[General Z]

Hello,

I had my Firebird running in the driveway tonight and revved it up from under the hood. The air filter was sucking in over 1/8” at the base and even the lid was sucking down. That’s with only the primaries pulling.

The engine is a 469, Holley carb, rpm intake, headers. The air filter is an Edelbrock version of a K&N with a filter lid too. 14”x3” I did clean and oil the filter last fall and likely over oiled.

What are you guys using for air filters? Maybe I can use a shop vac and suck some oil out?

I did take the car for a spin and drove it with and without the air filter. It was clearly stronger with no filter. Who’d have thunk a K&N style would be a choke point.

[Steve C.]

On my Trans Am the current 505 set up has direct port fuel injection. The air cleaner assembly is mounted on the fuel injection throttle body and it goes up inside the hood scoop.
It's a K&N 9" diameter filter, 2.875" tall with the a 9-inch diameter X-stream filter top.
I have a modified Victor intake.

Dyno tested on a Mustang chassis dyno with the air cleaner assembly in place it made 591 HP to the wheels at 6000 rpm.
Taking the air cleaner assembly off on the next pull it made 608 HP at the same 6000 rpm.

No attempt was made for any tuning changes to adjust for the no air cleaner, it was only done for general interest.

.

[Schurkey]

Originally Posted by General Z

I did clean and oil the filter last fall and likely over oiled.

The worst thing that folks can do to an oiled-gauze air filter is to clean it too often.
The second-worst thing folks can do is to over-oil the filter, especially on a vehicle using a MAF sensor. The sensor gets contaminated with oil pulled off of the filter.

K&N used to say that the filter should not be cleaned until there's a 1/8" layer of filth on the outside. In other words, if you can see that the filter has pleats, it's not dirty enough to clean. In certain applications, they might have you put a few drops of clean air filter oil on the filter from the inside. The build-up of dirt pulls oil from the filter gauze, and oiled-dirt becomes part of the filter media--the oiled dirt makes the filter MORE effective than clean gauze alone.

Of course, now K&N says that you should use an air-filter restriction indicator. Easily gotten from a Diesel vehicle in the Treasure Yard.

Some folks are saying that the "filter lids" on carbureted cars screws-up the carburetion--messes with the air-bleeds or somesuch.

I've used K&N air filters on multiple vehicles; at this point I'd have trouble buying them instead of good ol' paper filters.

[steve25]

Go watch the Engine masters air filter shoot out test and then decide if you still want to run a air lid with a filter in it a long with a normal side flow filter.

[Stan Weiss]

Originally Posted by General Z

Hello,

I had my Firebird running in the driveway tonight and revved it up from under the hood. The air filter was sucking in over 1/8” at the base and even the lid was sucking down. That’s with only the primaries pulling.

The engine is a 469, Holley carb, rpm intake, headers. The air filter is an Edelbrock version of a K&N with a filter lid too. 14”x3” I did clean and oil the filter last fall and likely over oiled.

What are you guys using for air filters? Maybe I can use a shop vac and suck some oil out?

I did take the car for a spin and drove it with and without the air filter. It was clearly stronger with no filter. Who’d have thunk a K&N style would be a choke point.

Put a vacuum on the engine when you do this. Maybe the problem is high vacuum and the secondaries should be somewhat open by now.

Stan

[General Z]

Originally Posted by Stan Weiss

Put a vacuum on the engine when you do this. Maybe the problem is high vacuum and the secondaries should be somewhat open by now.

Stan

Good call. I use the lightest vacuum spring too. Under load the secondaries would absolutely be open. In the driveway, they won’t open. Although, is there more or less suction on the filter with the secondaries open ?

[Stan Weiss]

Originally Posted by General Z

Good call. I use the lightest vacuum spring too. Under load the secondaries would absolutely be open. In the driveway, they won’t open. Although, is there more or less suction on the filter with the secondaries open ?

Even if the secondaries open some you still might have a problem with the air filter.

Stan

PS a 14 x 3 should be more than enough for your 469 ci engine. Yes double check that it is not over oiled.

[General Z]

I do think it’s over oiled. This morning I blew it out with my compressor and also used a shop vac. Didn’t drive though because of rain.

I got a used stubstack I’m going to dink around with too.

[Formulas]

don't recomend blowing the K&N filter or use high pressure water, can poke holes in the gauze reducing filtering allowing dirt to pass...

all this movement may be because the open top element cannot be as strong as a metal lid

[Schurkey]

Originally Posted by Stan Weiss

Put a vacuum on the engine when you do this. Maybe the problem is high vacuum and the secondaries should be somewhat open by now.

Vacuum under the throttle plates is not the issue.

Vacuum above the throttle plates will not be lessened by opening the secondaries. Would likely make it worse.

[Stan Weiss]

Is this a standard or dropped base air filter?

Stan

[General Z]

Originally Posted by Stan Weiss

Is this a standard or dropped base air filter?

Stan

Dropped. The only way it works with my Firebird.

[Formulas]

Technically a plenum is the area beneath the carb and before the intake runners, But any common area consisting of multiple flow paths that is soon to be directed into a certain dedicated path is also in effect a plenum

when those filtering lids are incorporated multiple flow paths are created on top of the carb, IE from typical direction then straight down from the top,
in any plenum competing air flows bouncing into each other produce turbulence which reduces overall flow and can disrupt flow siginals to air bleeds on the carb

thats why i believe when tested for HP those lids do not produce

I like K&N products not for HP which is what most people are fixated on but for clean air, when i bought a 2007 Honda it was my first car with a intake duct the first time i took the original paper filter out to blow it off at first oil change i noticed a thin talc dust like substance in the duct wiped it with my fingers and said yup i need cleaner air, got a K&N and never saw that buildup again

previously ran one on my 1970 firebird but obviously no intake ducting post filter

if i was you i would install the original metal lid for your air cleaner. clean re'oil the standard shape filter and run it