Understanding exhaust notes

Originally Posted by RoshDawg

Just curious about what causes different type of exhaust notes. For example, rumble sounding exhausts are normally caused by unequal length headers (ex STi), but what about:

1. Deep/low pitched exhaust
2. High pitch (not necessarily exclusive to rpm's above 8/9k)
3. Rumble sound even with equal length headers (ex. GT40, SLS)
4. Exhaust crackle when you let off the gas

I'm simply trying to learn about the acoustics of exhausts so any relevant info is appretiated. Other types of sounds and their explanations are very welcome.

Originally Posted by Hermitns

engine configuration, # of cylinders, total airflow (e.g. horizontally opposed or flat motors, 90* V, inline or even Volkswagons W motors....and the exotic 12cyls of Ferarri) plus exhaust pulse scavanging. I dont know if anyone here has the search skills to find this but....back in the 80's or 90's some NASCAR teams ran 180 degree headers (I cant explain why they're called that) but the cars sounded like they were reving much higher. Folks said it sounded like a swarm of bees compared to the standard configuration.
Ever wonder why Harley sounds so powerful but they can't make any horsepower?
(all you H-D lovers remember...the V-wad is a PORSCHE designed motor). V configuration and a tractor motor firing sequence.
I rode a 130 HP VTX 1800 for 4 years. V twin configuration...didn't sound or run like a Harley.

2nd question I believe the Meistershaft is the highest pitch I've heard.

Corvette with 180 Degree Headers - YouTube

Originally Posted by Motordyne

The engine type and cam phasing has a lot to do with all of it.

1. Deep/low pitched exhaust
Generally larger diameter tubing

2. High pitch (not necessarily exclusive to rpm's above 8/9k)
Generally small diameter tubing.
A system design that has sudden expansions or sudden contractions.
Chambered mufflers.

3. Rumble sound even with equal length headers (ex. GT40, SLS)
The "off beat" sound can be the total system design.

4. Exhaust crackle when you let off the gas
Engine tune and exhaust cam phase.
And it helps to have a high flow exhaust.

Originally Posted by Motordyne

The engine type and cam phasing has a lot to do with all of it.

1. Deep/low pitched exhaust
Generally larger diameter tubing

2. High pitch (not necessarily exclusive to rpm's above 8/9k)
Generally small diameter tubing.
A system design that has sudden expansions or sudden contractions.
Chambered mufflers.

3. Rumble sound even with equal length headers (ex. GT40, SLS)
The "off beat" sound can be the total system design.

4. Exhaust crackle when you let off the gas
Engine tune and exhaust cam phase.
And it helps to have a high flow exhaust.