Hi,
I'm sorry but that is just utter nonsense. Your confusing RPM with Hz.
rgds, sreten.
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My understanding of internal combustion engines leads me to think that it is extremely unlikely that what would come out of the exhaust valve (and likewise what "sound" would come out of the intake valve) would be a sine wave. Visualizing the four-stroke cycle, it might theoretically be approximated by a half-sine repeated every other cycle.
This is flat-out guaranteed to have an "octave tone" and lots of other harmonics, as well as general inharmonic noises caused by slightly different detonations on different cycles and stuff.
I just had an idea ... an "automotive exhaust sound simulator." I'll write an app, put it on the Apple Store... you can select make, model and year, and listen as you rev it up to your heart's content. I'll make a fortune, and finally buy those $75,000 interconnects I've always been dreaming of.
I presume this had already been going on for many decades.
This is flat-out guaranteed to have an "octave tone" and lots of other harmonics, as well as general inharmonic noises caused by slightly different detonations on different cycles and stuff.
I just had an idea ... an "automotive exhaust sound simulator." I'll write an app, put it on the Apple Store... you can select make, model and year, and listen as you rev it up to your heart's content. I'll make a fortune, and finally buy those $75,000 interconnects I've always been dreaming of.
I'm not a "car" person at all (though I occasionally still look into the "Sound Quality Vs. Chevys" thread), but I heard a lot about this when the Mazda Miata came out (1989), that they spent a lot of time "tuning" the sound of the car. I presume it had a positive effect, they were selling like hotcakes at something like $2,000 over list price.
I presume this had already been going on for many decades.
Perhaps the poster meant "by the time it got to top speed, you couldn't hear anything."
The Tesla electric cars work this way. Even at its lowest speeds, electrons are ignited at such a fast rate that the pitch is above human hearing.
Anyway, believe it or not, the higher end harmonics can be radically altered just by changing the dimensions of the tailpipe, without affecting engine tuning much at all, with diameter causing the biggest change. Or you can make the tailpipe way too big in diamter And too long, and there you have your later model Mustangs.
Benro2,
Great post, and don't worry about the longer length. You did a great job describing what you've heard. There are several means by which to create sounds like you have referred to.
One of the most prominent factors is the intake design. The manifold's runner length, diameter, the throttle valve diameter, and numbers thereof each have an impact on the sound. For example, and older Datsun with a six-carburetor setup (much like the earlier Lamborghinis) have a different sound from those with a single common throttle valve. The earlier Countach LP400S could sound like a harmonica. Common throttle intakes may have a lone butterfly, or two, four, even six. These generate tones differently.
During the '70's the four-barrel carburetor was famous for the "moo" sound it would produce. In the early 2000's, Nissan also introduced an active intake manifold on the QR25DE which had individual secondary butterflies for each inlet port. This manifold assembly improved low rpm power and fuel economy, while offering optimized flow at high rpm, when it was required. At low rpm, the short secondary runners would be closed, but at 5000 rpm they would flip open and let out a sound like a four barrel V8.
Cam phasing, lobe duration and timing change the sound, but a change in sound is more attributed to engines with varying lift. Honda's Vtec is well known for its sound, which is the result of an increase in lift with power and rpm and a combination of its intake design. Most of the remainder of the sound and overtones stem from the exhaust workings downstream.
Unequal length headers (UEL) with piping that varies in length across different cylinders can create a rumbling or growling sound. The theory and practice are quite simple; for a four-cylinder, combine two sequential firing cylinders on exhaust runners which are greater than 25% length than the other two. As the cylinder count increases, greater care is required. This is largely why some otherwise-identical engines sound very aggressive. You may recall the sound of earlier Subaru's WRX's, which could sound almost like a Buel motorcycle as they passed through a parking lot, as opposed to the usual humm of a four cylinder. This, however, is the sound of inefficiency - UELs eliminate much of the exhaust scavenging that equal length headers offer.
Mufflers are designed with internal chambers that act as Helmholtz resonators as the gasses rapidly move past, and through them. These resonators create a pressure wave approximate to that of the incoming flow, but with opposite phase. This nullifies much of the pressure variances and in turn reduces the noise output. Mufflers can be designed to leave pulses a certain rpm range and carry the higher frequency harmonics from the downpipes and through-channeling. Some will impart new beats as carriers of higher harmonics upon the gas flow, thus creating a different sound from the original.
Great post, and don't worry about the longer length. You did a great job describing what you've heard. There are several means by which to create sounds like you have referred to.
One of the most prominent factors is the intake design. The manifold's runner length, diameter, the throttle valve diameter, and numbers thereof each have an impact on the sound. For example, and older Datsun with a six-carburetor setup (much like the earlier Lamborghinis) have a different sound from those with a single common throttle valve. The earlier Countach LP400S could sound like a harmonica. Common throttle intakes may have a lone butterfly, or two, four, even six. These generate tones differently.
During the '70's the four-barrel carburetor was famous for the "moo" sound it would produce. In the early 2000's, Nissan also introduced an active intake manifold on the QR25DE which had individual secondary butterflies for each inlet port. This manifold assembly improved low rpm power and fuel economy, while offering optimized flow at high rpm, when it was required. At low rpm, the short secondary runners would be closed, but at 5000 rpm they would flip open and let out a sound like a four barrel V8.
Cam phasing, lobe duration and timing change the sound, but a change in sound is more attributed to engines with varying lift. Honda's Vtec is well known for its sound, which is the result of an increase in lift with power and rpm and a combination of its intake design. Most of the remainder of the sound and overtones stem from the exhaust workings downstream.
Unequal length headers (UEL) with piping that varies in length across different cylinders can create a rumbling or growling sound. The theory and practice are quite simple; for a four-cylinder, combine two sequential firing cylinders on exhaust runners which are greater than 25% length than the other two. As the cylinder count increases, greater care is required. This is largely why some otherwise-identical engines sound very aggressive. You may recall the sound of earlier Subaru's WRX's, which could sound almost like a Buel motorcycle as they passed through a parking lot, as opposed to the usual humm of a four cylinder. This, however, is the sound of inefficiency - UELs eliminate much of the exhaust scavenging that equal length headers offer.
Mufflers are designed with internal chambers that act as Helmholtz resonators as the gasses rapidly move past, and through them. These resonators create a pressure wave approximate to that of the incoming flow, but with opposite phase. This nullifies much of the pressure variances and in turn reduces the noise output. Mufflers can be designed to leave pulses a certain rpm range and carry the higher frequency harmonics from the downpipes and through-channeling. Some will impart new beats as carriers of higher harmonics upon the gas flow, thus creating a different sound from the original.
Unequal headers can definitely alter the sound. A classic example was the original Triumph/BSA triples, which split the centre cylinder header into two and joined them to the outer cylinder headers.
http://www.motorcycleclassics.com/~/media/Images/MCC/Editorial/Articles/Magazine%20Articles/2013/07-01/Classic%20Experience%20Life%20with%20a%201974%20Triumph%20Trident%20T150/Triumph-Trident-Engine.jpg
Quite Porsche-like in sound.
https://www.youtube.com/watch?v=kUX-I59Jbd0
Aftermarket pipes and later triples mostly had equal-length 3 into 1 systems which lost some of the magic.
http://www.motorcycleclassics.com/~/media/Images/MCC/Editorial/Articles/Magazine%20Articles/2013/07-01/Classic%20Experience%20Life%20with%20a%201974%20Triumph%20Trident%20T150/Triumph-Trident-Engine.jpg
Quite Porsche-like in sound.
https://www.youtube.com/watch?v=kUX-I59Jbd0
Aftermarket pipes and later triples mostly had equal-length 3 into 1 systems which lost some of the magic.
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