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Anyone see any difference on using the down draft air cleaners that allow air to enter from the top as well as sides? Of course the manufacturers claim you get more HP but are they worth it. How hard are they to service? They also tend to be a bit pricey.
TIA
John F.
 

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I think they actually hurt your numbers, never been to a dyno with one but, I've seen trucks and cars pick up numbers when they take it off. I just believe your air-speed increases when you have a breather that will direct airflow into the carb rather than having to pull it from all directions.
 

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While we haven't done any testing with them ourselves one thing to keep in mind is the air flow across the top of the carb and it possibly affecting the signal.

Similar to a car with a hood scoop where we want to have the back side blocked just behind the carburetor so the air can be routed into the carburetor it may be possible for an open top/side to set up a siphon at higher speeds .
 

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You have to REALLY watch out for how an air filter of any kind effects the bowl venting of the carburetor. Not long ago I was doing some dyno testing for a customer who has a Pantera. He wanted me to test some air filters when I was done with the rest of the engine testing and it was quite interesting. What he had was one of those Holley "dog bone" style filters fitted with two square K and N elements that were about 3 inches tall. They are on their sides, one on each side of the carburetor. Anyway, in the testing on the 425 horsepower engine the elements and more importantly the things that held the elements were very restrictive.

Even more interesting and where I'm going with this was that he also had some air filter spacers from B and B. There were two of them, a one inch and a 2 inch. Testing the filter with the one inch spacer made it run WAY better, so I tried the two inch, this made it run MUCH worse! Examining the filter revealed that without a spacer the vents were very close to the top of the filter housing, With the 1 inch they were in an area that was about even with the floor of the filter housing. And finally with the 2 inch they were way down from the floor of the filter in a big hole. What I think was happening was that without the spacer the bowl vent was obstructed causing metering problems. With the 1 inch the bowl vent was in a favorable location and then with the 2 inch the bowl vents were possibly being pressurized by the air turning and flowing down toward the carburetor. This was much worse than no spacer at all.

I'm thinking that having the filter top while flowing more air might tend to cause the air to "blow" straight down toward the top of the carburetor and thus upset the fuel metering. All carburetors are subject to this sort of influence and it can be a very big deal. In my case the engine was down about 12 horsepower with the 2 inch spacer combination!
 

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I run K&N stub stacks on top of my Holley 750's and they seem to work good. Back in the day, when I was dirt circle tracking, we used to either duct tape or sheet metal off the front of the air cleaner to keep the pulses of air from the agressive radiator fans from affecting the air signal through the carb (that and the dirt and rocks).
Rob
 

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In the dyno tests I know of a K&N XStream(down draft) filter lost power over a "regular" filter.

I also know of dyno tests that show no flow or performance change or improvement with a K&N stub stack on a Holley.

There are those who claim otherwise, and they may be correct. Per Dave's post, there are a lot of variables that can tip the scales one way or the other.
 

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In the dyno tests I know of a K&N XStream(down draft) filter lost power over a "regular" filter.

I also know of dyno tests that show no flow or performance change or improvement with a K&N stub stack on a Holley.

There are those who claim otherwise, and they may be correct. Per Dave's post, there are a lot of variables that can tip the scales one way or the other.
Do you believe that this loss of power could be caused by the down draft effecting the pressure in the bowls ??? If so do you think it would merrit running a line from each bowl vent to a less critical air speed area would help out on a max effort built running on eof these down draft filters ???
Just a thought.
 

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Somewhat related, I think someone dyno tested one of those Professional Products air cleaner inserts that 'direct' air flow down, and it helped?
 
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