I am planning to go with just a stage 1 once my warranty has expired on my '18 Slim. If all that I am doing in going to a stage 1 is it worth getting an extreme-flow ac over a high-flow ac (as described by HD in their SE parts)?

 

I wouldn't. The stock cams and heads will not outflow what the basic stage one can provide. Get into high lift cams. Ported big valve heads then you will need the extra flow.

 

Which SE were you looking at ? was it this guyhttps://www.harley-davidson.com/stor...ow-air-cleaner It flows quite well ,air acts like water and doesn't like to go around bends ,this fiter has a straight run at the TB , if you build the bike up a little you'll have enough flow from that one as well.

Peace.

 

Not worth it until you start building the engine, just stage one don't waste your money.

 

Here is a graph of a Stage1 after a dyno tune and it's quite remarkable. There are gains but they cost a motsa, worth it if you're staying at that level,not so much if you go further.

Peace.

 

I have a dyno chart of 4 different high flow air cleaners on a Stage 1 bike. Wish I could figure out how to post it here but I can't. 2 of the 4 air filters are the HD high flow and extreme. Bottom line is the dyno runs are more or less on top of each other. So no, there is nothing to gain. Best to worst there was a 1.5hp gain at high rpms.

 

Extreme flow sounds faster. Especially if black.

 

Depending on the model and your stature, you may find leg clearance an issue. For me, the air cleaner sits right where my knee goes, so I chose a SE ventilator since it has a lower profile.