Superduty

THERE WAS A MISTAKE IN THIS POST. THE CFM NUMBERS NEEDED TO BE DIVIDED BY TWO TO ACCOUNT FOR 4 STROKES. DUH ! It is now corrected.


I was looking at air filter setups for my truck today. I received a Donaldson 2003 Catalog #F110027, in which it lists the air flow rates of various filters and methods of calculating air consumption rates of various engines.

First of all, the air flow rate of the Cummins 5.9, outputing 325HP must be pretty high.

The Donaldson catalog lists the air flow for a 6BT (non intercooled) 230HP @2500RPM as 535CFM, but I think that is a misprint with a number above and should be 590 CFM. They only list one 6BTA with 180HP@2500 RPM and it is consuming 449 CFM, for only 180 HP.

The Catalog lists the air flow of other 300ish HP engines as follows:

6CTA8.3 250HP@ 2500 RPM: 632 CFM
3126B 300HP@2200 RPM: 660 CFM
3126B 330HP@2400 RPM: 709 CFM

The issue with using these numbers directly are that not all engines run the same air/fuel ratios (and thus exhaust temps) at WOT. Nor are the intake manifold temps all the same either. But they do serve as a guideline for our 5.9s as the amount of air the manufacturer will put into an engine to burn fuel for 325 HP from engine to engine won't vary that much. (They aren't going to put oversized turbos on more than they have to, for example.)

Added in edit: the 3126 has steel topped pistons, so I think it can tolerate higher EGTs and thus needs less air flow for its power. The 5.9 has light weight (relatively) aluminum pistons. I suspect it needs more air flow per HP to make it live. Furthermore more boost in a smaller engine means higher cylinder pressures and thus higher operating temps, which requires more air flow to keep it cool. I think the 5.9 flows more air than the 3126 or the 8.3.

Donaldson gives a simplistic formula for determining CFM as the following:

CID x RPM /1728/2 x volumetric efficiency = air consumption.

Volumetric efficiency is the absolute cylinder fill pressure versus atmospheric. Thus if an engine is making 30PSI of boost into the cylinders, the VE is (14.7+30) /14.7 = roughly 3x. Plugging this number into the above equation yields:

360 CI x 2900 RPM x 3 /1728/2 = 920 CFM.

There is a catch though... the air temp going into the cylinders won't quite be at atmospheric temperature, thus the above equation overstates how much atmospheric temperature air is required.

Under 20 pounds of boost it would require:

360 x 2900 x 2 /1728/2 = 600 CFM theoretically.

Lets start looking at air filters. The BHAF's Fleetguard part number of AH19037 crosses to a Donaldson B105006. 4" inlet, 10.5 OD filter, 10.5" long, standard media. This filter is rated to flow 450 CFM at 4" H2O, 590 CFM @ 6" and 680 CFM @8". For those that don't know, flow rate increases roughly as the square of the pressure ratio between two pressures. Put another way, doubling the flow rate causes the pressure to go up by 4x.

Example: A filter has a flow rate of 450 CFM @ 4" H2O. What will its flow rate be at 8" H2O ?

Solution: flow = flowinit x squrt(p2/p1) = 450 x sqrt(8/4) = 636 CFM. If you look above, Donaldson tells us their filter flows 680 CFM, so this estimation isn't that bad.

So... our filter flows 680 CFM at 8". What is the restriction pressure at 900 CFM ?
Pressure = P1 x (flow2/flow1)^2 = 8" x(900/680)^2 = 14 inches H2O.

A few things to note here:

a) turbochargers are pressure ratio devices, the best ones operating at a ratio of outlet to inlet of about 3:1. 14 inches of H20 is a bit over 1/2 PSI on the inlet side. That doesn't sound like much, but if the turbocharger is operating at a pressure ratio of 3:1, that is 1.5 PSI on the compressor side being lost.

b) Those flow numbers are with a clean filter. As the filter gets dirty, the flow rates get worse.

c) Lest anyone think the BHAF is small, tests have been run on various Duramax filters. The best flowing filter there was a K&N (which also flowed a lot of dirt). It had a restriction of 4.6 in H2O at only 350 CFM. The BHAF is way better than that. It flows 450 CFM at 4" H2O. The worst filter (for restriction) was an AC Delco that had 6.23" of restriction at 350 CFM. The BHAF would flow more than 590 CFM at that restriction.

Basically, the BHAF makes all other pickup truck filters look like soda straws. AND it keeps out all the dirt, unlike some of those other filters. (Donaldson is the #1 OEM filter supplier on heavy duty equipment.)

Lets put this to another test: go find a HD truck with a 300+ HP engine or a tractor or excavator and guess what ? The filter in those things make the BHAF look small. I'm sure some of that is due to the fact those machines need to work in very dusty conditions, but I do think even the BHAF is under sized for a high output 5.9.

At this point I have to ask if anyone is running a filter minder on a BHAF and if so, is it ever getting set ? And if so, what pressure does it set at ?

What is the solution ? I got two ideas:

1) They list filter #B085011, which is 8.5 x 11 long, standard media. It flows 280 @4", 400 @6" and 470@8". TWO of these would increase the available flow by 38%. Basically a stock 325/600 Cummins could run at WOT and see a restriction of 4" or so with 2 of these.

2) They list filter #B125003, which is 12.5" diameter by 15" long, standard media. This is the sort of filter you would see in a highway truck with 350HP. It flows 830 CFM @4", 1110 CFM @ 6" and 1295 CFM @8". A 5.9 with 30 lbs of boost could run at WOT and see a restriction of less than 5" with this filter.

There are probably 3 issue with using this filter: a) fitting it in the engine compartment. b) it has a 6" inlet, so it would have to be sized down to 4" and c) cost, although I haven't priced it out.

One more thing: Donaldon rates these filters as "for Light Dust Conditions". (Quote from page 64 in my catalog.)

Food for thought.

ds1rider

someones been doing theyre homework.

Superduty

I'm putting (trying to) put a 325/610 in a Superduty and I'm a bit tight for space to put a BHAF in.

I was hoping that the numbers would tell me the BHAF was overkill and I could use a smaller filter, but now I find that it seems to be just right for a stock engine. If you think a BHAF is marginal, you should see what the stock filter setup looks like for a PSD !

I always wondered how these engines could breathe through these small filters. I grew up around ag and construction equipment and the filters on those engines are enormous. The size of a full size microwave. Filter canisters (more than one) the size of 5 gallon pails.

It might be time for the RBHAF. (Really Big Honkin Air Filter).

I guess one thing that works in a pickup truck engines favor is that they only operate at WOT occasionally. But that is the time when EGTs are a problem. 10,000 pound trailer. 6 miles at 6%. 100F. 7,000 feet elevation. Who wants to choke an engine for air under those conditions ?

Haulin_in_Dixie

You better go back and figure some, you cannot compare a 300 hp 5.9 to a 300 hp N-14. You have lost something in your figures. You might check it by the air flow that the 5.9 uses compared to the air flow the larger engine uses. This would be computed by the bore and stroke at a certain rpm, not by horsepower.

Superduty

"You better go back and figure some, you cannot compare a 300 hp 5.9 to a 300 hp N-14. You have lost something in your figures."

I didn't ! I used the 2 smallest comparable engines in the list: the C8.3 and the Cat 3126. No N14s were used.

"You might check it by the air flow that the 5.9 uses compared to the air flow the larger engine uses. This would be computed by the bore and stroke at a certain rpm, not by horsepower."

If you look closely, I did.

PourinDiesel

I did the math and bought an AFE.

Superduty

For comparison, what does an AFE flow ?

nickleinonen

way too big... that would fit the engine compartment i think... there is a guy on the tdr looking to use a donaldson powercore filter that is a wee bit bigger than the standard bhaf... it flows much more and filters @ 99.9%.. i am happy with my 10.5x10.5 bhaf... there have been dyno tests done by a manufacture [DD i believe] and the bhaf lost you ±7hp on an engine that was making close to 600hp i believe when compared to a high flow oiled filter... 7 hp at those levels isn't enough to make me want to switch from paper to oiled...

HOHN

Thus, my efforts to "build a better BHAF". Find that thread and you'll see why I've been searching for a better dry filter than the Duralite BHAF, and why I believe that the PowerCore media is the way to get it.

justin

CTDHokie

What year is your superduty? My old 7.3L would pull 25-27inH20 with a clean stock filter, I replaced it with the BHAF style filter sold by SP Diesel and it dropped to 13-15inH20 and stayed that way for 50k miles until I decided to change it just cause it had been in there for a couple years.

I really think people would be suprised what kind of restriction we are really talking about, my guess would be the stock dodge filter would be around 20inH20, and the BHAFs would be down about 12inH20 when under full boost. This is a huge improvement when you use the fan laws you describe.

As soon as I get the chance I will install my restriction gauge so we have some real numbers to talk about.

Haulin_in_Dixie

How can you compare an 8.3 to a 5.9? Same difference that I used. Apples and oranges.

Superduty

"How can you compare an 8.3 to a 5.9? Same difference that I used. Apples and oranges."

I figured I could compare them because I suspect they run similar air-fuel ratios, ie both are running at their smoke limit at WOT. An N14-300 probably isn't running anywhere near its smoke limit, but the 8.3 probably is. The 5.9 uses more boost to get the airflow up enough to burn fuel for 325HP, but they are both probably at their limits. It is just a wild *** guess on my part, but probably not too far off. If anything, I suspect the 8.3 needs less air because it will run cooler due to larger displacement.

Haulin_in_Dixie

I guess that would be why the 8.3 uses an HX40 and the 5.9 and HX35, so the 5.9 can get more boost. Oh well to each his own. The 8.3 would use 1.4 times as much air at the same rpm. Course they don't run the same rpm.

Superduty

The boost level on the 325 HP 5.9 is much higher than that of the 300 HP 8.3, irregardless of which turbo is actually used. It might have something to do with throttle response expectations.

If my numbers and methods are so bad, where are your numbers ?

Haulin_in_Dixie

I guess you don't run a Cummins much. The Cummins is not a high revving, low torque engine like the ford. Put a restriction gage on it, see where you are. I have no interest in running numbers. I was only telling you that you cannot compare apples and oranges for your computations. Lower rpm is where the EGT's go up pulling. I would not beat my engine by pulling a grade as you discribe at what did you say, 2900 at wot in 100 degree weather. Of course I am talking about 30,000 pounds, with only a 10,000 pound trailer I would be in overdrive at part throttle at the speed limit with your hill, or to make it easier on the truck, I might down gear to direct and run light throttle at 60 mph and 2300 or so. Most of my pulling is below 2400, or I should say all of my pullng because it it is that hard of a pull I will downgear and feather it.

You are trying to say that a Dodge engine with a small turbo and three inch exhaust pulls more air than a larger engine with a larger turbo and four or five inch exhaust. There is also not much difference between the 8.3 and 5.9 in boost levels. Running on the drag strip or light to light the high boost is good but pulling hills it is not necessary or needed.

Have to go to work, you figure it out, good luck. My Scotty works fine, have had a gage on it. Have you ever driven an 8.3, it is a completely different animal, just no comparison with a 5.9. Neither one of them are any comparison to a 7.3.