V8 sound

I'm trying to understand the physics behind the V8 exhaust sound. For every full turn of the crankshaft, there are 4 power strokes and thus, 4 exhaust strokes. On a 4 cylinder engine, there are half as much. At any given rpm, the V8 engine should have a exhaust note twice that of 4 cyl. engine, however, the 4 cyl. emits a more or less buzzy sound and the V8 emits a low, uneven but rhythmic lub-lub-lub-lub sound.

So why is this?

Thanks, John

Reply to
jriegle
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All V-8 engines with 90-degree cranks have an imbalance in the firing order between the right and left cylinder banks. The firing order imbalance is a necessary sacrifice so that a dynamic balance of the rotating and reciprocating assembly (crank, rods and pistons) can be maintained.

Each time the firing order is complete (two full revolutions of the crank), two cylinders within each bank fire and exhaust within 90 degrees of each other. Because of this, this pair of cylinders will be exhausting into the header collector (on one bank) almost simultaneously. This overlap creates a back pressure.

Meanwhile, the header on the opposite bank has no activity (or pressure) in it at all.

Conventional full-length four-tube headers help separate the exhaust in the cylinders until it reaches the collector. After the header primary tubes dump into the collectors, the two cylinders close to each other in the firing sequence again are fighting for space in both the collector and exhaust pipe.

This results in reflected pressure waves traveling backwards though the exhaust system. What you get is more backpressure, diminished power and fuel economy, and the V-8's characteristic growl.

***

The above is not my text but it explains the V8's signature rumble quite well and saves me an assload of typing. ;-)

Hope that helps you some.

Reply to
Tungsten

It's a combination of effects, actually..... traditionally, V8s have their cylinder banks arranged 90° from each other (there have been exceptions, but they are rare) - add that firing pulses are 90° apart and we see a definite physical trait.

Modern V6s, are *generally* arranged so that the spacing between cylinder banks is something < 90° - this is a body styling ploy more than anything else. Firing pulses will be in the neighbourhood of 120° apart but the spacing of the V will also have an effect. Inline 4s have no bank spacing and firing pulses 180° apart..... they sound like neither half of a V8 nor anything close to a V6.

While I realize that I am not an engineer, you can pretty well take this description as pretty close to gospel. If you want to hear stuff that is real nifty, you should hear motors running 180° headers.

-- Jim Warman snipped-for-privacy@telusplanet.net

Reply to
Jim Warman

Interesting from both you and Tungsten... I wonder waht an inline 8 sounds like? I've seen a couple but never heard one run.

Reply to
Cory Dunkle

I suspect it would sound more like an inline 4 at twice the exhaust pulse frequency. In other words, like a big bore motorcycle engine at high RPMs.

Dana

Reply to
Dana Myers

Indeed! Great responses. I forgot to take in consideration that angular displacement of the cylinder banks for one thing.

From memory, inline sixes sound like inline fours, so I'd guess that inline

8 would sound similar.

I bought a Chevy Beretta with a 2.8L V6 as a beater once. Those had one of the nicest exhaust notes for a V6 I've heard. I don't know what the angular displacement of the banks are though.

Seems like the exotic V12 cars have high pitched exhaust note. I'd like to hear the exhaust of the V10 engines.

One thing I've noticed with the inline fours I've driven is that under acceleration, I do notice a slight undulation in the exhaust note. Perhaps this is caused by the slight difference in the very short "headers" used on them in front wheel drive configs (outer cylinders are slightly longer).

Thanks, John

Reply to
jriegle

It's so that people like me can stop in their tracks and give themselves whiplash trying to identify which car is making that wonderful sound. It's the same as with women that have that delightful 'hitch in their git-along'; it's intended to draw you closer to be ensnared. It's not physics, it's the will of God. :-P

Reply to
RayS

It seems that the number of cylinders and the angle between the banks have the greatest effect on the sound engines make. Most 90 degree v-

8's have the same sound characteristic, although differences ( I suppose due to firing order) are identifiable between brands.

IMO, v-10s don't have a pleasing sound. The next time you see a Dodge Viper, listen to the exhause note. To me, it's halfway between an inline 4 and a v-8. Just plain weird to my ears.

One strange exception is that v-12s seem to sound alot like straight 6s. I haven't figured that one out yet.

If you follow this link, you can see one of the most incredible model cars ever built. This is a Ferrari 312PB with a working flat 12 engine! There's a video clip (bottom of the page) that includes a start and run of this incredible engine. Long, but well worth the wait for any car fanatic.

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If you want to hear something really strange, listen to a Subaru WRX with an aftermarket exhaust system. That's a 180 degree flat four.

Each like a different genre of music...

Brian

Reply to
Heretic

Some of the "sound" has to do with exhaust systems too.

Listen to your typical V8 with dual exhausts. Now listen to the same car running an X-pipe and it will sound different.

I still seem to be able to pick out an "ol 5.0" Mustang's exhaust. There's just a certain sound associated with it in my mind.

Steve Something up my sleeve

Reply to
A Guy Named Steve

The reason being that a V-12 is two I-6 engines sharing a common crankshaft. The I-6 configuration is the epitome of balance, simplicity, intake/exhaust flow, thermal efficiency and general layout (cooling, lubrication, front PTO & rear PTO accessibility, linkage geometry, among other things). How about that 4.2L I-6 in the Chevy TrailBlazer / GMC Envoy? 290hp in a small I-6. A V12 is all that, with twice the power strokes per rev. Anybody remember the OHC Pontiac Tempest / LeMans I-6? That was a screamer...

Rob

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Reply to
Trainfan1

Somehow, GM does a thorough and impressive job exhausting their V-6's. Whether it's the 60 degree 2.8 family like your Beretta or the Buick based

3.8/3800 in the Gran Prix or the old Chevy based 3.8 and newer 4.3, they seem to get the exhaust note just right. I know what you mean on your Beretta, the Corsica was very similar too, and I hear them go by once in a while. The Ford 60 degree 4.0 family & the 90 degree 3.0 & 3.8 families just never sound that way.

Rob

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Reply to
Trainfan1

Oh, the other thing about a V-12, the banks can be set at any angle with ease, due to the inherent balance of the I-6. Wide flexibility and the option of a very compact high powered engine. Each bank could even have a different bore and/or stroke if you wanted...

Rob

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intake/exhaust

Reply to
Trainfan1

While at the Monterey Historic races I noticed how different the exhaust notes of the cars was. It was really interesting to hear a Cobra with side pipes go by, followed by a Shelby GT350. Same engines, same state of tune but completely different sound. The Cobra was a low, sharp bark. The GT350 was much higher pitched and not as sharp. The main difference was the GT350 had a crossover and the Cobra did not. I know the driver of this particular car and know how the exhaust is set up. Both cars have no mufflers, only diff was the cross over.

Erich

Reply to
Kathy and Erich Coiner

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