Air cleaner performance
Road Warrior
Joined: Mar 2010
Posts: 1,900
Likes: 12
The stock Harley air cover provides the engine with a stream of cool air being that its intake is located at the front.
And up to say 5500 RPMs it provides enough air to the engine that you will not really see much improvement at those engine speeds going to an open air cleaner.
When you get to the red line and run WOT you will definitely benefit from the open air cleaner, but the Harley Stage 1 backing plate that reuses the football or tear drop feeds the engine with elevated air temps.
But other than WOT pulls I don't see where the factory AC design wouldn't give you enough cool air. Just replace that dish rag air filter with a K&N, but keep the air box.
And up to say 5500 RPMs it provides enough air to the engine that you will not really see much improvement at those engine speeds going to an open air cleaner.
When you get to the red line and run WOT you will definitely benefit from the open air cleaner, but the Harley Stage 1 backing plate that reuses the football or tear drop feeds the engine with elevated air temps.
But other than WOT pulls I don't see where the factory AC design wouldn't give you enough cool air. Just replace that dish rag air filter with a K&N, but keep the air box.
Seasoned HDF Member
Joined: Feb 2012
Posts: 13,456
Likes: 10,452
From: Sunshine State
The stock Harley air cover provides the engine with a stream of cool air being that its intake is located at the front.
And up to say 5500 RPMs it provides enough air to the engine that you will not really see much improvement at those engine speeds going to an open air cleaner.
When you get to the red line and run WOT you will definitely benefit from the open air cleaner, but the Harley Stage 1 backing plate that reuses the football or tear drop feeds the engine with elevated air temps.
But other than WOT pulls I don't see where the factory AC design wouldn't give you enough cool air. Just replace that dish rag air filter with a K&N, but keep the air box.
And up to say 5500 RPMs it provides enough air to the engine that you will not really see much improvement at those engine speeds going to an open air cleaner.
When you get to the red line and run WOT you will definitely benefit from the open air cleaner, but the Harley Stage 1 backing plate that reuses the football or tear drop feeds the engine with elevated air temps.
But other than WOT pulls I don't see where the factory AC design wouldn't give you enough cool air. Just replace that dish rag air filter with a K&N, but keep the air box.
Road Captain
Joined: Jan 2007
Posts: 645
Likes: 215
From: Minneapolis
I have tested the zippers high flow screamin eagle style (5/8" thicker one). It looses 3 hp at every rpm vs no filter ( both using the hd se backplate). If you think the air cleaner/filter you choose doesn't matter, you don't know what your talking about.
Cruiser
Joined: May 2011
Posts: 142
Likes: 0
From: Central Pa
The only way to know for sure is if someone posted some factual and confirmed data on the various types of AC's...until then it is all speculation IMO.
Last edited by Das_Fatboy; Apr 29, 2012 at 08:33 AM.
That is why we have charts along with our A/C systems.
The Twin Cam Outlaws will be on the site next week.
Here is a chart showing a TC with an Outlaw HiFlow 587 System compared to a stock system. Part of the increased in power/torque is the A/C , the other is NOT putting hot oil air into the intake.
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Elite HDF Member
Joined: Apr 2012
Posts: 4,474
Likes: 2
From: Puerto Rico
Open filter K&N is the best, airflow is everything. Now when you take and cover it up all you do let the engine heat become part of that cover such as the football HD is so fond of. Fresh cool air is what it's all about. Quite a few gonna argue that since looks are everything to them but that is the nitty gritty.
Tampa, my thought exactly, went with a Velociraptor, nuttin' but cold, fresh air, no piping the Crankcase vent back into the intake.
Road Warrior
Joined: Mar 2010
Posts: 1,900
Likes: 12
That is your speculation.
I have read several articles that mention how the stock enclosure acts like a jet ram with it forward facing intake, and up to 5000-5500 RPMs there was zero difference in performance over an open air cleaner. Also it blocks the heat from the engine.
Replace the stock filter with a K*N free flowing, and what's to say that it isn't as good as any other air/cleaner and cover.
Prove your statement.
I will research for the articles I have read to back my statements. I think they are bookmarked on another computer.
But on article said sometime this this effect. They replace the exhaust and gained 7 lbs torque and 4 HP. That was with the stock filter. They changed the stock filter, and only got 1lbs of torque and 2 HP. Not enough of a change to even feel. Then main gain was with the exhaust, but get this. The gain was way past where you ride. So it likely would be a wasted gain to the everyday rider.
Sure for drag racing those open cleaners are awesome, and for a HP built motor they work fine, but I am beginning to think that the Harley Tax is a bunch of bull. Leave the stock cleaner, and buy a set of slip-ons and go riding. But everyone is different, and to each their own.
Next brand new Harley I buy will probably be left 100% stock.
I like to see the super bad-*** Harley's. I just don't have a need/want to build one. Although a small Sporty bobber that is loud as hell and quick off the line could be in the future.
Last edited by editbrain; Apr 29, 2012 at 12:10 PM.
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That is your speculation.
I have read several articles that mention how the stock enclosure acts like a jet ram with it forward facing intake, and up to 5000-5500 RPMs there was zero difference in performance over an open air cleaner. Also it blocks the heat from the engine.
Replace the stock filter with a K*N free flowing, and what's to say that it isn't as good as any other air/cleaner and cover.
Prove your statement.
I will research for the articles I have read to back my statements. I think they are bookmarked on another computer.
But on article said sometime this this effect. They replace the exhaust and gained 7 lbs torque and 4 HP. That was with the stock filter. They changed the stock filter, and only got 1lbs of torque and 2 HP. Not enough of a change to even feel. Then main gain was with the exhaust, but get this. The gain was way past where you ride. So it likely would be a wasted gain to the everyday rider.
Sure for drag racing those open cleaners are awesome, and for a HP built motor they work fine, but I am beginning to think that the Harley Tax is a bunch of bull. Leave the stock cleaner, and buy a set of slip-ons and go riding. But everyone is different, and to each their own.
Next brand new Harley I buy will probably be left 100% stock.
I like to see the super bad-*** Harley's. I just don't have a need/want to build one. Although a small Sporty bobber that is loud as hell and quick off the line could be in the future.
I have read several articles that mention how the stock enclosure acts like a jet ram with it forward facing intake, and up to 5000-5500 RPMs there was zero difference in performance over an open air cleaner. Also it blocks the heat from the engine.
Replace the stock filter with a K*N free flowing, and what's to say that it isn't as good as any other air/cleaner and cover.
Prove your statement.
I will research for the articles I have read to back my statements. I think they are bookmarked on another computer.
But on article said sometime this this effect. They replace the exhaust and gained 7 lbs torque and 4 HP. That was with the stock filter. They changed the stock filter, and only got 1lbs of torque and 2 HP. Not enough of a change to even feel. Then main gain was with the exhaust, but get this. The gain was way past where you ride. So it likely would be a wasted gain to the everyday rider.
Sure for drag racing those open cleaners are awesome, and for a HP built motor they work fine, but I am beginning to think that the Harley Tax is a bunch of bull. Leave the stock cleaner, and buy a set of slip-ons and go riding. But everyone is different, and to each their own.
Next brand new Harley I buy will probably be left 100% stock.
I like to see the super bad-*** Harley's. I just don't have a need/want to build one. Although a small Sporty bobber that is loud as hell and quick off the line could be in the future.
There is absolutely no doubt that exhaust plays a big part, but when you look at the two charts below, you will see that a properly designed K&N air cleaner set up ALSO make a big difference in the power/torque IN THE MAIN RPM RANGE that most people ride in.
Bone stock a/c with modded exhaust
Outlaw HiFlow A/C System with modded exhaust
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