Bonneville America Forums Forums Technical Forums Performance Mods Added bellmouth today

I had ordered the Norman Hyde bellmouth for my airbox from Brent and it came today. I'm not sure how much benefit it will be over just the open stock plastic lid, but it sure looks cool - like it was supposed to be that way. It also comes with a precut partition that fits on the frame behind the airbox intake to prevent rain from blowing in. I suppose no one but me will see it - sorta like sexy boxer shorts. My bike may feel more macho now.

While ordering I also bought the LED brighter dash light kit which does make a major difference. I can see the neutral light in bright sunlight.

Curious to see if there is any performance benefit over the standard "snorkel removal". Keep us posted.

I like the looks of the Bellmouth as well and have been contemplating picking one up. It just sucks that I will be the only only one that gets to see it!

Bob, it's been a while - what say you? Bellmouth better, worse, break even? For 150 clams it ought to sing Free Bird....

I think the improvement is slight but noticeable. I assume it increases the efficiency and ability to draw in air as needed. I've put about a 1000 miles on it. One thing I have noticed is that it seems to eliminate the effect of crosswinds cutting down the airflow.

It may just be a very small improvement, but I intend to keep my airbox and the bellmouth finishes it off. I like having the airbox and this makes it more like it should have been designed to begin with. It also comes with a stick on piece that goes behind the bellmouth (toward the rear wheel) that blocks any water that might get through. All in all, the cost of a UNI filter, removing the snorkels, and adding the bellmouth is not very expensive opposed to installing airbox alternatives and very simple to do. If someone did all three of those things at once, then they would go wow! that's an improvement.

I may try going up one size on the mains from 125 to 128 and see what it does to my top end. I would rather be under than over on the mains, but I was already on the edge and now might should go up one.

Thanks for the update Bob. I think I'm going to open up my filter retainer piece (Part the belmouth attaches too) to increase the intake size. Some fellows posted some nice pics of the trim jobs they performed.

I also think you should increase your mains. Mine might be a tad large at 135 and I'm thinking 132 might be a better size.

Greg, I'm not so sure. You can up mains and lose mid range performance. I can't agrue with the results I've gotten. I've done lots of dyno runs. BUT, I would try adding the Bellmouth before making any airbox modifications. The Bellmouth replaces the entire top piece of the airbox that originally held the snorkel.

Sorry Bob, Might have misled you. To clarify, I intend on modifying the top piece that held the snorkel only.
I wish we had a dyno here. Hate guessing on jet sizes.

By the way, I've seen various discussions about adding Norman Hyde Bellmouth, or hacking a Polaris snowmobile intake (cut in half) that apparently fits. I noticed on BikeBandit.com they have very nice section of OEM parts by schematic. Under America, they have "Airbox"... and you can apparently order the "Air Intake Cover" only, for $6.18. This should be the cover with the 3 screws to hold down the air filter, but with the air intake "nozzle" that sticks up, and hopefully also the long "pipe" that runs down inside (or that can easily be cut off). This way you can put a cheap "bellomouth" on while still retaining the stock setup in case ever needed.

I'll order and see what I get.

http://www.bikebandit.com/triumph-motorcycle-america-2008-air-box/o/m17668sch570120

NorCal Chuckles

After putting more miles on the bike with the Norman Hyde Bellmouth, I felt an update was in order. I've readjusted the carbs a bit and there is a noticeable performance increase over just removing the snorkel. It's probably more of a change than pulling the snorkel was.

One other thing I didn't mention before - It also makes the engine louder. Not in a bad way, but more like a racing engine way. It's sorta like when I was a kid I took the air cleaner off my Mom's Chevy 327 and ran it on a country road. If you've done that, you know what kind of louder I mean. The engine actually sounds like it is breathing better - definitely more so than just removing the snorkel.

Later this year I plan to put the bike back on the dyno to check tuning. I'll see then what changes I need to make. I'll see if a main jet increase is in order. I just repacked the pipe baffles to tone it down a bit and plan to add another layer. Sounds quite mean now when you open it up.

The classics and the America/Speedmaster air boxes are different. The filters are different sizes and the covers are different.

Thanks.