Royal Wrenches Tech Notes

Stealth Air Horns

I like to make noise. Even better, I like to be heard when I toot the horns on the bike. The stock unit, and that wimpy meep … meep … what were they thinking?? Aftermarket horns are a popular item on the Royal, and I figured air horns were the only way to go. Never did like the look of em, but the sound is awesome.

So, where to put them ??


Picked up a set of STEBEL triple trumpets at Pep Boys for about $45. They come in chrome and different colors, but I went with black, figuring they’d be more or less invisible when mounted. Did a bit of head scratching, and finally figured out I could get away with mounting the compressor in the stock horn location, but I’d only have room for the two smaller trumpets tucked in behind the radiator and low on the frame. The kit only had a 3 foot piece of air tubing, so back to the store for a 6 footer.

WIRING ISSUES
Make sure you use the relay that comes with the horn kit and follow the instructions provided with the unit. You'll want to run the power leads directly back to the battery or to an auxiliary fuse box. In either case use the recommended fuse rating. These bikes use a floating ground, so grounding to the frame is not recommended.

COMPRESSOR ISSUES
The maximum compressor diameter for this mod is approximately 2 3/4" due to the size of the original chrome horn body. Some high performance compressors require oiling (look for a fill hole) and should be avoided.
Manufacturer's may recommend vertical mounting for the compressor to avoid ingesting water and contaminants, but horizontal mounting shouldn't be an issue as long as the mounting location is reasonably protected. Only caution about mounting location on my system was "try to shield from water spray and dust". Difficult proposition at best on a motorcycle, but I figure mounting it behind the engine case is probably one of the better locations available to protect it from all the crap ... I installed this system a coupla seasons ago and haven't had any problems.

A little tip from the FIAMM website: reverse the actuator wires on the compressor occasionally (suck vs blow) and drop a bit of light oil into the hose connector to lube the internals.

TRUMPET ISSUES
The maximum length for the trumpets is 8" to avoid clearance issues when changing the oil filter.

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COMPRESSOR INSTALLATION
The compressor tucked right into the hole left by removing the stock horn. Some 1” aluminum flat stock and my Dremel, and a bit later I had a custom mounting bracket that bolted to the compressor and the original horn mounting tabs on the Royal frame. It's fairly easy to hide the wiring to the compressor if you mounted the relay under the seat. So there I am looking at one butt ugly, but sturdily mounted compressor.

Removed the chrome cover from the stock horn and tossed the rest. Took the handy dandy Dremel set up with a cutoff wheel and gutted the interior ribs of the cover, leaving enough meat to grip the end of the compressor tightly. Smoothed the interior with a deburring tool, and covered it with Velcro. Cover the end of the compressor with the magic stuff, mate the pieces up, and Wahoo!, it was looking choice. Only other thing I did to bling it up a bit was add some peel and stick chrome tape to the outside of the compressor body. Never enough chrome, doncha know ...

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Here's the stock horn cover after gutting out the interior ribs. Be sure to leave enough meat to grip the end of the compressor.	A bit of care, and the cover was a tight snap fit. I ended up lining the Interior with Velcro as insurance.	The compressor tucks right in using the stock frame tabs, and you can see the Velcro on the end. Cut the end off the original horn connector and stretch the leads to where you located the relay. Best place is under the seat where it's protected from the elements, and that minimizes the length of the new hot leads from the relay to the battery.

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TRUMPET INSTALLATION
Made a coupla 3” long brackets for the trumpets using 1” aluminum flat stock. One horn to each frame rail, attached to the same mounting bolts used for the crash bars. It’s a tight fit, so I ended up bending a half inch offset into the brackets to clear the bolt ends. Mounted up the horns, adjusted them to the correct angle, tightened em up. Installed the air tubing, capped off the extra nipple for the unused large trumpet, and ran the air tubing back to the compressor. Tied it up along the inside of the lower frame rail with nylon ties to keep everything neet, and the job is done! Stuck the key in the ignition, then hit the horn button. Did you know you can wire a compressor up to suck instead of blow? Interesting sound, but not all that effective. Reversed the wires, hit the button again, and knew the project was a reSOUNDing success once my ears stopped ringing.

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And the results. The trumpets tuck in nice and tight and are darn near invisible. Mounted right up front, they definitely sound off. And would you believe, I can still change the oil filter without having to rip anything apart?	Air horns? What air horns?? I have fun at meets challenging people to find them. You gotta be up close and personal to see the compressor body.