[Rodan]

Originally Posted by BDivine76

I may have missed this...sorry if I did, but at what distance are they measuring SPL?

Every track seems to be different at this point.

[sv340]

I can say that SCCA is 50' from the track. I was in Fontana and blew over, pulling from Idaho to So. Cal. to go home early was not an option. They had a 100 db limit and I was 102. I was able to build some "burritos" out of chicken wire and create a baffle system that allowed me to continue to compete. The chicken wire is rolled up like a burrito and wired in place, I also tied the valves shut. This was for autocross, not road racing. I am running Kooks with no Cats and factory exhaust.

[GunMetalGrey]

Originally Posted by BDivine76

I may have missed this...sorry if I did, but at what distance are they measuring SPL? Sound follows the inverse square law (double the distance and get a 6dB drop in SPL). This is true from 1ft to 2ft, 2ft to 4ft, etc. Distance will have a huge impact so I am just wondering what the reference point is.

I've been looking into this because of the new fine structure in CA, but here the distance is 19.5 inches from the exhaust...extremely tough. I did a quick down and dirty (Borla ATAK axle back) and saw 89dB at idle and 94.5 @ 2500 rpm. This was not with a calibrated mic however...so it could be off.

Just wondering what they are doing at tracks as I plan to do a few events this spring/summer.

Please clarify, do you have the Borla Atak axle back on your ZL1?

Borla told me their Atak Cat Back is rated at 105Dba at WOT

[Rodan]

Update on the 'Laguna pipe' project...

I finished welding the bends, and this is where things ended up:



The bends fit snugly in the stock tips, but I still wanted some bracketry to hold them in place securely for track work. I decided that I wanted to do some testing before I got into that.

I downloaded a decibel meter app to my cell phone, and we went out to do some drivebys. I have enough experience with cell phone dB apps to know the absolute numbers are not all that reliable, but I was mostly interested in the back to back delta. Measurements were taken from 50' at a 90* angle to the car's path.

The good news is my laguna pipes changed the exhaust by 1.5dB.

The bad news is they made it louder...

My wife said it was noticeably louder with the laguna pipes installed. Back to the drawing board...

Something of note... three 5-70mph runs back to back got the pipes too hot to hold with Mechanix gloves on... there is a LOT of heat being transmitted through this exhaust system. I can easily see how running in stealth mode on track caused the catastrophic damage posted earlier.

[BDivine76]

Originally Posted by GunMetalGrey

Please clarify, do you have the Borla Atak axle back on your ZL1?

Borla told me their Atak Cat Back is rated at 105Dba at WOT

Yes, Borla ATAK axle back. All other parts of the exhaust are stock. Does Borla mention the distance of their measurement by any chance (I looked on their site, but I didn't see it)? From that info I can get a pretty good sense of where I will have issues based on extrapolating. I didn't post this in my original comment, but I did Rev the engine to about 4K and it was just under 105 at about 20 inches so their published number seems close

[dlct3]

Update -Data Taken

See pics for conditions. Moving in the right direction though!! From here we’ll fabricate a short straight through muffler via Vband for adjustability and weld on a 90degree laguna pipe with approx 6-7” leg. Wrap the entire muffler and maybe the Laguna Pipe to the tip in header wrap. I’m hoping to decrease the set up another 4-5dB. Target range is 101 max.

Net result- 4 dB decrease
Test pipes were 3" mandrel 90 degree long radius with 3" & 9" leg lengths installed at approx. 45 degree angle in opposite direction of sound meter.

[Rodan]

Interesting.

Were the measurements all taken from the passenger side (ie, with the pipes pointing away)?

[dlct3]

Originally Posted by Rodan

Interesting.

Were the measurements all taken from the passenger side (ie, with the pipes pointing away)?

That is correct when the Laguna pipes were installed.

The 1 slight downhill run that didn't have the Laguna pipes installed was taken at about 53' in the other lane. That run netted a max of 106.6dB which was about 2.2dB lower due to increased distance and not as much load I believe. (I'm talking a "slight" downhill or uphill going the other direction like what some tracks will have coming out of a curve)

[dlct3]

Originally Posted by Rodan

Update on the 'Laguna pipe' project...

I finished welding the bends, and this is where things ended up:

The bends fit snugly in the stock tips, but I still wanted some bracketry to hold them in place securely for track work. I decided that I wanted to do some testing before I got into that.

I downloaded a decibel meter app to my cell phone, and we went out to do some drivebys. I have enough experience with cell phone dB apps to know the absolute numbers are not all that reliable, but I was mostly interested in the back to back delta. Measurements were taken from 50' at a 90* angle to the car's path.

The good news is my laguna pipes changed the exhaust by 1.5dB.

The bad news is they made it louder...

My wife said it was noticeably louder with the laguna pipes installed. Back to the drawing board...

Something of note... three 5-70mph runs back to back got the pipes too hot to hold with Mechanix gloves on... there is a LOT of heat being transmitted through this exhaust system. I can easily see how running in stealth mode on track caused the catastrophic damage posted earlier.

Rodan,

Thanks for the feedback! I'm no acoustical engineer, but I wonder if the reason your db increased was because they were pointing straight up instead of away at an angle? I also wonder how accurate the cell phone app is? Not knocking you for trying...just curious. Personally I could notice the decrease immediately in the cabin with them installed. So much I knew I'd know if one or both of them were to fall out during "testing" I asked Shane if he could tell a difference in sound when I went by and he said it sounded the same, just not as loud.

Keep us posted on your progress.

[Rodan]

I'm sure the straight up orientation was the reason for the increase. Unfortunately, our track has sound meters on both sides, so pointing them 'away' isn't an option.

I didn't post the actual numbers from the cell phone app, because I don't believe them to be accurate, but they were in the 108-110dB range. I do think the app was useful in showing the delta, however and it was pretty consistent at a 1.5dB increase with the pipes. I'm not all that concerned with specific numbers, as my wife stated it was clearly louder with the pipes in, and reported a slight increase in pitch. I know that a stock ZL1 won't pass sound at our track, so an increase is a definite fail.

My testing was done in both directions on level ground at full throttle, 50-70mph. My wife was standing at a measured 50ft, perpendicular to the car's path.

[dlct3]

Sorry for delay. However, we were finally able to modify and build a removable laguna pipe muffler system thats adjustable for any direction via the 2.5” vibrant vband. The whole setup is fairly lightweight at just under 8lbs. The fulcrum point is right next to an exhaust hanger for strength. We were able to achieve a lot lower DB level than expected especially on another fully built ZL1 with corsa extreme that we utilized Magnaflows 2.5” straight through 5” case. I wasn’t able to test at 50’ yet, but at idle the dB dropped approx 6db. On the highway under power I’m thinking the drop is just as much if not more than 10db.

Items used
Magnaflow Stainless 2.5” straight through design 14” long 4”case-ends cut down
2.5” 90 degree stainless mandrel with 12” leg and 3.5” medium radious
2.5” vibrant vband
1 extra vibrant Male vband for the stock tip
DEI titanium header wrap & stainless zip ties

I’ll update once I can head back to the same test location for an accurate DB check. However, I’m not concerned about being over 109 now.

*5” case used on the red ZLE as we had more room since we connected from the exit of the corsa muffler extreme system with headers, higher boost, no cats, and double x-pipe extreme system. That car’s idle lowered from 103 to 81.4 from 5’ away and 4,000 rpm revs very similar drop.

*disclaimer.. first time mig welding stainless and setting up the welder.. don’t criticize too hard.

[Rodan]

Looks good!

I'm very interested to hear the numbers on the stock muffler car.

I've been wondering if there's room for those resonators under the car somewhere? Something like the Borla 60608, but in 3"... Added to an otherwise stock exhaust, it might be enough to get under 95dB.

[HoldMyBeer]

question, and this may have already been asked, and will decrease your HP a small amount, but what about putting your car in 'Stealth' mode? When I put mine in stealth mode my valves dont seem to open and car quiet.

[Rodan]

You can't use stealth mode on track.