Originally Posted by spearfish25

Stillin CBE w/ stock exhaust on (A weighting) was 78 db
Stillin CBE w/ ERZ HFC on (A weighting) was 88 db
Stillin CBE w/ stock exhaust on (C weighting) was 85 db
Stillin CBE w/ ERZ HFC on (C weighting) was ?? db (have to measure it)

Please note that these are peak levels which were obtained for a split second under WOT acceleration with the windows closed. Routine driving gives readings in the high 60s or low 70s for all of these setups. The HFC with CBE combo is as quiet as the CBE alone when cruising.

While the idea of C weighting seems like the best measure, practical experience seems like it's not accurate. C weighting supposedly measures frequencies below 500Hz which A weighting does not measure. However, just driving along on the highway with a quiet engine gives a reading in the 80s for C weighting. Thus, I don't think it works well for car dB levels. I'd focus on the A weighting levels for the best representation of loudness.

I absolutely love the HFC addition to the Stillen. The loudness is now right where I like it...not too loud, but definitely can turn a head if you drop the hammer. No drone at all and rasp is very tolerable once things have warmed up to operating temperature.

Hope this helps. I know I was on the fence for a long time worrying things would be too over-the-top. I'm glad I gave it a shot.