Managing Exhaust Volume for Track Use

[Trackaholic]

So, I signed up for a track day at Laguna Seca on Feb 26th with NCRC. They are a great group, relatively low maintenance, with typically a good group of drivers.

However, I'm pretty sure that I will not pass sound since it is a 90 dB day (as are most days at Laguna now).

I should be able to run 3 laps with the exhaust in "sport" mode for a sound check, then three laps in "normal" mode. I realize that even in "normal" mode the valves are open at WOT, so I doubt it will make much of a difference, but one can hope. At that point I will need to do something to improve the sound, and I was wondering if anyone had ideas.

Ideally, I would like to force the exhaust valves to be closed at all times, which would hopefully be sufficient. I like that plan because it doesn't add any parts, could potentially be very easy to set (pulling fuse, or something like that?), and doesn't really have a chance of coming off the car.

There are also many people who add "diverters" that direct the exaust away from the sound booth towards the inside of the track. Picture someone crudely attaching right-angle gutter tubes to the end of the exhaust. That method doesn't really change the sound, but might mask it sufficiently. It is sorta hokey and would be a PITA with four exits that aren't even fully attached to the pipes, but it's something.

Does anyone have additional thoughts or suggestions, preferences, etc?

-T

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[Hack]

I would be a little hesitant to disable the exhaust valves without a tune - or at least checking the tune. With the exhaust restricted the car might run a little rich and the cats could get hotter than normal. All speculation, of course.

If you want to race at LS and to pass the sound check, the way to do it is find a shop with a dyno willing to do this kind of work. Run it on the dyno and check the volume, then change the exhaust (and tune if necessary) in order to meet the sound spec. Yes, resonators (if you have to add some) will add some weight and restrict the breathing some, but adding weight at the middle bottom of the car is the least crappy position to have to do it. And being able to run LS and having a good setup with no worries would be worth it to me. Spend the money and have it be done right. If you find the change is too significant to the sound you could have the shop build something that can be swapped back and forth. Hopefully you are right and just turning off the factory valves in the exhaust will be sufficient.

 

[mattlqx]

Just keep the exhaust in "normal" and use half throttle past the sound tower or just "happen to" shift there every time in a meandery fashion. That should be enough. I did WOT in my Boss all the time past there with only the passenger side exit blocked and it was fine for 90db.

 

[RoadRacer]

I'd find a way to deactivate the "exhaust open" at WOT as you mentioned. Keep an eye on the temps until you better understand the effect it's having (or not) on the engine. This thing is loud at redline WOT and will be a problem at more tracks than LS I predict!!:headbonk:

 

[krt22]

I think you will have to lift or work on some fancy turn-downs like everyone else. From everything ive read the valves are tied to the throttle mapping so I dont think forcing them shut and maintaining WOT will be a good thing. I was both bummed and excited when I read the valves open on their own at WOT

 

[Trackaholic]

Thanks for the thoughts. I don't think I could get a reading at an exhaust shop without first having a baseline from the track to work against. I'm sure the measuring locations won't be the same between the track and the shop, but if I can get a correlation I'd know how much to drop the exhaust.

I did do some "testing" at lunch today, and MAYBE there was a slight difference in volume between quiet mode and loud mode at WOT (or maybe I just wanted there to be a difference).

-T

 

[C7 B8]

Sub'd.

 

[CoastHighway]

I'm signed up for that event also. I've had the same question, since I was thinking of trading my 2015 GT PP for at GT350.

 

[Hack]

Thanks for the thoughts. I don't think I could get a reading at an exhaust shop without first having a baseline from the track to work against. I'm sure the measuring locations won't be the same between the track and the shop, but if I can get a correlation I'd know how much to drop the exhaust.

I did do some "testing" at lunch today, and MAYBE there was a slight difference in volume between quiet mode and loud mode at WOT (or maybe I just wanted there to be a difference).

-T

You know the track has a requirement and you could use a measuring tool at the dyno to see where you are. Yes, the measurements may not be identical, but if you stand behind the car on the dyno and it's putting out 90 dB or less in that enclosed area, you will know you have nothing to worry about.

 

[84venom]

It's just a damn shame about all these sound restrictions at a RACE TRACK!!!! That's where you're supposed to be LOUD and FAST...

 

[Rick R]

Just keep the exhaust in "normal" and use half throttle past the sound tower or just "happen to" shift there every time in a meandery fashion.

Yeah that should work, people have been doing that.

 

[krt22]

You know the track has a requirement and you could use a measuring tool at the dyno to see where you are. Yes, the measurements may not be identical, but if you stand behind the car on the dyno and it's putting out 90 dB or less in that enclosed area, you will know you have nothing to worry about.

Its really not that easy. Passing sound at Laguna is a well sorted science at this point, some guys have custom electronic valves that are actuated via GPS so they don't need to worry about doing something funky while cruising past the tower.

 

[Hughespj47]

Lots of good info above. First you want to be as far away from their microphone - sound falls off as the square of the distance. If guys are using gutter parts, that might work and would be much simpler than tunes and electronics mods. Attaching it at 3 points to the exhaust pipe should work. Also, apply some kind of damping material to the outside surfaces of the gutter elbow, although it needs to be heat resistant. Secure the fasteners with a double nut or something. I know this is crude, but it just might work

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