airflow formula

[Archive]

Michael T posted a formula for airflow that I believe would be correct for a 2 stroke engine but not for a 4 stroke. Unless I have become even more confused in my old age, it seems that it takes 4 strokes or 720 degrees of crank rotation to pump the full displacement through our engines whereas a 2 stroke does it on 2 strokes or 360 degrees of rotation. If this is correct, then the airflow figures for his new induction system would be for a 11. 8 liter engine. Am I confused again??

 

[Archive]

Not sure about the formulas and all, but I was interested in the effeciency rates at higher flow rates. Will the K&N filter filter effectively at moderate upgraded flow rates (see my mods in my sig)? I am sold on the Psychotty air system, just because I have followed Scott through the whole design bit; from the pre 0880 days on. BUT I am open to new info!

Its a shame Rob had to close that other thread... even with the bashing #ad


Jack

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1997 4x4, 3. 54 rear, 5 spd, red, vinyl floors.
Banks Stinger Plus, BD 4" cat back (minus muffler), K&N (not Scotty YET!), Delvac 1, Lund cold front, Shelf-it overhead storage system, CB mounted overhead like the BIG rigs!
Pull Trailswest 2 horse slant, 1972 8' Bell slide in camper (heavy son of a gun), Sylvan 1750 jon with 60/45 Merc. Jet prop, and one great hunting Black Lab

Check out my pics: http://communities. msn.com/BigRedDodge

 

[Archive]

I am glad you pointed the 4 stroke out. I completely forgot about 720 degrees per volume cycle. Thank you. Here's the updated formula:

CFM = (RPM/2)*(5. 9L=. 208 ft3)*(boost in atm)

where boost in atmosphere

boost(atm) = ((boost in psi - 14. 7) / 14. 7) + 14. 7

Hope this helps.

-Michael
SAE,ASME,ASHRAE

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'00 2500 RAM, RegCab, 4x2, Cummins, 6-spd, Driftwood/Agate...

 

[Archive]

Michael,
Can you please repost on efficiency at different flow rates for the stock mopar air filter? Also how does this equate with your new formula. Specifically, what cfm are we talking for 30 psi boost at 2200 rpm? Don't really feel like doing the math, I always seem to mess it up someway or another.
Jack

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1997 4x4, 3. 54 rear, 5 spd, red, vinyl floors.
Banks Stinger Plus, BD 4" cat back (minus muffler), K&N (not Scotty YET!), Delvac 1, Lund cold front, Shelf-it overhead storage system, CB mounted overhead like the BIG rigs!
Pull Trailswest 2 horse slant, 1972 8' Bell slide in camper (heavy son of a gun), Sylvan 1750 jon with 60/45 Merc. Jet prop, and one great hunting Black Lab

Check out my pics: http://communities. msn.com/BigRedDodge

 

[Archive]

Hi Horseman,

For the 5. 9L at 2200 RPM at 30 psi, the CFM required would be:

CFM = . 5*(2200 RPM)*(. 208 ft3)*(2. 04 atm)
CFM = 467

You don't want to configure a filter system at the max CFM of the filter because you still want low restriction.

I still only have the one Nelson catalog, but should be getting the Baldwin any time. As far as the Nelson goes, a feasible filter set up would be:

Nelson 71041N
20. 9" Long, 10. 1" diam, 6"H20 restriction at 800 ft3/min.

Here's what I have calculated for most modified engines...
CFM = . 5*(3200 rpm)*(. 208 ft3)*(35 psi=2. 38 atm)
CFM = 793

A low restriction air filter should increase throttle response, possibly reduce EGTs, and if the inlet is fed to a cool air source, should reduce the EGTs 50-100 F.

I have thrown around the idea of using two smaller cylindrical air cleaners located where each of the batteries are currently located. Then connect the air cleaners by a cross tube with a T to the turbo (just like a big rig with twin external filters). The two batteries could be relocated to your choice (tool box or frame rail) and a bypass filter located where the stock air box was located. What do you think? Sounds cool, but may require a little work.

On my commute home from work, I often think of ways to modify the truck. This was just one of the many ideas I've had.

-Michael


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'00 2500 RAM, RegCab, 4x2, Cummins, 6-spd, Driftwood/Agate...

 

[Archive]

I don't have those catalogs, but are there any of the flat filters like the stock one, only bigger? Perhaps one could make a larger air box for the same location out of sheet metal, still use the stock air intake hose, perhaps route a duct outside "somewhere" for cold air intake. It looks like there would not be room for a box that holds two stock filters, but maybe something shaped differently could fit and provide greater filtering area (?).