MB GPW dry air filter conversion?

[tsmgguy]

Say, does anyone here have any experience with the dry air filter elements and conversion kits now coming onto the market for the GPW and MB?

Is conversion really as easy as cleaning up the original housing and installing the gasket and filter?

Can the filters be serviced/cleaned?

How does the new filter effect the fuel/air mixture?

Thanks much!

[tamnalan]

If you search the modifications forum you'll find several threads on this conversion that will tell you all you need to know. It's a very easy change. Filter cleaning would depend on what you use - I just use replaceable NAPA filters for about $7 each. This one is a no-brainer in my opinion, but there are many who swear by the oilbath setup.

I'm a huge fan of everything Richard Sanders sells except for this one thing... I don't know why his air filter conversion kits are so expensive. The NAPA filter / McMaster-Carr rubber rings setup works great and will set you back about $15.

[918jeeper]

Somebody posted in another thread that thier jeep runs leaner with the dry conversion. Has anybody else personally experienced this?

[mikemc]

I converted my '42 GPW last fall using the NAPA/McMaster Carr method described above and I haven't noticed any difference in the way the engine runs.

Mike

[Ben Hovis]

Howard,
Most of our jeep club "Foot Hills Vintage Jeep Group", has converted to the dry system several years ago and we are very pleased with the conversions.
Just in case you need the code parts/mumbers that have been put together from others on the Gee, see below pictures.

air cleaner dry parts.jpg (22.18 KiB) Viewed 1351 times

Regards,
Ben

[tsmgguy]

Thanks, all! Very helpful indeed.

I was looking at a conversion "kit" for $85. Looks like this is not needed!

[tamnalan]

Welcome Howard!

You really have an L-4A? I first solo'ed in a J3 Cub. What a fun ride they are!

[Ben Hovis]

Howard,
We have been running that set up (above) for several years. Just clean the oil cleaner tray/system and be sure it is dry lay a ring on the bottom of the tray and one on the top of the new air dry cleaner and and tightned everything down. If I remember right total cost is under $25.00.

Have fun,
Ben

[breven52]

Mine is converted with the McMaster Car foam rings and the Napa filter. It works amazing and is very simple and maintaince free. Filters are $8 instead of $35 for an oilbath. Definitly worth doing.

[tsmgguy]

Done! Thanks for the tips and the part numbers, Ben! 12 bucks, plus whatever NAPA charges locally for the filter.

One just has to get over the fact that McMaster describes the gaskets as "toilet bowl to outlet rings".

[tsmgguy]

Welcome Howard!

You really have an L-4A? I first solo'ed in a J3 Cub. What a fun ride they are!

Thank you! I do have an L-4. Here it is. The MB is parked right next to it:

[Marty, SoCal]

When converting to a dry element be sure to clean out the bottom sump, epoxy over any rust-through pinholes, clean and paint the inside of the air cleaner to prevent rusting!

Changing to a high flow paper element can certainly effect the mixture on a G503, heres why:
The WO carb on the G503 has an external bowl vent (Under the unsealed top air horn). Restrictions in the air cleaner system have more effect on such carbs' mixture control than more modern carbs with fuel bowls that vent into a sealed air cleaner horn, like a M38 YS carb. If the air filter is plugged, you will run richer. If you replace a restrictive/restricted oil bath filter, with a clean paper element, you will run leaner. The relatively high pressure present above the fuel in the float bowl vs the lower pressure through the venturi is what PUSHES the fuel through the jets. Any changes in this pressure ratio effects the mixture. The atmospheric pressure remains contant in the outside air, but it lowers above and below the venturi as the filter plugs up in any engine. A restricted air filter system with the WO carb will always have atmospheric pressure in the fuel bowl, due to the external bowl vent, but have an even lower air pressure in the carb from the restricted air filter, causing the richer running condition. The internal bowl vent of more modern carbs allows the fuel bowl to vent only to the filtered air stream, which if it's restricted, balances the difference in air pressure across the jet/s, keeping the fuel flow more constant as the filter plugs up.

Why change to a paper element?
An oil bath air filter is highly dependant on the air flow speed for it's efficiency. The main design of them is such that the air needs to make a 180* turn above the oil bath, which causes the majority of the dirt will keep going straight into the oil, the air will make the 180* turn. Too high of air flow speed, and the smaller particles will pull around with the air flow. too low of a speed, and the lighter particles won't have as much kinetic energy to fall out, also. The screening material in the element is meant to try to catch these fine particles that make it past the oil. The screen element is usually oil wetted to help retain these particles, but it is relatively coarse, which could let dirt through it, especially if the element dries out. The oil viscosity used in the sump effects the air filtering efficeincy, too. Too thick and the dirt can actually deflect off the surface tension of the oil, too thin, and it can be drawn up unto the air stream at high air flow rates. The oil viscosity is usually spelled out in the TM, for any given temperature range. Also, if the oil level is allowed to raise too high from the trapped dirt building up in the sump, and the vehicle is operated at odd angles, there is a chance that the dirty oil will be drawn into the engine. Dirt laden oil makes a very good lapping compound between the rings, pistons and the bores! Proper maintanence, per the TM is meant to minimize these issues. These procedures are messy and time consuming, and with oil at $5 a quart, getting expensive, too.

A major benefit of a modern paper element is it is a 100% filter, meaning ALL the air entering the engine is 100% filtered no matter what the air speed. the paper/fiber element has pores that are very fine, mechanically catching the particles larger than the pores, at any air flow speed. Oil wetting on the fine paper will trap even smaller particles than the pores. AC brand air filters many times are oil wetted paper. Late model Jeep elements are also oil wetted paper. All modern vehicles use this type filter because of it's cost effectiveness and filtering efficiency. Even M1 tanks use a paper element! Yes, they can plug up faster, and the elements do have some cost. Most an be cleaned at least a few times with a vacuum cleaner, but even if you simply replace it, the cost is alot less than the damage caused by dirt entering the engine. Some Jeep paper elements come with an outer layer of oil wetted foam to help trap the larger particles of dirt, with the oil wetted paper taking care of the fine filtering, without plugging up as fast. These are/were used on TJ Jeep Wranglers, and on older CJ and SJ V8s in the late '70s. Some '80s GM diesel trucks also had these dual filter elements.

Oil wetted "Cheese cloth" elements that are meant to replace paper elements can offer higher air flow and better performance as far as HP. The higher air flow rating comes from the more open spaces in the filtering media (Cheese cloth element). The oil saturated fibers in the cheese cloth act like the mesh element in the oil bath filter, relying on the dirt actually contacting one of the oil wetted fibers, and then sticking to it. A problem comes from the open spaces in the element not 100% effectively cleaning the air of dirt, and any excessive oil carrying fine dirt into the air stream, or if the element runs dry, the dirt does not stick at all. These filters do not filter the air properly, in my experience, to be considered for an engine that is operated off-road. I've seen a few modern Jeep engines worn out bores in 20k miles that are running these elements, with 1/2" layer of oily fine dust laying inside the intake manifold!. They only approach the filtering efficiency of a good paper element when they are nearly plugged up with dirt. One more issue is if the engine filter gets a good splash of water while fording, the water will pull oily dirt off the filter through the element and into the engine. The manual that comes with them states not to clean them for 50k miles, and the instructions for cleaning them should be followed to the letter. They are easily damaged by blowing them out with compressed air, and over oiling them will pull dirt into the engine. I do not recommend them.

Hope this adds to the discussion!

[tsmgguy]

Thanks Marty SoCal for the detailed discussion!

I'll be going the paper filter route shortly, in hopes that the slighty lean running condition that you describe will at least partially cure what seems to be too rich running at my 4,000 MSL location. I have not yet insatalled a "lean" metering rod, and hate to mess with a WO carb that is otherwise perfectly behaved.

Is any one of the filters mentioned above better for our application than the others?

Thanks again!

Howard

[tamnalan]

I am NOT a fan of Fram products - they just seem poorly constructed to me - especially their oil filters.

WIX and NAPA are quality stuff, IMHO. I'm not sure who makes NAPA filters but I like them. Not sure about Mopar or Carquest - the Mopar stuff should be good if it's a Chrysler product.

Nice plane, Howard! I'm jealous...

[gearhead]

Wix makes NAPA filters, ( my NAPA guys told me years ago) look at the part numbers.
And Valvoline make their oil too.

Back to back tests, the paper filters seem to make the 134 more responsive.

Ed