Started my 2011 season this past Saturday.

[S0C0nFused]

150ft? Wow! well then, A turn up should work....one exception. Avoid walls or anything that the sound can 'bounce' against. I.E. move the car as far as possible (if possible) into open area. Also, I should point out that this does little for 'pops' or backfires. There just to multi-frequency to control. Also only works as I have said for upper-midrange and higher. But your only 15db off so I would think it should do it.
add >> it is assumed, but it bears mentioning. you don't want anything that mimics a flare for all the obvious reasons.You want to keep the exit speed of the gases high and directional (gas velocity affects sound pressure waves).