I've heard different stories about this. I have some FM 4" Dyno Tuned slip on's ordered for my 11' should I upgrade the whole AC or just the filter for now? (Cat still in)

 

I'd replace the air filter and back plate with a stage one set up. Be ready for some remap of the ECM....

 

you need to replace the back plate as well because that's where some of the restriction comes into play.

Stage 1 A/C at the least from HD.. if you want to spend more $, then there are plenty of others.

 

Unless you have a tuner for your bike then I would just upgrade to like a K&N filter. If you put on a hi flow AC then it will probably open things up enough that your current tune may run you a little lean. If you ever de-catted your bike then I would for sure consider getting a tuner for it so you can get it dialed in with your upgrades.

 

That is really more of a personal preference. If you are wanting to do a stage 1 upgrade, then you will want to replace the whole Air Cleaner with a non restrictive aftermarket. You can really do either that you want to do. In truth, it would be better if you changed the Air Cleaner to a non restrictive.

Almost all aftermarket A/C will flow more air than even a Stage III 103 can eat...notable exception is the HyperCharger.

However, there is more to how much air an A/C will flow.

Internal Combustion engines run best on cool dry air.

Most aftermarket, (and all street legal), A/C's feed hot oily air into the air filter.

This compromises performance and also contributes to carbon deposits on the pistons (which can bring a whole other batch of problems down the road, especially with the 103's)
There are only a few companies making true performance Stage 1 intakes anymore.

DK Custom
NRHS
Hammer

I don't know of any others.

Here is a video of our Air Cleaners if that is a route that you decide to take.

 

I don't see that a change of air filter element will have any benefit. The airbox is actually a silencer, designed primarily to reduce noise levels, so replacing the backplate with say an SE one, will provide improved air flow and also increase induction noise.

 

... and for the budget minded ( me) the ness big sucker ( chrome version) can be at your door for about $120 (check easternpc thru ebay)
Like the screaming eagle the ness has an air horn to order the air to the airtake, this is better than a 90º turn from flat backing plate to the intake

advantages over the screaming eagle:

easier install, the throttle brace and tank can stay in place ( mask the tank incase your wrench slips)

chrome backing plate complements the motor ( vs cast grey)

reusable washable oiled filter media

I see from your posts that you are trying to work through a stage 1.
once you open up the intake with a high flow air cleaner, and remove the cat ( as you mention in other post) you will certainly need tuning compensation- many of us use the nightrider.com Xieds/ Vieds to good result...and about $130
the budget minded- non complicated approach.

the ness and the screaming eagle both reuse the stock air cleaner cover- this conceals a very ugly plug and wiring on the TBW harley intake ( at about 8 o'clock as you look at it) which is a +


mike

 

The throttle body is the primary restrictive factor on the intake end (unless you have an air filter so dirty that hardly any air moves through it).

Even the stock air box and filter will usually flow more air then what the body and intake throats can pull through.

Do what suits your fancy with respect to the air box and filter.

 

the Evo air cleaner was good for about 140 CFM....the twin cam probably about the same ( excepting the 14).


Our pals at hot bike did some great air cleaner comparos back then, and a carb with no air cleaner was only able to pull about 110 CFM without an air cleaner to order the air.
a cupped hand held at the carb throat came in at about 125 CFM...the Hype at about 155CFM and the S/E and Ness about 260 CFM.
Winner was the Zipper's velocity stack at just under 400.

the last 3 having more flow potential than the motor.

mike

 

Exactly, the restriction is probably from the small intake slot in the airbox, not the filter. I just finished reading a article by Joe Minton (in AIM) where he installed a set of SE slip-on's and SE airbox kit on a stock 2009 FXD. The bike adjusted itself for the changes and ran great gaining something like 6hp, 4 from the intake, 2 from the exhaust. He said it also gained a good bit of noise. The hp gain didn't begin until 3,500 and gradually reached the full 6hp by 5,000.