equal mass of air rotating and balanced turbine rotation (the weight of the quantities between blades of air even being equal), and just a good life.
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Old 06-02-2013, 04:35 AM   #271
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Is the intake FAQ also for discussion about cabin air filters?
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Old 06-02-2013, 04:49 AM   #272
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Originally Posted by ENCHILADAS View Post
Is the intake FAQ also for discussion about cabin air filters?
No but the cabin air filter thread is.
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Old 07-09-2013, 07:07 PM   #273
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has anyone else besides Unabomber installed the Perrin? Not saying that I don't trust your opinion, but I checked out their site seeing that you listed them and it looks simple enough to install and the Live tech was quick to educate a noob like me with my dumb noob questions...anyway, any other users of Perrin wants to share their thoughts or opinion?
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Old 07-09-2013, 09:05 PM   #274
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A LOT of people have installed the Perrin. Look in the CAR PARTS REVIEW FORUM for a full review.
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Old 07-11-2013, 12:08 AM   #275
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A LOT of people have installed the Perrin. Look in the CAR PARTS REVIEW FORUM for a full review.
awesome, will give it a look...thanks
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