Twin Turbo Air Filter Upgrade

Herr-Kuhn · 06:07 AM

I had been struggling with a way to fit larger air cleaners into the twin turbo. The ones I have been using were rated to 406 cfm each, for a combined total of over 800 cfm...good for 500 HP or so.

Add boost and you quickly see the need for bigger air cleaners. If the air cleaners are too small on a turbo car this will ultimately show up as increased back pressure on the exhaust side of the engine. The turbo just continues to drive until the desired boost is reached...thus pressure ratio goes up and the exhaust pressure required to drive the compressor to this pressure ratio is increased over what it could have been.

I have located a set of larger filters, but fitting these took some thinking. All in all I think it will turn out nicely. The new filters are rated to 512 cfm each, for a combined total of 1025 cfm or about 650 HP worth of air. Now I'm feeling better about turning up the screws on the car.

See below of a photo of the two air cleaners. The new units will mount to a flange which will be bonded to the snout system...this will make install and removal much easier than the old filters. I had to eliminate the motor for the radiator flaps to make this work, but in my book that was a useless piece of hardware to begin with.

Herr-Kuhn · 08-18-2007, 06:06 AM

Herr-Kuhn · 08-18-2007, 06:10 AM

The wastegates are set to 12 psig

The timing has been shaved to a safe level for tuning at this boost level

Once I have the cleaners installed and sealed up I will be hitting the streets to get this car dialed in. If my math is correct, the additional 4 psig should yield about 75-90 ft-lbs to the tire and an additional 80 or so HP. 4 psi doesn't sound like much but spread over 5.0 liters, it's quite a bit of extra airflow.

Barbapapa · 08-18-2007, 07:25 AM

The filters accent your kitchen nicely!

Danglerb · 08-18-2007, 11:17 AM

What sort of pressure drop are you getting old vs new filter?

Is there a standard pressure drop that filters are rated at?

Herr-Kuhn · 08-18-2007, 12:11 PM

These are rated at 1.5" of water (manometer) of pressure drop at the rated airflows. I was not willing to push the smaller filters with the higher boost pressure setting. They woudl have worked, but could have cost some HP up top.

Danglerb · 08-18-2007, 12:56 PM

Inches of water to psi conversion factor is 0.036128, so 1.5" is about 0.054192 psi?

That seems tiny. My new dryer wants I think about a max of 3 or 6 inches of water for the basically unrestricted vent tube. Sounds like the filter drop might not be anything to be concerned with using a turbo, compared to the losses in the tubing.

Louie928 · 08-18-2007, 07:19 PM

What filters are those? K&N? I'm trying to fit some sort of filter in front of the radiator for a ITB intake. I don't like the way I did mine with moving the top of the radiator back 3" and using the stock filter. These might do the trick.

Herr-Kuhn · 08-19-2007, 08:00 AM

Louie,

These are K&N RU-1500 filters. The dimensions are 4" X 6.25 X 5" (end cap to end cap). The engineering staff at K&N gave me a rating of 512 CFM per filter.

The original rounds were an RU-2410. The same but in a round config...it is strange though, the RU-1500s have a deeper screen/gauze mesh...there is a lot more surface area.

Make no mistake, that a restrictive filter will throw the balance of the entire system off. With an NA car you would just lose power, but the turbo just drives harder and harder to make the same boost from less air (assuming you pull some vacuum in your piping). Higher pressure ratio means the turbo has to spin faster...more pressure on the exhaust side of the engine and a higher PR across the compressor wheel. The turbo itself cannot determine if it has too small an exhaust or too restrictive an intake...it just works off of pressure ratio.

Herr-Kuhn · 08-19-2007, 08:06 AM

Here is the K&N testing protocol for those interested. I also thought that -1.5" H2O is very low, but there is no doubt that the best filter is the largest one possible to increase flow and filtration area.

http://www.knfilters.com/testmethod.htm

Herr-Kuhn · 08-19-2007, 08:08 AM

I'm glad you like the color of the kitchen as it relates to the filters...did you notice the salt and pepper shakers, these are from 1966!

Louie928 · 08-19-2007, 10:12 AM

Thanks. This one may work.

Herr-Kuhn · 08-21-2007, 08:18 AM

Let me know if you want a set of the snouts and filters. I've already sold one set of them.

Louie928 · 08-21-2007, 08:25 AM

I have to have something different since the air comes in over the radiator top in the center.

Quote:

Originally Posted by Herr-Kuhn

Let me know if you want a set of the snouts and filters. I've already sold one set of them.

Herr-Kuhn · 08-21-2007, 08:37 AM

Here is a shot of the layout now...it is still WIP as seen in these pics, but tonight I should have them urethane sealed and ready to go. It has been a bit of a chore, but this is what R&D takes...a lot of trial and error.

Herr-Kuhn · 08-24-2007, 02:47 PM

Okay....seems at though people want some price data on the filtration system. I am more than willing to reproduce this system outside of the twin turbo system and release it for sale. I have sold one set of snouts and mounting plates already. I will work up some numbers on the system this weekend and present them here.

In the interim, like anything else that is manufactured, there are cost benefits to producing in higher volumes. If I have an idea of how many people are interested I can tailor a better sell price than I could on a one off basis. Please realize, this is hand laid fiberglass and there is a lot of time involved in the fabrication process. The first set I sold actually had no outer seam lines...they were totally smoothed over and were beautiful...they looked better than the ones on my car.

This system (right now) will fit manual transmission S4 only. AT S4 could be made to work if the ATF cooler is removed and replaced with an aftermarket unit. It will not fit the older style fan shrouds as the cutouts are different.

Darien Nunn · 08-25-2007, 12:05 AM

Looking good John!!

Brian Felts · 08-25-2007, 02:37 AM

OK quick question for you. DO you still run A/C and can you get away without the secondary fan?

Brian

Herr-Kuhn · 04:42 AM

Yes, I run AC in my car. I think you are referring to the small frontal fan in the pre-S4 cars. I know a lot of poeple who remove those. On the older cars, I really like the viscous coupling fan. I tried to replace that fan with a Spal fan, but between that fan and the frontal fan the amp draw was horrific...so I went back to the viscous coupling fan. It cools better too. The early electrical systems were terribly weak. The S4 doesn't appear to have this issue at all.

I would think you could run without the secondary fan, Remember, it is only triggered when the coolant temps get higher or the AC is on.

Herr-Kuhn · 08-25-2007, 04:41 AM

Darien...if you did this on your Keel-Car you could re-join the airflows aft of the radiator with some pipe-work. We will see how well this system works out soon...I'm getting around to putting the filters back on the car today. I wasn't happy with the adhesive showing so I did some paint touch-up last night and that had to dry. I'm also waiting for some cooler weather to re-tune the fuel. No sense trying to do that in 100F heat. It's been really bloody hot this year.