The ground absorbs some of the sound. When the sound waves reflect off the ground, they reflect with a percentage of their original energy. Thus reducing sound..

 

There's a LOT of people that got it all wrong.

 

I would assume you'll be fine with what you've got there. I think the reason for pointing up is exactly as you say.

 

I'm trying to get my car quiet enough to run Sonoma and Laguna Seca. A very unscientific test (dB meter at side of road) shows I'm right around 93dB at full tilt, in 3rd gear.
While researching options, I came across a sprial-flow bullet muffler from Moroso that the GASS guys use to run at Sonoma. I'm also looking at two mufflers that have an offset inlet and centered outlet. Both are physically larger than my current straight-through Magnaflow using a L x W x H method. 617-681" vs the 616" of my Magnaflow.





I also have a 4" 90-degree bend to clamp onto the muffler for Laguna Seca, but if I can NOT use it, that would be greeeeat. Plus that wouldn't solve my problem at Sonoma.




I'm okay with loosing some power, running less boost, etc as long as I can pass without having to lift, worry, blah blah.




So, has anyone had success with any of these items?

 

I don't think you'll have a problem. I never got flagged with my HKS at 93db. I don't think you need the laguna pipe but bring it just in case.

 

Damn neighbors. If you don't want noise don't move into a neighborhood by a track. If you don't want 5 kinds of cancer, don't move next to a xyz plant.

 

Hard agree.

Also, 90dB is ridiculous. You literally couldn't take a lot of factory stock cars to that track day.

 

Which HKS exhaust? I am 99% sure mine is way over 93db at WOT. I have the HKS Ti, the one with the carbon muffler.

 

Even CHP allows 92dB 😂

I'm not certain I can make the 90dB without causing problems. I'm super paranoid about back pressure.

I believe Sonoma is kinder than LS, so I *think* I'll be okay there.

 

It all depends on where the sound check station is located.

Most track guys just run a "Laguna pipe" which will point in the opposite direction of the sound station

 

Allegedly, they have someone who occasionally roams the course with a portable. It hasn't been confirmed, so I dunno for sure.

Otherwise it's to the right of one of the turns, so my LS pipe should help with that one.

 

IIRC Sonoma is pretty hardcore and does have a guy with a sound meter going to random points on track.

Kaj,at what distance are you at 93dB? If that's at 10ft, it'll be much lower at 50ft.

 

I believe I googled the distance of the meter from the track at LS and placed the meter that distance from the side of the road. I then went by at WOT in 3rd gear. Definitely not a scientifically sound method, especially seeing that the mic at LS is actually aimed up the track, right at our exhaust.
Fun bit of trivia: ambient noise at the track with NO vehicles is already 53dB Also, in 2008, it was confirmed they had a roaming meter to catch people that would while passing the booth.

Sonoma seems to be 96dB, so I think I'll be okay there.

 

That's the exact one I was running. Never been flagged at Laguna, although I haven't run at Sonoma with that exhaust. Running a Tanabe Medallion now, much quieter.

 

How close are these guys getting to the track? The db level falls off pretty rapidly with distance, sound may only be a big issue with large straight-through exhaust systems.