crankshaft RPM

Kylie

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I don't think you can tell. The exact RPMs would depend on the specific engine (different engines may produce different sounds to provide the same RPMs), and also it depends on the gearing, as the sound is dependent on engine speed, not crankshaft speed.
 
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essentialsaltes

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I think in most V8s, the pistons are paired up, so there are, I guess, 4 firings per complete revolution of the crankshaft.

If the strongest frequency is tied to the firings, then

1000 firings per second = 250 rotations per second = 15,000 rpm

which means I either screwed things up, or you have an F1 racing engine.
 
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whois

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I think in most V8s, the pistons are paired up, so there are, I guess, 4 firings per complete revolution of the crankshaft.
right answer, but the wrong reasoning.
there will be 8 firings for every 2 revolutions for the crank, average 4 firings per revolution.
1000 firings per second = 250 rotations per second = 15,000 rpm
gold star cookie man ! !
which means I either screwed things up, or you have an F1 racing engine.
actually, 1000 pps was an arbitrary number
 
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RedPonyDriver

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In a V8, each piston fires individually. I don't think you can get RPM from just the sound frequency, as the frequency is dependent on many factors. What RPM are you trying to determine? Idle RPM? Redline RPM? RPM in an engine is almost meaningless unless paired with the rest of the drivetrain.
 
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whois

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In a V8, each piston fires individually. I don't think you can get RPM from just the sound frequency, as the frequency is dependent on many factors. What RPM are you trying to determine? Idle RPM? Redline RPM? RPM in an engine is almost meaningless unless paired with the rest of the drivetrain.
the pulses per second coming from the exhaust is in direct relation to the number of cylinders present.
all that is needed to determined crankshaft RPM is the number of cylinders and the pulse frequency.
however, i have made one important assumption here, and that is we are dealing with a 4 stroke cycle.
this is why i said 8 cylinders, i have never seen an 8 cylinder engine that WASN'T a 4 stroke cycle.
a single cylinder 4 stroke engine delivers one power stroke for every 2 revolutions of the crank.
4 stroke cycle engines are commonly referred to as 4 cycle engines and commonly found in cars.

the other type of engine, the 2 stroke cycle delivers one power stroke for every revolution of the crank.
this implies more power can be had with the same displacement.
this however comes at the price of increased pollution.
these engines are commonly found in chainsaws, weedeaters and less commonly in lawnmowers.
they usually require oil to be mixed with the gas.
 
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Kylie

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to clarify:
no gears, just an engine on an engine stand (gears wouldn't matter anyway)
also, change hertz to pulses per second.
yes, the question has an answer.

Is the burning of the fuel/air mixture the only thing producing the noise? What about all the other moving parts in the motor? Surely they will produce some noise that will affect the sound as well.
 
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whois

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Is the burning of the fuel/air mixture the only thing producing the noise?
yes, the sound you hear from the exhaust is the result of the pistons forcing the burnt mixture through it.
other parts of the engine can make noise, such as alternators and fan belts, but these aren't heard through the exhaust.
 
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