[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.