Engine note - what are the determining factors?
Discussion
The sound an engine makes is something which can turn you on or off a car without even seeing it or driving it anywhere. Its also one of those things that journalists often use to criticise a car when there isn't anything else wrong with it but they dont like it, or to stick the boot in just a little bit more, or to redeem a car that is otherwise hopeless.
So what actually determines how the engine sounds? I'm aware that revs, valves timing, cylinders, intake and exhaust play a part in this but what plays what part? Is it analogous to a musical instrument? I remember the video of the renault F1 team playing tunes on their F1 engine so clearly its something that can be fine tuned to a great degree. If this is the case why do most turbo diesels still sound sh!t and not sound like a nice turbo petrol? Any rules of thumb for tuning for a good engine note?
And no I don't want to stick a big catering size bean tin on the end to make it sound like its bowels are loose.
So what actually determines how the engine sounds? I'm aware that revs, valves timing, cylinders, intake and exhaust play a part in this but what plays what part? Is it analogous to a musical instrument? I remember the video of the renault F1 team playing tunes on their F1 engine so clearly its something that can be fine tuned to a great degree. If this is the case why do most turbo diesels still sound sh!t and not sound like a nice turbo petrol? Any rules of thumb for tuning for a good engine note?
And no I don't want to stick a big catering size bean tin on the end to make it sound like its bowels are loose.
You have mentioned just about all of the possiblities that affect the engine sound. One of the reasons why engine sounds vary so much is that all road engines are built to massive compramises. Hence why a chevy v8 truck sounds similar to a corvette but not quite as nice! This can be due to altered cam profiles, exhaust length and expansion chambers. The reason why ferrari V8's and the TVR AJ V8 sound different to the american V8's is that they use a flat plane crankshaft. To cut a long story short, this changes the firing order of the engine.
A "conventional" V8 has crank pins at 90 degrees to each other. It has 2 power strokes per revolution but not a the same time. The "flat plane" crank used in the AJP 8 also has 2 power strokes per revolution but sounds like 2 four cylinder engines running at the same time, because that's (effectively) what it is!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
Avocet said:
A "conventional" V8 has crank pins at 90 degrees to each other. It has 2 power strokes per revolution but not a the same time. The "flat plane" crank used in the AJP 8 also has 2 power strokes per revolution but sounds like 2 four cylinder engines running at the same time, because that's (effectively) what it is!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
Thanks for explaining that, it saved me sometime! Please do not quote me on this, but i think that the reason why cross plane (conventional) makes a differnt noise is that it is common for the 2 power strokes to come from the same 'bank' of cylinders. A flat plane as mentioned above does not. It is the multiple pulses in the exhaust of a cross plane engine that gives it the distinct 'bubble'.Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
Hope this helps
Ah, I guess its obvious when you think about it. So the main distintive noise is entirely firing order timing and everything else follows as it sets the pulse spacing that hence why you can listen to an engine and immediately tell its a V8 e.g. the Rover lump. So if you have a cross plane crank V8 its something like 1-8-7-2-6-5-4-3 out of the exhaust pipes you get on one side 1 wait 7 wait wait 5 wait 3 while the other pipe is producing wait 8 wait 2 6 wait 4 wait.
For the flat plane its more like a pair of 4 cylinders twinned so something like 1+8, 3+6, 4+5, 2+7 which gives you out the pipes a continuous 1,3,4,2 and 8,6,5,7 all equally spaced.
I'm gonna have to do some more reading on this and how sound an musical notes are created. But that alone explains why V8s sound so much 'richer' than 4s and why most 4s have a plain dull sound to them.
For the flat plane its more like a pair of 4 cylinders twinned so something like 1+8, 3+6, 4+5, 2+7 which gives you out the pipes a continuous 1,3,4,2 and 8,6,5,7 all equally spaced.
I'm gonna have to do some more reading on this and how sound an musical notes are created. But that alone explains why V8s sound so much 'richer' than 4s and why most 4s have a plain dull sound to them.
Avocet said:
A "conventional" V8 has crank pins at 90 degrees to each other. It has 2 power strokes per revolution but not a the same time. The "flat plane" crank used in the AJP 8 also has 2 power strokes per revolution but sounds like 2 four cylinder engines running at the same time, because that's (effectively) what it is!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
A cross plane crank in a conventional 90 degree V8 has firing intervals at the same 90 degrees as a flat plane crank but the firing order is different.Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
On a cross plane you get two consecutive firing strokes on the same bank followed by two consecutive ones on opposite banks repeated ad infinitum. On a flat plane the consecutive firing strokes are always on opposite banks. This leads to a different sequence of exhaust gases and pressures going down each manifold. For the most usual Chevy firing order where cylinders 1,3,5,7 are on the left hand side of the car and the even cylinders on the right the firing order is as follows.
...1
8
4
...3
6
...5
...7
2
So you get an exhaust sound (and god I'm going to feel like a tool for trying to put this into words) dum, dah dah, dum dum, dah dah, dum.
So there are two high pitched notes followed by two low pitched ones and then repeat. With a straight 4 or flat plane v8 it's the same pitch, and therefore a much less interesting sound, from every piston.
To answer the OP the main influences on engine note are firing order and exhaust system. The induction sound will only be a factor if it's not well silenced which it is on all production cars via the air filter. An open set of DCOEs can drown the exhaust sound quite easily though.
Dave Baker
Puma Race Engines
Edited by Pumaracing on Wednesday 24th September 13:41
Pumaracing said:
An open set of DCOEs can drown the exhaust sound quite easily though.
Or any individual throttle system that is silenced...http://ie.youtube.com/watch?v=mN5cX6NuPeg
Steve
Pumaracing said:
Avocet said:
A "conventional" V8 has crank pins at 90 degrees to each other. It has 2 power strokes per revolution but not a the same time. The "flat plane" crank used in the AJP 8 also has 2 power strokes per revolution but sounds like 2 four cylinder engines running at the same time, because that's (effectively) what it is!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
A cross plane crank in a conventional 90 degree V8 has firing intervals at the same 90 degrees as a flat plane crank but the firing order is different.Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
Excellent post, thanks for explaining it.
On a cross plane you get two consecutive firing strokes on the same bank followed by two consecutive ones on opposite banks repeated ad infinitum. On a flat plane the consecutive firing strokes are always on opposite banks. This leads to a different sequence of exhaust gases and pressures going down each manifold. For the most usual Chevy firing order where cylinders 1,3,5,7 are on the left hand side of the car and the even cylinders on the right the firing order is as follows.
...1
8
4
...3
6
...5
...7
2
So you get an exhaust sound (and god I'm going to feel like a tool for trying to put this into words) dum, dah dah, dum dum, dah dah, dum.
So there are two high pitched notes followed by two low pitched ones and then repeat. With a straight 4 or flat plane v8 it's the same pitch, and therefore a much less interesting sound, from every piston.
To answer the OP the main influences on engine note are firing order and exhaust system. The induction sound will only be a factor if it's not well silenced which it is on all production cars via the air filter. An open set of DCOEs can drown the exhaust sound quite easily though.
Dave Baker
Puma Race Engines
Edited by Pumaracing on Wednesday 24th September 13:41
[quote=Pumaracing
A cross plane crank in a conventional 90 degree V8 has firing intervals at the same 90 degrees as a flat plane crank but the firing order is different.
On a cross plane you get two consecutive firing strokes on the same bank followed by two consecutive ones on opposite banks repeated ad infinitum. On a flat plane the consecutive firing strokes are always on opposite banks. This leads to a different sequence of exhaust gases and pressures going down each manifold. For the most usual Chevy firing order where cylinders 1,3,5,7 are on the left hand side of the car and the even cylinders on the right the firing order is as follows.
...1
8
4
...3
6
...5
...7
2
So you get an exhaust sound (and god I'm going to feel like a tool for trying to put this into words) dum, dah dah, dum dum, dah dah, dum.
So there are two high pitched notes followed by two low pitched ones and then repeat. With a straight 4 or flat plane v8 it's the same pitch, and therefore a much less interesting sound, from every piston.
To answer the OP the main influences on engine note are firing order and exhaust system. The induction sound will only be a factor if it's not well silenced which it is on all production cars via the air filter. An open set of DCOEs can drown the exhaust sound quite easily though.
Dave Baker
Puma Race Engines
[/quote]
That's brilliant! Ta Dave. It all makes perfect sense to me but I'm struggling to understand why the pitch of the note should be higher or lower each time - assuming the manifolds are fairly symmetrical.
A cross plane crank in a conventional 90 degree V8 has firing intervals at the same 90 degrees as a flat plane crank but the firing order is different.
On a cross plane you get two consecutive firing strokes on the same bank followed by two consecutive ones on opposite banks repeated ad infinitum. On a flat plane the consecutive firing strokes are always on opposite banks. This leads to a different sequence of exhaust gases and pressures going down each manifold. For the most usual Chevy firing order where cylinders 1,3,5,7 are on the left hand side of the car and the even cylinders on the right the firing order is as follows.
...1
8
4
...3
6
...5
...7
2
So you get an exhaust sound (and god I'm going to feel like a tool for trying to put this into words) dum, dah dah, dum dum, dah dah, dum.
So there are two high pitched notes followed by two low pitched ones and then repeat. With a straight 4 or flat plane v8 it's the same pitch, and therefore a much less interesting sound, from every piston.
To answer the OP the main influences on engine note are firing order and exhaust system. The induction sound will only be a factor if it's not well silenced which it is on all production cars via the air filter. An open set of DCOEs can drown the exhaust sound quite easily though.
Dave Baker
Puma Race Engines
Edited by Pumaracing on Wednesday 24th September 13:41
[/quote]
That's brilliant! Ta Dave. It all makes perfect sense to me but I'm struggling to understand why the pitch of the note should be higher or lower each time - assuming the manifolds are fairly symmetrical.
Pumaracing said:
Avocet said:
A "conventional" V8 has crank pins at 90 degrees to each other. It has 2 power strokes per revolution but not a the same time. The "flat plane" crank used in the AJP 8 also has 2 power strokes per revolution but sounds like 2 four cylinder engines running at the same time, because that's (effectively) what it is!
Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
A cross plane crank in a conventional 90 degree V8 has firing intervals at the same 90 degrees as a flat plane crank but the firing order is different.Someone did explain it to me once but I'm not quite sure about the precise explanation - something to do with the 90 degree engine producing a "richer" sound because more of the harmonics of the "note" were present. I have to say I much preferred the Rover engine notes to the AJP ones, although the AJP did have a certain "something" at 7000RPM!
On a cross plane you get two consecutive firing strokes on the same bank followed by two consecutive ones on opposite banks repeated ad infinitum. On a flat plane the consecutive firing strokes are always on opposite banks. This leads to a different sequence of exhaust gases and pressures going down each manifold. For the most usual Chevy firing order where cylinders 1,3,5,7 are on the left hand side of the car and the even cylinders on the right the firing order is as follows.
...1
8
4
...3
6
...5
...7
2
So you get an exhaust sound (and god I'm going to feel like a tool for trying to put this into words) dum, dah dah, dum dum, dah dah, dum.
So there are two high pitched notes followed by two low pitched ones and then repeat. With a straight 4 or flat plane v8 it's the same pitch, and therefore a much less interesting sound, from every piston.
To answer the OP the main influences on engine note are firing order and exhaust system. The induction sound will only be a factor if it's not well silenced which it is on all production cars via the air filter. An open set of DCOEs can drown the exhaust sound quite easily though.
Dave Baker
Puma Race Engines
Edited by Pumaracing on Wednesday 24th September 13:41
renrut said:
Cool! Cheers mate, and thats explains the typical 4 pot sewing machine sound too. So would they all sound the same if fitted with a single final exhaust?
No. The offbeat sound is formed because when two consecutive plugs of exhaust gas on the same bank meet each other at the primary to secondary manifold pipe join they create a higher local exhaust pressure and different pressure waves compared to where the next two consecutive plugs of gas on opposite banks don't meet until much later down the system, if at all. The rest of the exhaust system can mask this with high levels of silencing but not fundamentally change it.With an open exhaust on a dragster you hear the full effects of the cross plane V8 offbeat 'burble' at idle and on a Cadillac with the same basic engine you hear very little because it's silenced so well. The same things are happening inside the manifolds though.
It's also the reason why a flat plane crank has a slightly higher theoretical power output because the exhaust is less restrictive as each manifold bank only has to deal with one pulse of gas at a time.
Dave Baker
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