What is a good DB sound level?

[Excaliber]

I recently took a sound meter to measure DB's at a local auto cross here. Many tracks DO have a DB limit, which seems to vary with the day of the week, time of the day and the particular event. Some tracks are more strict than others. The DB requirement seems to vary from 99 to 103 or so. I would ASSUME they all take the measurements at about 50 feet? Typically at a turn on the track somewhere. So, if you know what turn and where the sound meter is you could adjust throttle opening or turn your side pipe exit port to face away. Some car's do have an adjustable exit tip on the sidepipe specifically for this purpose. I may modify my side pipes in such a way.

Where was I? Oh yeah, so I took some DB readings at the START line as well as a straight section "at speed". The start line was consistently higher DB. Plenty cars exceeding 103 DB on the start, 105, 106. Surprisingly "at speed" showed a significant drop in DB, 5 to 10 points.

My ERA idles at 106 as read from the cockpit with me sitting in the drivers seat. I ALWAYS wear ear plugs, everytime, even for a short trip. I already wear two hearing aids, I'm just trying to save what I got left.

Because this is becoming more and more of an issue (in particular California) there are some ongoing studies as to what works and what doesn't. Glass packs don't work, period (that would essentially be side pipes). Borla and many other after market exahust systems don't work. The list of systems that don't work is long, the list of systems that do work is short. On the short list is Spiral Turbo inserts.

When I was talking to the Spiral Turbo folks and told them I had an FE, I could hear them groan. Apparently the FE engines are among the toughest to get the DB down on.

http://www.spiralturbobaffles.com/index.html

[Hotfingrs]

I think it was 2003 when STB did their prototype for the Cobra on my car. They were the ones that measured my db at 104 at idle. After install of their product my db went down to 97 or 98, so they will quiet your car. On a side note, I lost a second and a half and 16 mph in the quarter. Needless to say, they are sitting on my shelf.

[Excaliber]

Prototype may be the key word there Jack.

Toms Motorsports have been running their small block FFR with spirals (no choice as per required DB levels at some tracks) and have met with some pretty good results in reducing DB without loosing much HP.

I loose close to a 100 horse with my STOCK side pipes all ready. Of course the bigger the engine, the more flow of cfm, in and out, the more significant the loss will be. A big inch engine is going to be hard to handle no matter what you do. I'm pretty sure I would lose less and be quiter with spirals.

[Hotfingrs]

You're probably right Ernie, everything is going to be a trade off. Quieter, more hp loss, some performance loss. Open exhaust, quite loud, and zero performance loss. Now you just have to find a place in between that you can live with.... You've already found out that losing a couple hundred horses, didn't cost you that much in the quarter... and you have a street friendly engine now.

[undy]

I dumped the spirals after suffering massive HP losses. i'm running 3" ID pipes now. They're a bit louder than the spirals but I picked up 50 RWHP. The flow's still crappy though.

[Rare Iron]

Originally Posted by undy

I dumped the spirals after suffering massive HP losses. i'm running 3" ID pipes now. They're a bit louder than the spirals but I picked up 50 RWHP. The flow's still crappy though.

Dave, you are really up there in HP correct? The Cobrapacks you are running now are as good as you are going to get as far as flow - with a 4" OD muffler body. As I recall, your HP is enough so that you could be running 4" flowpath mufflers....... This would then require you to have a 4" min. diameter in your merge collector. Hey look at it this way - you gained a lot by going with mine & still some noise control. You could run zoomies through the hood??

[undy]

Rare, I'm very pleased with the Cobrapacks. I didn't mean to hint that I wasn't happy with them.

It's just the Cobra's side exhaust as a package flows like poop. Under the car exhaust seems to do much better as a rule (at least with other vehicles). The Z06 repeatedly only loses 11% from rated FWHP to RWHP. My slightly modded Z06 is "supposed" to develop 20 to 30 less FWHP than my Cobra yet it's RWHP is about 25 more... go figure. I honestly think we see a lot of inflated ratings for our builders in relation to "real deal" HP numbers. It seems to be more about sales and the associated bragging rights.