If you want train horn kits to be over 150 dBa, listen to these tips. Train horn kits get its sound from interlocking waves within the trumpets. One popular method to make your train horn louder is to increase the valve openings within the horn itself. Watch out, you want a professional to take apart your horn and increase the size, if you do it yourself you may ruin your expensive horn and be forced to throw it away. Another technique is to enlarge the opening of the trumpet. You will need to soften the metal and make sure you keep the tips round like the original. Bobby got me into buying train horn kits for my truck. He said air horns will keep my truck safe because I can hook it up to a car alarm. I own an expensive stereo set up and other gadgets, so security is a top priority for my truck. I picked up an air horn kit at a local aftermarket store after work yesterday, and then asked my mechanic friend to install it. The total cost was a bit over $400, something I don't have a problem paying for if it keep my investments safe and sound. The loud sound isn't too bad either.