Exhaust Silencing for NCM - LS Swap

My race car is dual 3" to center magnaflow high flow muffler to rear magnaflow high flow muffler. Even adding the second muffler in the back, still going to be too loud for NCM. To complicate matters, exhaust is currently down turn tips which means I would have to hack the tips to add two of the tailpipe silencers.

I see many of the silencers are just reduction in the size of the tailpipe hole/diameter. Wondering if an option would be to just fully plug one of the two exhaust ports? Would that be a problem in anyone's opinion? Or just get some flexipipe and two of those silencer cones and really redneck it up?

Hacking the tips would give you a lot more options to add silencing devices to the ends, if you want to do something temporary that's probably your best option. Just plugging a tip will make part of the exhaust act like a dead-end resonator, but with more flow than it should really get...it could be worth a try and isn't a terrible idea.

If it's not burning leaded fuel, you could add a performance catalytic converter. Note that I'm suggesting this only because they're decently effective at noise attenuation as well as their primary function: the environmental benefit for one track car is at best a very distant fringe benefit. Sure, there's a risk you'll melt it with bad tuning, but it might be the path of least resistance to get to the required noise level. I have one on my track car too, only because it was once a registered street car that had to pass emissions tests, and I have no motivation to cut it out and rework the pipes.

The 3" pipe size is awesome for flow and performance, but is definitely working against you for noise.

I had the same issue before time trial nationals last year. Luckily I had plenty of room to mount a giant muffler in the truck bed. 

Some people at Laguna Seca do some pretty ridiculous things to just route the noise away from the sound detectors.  This includes directionally angled pipes, Supertrapps on tailpipes, extra mufflers appended in really ugly ways just for the event, and so forth.  Magnaflows just kind of tend to be loud, but the only thing really likely to silence a dual 3" system is a pair of turbos (or huge, heavy, truck mufflers).

I did a dual 3" to a 2-1 Borla, and then single 3" into a 1-1 Borla at the end, and it's actually fairly quiet, probably definitely under 92db at a low scream, but I am of course losing precious top-end horsepowers.  

rustomatic said:

Some people at Laguna Seca do some pretty ridiculous things to just route the noise away from the sound detectors.  This includes directionally angled pipes, Supertrapps on tailpipes, extra mufflers appended in really ugly ways just for the event, and so forth.  Magnaflows just kind of tend to be loud, but the only thing really likely to silence a dual 3" system is a pair of turbos (or huge, heavy, truck mufflers).

I did a dual 3" to a 2-1 Borla, and then single 3" into a 1-1 Borla at the end, and it's actually fairly quiet, probably definitely under 92db at a low scream, but I am of course losing precious top-end horsepowers.  

Yea, I hate the idea of having to spend 140 per pipe to put supertrapps on. Thats what led to me considering sealing one outlet somehow. Then if its too loud, Just putting a supertrapp on the one remaining outlet? Otherwise putting a set of resonators or high flow cats on would be the same price. 

Supertrapps are available as a slip-on to a tip. They're fairly high restriction if you've got them clamped down for sound, but it's an easy and removable option. If you cut off your downturns, you could use band clamps* to switch between the Supertipp and your normal tips.

The only time I've done a 92 dB day at Laguna, I was failing sound for intake noise. So we just had a "short shift before 5" rule and that seemed to deal with it because we weren't going past the mic at 6500 rpm. Is that sort of behavior possible for NCM?

I'd do resonators before a cat if my goal was noise reduction.

*this one time, at band clamp...

Keith Tanner said:

*this one time, at band clamp...

Are you suggesting a flute would work in this application?

Lol - that escalated quickly.  

Do you have a spot to just add resonators?  They only cost you  weight.  I had stainless works add one to each rear pipe on caddy's dual 3" and it helped a great deal without killing the growl.  I have a couple unused three" stainless slip band clamps you could have for shipping cost if you go that direction.

84FSP said:

Lol - that escalated quickly.  

Do you have a spot to just add resonators?  They only cost you  weight.  I had stainless works add one to each rear pipe on caddy's dual 3" and it helped a great deal without killing the growl.  I have a couple unused three" stainless slip band clamps you could have for shipping cost if you go that direction.

My only concern with the resonator option is the potential they do not tame the dual 3" exhaust enough and I still have to add supertrapps. Also considering if I can find a "Quiet Muffler" option for the dual 3" setup and I could hot swap the magnaflow out depending on the track. 

May see what welding one of the two 3" tips shut does to the sound level since I have a welder and steel laying around. If that doesnt work, maybe some steel zip ties and stainless brillo pads? 

Is sound checked at fixed point? Lift?

The only time I was at NCM, they wouldn't say where the mics where. After you "blow sound" once, you only get one more attempt for the day. Fail twice = done for the day. 

Slippery said:

Is sound checked at fixed point? Lift?

I have done that and they were unappreciative to say the least :-). Just trying to play nice. 

Wait, nobody said it yet?

Rotary muffler!  Chinese spoli Boi!  Turbski!

WRC cars run a catalyst at the end of the tailpipe. Could that work?

kevinatfms said:

WRC cars run a catalyst at the end of the tailpipe. Could that work?

Something cheap/short like these?: https://www.amazon.com/Universal-Catalytic-Converter-410300-Stainless/dp/B06ZYHM84X

I pretty much live at NCM, the sound level is pretty high - it's not like Laguna - it's 102 db @ 50ft I think. Most cars pass, but a cold clear day can cause problems. 

Busby covers it pretty good here

https://www.corvetteblogger.com/2019/09/17/video-ncm-motorsports-park-matt-busby-talks-track-noise-limits-and-how-to-plan-accordingly/

accordionfolder said:

I pretty much live at NCM, the sound level is pretty high - it's not like Laguna - it's 102 db @ 50ft I think. Most cars pass, but a cold clear day can cause problems. 

Busby covers it pretty good here

https://www.corvetteblogger.com/2019/09/17/video-ncm-motorsports-park-matt-busby-talks-track-noise-limits-and-how-to-plan-accordingly/

Let's just say with one muffler, my car was the loudest thing at the track. Now with two mufflers, it sounds like more of a tie with the other loud vettes at the track so pretty sure they are still going to eyeball me. I was hoping the second muffler would tone it down to a non-modified vette but no dice. Really should add resonators, just didn't need another project :-(.

Just google "laguna seca exhaust"

In reply to DirtyBird222 :

I think NCM you want the turns sent the other way if some of the exhausts I've seen are to be trusted. Pointed towards the right of the car - though don't quote me on that, my memory sucks. 

Keith Tanner said:

Supertrapps are available as a slip-on to a tip. They're fairly high restriction if you've got them clamped down for sound, but it's an easy and removable option. If you cut off your downturns, you could use band clamps* to switch between the Supertipp and your normal tips.

The only time I've done a 92 dB day at Laguna, I was failing sound for intake noise. So we just had a "short shift before 5" rule and that seemed to deal with it because we weren't going past the mic at 6500 rpm. Is that sort of behavior possible for NCM?

I'd do resonators before a cat if my goal was noise reduction.

 

 

*this one time, at band clamp...

We've been dinged for our VTEC bwahhing too hard before too. Putting a heat shield box over the intake filter helped out a ton. 

In reply to Olemiss540 :

Yeah, corvettes have a bark for sure - My new-to-me supra passes sound easy with a 3" exhaust and a single resonator/muffler and for the driver - it's too loud IMO, I can't imagine driving something that doesn't pass sound for 1+ hour stints. 

Maybe you can drop it by an exhaust shop and have them slap a resonator in for fairly cheap? 

Sick of flirting with a DQ at every national event, I have two of these arriving tomorrow.  Not cheap, but I have been told they are almost too quiet.

https://www.borla.com/products/xr-1-raceline-400372

I was researching mufflers yesterday, and came across these:

Spintech

According to the site, the muffler linked is designed specifically for tracks with dB limits.

I've had Spintechs in the past, and they're a little on the heavy side, but sound good.

OK I am an idiot but we will see. Bought one of these on Amazon "used" for 60 bucks and some VBand clamps. Plan to use some 3" scrap pipe in the garage to get this mounted possibly backwards. 

https://www.amazon.com/dp/B001DR7VTC?psc=1&smid=A2L77EE7U53NWQ&ref_=chk_typ_imgToDp

Should be easy to swap on/off with the magnaflow for events like NCM, or maybe it will not suck too much power and I leave it on full time who knows.