Technical Holley 4 BBL problems - Expert help no longer needed

Yes. Air is a hard thing to see moving around.

 

Maybe I'm stupid, but I fail to see how an air filter can change a car's behavior THAT drastically unless the K&N was absolutely caked by a mouse nest or the K&N oil in the filter somehow congealed. Furthermore, I fail to see how running a 3 inch filter versus a 4 inch can drastically change unless you're running WOT.
This sounds like dumb luck more than anything...

 

The K&N I had ,looked perfectly normal,,,I even cleaned it an extra time,,thinking that I had not done a good job the first time.
I used K&N filter oil too. Maybe I had a bad can of oil,,,I don’t know,,I threw it all away later.
The engine blubbered just like it was way too rich,,,ran like a pure dog!
After many weeks and untold changes and expense,,,,I finally decided I had nothing else to lose.
A new filter fixed it all,,,except for having to go back and change my jetting back to where it was.
It sure stumped me,,,I have tried not to forget it.

Tommy

 

Strange, but I guess not unbelievable considering the crap the aftermarket provides all too often.

 

The K&N filter on the Corvette was brand new, in the box. If you combine Tommy's experience with what I have seen it looks like air flow restricted by the filter can cause strange things to happen with an engine. I do know I am going to buy another 4" conventional filter to replace the K&N on the hemi in my race car (Avatar).

 

I know it sounds strange,,,I wouldn’t have believed it if not for my trouble.
And I am in no way knocking the products made by K&N,,,I know they make a great product.

It did make me realize that sometimes you have to suspect the un obvious things to get to the problem. As usual,,,I had to learn the hard way! LOL!

Tommy

 

I have been an anything else is preferable to K&N filters for over 30 years. I haven't tested the flow rate of the newer versions, but the older filters were not efficient at filtering smaller particles, and I am guessing that what the company has done, is to make the filters more efficient at filtering but at the same time made them more restrictive.
I have the device needed to test this, but don't feel like buying one to just to test it.
I always use the largest premium quality paper filter that I can install, and I clean them frequently.
Bob

 

Listen to what J-jock says! Those oil mesh filters are junk! Do yourself a favor and throw them in the trash!





Bones

 

The simple reason that K&N filters supposedly flow more: they don’t filter shit. I would not use one on a lawnmower. I think way too much of my engines for that. It kills me when I see someone using one on a turbo Diesel engine. If you have a late model GM vehicle that is still under warranty, and the dealership tech pulls out a K&N or that type, your warranty on the mass airflow sensor is null and void.


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I have had trouble in the past with an air cleaner lid being low enough that it choked off the airflow when driving. It would idle just fine, but would not run worth a crap when going down the street. I discovered the problem, or maybe the answer, when in desperation I took the thing for a drive with the air cleaner removed. This one had been mashed down by years of overtightening the wingnut. I put it on something, don't remember what, and pushed it back into shape and it ran fine for years afterward. I recently worked on a Holley equipped 390 that had such a low profile air cleaner, that the lid contacted the bowl vents and left an open gap between it and the filter. Not saying any of this applies here, but it pays to pay attention to how your air cleaner interfaces with the carb. Glad you got it going, even if it puts you in the "Day 2" class

 

Talk it up.. ! Andy, I can’t believe that people put that crap on their engines! Obviously they don’t give a shit about their mill!





Bones

 

I think the snavus rod on the knockulator was somehow compromised

 

Funny how that works,
The dropped base for air cleaners force the air into a contortionist dance. Sometimes it (the air) don’t like it.
Just draw yourself up a section view of that dropped base with a 3” aircleaner and the lid and the carb choke horn.

In “those” cars like yours the best parts to use are the factory stock stuff for fitment. Once you expect more performance & who wouldn’t ,,, better cam, better intake, better carb you can’t forget that it may require more room. Fixing the fitment issue by resorting to that section view of the dropped base air cleaner makes no sense.

 

Huh?

 

Huh to what ?
Draw it up, you’ll see the issue
Do you know what I mean by “section view”?

 

@carbking

I remember reading somewhere that the height of the air cleaner above the carb is important, if it's say 2.5" and something is installed that's markedly taller or shorter it changes the operating characteristics.

 

I think you ran into a rare condition where the new cam increased the intake velocity. This caused turbulence in the air flow as the air tried to make the 90 degree plus bend into the carb. The extra inch of height allows the air to make the transition. If there was a way to see the flow, you would likely find that the drop base is making the situation worse. You are probably only getting air flow from the upper part of the filter that rises above the base.

It would be interesting to substitute a flat base housing and a shorter filter to see what happens. I'm curious if the top and bottom housing pieces are miss matched.

 

Guys with C2 Vette have all sorts of fittment issues involving hood clearance and hood vs aircleaner wanting to occupy the same space once they start changing stuff like manifolds and carbs. They have got it down to modeling clay and play dough fighting for fractions of an inch.
The swap in intakes is to promote better air flow into the engine and the swap in carbs is to utilize that better flow... then choke that now required increase in air flow down with the crowning jewel low profile element and dropped base air cleaner so it fits.
It forces the air up a 45* slope, back down 45* across the lid, around the choke horn then thru a narrow passage and finally a hard 90* down the carb throat.
Cut the hood, drop the engine down or leave the thing stock. No problems

 

Here’s a section of a 2” drop base with 4” air cleaner. Imagine that with a 3” element

 

A perfect example.
There is nothing like a live demonstration,,,or a cutaway version.

Tommy

 

For street use, my first priority, is to use the largest diameter filter that I can practically use with the application. My second priority, is to use the tallest filter available in that diameter.
I don't know if I can find the study, but back in the 60s or 70s, there actually was a flow study done on a high performance engine using a factory designed drop base against a flat base using the same size filter. The conclusion was, that for that particular application the drop base flowed better than the flat base.
I wouldn't suggest that this would be a finding that could be applied universally, but it does indicate that a person interested in every last bit of reliable performance would want to do some research.
If a person was seriously interested in the subject, he could make an inexpensive comparison type flow tester using a vacuum motor, a variable speed controller, a vacuum gauge, and some connector tubing.
The results would not be scientific, but they would give an accurate indication of comparative flow rates for different designs.
A good visual representation of 600 cfm is, to imagine the air in a box 8.5ft x 8.5ft x 8.5ft going through your car every minute. It puts the problem in a more realistic perspective.
Bob