Balancing The Carburetor Is Not A Cure All

[Bob Bidonde]

This is a negative argument for mounting anything to the carburetor's intake throat.
There is a misconception that the engine's performance degradation due to an air filter on the carburetor is negated by cutting a balancing slot from the air intake throat to the float bowl. Yes, it does eliminate the excessive suction of gasoline from the Cap & Main Jets, but it does not eliminate the restriction to the air flow intake into the carburetor.
There is definitely a degradation to the engine's breathing of intake air from an air filter / air maze that balancing does not cure! As the air filter becomes dirty, the intake air breathing is further reduced. Also, mounting an air filter so it causes a bend in the intake air flow decreases performance. Perhaps the most serious consequence of an filter is the fire hazard it makes when it becomes saturated with gasoline.
I have yet to see dirt particles captured by a filter large enough or abrasive enough to be a concern to the longevity of a Model A's engine. Certainly if the air is that dirty / abrasive, my nose would be hurting.
What is your opinion about running an air filter on a Model "A"?

 

[alexiskai]

Oddly enough, Dave Renner found in his tests that mounting just the elbow - not the filter - of an Air Maze actually increased airflow through a Zenith carburetor by a small amount. But only if the elbow was pointed down. He hypothesized that it was acting as a crude velocity stack.

 

[jg61hawk]

The nose filters the air. Don't cut it off to get more air flow!

 

[Jim/GA]

Bob, you are correct that any restriction on the inlet to the carburetor will lessen ultimate flow through the carburetor at Wide Open Throttle (WOT), compared to what you could get without the air filter, and reduce peak performance. It would be like not quite being able to open the throttle all the way, the engine would breathe a bit less.

The excessively rich mixture that you get when running an air filter on a carb that is not pressure balanced happens at all speeds, all throttle positions, all RPMs. It is rich all the time. It is not good all the time.

The mixture is not altered with an air filter on a pressure balanced carb. That's the benefit. But, yes, you are not quite getting full WOT potential performance with the air filter installed.

How often do you run your Model A at WOT? Especially at higher RPM. I seldom do, if ever.

So your theoretical loss of performance is REAL if you drive at WOT, if you are racing, if you are trying to squeeze every last drop of HP out of the engine, but it is less of an issue when you run at most anything less than WOT.

And the performance loss at WOT due to air filter restriction depends a lot on what the filter element is made of, how large it is, and how clean it is. The wire mesh screens are not very restrictive. A small paper element of the same size would be much more restrictive. I have seen larger elements that look like a K&N filters that are probably not too restrictive. If you have an pressure balanced carb, you don't care (unless you run at WOT a lot).

Fuel collection in the air filter and fire hazard are real. If your carb leaks fuel, you should fix it.

I carry a fire extinguisher.

If you run engine pans, you get less dirt and dust and grit blown up into the engine compartment while driving down the road for the carb to suck in. Before adding an air filter, I'd add engine pans. They work well if your carb is not pressure balanced.

When I clean my metal mesh screen Air-Maze filter, I see lots of dirt and grit come out in the cleaning solution. It's doing something. That was without engine pans. I recently added engine pans and I will see if that makes a difference on what the filter collects the next time I clean it.

My engines have pressure balanced Model B carbs, with larger throttle plate and throttle bore diameter. Also larger bore intake manifold inlet. Any loss of ultimate flow potential at WOT due to the air filter is made up by the larger throttle bore. I'm still better off than stock Model A Zenith. But I don't run much at WOT anyway, if ever, so it does not really matter.

Bottom line: add engine pans if you don't have them.

 

[P.S.]

I agree with Dave Renner and Jim Cannon. With that made clear, I run air filters on my Model As. Call me whatever you want. If the carb is running rich, I just close the GAV a bit. No big deal.

I have also spent 58 years on this planet almost never wearing shoes, so please don't use me (the barefoot autistic kid who was doing algebra in 5th grade) as any kind of role model.

 

[Big hammer]

Air horn pointed forward = air filter needed

Air horn pointed up = air filter needed

Air horn pointed down = air filter needed

Air horn pointed backwards = not needed why would engineers at ford NOT design a air filter ?!! When dirty air turns 180 degrees the dirt falls out of the air stream

Jim Cannon is your oily dirt attracting filter catching dirt on the front side of the mesh ? Put a cloth bag over it and you’ll see dirt on the front side of the bag clean on the backside

 

[BButturff]

I also run a metal mesh screen Air-Maze filter. I had it fall off once at the beginning of a 50 mile trip and it landed in the engine pan. I heard the "clunk" but didn't realize what it was until the trip was over. I also didn't notice any change in how the engine ran and didn't adjust the GAV. Just for giggles I pulled the spark plugs and they looked just like they always do. Maybe I'm just lucky.


Edit: My Zenith carb is not air balanced but it does have Renner's "innerds".

 

[Kurt in NJ]

I have had the air maze filter on since the car has been on the road.
The car is stock compression ratio and rear ratio.
It has a 1970s repro muffler that Aires says has more back pressure that reduces performance (yes it is not a stock design inside just 2 baffles with holes)
The carburetor is stock with no balancing modifications.
Using the same oil I believe that it is more efficient than the K&N — definitely can’t read looking through it like I have with a k&n.
I have done mixture testing under load up to over 3000 rpm (I know Bob you are afraid to take your modified later engine that high a rpm)— Me,I have been try to break it for the last 40 years by lugging ,riding the clutch,long parades at low idle , running full advance and whatever is said to damage babbitt.

the emission/mixture testing even though over 10 years apart the only change was the fuel— the ethonal fuel made it leaner and that test was over 3300 rpm.
As you can see the emissions were well under the limit for the 2000 Honda civic I had to use, the earlier test was 1980 Civic — model A not in database and the load the machine used was based on weight.

Since I have not done any tests without the air maze and old repro restricted muffler what improvements should I expect from removing the filter and installing an original specification muffler?

With those CO numbers at over 3000 rpm and the not air balanced Zenith I would say the air maze is not very restrictive .

 

[ModelA29]

..... why would engineers at ford NOT design a air filter ?

Easy Henry saved a lot of money not installing one. It was an accessory. His Fordson Tractors used Bennett or Holley air filters - centrifugal types.

 

[Keith True]

The ones I've seen on Fordson tractors was called an air wash.I've owned three Fordsons.One was just a plain steel wheeled tractor.One was an odd one,it had dual hard rubber tires,and was used in airplane hangers.It ran on straight gas,not set up to run kerosene.Gas exhaust fumes were easier to take in the hanger than kerosene exhaust.The one I liked the most was the Traxon.On steel tracks instead of wheels,That had the air wash on it too.

 

[Synchro909]

I have posted about our long outback trips often enough here that you guys must be aware of whet we do. Before the first one, I rebuilt the negine for a little more power but a lot more staminar. As part of that, longevity was a big consideration including clean air. It get VERY dusty out there and I figured no air cleaner was asking for anoher rebuild sooner rather than later. The first couple of trips wre done before I switched to a down draught carburettor so here's what I did and the results.
From the carburettor intake, I made a fitting to get around the steering column that pointed upwards (not a problem for you guys). From there, I used a piece of vacuum cleaner tube to a fitting from the back of a toilet bowl to connect to a 12X2 inch paper element air cleaner that I mounted high up on the radiator stays.
It would be pointless to give any numbers on fue economy because we were towing a camper trailer all the way but every other observation indicated that the engine was running well. No popping or farting, smooth power to max revs, no cutting out at a quick stop, light tan plugs etc. When I was running without a trailer, the engine returned high twenties mpg. That is per imperial gallon - I have no idea what that would be in US gallons.
My take away from all of this is that while an airfilter does restrict air flow, if it is big enough (the filter), the restriction is so minor that I could forget it.
FWIW, I also run an oil filter on that engine and I built it with oil pressure tothe middle main bearing, a bew Burlington crank nad new rods all running on insert bearings, a 5.5:1 head and a slightly better cam. I use an additive which stops valve seat recession and lubricates the upper cylinder area with every fill. While driving, I watch the gauges. Once the engine is warm, they sit on 170 °F, 26 psi oil pressure and 50 mph. That goes on hour after hgour, day after day for weeks on end. Once the oil pressure stars to drop, 25 psi, 24 and finally, 23psi, I figuer the oil has "lost its guts" so I change it. oil pressure goes straight back to 26 psi and the cycle repeats. Oil changes happen every 3,800 miles regularly. That engine is now in another vehicle after about 55,000 hard miles as the tow car and another 20,000 miles solo. A couple of weeks ago, it deveoped a leak from the head gasket into the water jacket so the head had to come off. When I looked down the bores, I could still see hone marks. Remarkable!
I'll stop rambling now.

 

[ModelA29]

The ones I've seen on Fordson tractors was called an air wash.I've owned three Fordsons.One was just a plain steel wheeled tractor.

Kinda like an oil bath but used water - drain and refill no messy cleaning.


In the late 50s I played on my dad's aunt and uncles Fordson in their MI barn. My dad said it had been a bad deal. Henry was so busy selling new tractors you couldn't get parts to keep it running.