Redline filters and air horns...

[HaZmatt]

Hey guys I purchased these Redline filters for my triple weber setup. It states that they are capatable with all air horns but mine seem pretty close to the outside. I'm worried that it will restrict air flow. I may have to purchase the shorter horns but would like not to, What do you guys think?

 

 

 

[rossiz]

looks pretty close to me, i'd be concerned you aren't getting full benefit from those horns. a few years ago i set up a ducati with air horns on flatslide carbs and was trying to figure out how to keep dirt/debris from going in (one of the carb horn points up under the tank, the other points directly forward, right behind the front tire) and i rigged up a circular aluminum plate with spacers which sat about 1" in front of the horn thinking things would bounce off it rather than getting sucked right down the throat. i ran it on the dyno to tune and that carb wanted a completely different set of jets. pulled off the plate and saw an immediate gain across the whole curve. i was shocked how much that plate affected flow - even though it didn't really restrict flow directly. the horns are designed to work w/laminar flow, with the trumpet shape increasing the velocity of the air as it is compressed to the diameter of the carb body. when you introduce turbulence things don't work as well. that's why modern engines use a large airbox - it allows the horns to draw from a controlled pool of air and the flow through the horns is as designed for maximum benefit. shiny air horns hanging out in the open look cool but don't do a lot because the turbulence of the airflow is uncontrolled depending on the speed you are driving, wind conditions, heat in the engine bay, etc.

the best air filter setup would have a large outer can (the airbox) and filter elements that have enough clearance to allow the horns to provide max benefit. unfortunately, this doesn't look nearly as cool as a row of shiny horns...

btw - i also tested multiple filter types (foam, paper, oiled fabric) as well as screens of various density. the screens choked off flow more than filters, with a corresponding dip in performance. screens are specified by open area, so an 85% open area mesh cuts 15% of your flow. my bike has a pretty high hp/weight ratio compared to a z much (100hp pulling 325lbs), so a small change and you could feel the difference in performance directly. not sure if this exactly the case w/a z making roughly twice the power but weighing almost 8 x as much...

 

[HaZmatt]

20 hours ago, rossiz said:

looks pretty close to me, i'd be concerned you aren't getting full benefit from those horns. a few years ago i set up a ducati with air horns on flatslide carbs and was trying to figure out how to keep dirt/debris from going in (one of the carb horn points up under the tank, the other points directly forward, right behind the front tire) and i rigged up a circular aluminum plate with spacers which sat about 1" in front of the horn thinking things would bounce off it rather than getting sucked right down the throat. i ran it on the dyno to tune and that carb wanted a completely different set of jets. pulled off the plate and saw an immediate gain across the whole curve. i was shocked how much that plate affected flow - even though it didn't really restrict flow directly. the horns are designed to work w/laminar flow, with the trumpet shape increasing the velocity of the air as it is compressed to the diameter of the carb body. when you introduce turbulence things don't work as well. that's why modern engines use a large airbox - it allows the horns to draw from a controlled pool of air and the flow through the horns is as designed for maximum benefit. shiny air horns hanging out in the open look cool but don't do a lot because the turbulence of the airflow is uncontrolled depending on the speed you are driving, wind conditions, heat in the engine bay, etc.

the best air filter setup would have a large outer can (the airbox) and filter elements that have enough clearance to allow the horns to provide max benefit. unfortunately, this doesn't look nearly as cool as a row of shiny horns...

btw - i also tested multiple filter types (foam, paper, oiled fabric) as well as screens of various density. the screens choked off flow more than filters, with a corresponding dip in performance. screens are specified by open area, so an 85% open area mesh cuts 15% of your flow. my bike has a pretty high hp/weight ratio compared to a z much (100hp pulling 325lbs), so a small change and you could feel the difference in performance directly. not sure if this exactly the case w/a z making roughly twice the power but weighing almost 8 x as much...

 

Thanks for the info! I think I will look for some shorter stacks.

[gundee]

With air filters on, mine runs better without air horns. Try it.

[Jarvo2]

I found some shorty air-horns for mounting to my SU's.  I would think something should be available for Webers as well.

 

  

Edited June 2, 2016 by Jarvo2

[rossiz]

just to be clear - regardless of the clearance around the air horn intake, unless you have an air box around the filters you won't be taking advantage of the horns design due to turbulence while driving. you can tune to perfection on the dyno and then when you're on the street/track (where it counts) you will not hit that mixture/performance. this will be the case with any open filter design - again, the tradeoff is aesthetics vs. performance. i'm not saying the car will run like crap without an air box, just that it won't really be taking advantage of the horns and most likely you can just take them off and run the filters without horns since they won't be really doing a lot if what you want is the visual of the open filters. 

[LeonV]

7 hours ago, rossiz said:

just to be clear - regardless of the clearance around the air horn intake, unless you have an air box around the filters you won't be taking advantage of the horns design due to turbulence while driving. you can tune to perfection on the dyno and then when you're on the street/track (where it counts) you will not hit that mixture/performance. this will be the case with any open filter design - again, the tradeoff is aesthetics vs. performance. i'm not saying the car will run like crap without an air box, just that it won't really be taking advantage of the horns and most likely you can just take them off and run the filters without horns since they won't be really doing a lot if what you want is the visual of the open filters. 

Air horns don't depend on air turbulence around them for functionality. They work by smoothing out the airflow (reducing flow separation) as air enters the intake. They also perform another function of increasing the effective intake length and altering intake resonance in order to tune the engine's powerband.

[rossiz]

the issue is pretty simple: air horns do a lot of things to help performance, but they provide the best benefit when the air entering them is controlled. i'm not saying don't use 'em, just that the actual performance gains are significantly reduced when they are out in the wind. i think they look cool as hell and that's a perfectly good reason to have them. the other thing to remember is the performance gains we're discussing aren't really all that noticeable on the street anyway, so it's really a matter of personal preference. 

flow separation is a result of localized turbulence. negligible in comparison to wind rushing past perpendicular to the air horn intake at 60 mph...

[z boy mn]

Hey all, I posted something similar just now and had the exact same observation. After a lot of reading, the technology of keeping the air horns seems to warrant figuring out how to make them fit into the air filter housing. I'm definitely not an engineer, but as was mentioned here and other forms, the variables concern runner length, air turbulence and "flow," and also the issue of resonance. If I remember correctly, the longer the runner the better the set-up is for low-end torque, and the horns both condition the air going in and help balance the air coming out when valves, etc. open and close.

I did finally find a site which sells shorter horns. My post earlier today was about how short I should go to get the most benefit. I'll post the link to the horns and my post as a cross reference...maybe I should have posted the question here, idk.

Air horn options: http://www.carburetion.com/sitesearch.aspx?category=DCOEstack&Title=Stacks for Weber DCOE Carburetors

Previous post on same topic with question about clearance: http://www.classiczcars.com/topic/56876-recommended-breathing-room-for-velocity-stacks/