Restriction of the factory airbox with a bigger turbo

The other day I came across something interesting while reading some info on Garretts website about choosing the correct filter size for a turbocharger. They have a few nice formulas that you can use to determine flow and this led me over to K&N's website.

 

Apparently, according to K&N, their panel filter flows better then the typhoon intake for the Legacy GT. Filter 33-2304 (panel filter) flows 459.8 cfm and RP-5113 (the cone filter the typhoon uses) flows 330.1 cfm. I remembered reading this a year or so ago and actually mentioned this to my tuner. I did my mods backwards to most and after upgrading turbos, I was contemplating getting an intake as my next one. He dismissed the idea completely. He said that there was no way that a panel filter could out flow a short ram intake. I let it go, but always thought that my car seemed fastest with the stock airbox over the typhoon.

 

After seeing all this again, I decided to do the math. According to garrett, a turbo that flows around 44lbs (HTA68) at my elevation, requires a filter that flows around 725cfm without restriction. The math for the panel filter proved correct when compared to K&N's flow numbers. The math for the cone said it should flow slightly better then what K&N said, but it's close enough.

 

All this leads me to three questions.

 

#1) Are people wasting money on the typhoon, when a K&N panel filter is better?

#2) Are people with larger then stock turbos being held back by sub-par CAI/SR filters?

#3) Is the rumor that the stock airbox is good for up to and around 300whp true?

 

http://www.turbobygarrett.com/turbobygarrett/air_filter

http://www.knfilters.com/dynocharts/RP-5113.pdf

http://www.knfilters.com/dynocharts/33-2304.pdf

 

We all know that leading up to the turbo, the intake is always under vacuum. But how much would different restrictions change the amount of vacuum?

 

After a bit of research, I decided that the best way to proceed with this test was to get a manometer and test the increase in vacuum with the different intakes. This would show how much restriction there physically was on the intake. A manometer tests the difference in pressure in relation to the external pressure, or the outside air (But at a more sensitive level then the normal PSI that we are used to seeing). The measurement I would be using was inches of water. 1 psi of vacuum is the equivalent of 27.7 inches of water. Basically the amount of pressure it takes to move water a given distance in a U-shaped tube with a vacuum on one end.

 

The setup:

I hooked the manometer directly to the port where my three port BCS normally vents back into the intake (I let the 3port just vent to the engine bay). This was the best spot since it was the point where the two intakes connect to the turbo inlet. I also wanted a point that wasn't being disturbed from boost being recirculated back into the intake. This manometer also had a record function so I was able to strap it into the engine bay and not have to worry about running a bunch of vacuum lines.

 

The test:

This test would be on my 05 LGT with a BNR HTA68 on E85 tuned for 22psi peak. This car makes approximately 330-360 whp at 5280 feet (I never dynoed because this is a very common setup so the power is predictable). I did two tests. One with the K&N typhoon and one with the stock airbox with a K&N panel filter. The first was a reading at idle and the second was recording the maximum restriction after a WOT pull to redline in second and then third gear.

 

The results:

Both intakes at idle had zero restriction regardless of the intake. However, the results under load were quite different. The Typhoon had 16.58 inches of water under load and the stock airbox had 50.52 inches of water under load. Basically the typhoon creates a restriction of .60 psi, while the stock airbox creates a restriction of 1.8 psi.

 

update:

stock airbox with snorkus removed showed 38.62 inches of water.

Typhoon with only 16lbs of boost was 13.24 inches of water.

 

 

added MAF voltages and the last datalog I took for the e85/typhoon/22psi

typhoon.csv

Been waiting for this. Lazy sub.

Excellent. Nice to see data instead of speculation!

 

Interesting that the panel filter flows more on paper but in testing produced more vacuum... You didn't happen to grab the data for MAFv as well did you?

No I didn't. I thought about it for a minute, but figured that it could be had from other peoples data logs. But in hind sight, those logs would not be as accurate as mine. The next time I do a test, I'll post some data logs as well

In for results.

how much is this also depends on the panel filter material? oil-less vs oiled panel filter?

 

*I see you did compare K&N to K&N and this is what your results are based on. Do you predict a much different result with another panel filter? K&N isnt much liked in the subie community because of the oiled filter and MAF

sub'd

Good work. Subscribed for more knowledge.

Funny I was thinking about the stock AB the other day. I think you need to keep in mind the flow rates are for the FILTER, not the intake. So yes, I could see how the panel filter would flow more. However when attached to the airbox it might not flow that amount, the box being the restriction not the filter element. Another post brought up a good point about the oiled filter.......if more oil on the filter could affect this.

 

Subscribed.......I honestly would love to dump my Typhoon and go with the OE air box with a panel filter.

Nice work bigjweb! Sub'd for t3h infoz

Subscribed.......I honestly would love to dump my Typhoon and go with the OE air box with a panel filter.

 

Mind if I ask why? The reason I'm wanting to know is I was thinking of going with a typhoon.

 

*EDIT*

I completely agree with the oil situation. I had the same issue with both my LSx Camaro's. I finally switch back to a paper filter. If I can get a typhoon type intake with a dry filter, that would be ideal.

Mind if I ask why? The reason I'm wanting to know is I was thinking of going with a typhoon.

 

*EDIT*

I completely agree with the oil situation. I had the same issue with both my LSx Camaro's. I finally switch back to a paper filter. If I can get a typhoon type intake with a dry filter, that would be ideal.

 

I had to shorten the metal MAF tube to work with my front mount piping, and it still is jammed behind the headlamp. I've given up trying to scale it, I am getting inconsistant readings and I think because it is beacuse the cone filter is up against the back of the headlamp and the IC pipe....causing some turbulance around the MAF sensor. Otherwise I might go with a Cobb short ram.

As for the oil "problem" on the K & N filter: I have been running a panel filter for 60,000 plus miles and NEVER had a problem. When I clean the filter, I just spray the oil on in light coats and try not to over do it.

 

I have put too much oil on a few times and the solution is to get compressed air and use it on the filter. It ends up blowing the oil from the metal screen to the filtering media underneath. Works like a charm.

 

OP, it's interesting that the panel filter is supposed to flow more air. There was a guy on here awhile back who fabbed up a stock intake where the panel filter is exposed directly to the air (took out the piping feeding it). I wonder how a set up like that would measure out with flow rates.....

how much is this also depends on the panel filter material? oil-less vs oiled panel filter?

 

*I see you did compare K&N to K&N and this is what your results are based on. Do you predict a much different result with another panel filter? K&N isnt much liked in the subie community because of the oiled filter and MAF

 

I think that a paper filter would flow close to the the same. There have been other tests (not by me) that show that the difference between a K&N style and and oem drop-in make hardly any difference. What I don't like about the oiled filters is the increased amount of silica that is found in an oil analysis.

 

OP, it's interesting that the panel filter is supposed to flow more air. There was a guy on here awhile back who fabbed up a stock intake where the panel filter is exposed directly to the air (took out the piping feeding it). I wonder how a set up like that would measure out with flow rates.....

 

The panel filter flows more because it has more overall surface area

Subscribed. Excellent work and can't wait to hear more.

"read" more...LOL

Updated to include maf voltages and two more tests

Updated to include maf voltages and two more tests

Are you able to run the same boost curve for both the stock airbox and Typhoon pulls? Or put the other way, what boost target was in play when you ran the pull on the stock airbox, 16psi or 21psi?

 

Looking at your stock airbox pull you're getting to 4.5MAFv @ 6k0rpm while on the Typhoon on the 21psi map you have 4.57 or 4.58MAFv. On the 16psi map with the Typhoon you have just 4.41MAFv. On the face of it the Typhoon would therefore seem to beat the stock intake.

 

I have a well-developed scaling for the K&N from a well-respected pro tuner but since it's proprietary I cannot share the whole thing with you guys. Sorry.

With the stock MAF scaling vs. that for the Typhoon that changes somewhat.

 

Stock intake and scale: 235g/s

K&N intake and scale @16psi: 275g/s

K&N intake and scale @22psi: 309g/s

 

I think you can see why I'm curious as to what boost you were running at 6k0rpm on each of these three pulls.

The 16 psi typhoon map is basically the same map as the 22 psi typhoon. My tuner creates the high boost map first then sets the wastegate duty to 0. I always ask for this map as a spare safe map for road trips and such.

 

 

stock intake @ 6000: 17.35

typhoon 16 psi @ 6000: 14.13

typhoon 22 psi @ 6000: 19.21

hell of a write up. subed

Thanks Jason. That makes it pretty much impossible to tell which part of the differences in flow are due to the intakes and the different boost pressures. Lack of compressor maps from FP make it even harder!

I'm interested to see what part of the stock intake causes the most restriction. I doubt i'll do that test though, as I'm not willing to drill holes in my stock airbox to create new vacuum points.