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Old 04-08-2013, 01:54 PM
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mach4 mach4 is offline
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Join Date: Jul 2011
Location: San Diego County, CA
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I had no choice but to eliminate the CA air filter on my car. I'm using a CA version OM617.952 in my SL. As you can see, there is just no room for the CA filter. While this setup is not technically a cold air system, you can see that almost the entire filter is outside the sweep of the fan meaning that the dominant air source is cool outside air not hot air from the radiator or the engine compartment.

I fabricated a backing plate from aluminum plate and a fitting from a Ford Taurus. The filter housing is from a Ford Escort.

The system worked great for 15k miles, but I began to get concerned about the sizing of the filter. The CA version of the MB filter flows 450cfm and the one I was using only flowed 250cfm.

I did some research and determined that there was actually a conical paper filter with the same base dimensions that flowed 350cfm.

So I went to the junkyard and picked up a filter housing for the larger filter. It fit perfect.

But then I got to wondering about actual flows in practice, so I picked up a flow meter that provides positive measurement of filter element restriction.

I tested it against both filters and there was 0 measurable restriction. So I went even further in my testing. There was a horribly dirty 250cfm filter in the second housing I picked up so I stuffed that in with the tester installed and believe it or not, there was 0 measurable restriction. Shown on the left is the filter I was planning on replacing as too dirty.

So the conclusion is, for the turbo 617 engines even a 250cfm filter element is entirely adequate for normal operations. Obviously it will require replacement more often since it has about half the actual filter area, but the filter can appear really, really dirty and still function without measurable restrictions. And compared to the CA filter, it's cheaper than dirt.

Now, if you go this route, then you introduce the issue of what do you do about a proper oil separator and where do you plumb it... for which good solutions are readily available.
Current Stable
  • 380SL (diesel)
  • Corvette C5
  • Manx
  • Baja Bug
  • F350 Powerstroke
  • Auburn Boattail Speedster replica
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