Need Stroker CFM requirements

[eroc37]

OK, I've searched everywhere and can't find a straight answer. I need to know the CFM my 4.2 stroker is looking for before i choose a filter system.

Any opinions out there?

 

[5-90]

4.2L = ~260ci

260ci/2 = 130ci (you only move air for two of four strokes, or one of two RPM.

130ci * 4500 (estimated max RPM) = 585,000cim

585,00cim/1728 (ci per cf) = ~338.542cfm

Follow that? It's really a fairly simple calculation, once it's broken down.

The primary flaws are thus:
- I don't know your exact ci displacement - but 260 is "close enough for government work."
- Jeeps don't get the engines redlined very often - 4500 is probably too high, but that can be easily changed.
- This doesn't take into account the volumetric efficiency of the engine. This depends on a number of factors, but we can usually take the VE of the AMC six to be ~75-80%. 85% would be an "outside best." Therefore, you're probably flowing ~288ci, tops (assuming 85% VE - which is high.)

However, even with these flaws you'll still get a useful answer.

 

[yossarian19]

As usual, good work 5-90.
Only side note I'd put in is this: as a filter gets dirtier (dusty conditions, age, etc) it will flow less. A filter with fewer CFM to spare will impede performance earlier than a filter with more CFM.
Depending on your intended use, this may be unimportant. Thought I'd throw it in, though.

 

[eroc37]

Wow... thanks for the great info!

playing with the numbers a little, adding for dirty filter restriction and the like looks like the neighborhood of 400 give or take would be good.

 

[Dr. Dyno]

Throw on the biggest, highest-flowing filter you can find that fits in the available space. That way even if it's dirty it'll never be a restriction.

 

[Talyn]

The largest filter system I have found is the one by Volant. 3" pipe for the filter. I got a large Amsoil filter to replace the smaller one it came with. It comes with a crappy shield though, so you will probably want to fab up your own shield.

 

[gradon]

I have the k&n fipk and ditched the k&n cone long ago when I got tired of the dust build up inside the tube. I'm using the Amsoil Eaau3090 and it does a good job--the nano-pore technology has smaller holes than the stock paper, but more of them, so you get the best of both worlds: more cfms of air and better filtration. I cut a bunch of the metal out behind the headlight to let more air in and also am using a windshield shade to box off the filter(the fipk wall doesn't cut it for me).