Does an air filter help to reduce turbulence around the carb top (by "straightening" the flow)? Afaik too much turbulence will screw up the air metering in the carb which can be the case when using a carb hat (especially at higher rpms). I also heard that it's very important to have a plenum on top of the carb (I assume to slow down the incoming air and therefore reduce turbulence).

Background to my question is if I use a cold air intake with a remote air filter should I use an air cleaner housing with a plenum or just a carb hat. Or am I better of to make a cold air intake with the filter around the carb?

Thanks

I had a 440 running low 12 - hi 11s with a GM dual snorkel breather with 4" alum dryer ducting running to both sides of radiator support.
I raced without a filter.
Put in a K & N 3 x 14 filter and picked up .10 in the quarter mile.

An air filter can make a difference, but is must not be restrictive, either. The air cleaner base plate design plays an important roll, too, as far as smoothing air flow into carb. There is a reason why so many raise up and then roll down to the air filter lip.

+1 on not being restrictive. I picked up 0.07-.1 going from a K&N 14x3 element to a WIX racing element, but lost ET when I pulled it off all together.

I would think that the air filter helps to guide the air around the carb so it can enter from all sides instead of primarily from one or two sides (when using a an air cleaner housing).

FWIW...Patrick at Pro Systems Carbs once told me that if the car went faster w/ an air filter on it, then the mixture isn't right.

Now IMO, an air filter can help if you have a hood scoop setup that is creating a lot of turbulence at the carb inlet. Doesn't mean the filter made it faster (like K&N claims), it just proved you need to rethink your hood scoop setup.

instead of using an air filter to reduce turbulence a honeycomb should do the same job while being less restrictive.

Agreed with Chip.
Car running here with limited clearance under scoop finds wind sheer will kill carb .
K&n filter that you oil will kill 12 to 20 hp if oiled too much/ used too soon- dyno tested that here.

Engine masters did a air cleaner “ shootout “ that basically showed the same things we found on dyno here - air filter bases/ tops generally hurt power .

Best we tested was double stacked filters in straight base - I think this goes to posts above about having plenum area and low restrictions.

We found static fans cost 14 to 20 hp- pretty much proving Engine Madters rests on those as well.

In both cases there is a caveat :

1. Testing in dyno doesn’t replicate running in car with engine bay heat and air flow.

2. Front opening scoops may positively effect air filters where as rear/ negative pressure scoops don’t pick up that advantage.

3. It is my opinion ( untested as yet) that static fans will have greater hp loss on the big end of racing than on dyno due to dealing with air flow through radiator .

4. Wind sheer effect across high speed air bleeds and boosters is much, much worse than a little restriction.

Just my thoughts and results from dyno sessions.

My builder uses a stub stack on some of his 2 barrel hydroplane builds and he says the gains are significant. Fuel curve is much more stable.

I'm pretty sure he has finnesed them on the flow bench to optimise the inlet shape


Kevin

One more carb port to RustyM's list.
* Airflow that effects pressure on the bowl vents.

Years and years ago some of the Hot Rod magazine writers got involve on a 1932 Ford Roadster fenderless Bonniville salt flat racer, it had a BB Chevy 427 in it with a tunnel ram with two Holley 750 D.P. carbs. and no air cleaners on it, the first couple of runs they ran it with the air scoop mounted on the front of the radiator shell block off so the motor had to run on air entering the engine compartment from under the car, they ran within 3 MPH of the existing record back then for that class, They unblock the scoop and hooked up the air channeling device built into the car to force air into the carbs, that slowed that car way down and ended up causing engine damage from detonation, once they fix the motor and finally block off the scoop again it ran fine. Their message was Holley carbs hate air turbulence over the top of the carbs
I've pick up .3 MPH on my old Max Wedge stocker in the 1/4 mile by adding the air cleaner bases with no elements or tops That proved to me that a lot of carbs. out there need help on channeling, guiding, smoothing up the air flow into them
On your deal do the test and see what your car and motor like

Kind of remembering Thumpman did a deal were he drill hole in the back of his hood, to stop some of the turbulence under his sixpack hood, I think he said it pick up .

Yes it did and the afr's smoothed way out as well..........As for K&N filters, done w'those and only run Wix Racing filters w/damn near zero restriction...........

I won't drill holes in the back of my scoop, but you did just give me an idea for a spring-loaded pressure bypass in the plate that seals my carb to my hood.

But will it smooth out the air flow above the carb ?

I worked on a friends FED (nick name balls cooker...long story) and it two 2.250 holes in the back of the scoop to make it run. Before that it was pissed off. I don't remember who it was that told me to drill the holes but it went from untunable to tunable.

I always ran a K&N Stubstack with the carb sealed to the scoop. On the last deal we ran, we paid attention to the shape of the pan in the scoop and used a K&N tall velocity stack style air cleaner without oil. Just trying to straighten up any turbulence and keep the big stuff out and it made a difference in how the cylinders looked after a year. Never tried A-B-A tests. Ran good MPH and seemed happy.

We called that "air packing" which basically creates a blockwall of high pressure in the scoop/opening. Drill holes, pressure is released and flow is re-established.

A good filter is beneficial on a drop base. Not so much in a velocity stack, etc.

Carbs like air coming in from STRAIGHT down, not turning corners to enter the venturis. There are test out there that display this.

One of the last drag race motors I dyno tune in SO CA was a 440 block stroke to 3.91 stroke with a set of CNC ported B1-BS heads taken out to M.W. intake port size, they flowed right at 350 CFM at .700 on the intakes. The motor had a little over 12.0 to 1 compression and a M.W. port size tunnel ram with a pair of Holley 750 D.P. prepared by JET performance in SO CA and a old Crane custom ground solid roller cam, nothing all out race at all
We played with timing, valve lash, spark plug gap and heat range and finally treid a set of nine inch tall velocity stacks with a set of 11 inch diameter by three inch tall paper air filter elements on top of the stacks, George, the dyno operator, said that change will make the motor lose HP, it didn't It gained around 8 HP from the bottom RPM all the way up to the peak RPM, 7000 RPM
I'm a firm believer on all Holley D.P. that straightening the air flow up above those carbs. really help them run better

Cracked, that crazy trio on Engine Masters showed that of which we already know from days gone past but tend to forget due to time and age. Velocity stacks have always worked.

When it comes to a regular traditional air cleaner set up, I have always run a flat base with as much filter height as I could get. 4 inch in height if I could. Hole in the hood was always OK. If not needed with a Holley Strip Dom, 1 inch spacer set up. Tops were solid until K&N came out with that flow through top which went on top right quick to my bennifit.

The hardest thing always was good clearance. Everybody wants a bitchin big filter under the hood.