Exhaust decibel data

[vex]

I'm looking to give the RCC a nice leg up to throw into the RCC membership tool box. I'd like to ask those that are willing and able to purchase a decibel meter (one can be had for your Iphone for $2.00 or free if you look hard enough, or from radioshack for around $50). I'd then like you to record your exhaust decibel in nuetral fully warmed up. Here's how it will work:

Measure back 6 feet from the center of your rear wheel. Have some one place the decibel meter on the ground inline with the exhaust and stand opposite of your exhaust pipe and the meter. Get in the car and record the Decibel reading at idle, 2000, 3000, and 5000RPM. If you'd like you can also do a nuetral rev and take the Peak Decibel value you receive.

(This is when it gets tricky) Record what kind of exhaust you have. If you have stock you can simply state 'stock'. If you don't have a 'stock' exhaust system state the style of exhaust you have. IE:

Racing beat Universal 3in Presilencer to Dual Magnaflow 2.5in perferated packed mufflers.

NOT Magnaflow XL3 mufflers (though that information may be useful, the muffler type is more important).

Further more those that go to the Dyno often (I'm looking at you TTT), can record their exhaust decibel levels under load for even further information.

You may be asking yourself what's the point? This seems like a lot of work and no immediate gain.--And you'd be right. The immediate gain would not be there, but the future gain would be extremely useful in getting new products made, or finding better products to help gain performance over 'stock' while not causing our ear drums to bleed.

This is how I envision it to work:
You're in the market for a new exhaust system and would like to know exactly what to look for before picking it up. You know RB is an awesome way to go but you don't want to deal with the price tag that's associated with it. So you come to the RCC toolbox and look at the exhaust numbers (don't worry I'm sure we'll come up with a better title for it later). You are then presented with actual numbers that represent the decibel level at a specific distance from the exhaust exit. If stock has a decibel profile of say 70db, 80db, 82db, 90db and you know you want to stay close to those numbers you can easily look at others individual set ups and see that another individual has these types of muffeling devices installed and has the following decibel profile; 75db, 82db, 85db, 92db. Wham bam you record the muffeling device type, order the parts you want, and are on your merry way to more performance.

[NoDOHC]

This is a really good idea. Maybe I can sneak into work on a weekend and get accurate readings on two exhaust systems (one of which is Racing Beat). Unfortunately, the data would be more accurately comparable if we all used the same measurement system. Probably IPhone is easiest (although I don't have one, I have many friends that do).

[vex]

I agree, but I wanted to leave it open for the decibel tools available to other individuals. In my case I don't know anyone who has an iphone, and I am not willing to drop coin on an itouch (unless there's a significant price drop)

[vex]

http://www.warrencenter.org/Images/howloud.gif
http://nasdonline.org/static_content...ts/1975/11.gif
http://www.umlan.com/img/reviews/h81...ibel_chart.jpg
http://www.maxim-ic.com/images/appno...DI127Fig16.gif

I thought this might be helpful. I should be recording my exhaust db levels sometime within the next week. Just have to remedy some things first.

[vex]

I have started the construction of the database as a spreadsheet won't do what I need it to.

For those who want to post the information please provide the following:

Car:
Year, Stock Model configuration (GXL, GTU, etc), and a short list of modifications that may affect exhaust level (porting, turbo, custom manifolds and/or exhausts).

Exhaust components:
Manufacturer, Model Number, Style (Perforated Tube, Chambered, etc), Inlet number, Inlet Size, Outlet number, Outlet size, Offset (yes/no)

interior db data:
db reading at idle (or 1000 rpm), 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm.

Those measurements are to be done stationary to remove wind-noise or other forms of noise from measurement.

Exterior db data:
Measure 6 ft back from the rear wheel for recording and record the same db levels for the various rpm (idle, 3000, 4000, 5000, 6000).

[NoDOHC]

What measurement method are we using?

[vex]

I'm using a free program I was able to find that measures db level (was actually intended for use as an applause meter). I figure you can't argue with free. As it stands I do not have enough money to go out and buy the $50 one from radio shack, nor do I have an iPhone.

I'm going the cheap route and it seems to be fairly accurate with regards to the above mentioned graphs.

[vex]

Not from 7's but useful to know:

[j9fd3s]

this is a great idea. i tried the hearos (they make earplugs) iphone app about a year ago, and its too sensitive, instead of giving you an average, its more instantaneous. so its fairly unusable, normal conversation is like 115, and the fuel pump pegs the meter... it might be a piece of foam over the mic would fix it, or maybe its just the free app from an earplug company!

part two is that last time at the track we learned that a cloud makes the cars louder. i have a 1st gen with a P port, and Jack has an ITS prepped FC, we're both running 3" borlas. on a normal day we both pass the 103DB sound limit, on that day with the cloud we both did 105DB

part three, is that i don't recommend the borla as a main muffler, its LOUD!

part four, what did the rotary racer say to the other rotary racer?

WHAT?

[RETed]

I like the idea, but too bad the chart doesn't include Borla and Magnaflow.
You can pick up a digital SPL meter from Radio Shack for $70.
If you're lucky, you can get the old (back stock) analog meter for $14 - Radio Shack put them on clearance a few months ago.

Most of us turbo guys won't run anything under 3", so we need a whole new chart for 3" mufflers?


-Ted

[josh18_2k]

bunch of common mufflers:
http://ls1tech.com/forums/generation...al-street.html

[RETed]

Nice data...
I'm sitting on a Borla ProXS (18" case, I think) right now, but I was looking for a bigger can for "more muffle".
I think the FC rear can easily go 20" long case, with the possibility of going 22" case if you got good welding skills and patience.

In our experience, the best power versus price / size muffler is an off-set in / out with perforated tube design.
Makes sure the perforated tube is the same diameter as the in / out pipe - there are some mufflers who neck down the tube inside the muffler itself.
The offset design attenuates the acoustic element of the exhaust noise very well.
Offset = one side center; opposite side to one side of the muffler.
In a pinch, you can use a center in / out muffler, but angle the inlet and outlet pipe as much as you can.
This design doesn't muffle as well as an offset muffler, but you'll get kinda close.


-Ted

[sa22c]

In my experience the starting point should be how much muffler you can get into what car.

The best place to start would be to find a rear muffler for each car. For eg for the 1st gen rx-7 guys.

Price between $100 and $200
Pipe size between 2.5" and 3.5" (to cover NA, small and large turbos).
Sized to fill the entire rear muffler section ~8.0"x10.0"x22.0"
Centre offset and centre centre available.

The non turbo guys will need a 2nd muffler before the diff hump to keep noise reasonable

You could do the same for the FC3S and the FD3S, and then 99% of cars would be covered.

For the FC3S I'm thinking twin rear section 2.25 for non turbos, 2.5 and 3.0 for turbos.

[GySgtFrank]

This thread is fairly old and nobody has actually posted any data yet. Unless I'm missing it. I picked up a digital sound level meter on EBay for 16 bucks and I'll get some pics/data and post on my setup if we're stilling doing this. Which setting A - human ear or C - standard engine/machinery setting.

[GySgtFrank]

Seeing as how no one else has ponied up data yet, I'll start off.

Car: 1979 RX-7 SA S (base model)

Recording device: AZ brand ($16 on EBay) digital sound level meter. (accuracy unknown, seems to be in the ballpark though)

Test (Control sample): Flushed toilet in quiet bathroom, door shut, A weighting. Avg approx 55db with a momentary peak of 67.4db.

Engine: 13B EFI Naturally Aspirated. Stock 1987 (internally and externally). The only exception being a Racing Beat Road Race exhaust header.

Exhaust: Custom. Dual 2 1/2 inch.

Components:
1. Racing Beat road race header (2 inch primaries)
2. Dual 2 1/2 inch pipes out the back of the car. (exceptions noted below)
3. Pipes siamesed 6 inches back from header flange for a distance of 10 inches. This was to form a collector as there was not enough room for a traditional collector with my layout.
4. 2 1/2 inch pipe to dual Stainless Works smooth tube mufflers, 2 1/2 inch inlet / 2 1/2 inch outlet, perforated tube, stainless steel packing. 2 1/2 inch ID, 4 inch OD, 32 inch body length. These were used as presilencers which are arranged on either side of the driveshaft.
5. 2 1/2 inch pipe from the pre-silencers over the axle to the rear mufflers. Note: the pipe going over the axle had to be bent in so many different directions that it is effectively about 2 1/4 inch diameter over the axle.
6. Dual Spin Tech XL mufflers (no packing, mini-chamber style baffling). 10 inch wide X 16 inch long X 4 inch deep. Offset 2 1/2 inch inlet, dual 2 1/4 inch outlet out the rear just under the bumper. One muffler on either side of the car.

DB data:

Interior Db data:
NOTE: (taken from driver's seat, outside in open area, car in neutral, windows rolled up)

Weighting.............................A........... ...C
idle (750 rpm):___________ 81db______87db
1000 rpm________________ 86.5db____89db
2000rpm_________________83db______90db
3000rpm_________________89db______93.7db
4000rpm_________________87db______85db
5000rpm_________________84.6db____88.8db
6000rpm_________________90db______90db

External Db data:
NOTE: (car in neutral, open area, measured from 6 feet behind center of car. [split dual system])

Weighting............................A............ ...C
idle (750rpm):____________91db______93db
1000rpm_________________93.5db____96db
2000rpm_________________93db______94.5db
3000rpm_________________100db_____103db
4000rpm_________________99.5db_____99db
5000rpm_________________106db_____105.5db
6000rpm_________________106db_____107db
Peak____________________118db_____116db (quick rev past 7000rpm)

THe XL mufflers are a little louder than I wanted. Might go turbo one of these days which would help quiet it down some. Sounds good though.