Filter Minders for Dummies

[davidbrady]

(03-31-2013 14:06)pgchin Wrote:  I did TOO much celebration last night and lost the fight to a 12year old bottle of single malt scotch! So I am a bit SLOW so David I have some questions for you but I MAY be wrong so please treat me gently given my current zombie condition!!!!!!

Pete you crack me up as always big Bros.

Well played last night! You gotta watch that high octane imbibation (is that a word)! Hahaha! To much of that and you'll have your SI's mixed up with your CI's.

You Wile-E-Coyote, you're trying to pull one over on us aren't you?

Let's see if I can dredge up some good solid science and engineering to set the matter straight.

Compression Ignition (CI) engines (diesels) are fun to play with cause they run in wide air fuel mixture ratio, from 40:1 (lean) to 8:1 (rich) or lower.

The DDEC ECM doesn't have too many sensors for predicting the proper amount of fuel to deliver. All it has is throttle position sensor and a boost sensor. It runs open loop without a Lambda O2 sensor.

Under a specific load sensed by the TPS it wants to see a specific boost.

If a backyard mechanic plugs up the air intake by say, I don't know, installing an ultra restrictive air filter like the NAPA 6580 then the ECM is going to over fuel in an attempt to see the right boost pressure, right?

Exhaust temps will rise and if the driver lets it go to far, say in excess of 1250 deg F for an extended period of time he may melt a great big hole in a piston!

Unlike Spark Ignition (gasoline) engines, running lean on a diesel doesn't create engine damaging heat; it's the opposite but you know that you're just playing with us , running rich creates engine damaging heat.

When the intake is starved of oxygen by using a NAPA 6580 panel filter, the ECM will compensate by dumping in more fuel to increase boost. So you end up with a drop in efficiency because of the additional pumping losses and the injection of more fuel in an attempt to restore boost.

Let's say you leave your house in Florida for an 80 mile round trip and your pulling the toad. You're in cruise mode, right? So you're poking down the road at 60 to 62 mph has your apt to do.

Let's say you cut one of the 90 deg bends out of your stock intake system, your down to two 90's from three, and you mounted a diffuser to house your restrictive panel filter.

Well CI engines run without a throttle, right? This means that they aren't fighting to draw air against a vacuum created by a butterfly valve as spark ignition engines do. Turbo charged CI engines will always breath at least their full displacement of air.

The problem now is that the NAPA 6580 is more restrictive than the 90 deg bend you removed. What happens? Well the diesel is still trying to breath in it's full allotment of air, but now it's fighting a vacuum, in fact it's fighting a vacuum larger than the stock system! That 6580 is ruining any gains that removal of a 90 deg bend afforded. The diesel is now experiencing increased pumping losses.

We said before that all engines are just air pumps. Well, pumping air takes power and pumping against a vacuum sucks a lot of power and ruins efficiency and MPG goes down. NAPA 6580, no thanks! Stay away!

We know that a 90 deg bend is about 0.75 (in. H20) and the stock LXi intake system has two (plus the air filter). The stock ECO-SM air filter has a 4 (in. H20) drop at 1170 CFM. I don't know what the NAPA 6580 does at 1170 because it's only rated for 570 CFM; however, we can be sure it'll be worse than the stock filter's 4 (in. H2O). Each system will have 2 90's and one filter. The only difference is the filter and the NAPA 6580 doesn't breath the air required, and if forced to do so it'll develop a large pressure drop at best, and disintegrate at worst.