K&N Air Filters

[Conabear]

I've been looking at the K&N high-flow Air Filter kits for my FLSTF 2009 Fatboy. K&N has two types listed, the RK-3909 and the RK-3910. What are the differences between the two other than the HP gain and the height? I guess I want to know which one would be better. Mitch

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[DMJFatboy]

I think one is oval shaped and the other is round. I have the round one but don't know the model number. All I know about the k&n filters is that they are better than Harleys SE filters.

[oct1949]

The (HD) SE K&N is different from the Lifetime K&N filter.

Don't have the no's in front of me, at my 15k service got a call that the rubber backing on the HD, SE K&N was bad. Asked about the warranty & was told that the HD, SE K&N is not the same as K&N's LIFEtime filter... $35 vs $50..

The HD one is washable, there was a recall in 08, the 07's were defective. They had both and Finally let me pay the $15 diff and got real K&N.

[tk353]

i would guess the rk-3009 is for 09 and the rk-3010 is for the 2010 year

[Belfast_tmy]

Straight from K & N's site:

"The RK-3910 comes with a larger air filter and longer spacers than the RK-3909."

I run the RK-3909 on my 07 FatBoy.

[DragonSlayer08]

Originally Posted by Conabear

I've been looking at the K&N high-flow Air Filter kits for my FLSTF 2009 Fatboy. K&N has two types listed, the RK-3909 and the RK-3910. What are the differences between the two other than the HP gain and the height? I guess I want to know which one would be better.

Mitch

The following is from the K&N website regarding the two filters:

"The latest addition to K&N's RK Series was developed to get more horsepower from your Twin Cam® Harley-Davidson® engine. Built around the legendary K&N High-Flow Air Filter, the new RK Series assembly includes an innovative powder coated billet aluminum backplate that eliminates external breathers and features a built-in, dyno-tuned velocity stack. The result is a significant airflow increase to the engine without sacrificing filtration. This RK Series assembly retains a factory appearance by utilizing the stock air cleaner cover. The RK-3910 comes with a larger air filter and longer spacers than the RK-3909."

RK-3909 Specs:
Product Style: Custom Assemblies
Estimated Horsepower Gain: 7 HP @ 5000 RPM
Replacement Filter: E-3014
CARB EO Number: D-269-33
Weight: 3.4 lb (1.6 kg)

2009 HARLEY DAVIDSON FLSTF FAT BOY 1584 - 1-5/8 in tall filter
CARB Exempt: No



RK-3910 Specs:
Product Style: Custom Assemblies
Estimated Horsepower Gain: 12.05 HP @ 5000 RPM
Replacement Filter: E-3037
Weight: 3.7 lb (1.7 kg)

2009 HARLEY DAVIDSON FLSTF FAT BOY 1584 - 2-1/4 in tall filter
CARB Exempt: No



Given the information listed it appears that the only differences are height and HP gain, which appears to be 5.05 with the RK-3910.