Quote:
|
Originally Posted by JimF
|
Greetings Jim,
Appreciate the link to this interesting whitepaper.
I want to share a maximum airflow formula to use when determining whether the air filter is really the bottleneck in your intake system. The background for this discussion is my previous experience tuning forced-induction V6 engines. Effective displacement of those engines was comparable to any respectable V8, and the tuning requirements arguably more complex.
Unfortunately most of my "black art" tuning models were developed using output from the MAF/MAP as measured by an OBD-II compatiable scanner. My 1995 E420 more or less leaves me "blind" to engine performance tuning at this point. One of the sacrifices I made by choosing a pre-1996 model Mercedes... anyhow, back to the formula:
(eng speed * displacement) / 3456 = xxxx cfm * VE
where units are standard, and VE is engine volumetric efficiency.
Let's use the 5.0L 119.974 as a working example:
The maximum engine speed for an unmodified 119.974 is 6000 RPM. Displacement is 4973 cubic cm, or 303.5 cubic inches. Maximum horsepower is measured at 5700 RPM, the stock full-throttle (WOT) shift point. Our question is whether the filter affects ability to reach peak engine output at the highest shift point.
(5700 * 303.5) / 3456 = 500.56 CFM
This figure represents the theoretical airflow through the engine without restriction and without accounting for thermal issues. The volumetric efficiency (VE) factor allows us to account for limiting factors (material, thermal, etc.). The M119 mostly suffers from underhood thermal issues, especially with an aluminum block that soaks up ambient heat.
If we use the common 85% VE factor, estimated airflow at 5700 RPM becomes 500.56 * 0.85, or 425.47 CFM. The 119.974 engine attempts to pull a maximum of 425 CFM through the filter and intake, assuming no underlying mechanical problems that would decrease peak airflow.
It seems to me that most stock (paper) filters are tested to flow at least that much air, if not more. My interpretation is that you will never encounter a need with an unmodified 119.974 to flow more air through the air filter than a stock paper element allows.
It also goes without saying that a comparable K&N product flowing 3000 CFM allows more dirt, oils, woodland creatures, etc. to pass through the filter than the paper filter. This has been demonstrated using empirical methods like those described in the whitepaper, and through basic oil analysis from engines where a free-flowing intake filter is used (higher silica content and other particulate matter). I wonder just how many performance engine failures are due to oil breakdown once too much airborne junk passes the filter barrier.
Agreed with Jim -- make mine a quality paper filter!
-DM