Exhaust Sound - What are you hearing?
#1
Exhaust Sound - What are you hearing?
Just a thought, not really a question.
Ever think about what we're actually hearing through the pipes? Is it primarily
several explosions per second resonating down an exhaust system through
closed valves?
Sounds of valves smacking valve seats? Pulses of air escaping the chamber
at high speeds? A little bit of everything combined?
What ever the mix, the "big guy" upstairs knows the way to my heart.
Ever think about what we're actually hearing through the pipes? Is it primarily
several explosions per second resonating down an exhaust system through
closed valves?
Sounds of valves smacking valve seats? Pulses of air escaping the chamber
at high speeds? A little bit of everything combined?
What ever the mix, the "big guy" upstairs knows the way to my heart.
#3
Pulses of air escaping the chamber at high speeds?
#5
Actually, except when detonation ocurrs, a combustion event is a very rapid burn, not an explosion. The high pressure pulse (50-100 psi at WOT) of escaping exhaust when the valve opens causes the noise. You can verify this by screwing an air fitting into the plug hole, applying 100 psi and then tapping the exhaust valve open with a hammer and soft punch. (with the manifold removed)
#7
That's correct. The combustion is complete before the exhaust valve opens, so if there was any noise to speak of, it would have stopped by then. The pinging/knocking sound you hear when an engine detonates from bad fuel or too much spark advance is caused by a very small portion (usually <10%) of the mixture exploding. If the whole combustion event was an explosion, it would be 10X as loud, and wouldn't change much with an unmuffled exhaust.
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#8
MadBill,
I've used compressed air (100 PSI) to change valve springs. Some of the
retainers were stubborn and I had to use a soft faced mallet to tap the
retainer loose.
Those pops are pretty loud through the manifold.
I'd also like to edit my definition of "combustion sound". It's not an explosion
(instant spike of pressure), but rather an expansion of gas in a somewhat
controlled manner as you stated.
I can also hear sounds of valves, or lifters. There is a distinct sound between
mechanical and hydraulic cams that sticks out (especially at idle).
As far as tailoring the sound it could be anything from engine load, to atmospheric
conditions.
We could turn this into quite a novel!
I've used compressed air (100 PSI) to change valve springs. Some of the
retainers were stubborn and I had to use a soft faced mallet to tap the
retainer loose.
Those pops are pretty loud through the manifold.
I'd also like to edit my definition of "combustion sound". It's not an explosion
(instant spike of pressure), but rather an expansion of gas in a somewhat
controlled manner as you stated.
I can also hear sounds of valves, or lifters. There is a distinct sound between
mechanical and hydraulic cams that sticks out (especially at idle).
As far as tailoring the sound it could be anything from engine load, to atmospheric
conditions.
We could turn this into quite a novel!
#9
If you've ever heard a Spin-Tron machine spin up a motor to test valve-train stability, it sounds just like an engine at WOT. All it is, is an electric motor spinning a gutted motor assembly. Lots of the noise we hear is valve-train, air-pumping noises.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
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2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
#12
Originally Posted by 300bhp/ton
Doesn't the LS1 have a different firing order to the LT1??
#13
There is one point that has been debated here and it's the difference between a controlled burn and an explosion. An explosion is not an instantaneous event. It is the 'explosive' burning at a very high rate. For instance C4 'burns' at 20,000 feet per second. I'm not sure of an air gas mixture's rate of burn, but it must be much less given that optimum timing is based on some number of degrees of ignition before TDC and the time it takes for the crank angle to reach it's optimum torque angle. Also, I recently had a fouled plug that manifested itself as a 'shotgun blast' due to misfire out of my exhaust because the a/f charge exited the cylinder and wasn't burned there but somewhere in the header. It was a MUCH different sound than the exhaust leaving the cylinder when burned at the proper time. Also we should keep in mind that the exhaust gases escape at a slow rate at first, as the valve starts to open, then faster until the valve opens fully. So the wavefront attack is logarithmic in nature and not instantaneous.
#15
Yeah, to continue the discussion of 'explosion' vs. 'burn' listen to a top fuel (80:20 Nitromethan : Methanol) compared to a gasser. The nitromethane burns at a much higher rate and sounds more like an explosion than a burn.
The greatest thing I've ever heard is the first time I was standing in the pits and a top fuel funny car started up doing his morning tuning session. The sound is intoxicating much less the vapors that burn your eyes and lungs.
The greatest thing I've ever heard is the first time I was standing in the pits and a top fuel funny car started up doing his morning tuning session. The sound is intoxicating much less the vapors that burn your eyes and lungs.
#16
If you think about it, once you close the throttle at high speed you're not getting any fuel anyway. The sound does change a bit because of the relative low volume of air flowing through the closed throttle, but the sound is mainly the pumping of air into and out of the engine.
Years ago, I ran out of gas in my old car with full lengths and dual exhaust. I was suprised how similar it sounded, even with no combustion at all.
Years ago, I ran out of gas in my old car with full lengths and dual exhaust. I was suprised how similar it sounded, even with no combustion at all.
#17
True.
On a stock car, you hear "boom boom boom boom boom boom" as it's idling. Is that everytime the motor makes a revolution? It definitely doesn't seem to be the cylinders firing, as it's too slow.
On a stock car, you hear "boom boom boom boom boom boom" as it's idling. Is that everytime the motor makes a revolution? It definitely doesn't seem to be the cylinders firing, as it's too slow.
#18
Originally Posted by blackz93
True.
On a stock car, you hear "boom boom boom boom boom boom" as it's idling. Is that everytime the motor makes a revolution? It definitely doesn't seem to be the cylinders firing, as it's too slow.
On a stock car, you hear "boom boom boom boom boom boom" as it's idling. Is that everytime the motor makes a revolution? It definitely doesn't seem to be the cylinders firing, as it's too slow.
As stated above:
LS1 is 1-8-7-2-6-5-4-3
as opposed to the LT1 and traditional SBC, which is 1-8-4-3-6-5-7-2.
#19
Originally Posted by MadBill
Actually, except when detonation ocurrs, a combustion event is a very rapid burn, not an explosion. The high pressure pulse (50-100 psi at WOT) of escaping exhaust when the valve opens causes the noise. You can verify this by screwing an air fitting into the plug hole, applying 100 psi and then tapping the exhaust valve open with a hammer and soft punch. (with the manifold removed)
#20
Originally Posted by ArKay99
I believe that is the 2 cylinders on bank 2 that fire one after the other, every OTHER revolution.
As stated above:
LS1 is 1-8-7-2-6-5-4-3
as opposed to the LT1 and traditional SBC, which is 1-8-4-3-6-5-7-2.
As stated above:
LS1 is 1-8-7-2-6-5-4-3
as opposed to the LT1 and traditional SBC, which is 1-8-4-3-6-5-7-2.
1-8-7-2-6-5-4-3
It is easier to see on a Gen I/II SBC, as it is buried in the firing order, not at the end.
1-8-4-3-6-5-7-2