Noise: or, put a muffler on that thing, buddy. (Page 2 of 3)

Mike,

Maybe it was just me, but I thought Scrubby was quite a bit louder on Saturday than previous races.  But then it seemed to quiet down a bit either Saturday afternoon or on Sunday.  I'm guessing that was after you made a change to the exhaust.

All that to say that, despite being the same exhaust, it was definitely making more dBs on Saturday.

-Mike

Perennial Losers
Mazda 787b aka '75 914 - Org Choice @ The Ridge, 2015; IGS @ TH, 2018
BMW M1 Procar aka '80 RX-7 (retired) - Zero awards

Noise was our main problem this race. We've got short headers to a 3" pipe to a single 3" glasspack. That used to be enough, but that was installed 8 races before. From what I hear the glasspacks will blow out after a while (and we just though our car sounded more awesome). Our car dumps out the passenger side just ahead of the rear tire, so while you can barely hear it at the Buttonwillow front straight, it's singing the song of its people while it circles the paddock on the back and front straight. All our fixes were hokey, and mostly worked, but for the next race we'll actually install a real muffler.
I don't think the steel wool we packed in there is a permanent fix....

E: Mike you should have asked John what they were measuring you at. We were told 104, so we knew we had to make some serious changes.

I think Mike's request is pretty reasonable. It is very helpful to know just how bad you are to judge the effort needed for a fix.

It would also be nice if they kept a log of cars near the limit... I'd like to know if we're at 91.9dB

They do this at Laguna Seca where all the rich idiots moved next to a racetrack and then complained about the noise.

The Festiva failed tech for loud exhaust (among other things) at MSR.  The tech inspector (Evil John, was that you? I don't know all the Lemons people) said our car was "probably too loud" and warned us we may have to quiet it.  This was not terribly helpful, because I have no idea what 92dB sounds like, so I asked if smartphone apps were anywhere near accurate enough, since I had a couple.  He said he had a sound meter that they'd be using during the race to check.  Well, that's also not useful, since I wanted to make sure we didn't have to fix it during the race, so I pressed on how we could check beforehand.  The inspector offered to measure right then and there, and I figured better to fail now than fail on track, so he got the meter and measured 116dB at the tailpipe (like, right behind the car).

We got a performance muffler from Autozone or wherever, put it on, the inspector took one look at it and said "I'm sure that's quiet enough" and didn't need to measure it a second time.  Even after it exploded on track, we didn't get flagged.

So my advice to racers is: check before tech.  Even a smartphone app is better than nothing, and should at least get you a ballpark reading.  Have a plan to replace if necessary.  Even the HP loss from a stock muffler probably costs less time than a mid-race black flag to replace a loud exhaust.

And my humble advice to tech inspectors is: offer to check the cars with loud exhaust at tech.  You're doing us a helpful service if you let us know before green flag that it has to be fixed.  "If you have to ask, it's too loud" means nothing to someone like me who thinks all race cars are loud, and who has no idea where 92dB falls on the loudness scale.  It never occurred to me our car was too loud, and it was WAY over the limit.

Also, the other reasons we failed tech were all for items that have passed half a dozen other tech inspections, and the inspector made some subtly disparaging remarks regarding tech inspections in other parts of the country.  He wasn't being a jerk - just blunt, and helpfully suggested how we could fix all our problems.  So racers, be on notice you may fail tech even though you've passed umpteen dozen times.  Get in line early!

There's no way to get a fully accurate check of the exhaust noise at the tech inspection, even with a decibel-meter, because the car needs to be at full throttle under load. I suppose we could do it if we had a dyno handy, but otherwise all we can do is guess until the car gets on the track.

What Erik doesn't know is that we had attacked the noise problem before the race with an iPhone app with the motor at WOT in the driveway. Prior to the at-track modification, we were running a muffler and two resonators. My pre-race testing at home had us under 92dB at 50 feet at WOT, which is the noise limit per the rules. Apparently different atmospheric conditions make a big difference in how sound carries.

My takeaway from this is that you need to get your sound well below the established limit if you do not want to get dinged DURING THE RACE for an exhaust, since apparently there will not be pre-race testing of exhaust volume.

Yeah, a good rule of thumb is: if it's loud, put a real muffler on it.  It's not that hard to do.

I've been contemplating this since New Jersey, I need to know what yinz guys think about the Gremlin? Is it too loud, should I make it quieter? It's not as easy as it has 6 exhaust pipes, each has it's own glasspack style muffler.

We tested our cars to about 20' with the smart phone app, finding our cars to pass the 92db even there, full throttle and wound up under load. Consequently, people were commenting on the fact that our cars were so quiet that they can barely hear them.

Testing in a driveway won't nessesarily tell the whole story. Sound levels change with engine load as well as throttle position. So even if you're under in the driveway at WOT, you might not be under load.

Thankfully our car is quiet.

can we run exhaust like that ? That would be awesome!

no it looks like a cherry bomb but thrush makes it.