Just got a db noise meter......

[AirCooledExcellence]

Hi All,

Just hired a noise meter, tested my SC with SSI's and (what I think is!) a dansk 2 in 1 out.

I Tested it running at about 4700RPM (3/4 of max revs) at half meter distance at a 45 degree angle from the tail-pipe, and got a maximum reading of 107.2DB!!, WTF is going on? have I tested it wrong?

Most tracks in the UK seem to have a 102DB limit!

Looks like I may have to get a quieter muffler!

Cheers,

[cstreit]

Many tracks around here have a similar noise limit. THe measurements are usually taken from 30-50 feet away. (That's 10-15 meters for you UK guys).

I have an equal length exhaust header with straight back pipes and pass at 103-104 db

If it's really a concern, call the tracks and ask them the distance the db level is measured and what the incidence angle of the measuring device is relative to the cars travel to get an accurate reading.

[AirCooledExcellence]

Chris,

I've just got her really warmed up nicely and re-tested at 104DB.

The folks at www.bookatrack.com told me to do the test 0.5 meters from the tailpipe, and the nearest track to me also specifies 0.5 meters!!

Cheers,

[Joe Bob]

At least on my Db meter...
The default scale is C, try resetting it to "A" scale....C is for music, "A" is for the decible level of mufflers....

My 2in 2 out Dansk read 88-90 dbA.....

BTW....standard measurement is at 4500 rpms and 50 feet away. Meter on a tripod with it pointed at a 45 degree angle from vertical.....1/2 way way between flat and straight up....

[964RS]

Tim
You're test is the one most tracks in the UK seem to use - 0.5m from the tail pipe. I'm told that a 2 in 2 out rear box helps as half the exhaust gases exit further away from db meter - anyone got any noise measurements compared to standard?
Seems like you should be alright but there are some tracks who have quiet days at even less than 105dbA so beware as they won't give you youre money back if you're too loud.
Steve
2.7RS Replica
964RS

[cstreit]

Strange, most of the tracks out here use trackside setups, but these are typically set back off the track... Perhaps to keep the loud boys from vindictively running over them

[TimT]

At Lime Rock, the noise monitors move to different locations on the track. They know the locations where we really get on the gas, and hence check the levels from trackside at those locations.

I think LRP is 92 db, could be 97 db?

At Watkins Glen the cows really dont seem to care to much about the noise

[jluetjen]

A couple of cheap tricks to try to save 1 or 2 db's:

1) Put a bend at the end of the pipe so that they point to the ground. Whatever you do, make sure that the pipes don't point at the meter! The rotory Mazda's have used this trick going back to the IMSA days.

2) I seem to remember seeing somewhere that just cutting the exhaust pipe at a 45 degree angle to the ground has a similar affect to option 1. Thus the little caps that you will sometimes see ono megaphones.

[autobonrun]

Originally posted by 964RS
Tim
I'm told that a 2 in 2 out rear box helps as half the exhaust gases exit further away from db meter - anyone got any noise measurements compared to standard?
964RS

I have a comparison to the standard on this thread.

Performance Test done - SSI vs Stock SC

[cstreit]

At one track where I'd consistently peak a couple decibles above the limit, I had a set of pipes made with a 30 degree bend. Then would rotate them towards the inside of the track because the meters were on the outside!

Worked like a charm...