Air Intake Redesign

[Project_Mayhem]

I'm redoing the air intake on my M25XP. The primary reasons for doing this includes proper routing of PCV and replacing the steel wool air filter that's disintegrating. This is a 23hp/57ci engine with a max operating speed of 3100RPM. I found a calculator online to find the liters per minute of airflow coming in to the engine at max speed. Would a 4x2" filter be enough?

Seat of the pants calculation:
There's one reviewer that stated that they saw a drop in RPMs when they installed one filter on their 53' Chevy 235ci gas engine. They discovered that they needed four of them stacked one on top of another to get enough airflow. The same calculator states that this engine requires 18cfm. Since I plan on using a single filter, I divided this number by four to get 4.5CFM per filter. Since my little diesel only needs 3CFM, it should work but I'd love to hear a confirmation from someone with a bit more knowledge on this subject

 

[Ward H]

Switching to a K&N Filter is pretty common on the M25XP as the can filters with the metal mesh that disintegrates has it gets older.
Here's a link to a C34 forum page where it is discussed and the part number is listed.
K&N RU-2450 filter assembly.
I installed one in 2018 and it appears to work well. It's still clean so I don't anticipate needing to replace it.

Edit: I just checked on line. The price has more than doubled since I purchased mine. Maybe the CFM listed for the K&N can help you decide on a much cheaper option?

 

[Richard19068]

... This is a 23hp/57ci engine with a max operating speed of 3100RPM. I found a calculator online to find the liters per minute of airflow coming in to the engine at max speed. Would a 4x2" filter be enough?

Seat of the pants calculation:
There's one reviewer that stated that they saw a drop in RPMs when they installed one filter on their 53' Chevy 235ci gas engine. They discovered that they needed four of them stacked one on top of another to get enough airflow. The same calculator states that this engine requires 18cfm. Since I plan on using a single filter, I divided this number by four to get 4.5CFM per filter. Since my little diesel only needs 3CFM, it should work but I'd love to hear a confirmation from someone with a bit more knowledge on this subject

I don't know what the spec on your posted filter is but doesn't your calculator show 46 CFM (1,303 LPM) demand for your engine? Not 3CFM?
Maybe I'm reading it wrong.

 

[Project_Mayhem]

Something is up with the calc I used. It was giving me different results when I reloaded the page. Another calc estimated somewhere in the range of 52-53CFM which sounds a lot more accurate than 3CFM

 

[Project_Mayhem]

Switching to a K&N Filter is pretty common on the M25XP as the can filters with the metal mesh that disintegrates has it gets older.
Here's a link to a C34 forum page where it is discussed and the part number is listed.
K&N RU-2450 filter assembly.
I installed one in 2018 and it appears to work well. It's still clean so I don't anticipate needing to replace it.

Edit: I just checked on line. The price has more than doubled since I purchased mine. Maybe the CFM listed for the K&N can help you decide on a much cheaper option?

$60 is a bit steep for a tiny air filter. BTW, you can clean yours when it gets dirty. A dirty gauze based filter will have less flow than a dirty paper air filter according to K&N. I'm leaning more towards replacing a paper filter every couple of years as it takes less time. There's never a shortage of boat projects

 

[Project_Mayhem]

I couldn't find exactly what I wanted so I designed a filter assembly for the Spectre SPE-4809 that I will 3D print. The outlet is on the inside of the assembly due to height restrictions. There's a hole for a grommet and barb elbow for the PCV hose. I plan on using a catch can on this hose to collect the hose.

I plan on taking the screen out of my original filter to reinstall on the intake, within the filter assembly. I will not be re-using the steel wool from the original filter. This should guard against accidentally dropping parts in the intake manifold during filter changes. I decided against printing this as plastic may become brittle over the years when subject to heat. I don't think engines like to eat plastic.

These filters are often used on vintage VW bugs with a single carburetor. I think this will provide sufficient flow but I won't truly know until spring.

For those that are looking for something pre-made, the EMPI 17-2978-0 filter with cleanable gauze filter and barb is a strong contender. It's a little tall but I think it'll work well for the C30. Price is also less than half of the K&N filter. Note that it is wider and I have not verified width clearance in the engine bay.

Does anyone happen to know the size of the breather hose?