Are air filters a bad idea?

[glenn in camino]

I just put a K&N air filter attached with a C shaped PVC pipe on my A carburetor. I can't notice any difference in the way it runs but I've heard that air filters are a bad idea. Please explain. Out here in the country many of our tours encounter dirt roads. I've also installed an Afordable oil filter. I want this engine to last a long time.

[Logan]

When you flood the carb, gas pours down into the filter. if the engine back fires, it will catch the filter on fire. not that an air filter wouldnt keep the engine clean, but its not needed on an A, and its more dangerous on an updraft. You'll get plenty of miles on your motor without an air filter.

[Special Coupe Frank]

The only down-side I've heard about running real air filters is that the slight restriction in air-flow affects the function of the carb; this is resolved by drilling a balance passage between the float chamber and the air-horn...

I don't know all the details... have seen some down with right-angle hose fittings and rubber hose... kind of clunky to look at...

Someone will come along with better details on the carb mod...

Can't think of a good reason NOT to use one on an engine you want to last... we may not drive on dirt roads (much) any more, but cars are still equipped with air filters, and there is still dirt and grit in the world....

SC Frank

[Roger V]

Supposedly, K&N air filters have zero restriction. If that is true then you don't need to balance. Dave Renner, Manchester, MI does modify carbs if needed. Involves milling a slot, turning a mating groove in the venturi, and drilling.

[1crosscut]

I'm with Logan on this one. With the gravity flow fuel systems on A's if the fuel valve doesn't seat correctly or you flood it you end up with your air filter soaked with fuel just waiting for an ignition source.

[Special Coupe Frank]

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Reasonable point on flooding / fire hazard...

I believe someone makes a vertical riser that keeps the filter element above the air-horn / fuel level ?

[pat in Santa Cruz]

K&N filters have almost zero restriction, so not to worry. I have K&N filters on my engines, with no problems running too rich.

On paper filters, the restriction causes lower atmospheric pressure in the intake chamber. The imbalance with outside atmospheric pressure in the float chamber causes fuel to siphon out the jets, causing the fuel mix to be richer. An ambient air tube between the intake and the float bowl will rectify this. All "modern" carburetors equipped with air filters (circa 1932 and later) have this feature. It can be done to a Zenith, as mentioned in earlier posts.

BTW, an Airmaze screen should be drenched in oil, which would make it more effective against dust. Most Airmazes I have seen were dry, rendering them effective against stones and small birds only.

[Kevin in NJ]

Without any filters you can expect 50,000 or way more miles from your engine if it is built properly and you do not try to over maintain it.

We tend to want to apply modern car ideas to the old design. Filters may have advantages for a few that live in areas with high dirt content, but really most cars see some fraction of the dirt per mile compared to when the car was new and the engines were expected to run 50,000 to 80,000 miles before a major rebuild. To get a better idea read about the cars in police service.

Modern detergent oils with additives keep the nasty stuff at bay and allow for most of the problem stuff to be drained with the oil. The rest of the engine is designed to digest dirt. One of the benefits of the thick babbitt is its ability to embed dirt and prevent it from damaging the crank.

Do you need the filters? Not really.
Do the minor benefits out weigh the increased complexity of the system that that is so simple it never fails?

[Special Coupe Frank]

Snyder's sells a "Hi-Boy" air cleaner kit, with a vertical riser, and the filter (K&N type) on top.

FWIW.

For me, when I spend four figures rebuilding any engine, I'm going to want both an air filter and an oil filter.

Even Old Henry allowed the new Model V-8 to go out the doors with a factory air filter...

[eagle]

I live on a gravel road and use an original AirMaize off my Grandpa's A. I do not oil the element, I use a furnace register filter wrapped around the element. As dirty as it gets, it IS doing something. I have an original Zenith carb and cannot tell any difference at all with performance. While its running I can take the filter on/off and the engine doesn't change at all. I run 1/4 turn on my GAV, except when hwy cruising, I run 1/8 turn.

[MrTube]

For anyone who questions the need of an air filter on ANY engine, I'm going to assume you have removed the air filters from all of your modern vehicles and engines such as ATVs and lawn mowers?

There are no real differences between a model A engine and a modern engine as far as an air filter is concerned in my opinion. Further more even Ford added air filters in the 1930s and they did it for a reason. Many people mention dirt, yet if you research it silica is the most dangerous thing for an engine and commonly found on all roads. Will a model A engine go 50K without an air filter? Maybe but it will go a hell of a lot longer with one under all conditions.

Your model A is suppose to be very important to you, if you feel it doesn't need an air filter than neither do your modern vehicles.

Me? I run a K&N on the "A" and air filters on all of my engines. I hate to even see snowblowers without air filters.


I suppose, if you leave your "A" in the garage 98% of the year it really doesn't matter but there are others here who drive their "A" constantly racking up thousands of miles a year.

[H. L. Chauvin]

Almost impossible to find a highly intelligent, true "professional" vintage master mechanic today, who was:

a. Well experienced with day-to-day hands-on vehicle mechanical repair work from the 1920's through the 1970's; &.

b. Fully informed of vehicle mechanical engineering changes & upgrade information provided through car manufacturer's mechanic certification programs offered by learning through "graded" correspondence certification courses; &,

c. Was intelligent & interested enough to observe results of modern mechanical maintenance development through the 1920's -1970's.

I happened to know one such person & learned a lot from him.

For what it is worth, (almost like discussing what type of oil to use), here is what he explained:

1. Model T's & A's with no oil & air filters on early dirt & gravel roads; engine smoking profusely & needing a ring job after about 8,000 miles; rebored for larger pistons at about every 15,000 miles.

2. Later models cars with oil filters, & oil bath air filters, (where sand fell from the air in an oil container below by gravity); engine smoking profusely & needing a ring job after about 30,000 - 40,000 miles; rebored for larger pistons at about every 60,000 miles.

3. Even later models with similar oil filters; but with "paper cartrige" air filters; engine smoking profusely & needing a ring job after about 130,000 miles; rebored for larger pistons at about every 210,000 miles.

4. Also, with extra cautious people religiously maintaining vehicles, some engines in 1970's got up to 350,000 miles before engines were slightly smoking with engine blow-by.

5. Again for what it is worth, in sharing only "his" opinion, the main cause of engine wear prior to "paper cartridge" air filters was drawing in partially filtered air, mainly causing "top halves" of cylinders to wear much more because of injecting sand & grit through the intake valves.

Maybe, the bottom line for making an air filter decision today would be:

A. That, hard surfaced roads today do have less dirt & sand;

B. Also, that lubrication products have improved;

C. Then, how many miles does one drive one's Model A per year; if not many miles, a rebuilt engine could last a lifetime or longer.

Maintenance for the engine one wears is truly an owner's decision.

Hope this helps.

[cpetku]

Originally Posted by Special Coupe Frank

Snyder's sells a "Hi-Boy" air cleaner kit, with a vertical riser, and the filter (K&N type) on top.

FWIW.

For me, when I spend four figures rebuilding any engine, I'm going to want both an air filter and an oil filter.

Even Old Henry allowed the new Model V-8 to go out the doors with a factory air filter...

Don't bother with the high boy from Snyders. It shook itself off the carb twice before I changed the hose that came with it. Then it shook the rubber mount for the air filter to pieces within 20 miles. Junk.

The one which wraps under the carb doesn't come with a gasket to seal it to the carb, so again it doesn't do what you want. I ended up sanding down a pice of hose to make a gasket.

Could have saved over $100 if I read this post first, but ultimately I'd rather have some protection as I do drive on dirt roads. If you add a filter under the carb, use the fuel shut-off valve when the car is parked and make sure you design a decent seal between the filter element and the carb with enough support to prevent it from falling off or damaging the carb due to cheap mounting methods.

If you really want a high boy I could sell you one cheap that has been powdercoated to hide the fact that it's had a very rough life. It's also had to be epoxied back together all over the course of three trips under 40 miles each. That said, shipping would exceed the value of the unit. In my opinion new ones (high boy) are pretty over priced being they are made from copper plumbing parts an aftermarket air filter and paint that bubles off the first time the carb drips on it...

[Kohnke Rebabbitting]

Dirt wears every part in an unfiltered engine. The dirt is there, if you can see it or not. It will prematurely eat up all moving parts.

Clean your house real good, then open the curtains, and let the sun in, And it is dust every where showing, in the air.

Every time a Semi, car, Ect, passes, most of the time you can see the off road surface dirt rile up.

It is the same out side, only bigger pieces. Just look what is on the out side of your Modern filter! That would go through the engine

[1crosscut]

Originally Posted by MrTube

For anyone who questions the need of an air filter on ANY engine, I'm going to assume you have removed the air filters from all of your modern vehicles and engines such as ATVs and lawn mowers?

There are no real differences between a model A engine and a modern engine as far as an air filter is concerned in my opinion. Further more even Ford added air filters in the 1930s and they did it for a reason. Many people mention dirt, yet if you research it silica is the most dangerous thing for an engine and commonly found on all roads. Will a model A engine go 50K without an air filter? Maybe but it will go a hell of a lot longer with one under all conditions.

Your model A is suppose to be very important to you, if you feel it doesn't need an air filter than neither do your modern vehicles.

Me? I run a K&N on the "A" and air filters on all of my engines. I hate to even see snowblowers without air filters.


I suppose, if you leave your "A" in the garage 98% of the year it really doesn't matter but there are others here who drive their "A" constantly racking up thousands of miles a year.

I agree that filters were added in the 30's but that is about the time that fuel pumps were added and the chance of flooding a filter with a gravity flow fuel system was pretty much eliminated. If you shut off your fuel valve and run the carb dry the chances of a fire on start up are much less. I make it a point to shut off the fuel valve and run the carb dry each time. But.... being human I don't always remember. I drive mine quire a bit and struggle with the filter vs non filter question. I would like to run a filter but perhaps I like my truck and garage as a whole much more than running with a filter and elevating the risk of a fire. I always have a fire extinguisher with me and hope that the only time that I have to use it to help others. Decisions, decisions....
Dave

[columbiA]

I think many "A" owners are paranoid that their engines will wear out without air & oil filters.In the 50,s I put 75.000 plus miles on a 31 Victoria & it still wasnt burning oil or leaking out the rear main.A lot of the miles was on heavily traveled gravel & dirt roads where you were eating dust from the traffic in front of you.Because of the conditions,I changed the oil & greased it every 500 miles.These days I change the oil in my "A",s every 1000 miles & still grease them every 500 miles as a tube of grease will lube the car a number of times,so the cost is negligable.Changing the oil every 500 miles today is only for those that like to throw their money away.

[George Miller]

There were a lot of things besides the air cleaner that let engine run longer between over hauls. PCV valve lets oily fums in the cylinders,which lubs the cylinder walls. plus draws clean air in the engine crankcase through the air cleaner. Thermostat keeps engine at high temp and evaporates the water out of the crankcase. Then it does not turn to acid. This helps in cold weather and short trips. Better pistons and rings, shorter strokes, which makes for slower piston speeds. Higher gear ratios so slower engine RPMS. This is just a few things that help.

[V4F]

Supposedly, K&N air filters have zero restriction.

i have a weber on my car . it came with a K&N filter . chocked it so bad it was quit rich . took it off & great , clean running !

[MrTube]

Originally Posted by George Miller

There were a lot of things besides the air cleaner that let engine run longer between over hauls. PCV valve lets oily fums in the cylinders,which lubs the cylinder walls. plus draws clean air in the engine crankcase through the air cleaner. Thermostat keeps engine at high temp and evaporates the water out of the crankcase. Then it does not turn to acid. This helps in cold weather and short trips. Better pistons and rings, shorter strokes, which makes for slower piston speeds. Higher gear ratios so slower engine RPMS. This is just a few things that help.

Though you really already mentioned these items I would like to add that sometime around the 1970s-80s they also started using 195F thermostats which I've read was to keep fuel from condensing on cylinder walls and washing the oil off. This combined with overdrive transmissions of the time and computer controlled lean running carburetors or fuel injection is when we started seeing engines lasting 200-300K miles.

[Duffy1]

Logan ;
Do not mean to hijack this thread ,but , I have not seen anything on your engine problems lately . Any updates . Thanks