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Interesting post. If you are looking for maximum HP, the airbox has to go. Check any of the few Bonnie's built to race, I guarantee they aren't using the stock airbox.



Where are you going to use your Bonnie, on the street or for race?

On street use +/-1 or 2 hp at higher revs is less important than a good overall driveability.

Bonneville America/Speedmaster is not a race bike, just a cruiser.

When I'll see a detailed comparison between a good airbox mod and pods where the power delivery, overall performances and mileage between is far similar, I'll accept that the best intake mod also for street use on this bikes is only the airbox removal.

Experience teached me that maximum top HP is useless without a good power delivery. And frame/suspensions efficiency often are more important than engine top power.

Maybe between you and me (between Italy and USA) there's a far different phylosophy about motorcycle driving.
I want to invite you to visit me in my area, we'll go in that mountain's roads haunted by riders with sport bikes.

I can show you how a well tuned Ducati Monster 4valve engine with "only" 86bhp is able to outperform a Gixer 1000 with it's 140+ bhp on mountain roads.
Lower centre of gravity, smooth power delivery, hi quality suspensions. A well balanced bike on climbings and twisties is better than a bike where you have to fight against easy wheeling and where you can go fast only on straight roads or racing circuits.

What a Speedmaster/America was intended to be, is an overall good performer for nice short/mid range trips with the girlfriend and habby driving around the town.
The power delivery has to be maintained smooth, the torque higher at low/mid range, and an overall good mileage.

If your mods bocome too much radicals you have a strip racer, unusable on the road in everyday riding.

That's why on my and my friends's bikes I start modify only after have kept in mind how and where we are going to use the bikes.

A 3 litres airbox is enough for an 800-900cc engine. There's only to study how better open it cleaning the air using the better filter around.

Suspension setup is another matter to treat a part in a different room...