Subaru and other abnormal sounds - why?

[Jazzbass 1]

One thing about modern Subarus is their distinctive sound - their distinctive exhaust note. From an engineering standpoint, why is this?

If you are wondering what the hell I mean, I'm referring to that 'tractor' sound they make under throttle. Harleys are similar and their distinctive 'tractor' sound is due to the 45 degree angle of the V Twin and the firing cycle. American V8s, of course, are famous for their distinctive sound which, as I understand it, is also caused by a difference in firing angle of the cylinders. Its all subjective, of course, but I loathe the sounds of all of these equally - boxers, HDs and US-V8s are vomit-inducers to my taste. (ymmv) - btw - why don't BMW and other Euro V8s sound as bad as their US counterparts?

As I understand it, Subarus and Volkswagen Beetles, whcih also sound similar are just horizontally-opposed engines. This means to me that its just like a normal 4 cyl motor, which has been sort of divided and flattened out so that all the pistons move on a horizontal plane. However, I would have thought that the firing cycle would have been the same as a normal 4-cyl engine, so I can't see why they make that horrid noise.

Any thoughts on this?

[Carl 3]

The standard manifold on the subaru could be the cause, if replaced with tuned length headers the scooby sound disappears

[CaM 0]

alot of it's down to the design of the exhaust manifolds, on the boxers.

I've heard subarus, dubs, porsches even alfa romeo suds that have engine sounds that are poles apart.

I enjoy the sound of volkswagen/porsches flat fours, the alfas, and some subarus. usually highly tuned subarus sound miles better than the stock "drainpipe" style, shithead modified examples which you've probably encountered around palmerston north (there's a guy whom I work with who's STi impreza sounds terrible)

yank v8s often lack any form of mufflers and resonators. they sound like they're running half under water at low engine speeds.

all the aforementioned engines sound best at full chat, I think that's a given of almost anything

[MADBMA 0]

gotta disagree with the vomit inducer comment, the sound of american v8s is enough to make me cream my pants, subarus on the other hand i can hear them coming from miles away all sound the same and i cringe everytime i hear them, hate that sound.

[AntonyG 0]

Do you guys get excited over the sound of the S54 (E46 M3) ???

[cainchapman 0]

So you don't mind the sound of a 2 stroke motorbike?

The key thing to note is that while a boxer-4 does alternate firing fore and aft cylinders, it does not evenly alternate firing between its left and right cylinder banks. It cannot due to the 180 degree orientation of crankshaft pins selected for balance. So instead it must fire twice on one side and then twice on the other. And unlike an inline-4, a boxer-4 must have two separate exhaust manifolds.

One manifold exhausts [fire, fire, wait, wait] while the other side exhausts [wait, wait, fire, fire]

So in addition to the evenly spaced firing of each cylinder (just as from an inline-4) the boxer-4 has exhaust pulses exiting the left and right manifolds at half that frequency. This cadence is perceived as a half-pitch "rumble".

[Guest Ken]

It is all down to the timing of the exhaust pulses, U.S. V8s fire generally at 90 and 270 degees - (single plane crank

Are you sure? As far as I'm aware "Detroit Iron" has 2 planes, single plane is usually the preserve of racing engines such as the Cosworth DFV. The single plane configuration is essentially 2 4 cylinder engines running side by side which, (amongst other things) allows for a simplifed extractor setup. The nicest V8 sound - for me the (original) GT40, 2 plane crank but sounds completely different due to the crossover pipes that the mid engine layout allows.

The nicest sound ever? Try 16 cylinders...

http://www.billzilla.org/BRM-loudpass.mp3

[m325i 705]

Glad to hear you love the rumble. Thats me waking you up at night and setting off your car alarm

[Guest Ken]

1) If the connections to a crank are made at either zero or 180 degrees and the cylinders are arranged in a V they can NEVER have an even rotational spacing on the crank. Hence the sound of most U.S. V8s as pointed out. -

This is my understanding of a single plane crank.

Example - 90 degree V twin : if you take the cylinder on the "left bank" at top dead centre then rotate the crank, next cylinder on the right bank comes up 90 degrees later, the "left" cylinder does not come back up for another 270 degrees. If the pistons are connected on a common big end or big ends displaced by 180 degrees the result is the same.

Then the above repeats , A V8 is just 4 V twins stacked on a common crankshaft.

2) If the crank has connections which line up ( in plane) with the cylinder arrangements then this is the same as having all the cylinders in one plane, in which case the rotational timing can be evenly spaced. This is my understanding of a multiplane crank.

Multi-plane cranks are more complex to engineer and balance but the timing is correct, the sound is the identifier. If it sounds "even" (the connections line up with the cylinders) - must be multi plane- Won't sound like a "U.S. V8"

Single plane cranks have been used in racing , in some configurations they develop more torque, much like the big 4 cylinders that were used at one stage, but for outright power and hence high speed like F1 they are not the best.

Multi-plane cranks with un-even length headers will sound slightly "flat" at certain engine speeds, but this is not the "U.S. V8 sound" that I think the above were referring to , even a BMW 6 sounds flat at certain speed with standard pipes.

U.S. "Iron" is not my speciality - I was replying to the "sound" question" . Perhaps some one with Knowledge on US iron would comment.

Yes - The world of physics as applied to engineering is never simple!

My understanding over the years is basically this (via AJ6 Engineering):

"Purpose designed four valve V8 racing engines use a single plane crankshaft (like an in-line four cylinder) to obtain evenly spaced firing impulses along each bank to allow for optimum exhaust tuning, the downside being that the engine shakes laterally because of unbalanced forces. Even with a regular firing order such engines are notorious for timing gear problems associated with severe instantaneous torque reversals, which at different times have caused much trouble in four valve V8s from such illustrious names as Coventry Climax, Repco, Cosworth and Ilmor.

Production V8 engines almost always use a two plane crankshaft (four crank throws disposed at 90 degree intervals) which provides good balance but an uneven firing order along each bank. Because of this a four cam production V8 inevitably has the cams asymmetrically phased around the axis of each camshaft as shown in the diagram. This gives rise to irregular loads on the drive between the crankshaft and the cams and between the two camshafts on each head."

Via good ol' Wikipedia:

Cross-plane and flat-plane

There are two classic types of V8s which differ by crankshaft:

"The cross-plane V8 is the typical V8 configuration used in American road cars. Each crank pin (of four) is at a 90° angle from the previous, so that viewed from the end the crankshaft forms a cross. The cross-plane can achieve very good balance but requires heavy counterweights on the crankshaft. This makes the cross-plane V8 a slow-revving engine that cannot speed up or slow down very quickly compared to other designs, because of the greater rotating mass. While the firing of the cross-plane V8 is regular overall, the firing of each bank is LRLLRLRR; this leads to the need to connect exhaust pipes between the two banks to design an optimal exhaust system. This complex and encumbering exhaust system has been a major problem for single-seater racing car designers.

The flat-plane V8 design has crank pins at 180°. They are imperfectly balanced and thus produce vibrations unless balance shafts are used, with a counter rotating pair flanking the crankshaft to counter 2nd order vibration transverse to the crankshaft centerline. As it does not require counterweights, the crankshaft has less mass and thus inertia, allowing higher rpm and quicker acceleration. The design was popularized in modern racing with the Coventry Climax 1.5 L V8 which evolved from a cross-plane to a flat-plane configuration. Flat-plane V8s on road cars come from Ferrari (the Dino), Lotus (the Esprit V8), and TVR (the Speed Eight). This design is popular in racing engines, the most famous example being the Cosworth DFV.

In 1992, Audi left the German DTM racing series after a controversy around the crankshaft design of their V8-powered race cars. After using the road car's cross-plane 90°-crankshaft for several years, they switched to a flat-plane 180° version which they claimed was made by "twisting" a stock part. The scrutineers decided that this would stretch the rules too far.

The cross-plane design was neither obvious nor simple to design. For this reason, most early V8 engines, including those from De Dion-Bouton, Peerless, and Cadillac, were flat-plane designs. In 1915, the cross-plane design was proposed at an automotive engineering conference in the United States, but it took another eight years to bring it to production. Cadillac and Peerless (who had hired an ex-Cadillac mathematician for the job) applied for a patent on the cross-plane design simultaneously, and the two agreed to share the idea. Cadillac introduced their "Compensated Crankshaft" V8 in 1923, with the "Equipoised Eight" from Peerless appearing in November of 1924."

[Guest Ken]

So I know sh*t about V8 engines and american ones in particular. I will stick to the sound side - It is all to do with the pulse timing

Don't be so hard on youself! Engine sounds are like music - best suited to the individual taste; except for Renault programming their F1 car to play God Save the Queen!!!

Also, the most useful piece of knowledge you can retain about American V8s is... NEVER NEVER NEVER drop one!

[conrod 1]

Are you sure? As far as I'm aware "Detroit Iron" has 2 planes, single plane is usually the preserve of racing engines such as the Cosworth DFV. The single plane configuration is essentially 2 4 cylinder engines running side by side which, (amongst other things) allows for a simplifed extractor setup. The nicest V8 sound - for me the (original) GT40, 2 plane crank but sounds completely different due to the crossover pipes that the mid engine layout allows.

The nicest sound ever? Try 16 cylinders...

http://www.billzilla.org/BRM-loudpass.mp3

Most Ferrari V8's (if not all) run flat plane cranks, pretty much everything else this side of exotica runs crank pins spaced at 90 degrees. The "more mature" among us may remember Roger Freeths V8 Starlet- this ran a Rover V8 which was fitted with a flat plane crank and sounded very cool! It does tend to induce a lot more vibration into an engine than a 90 degree crank though.

BRM V16 is THE sweetest sounding engine ever- pity it would only give you a lap or two of music before blowing up! If you are into this sort of thing, go and buy Nick Mason's (Pink Floyd drummer) "Into the Red" book, which details his car collection, and provides a soundtrack on CD, including the fabulous BRM.

BTW- the S14 sounds pretty good at 9000 rpm!...............

Edited January 14, 2007 by conrod

[Guest Ken]

Most Ferrari V8's (if not all) run flat plane branks, pretty much everything else this side of exotica runs crank pins spaced at 90 degrees.

BRM V16 is THE sweetest sounding engine ever- pity it would only give you a lap or two of music before blowing up! If you are into this sort of thing, go and buy Nick Mason's (Pink Floyd drummer) "Into the Red" book, which details his car collection, and provides a soundtrack on CD, including the fabulous BRM.

Yeh - The .mp3 link I posted has been ripped from that book/CD. I first heard it at Hartage's place one night over a few bevvies, music indeed!

[Guest Ken]

Not the best of GT40 vids but something interesting to listen to anyway...

[Jazzbass 1]

WOW!!

Thanks guys - great responses and good info for me to get my head around!!

Cheers,

Rog

[BMW POWER 2]

Yes - The world of physics as applied to engineering is never simple!

Yuck, I don't think I want to do physcis anymore.

[Guest Ken]

Yuck, I don't think I want to do physcis anymore.

Trust me - Physics and maths are core essentials of education!

[cainchapman 0]

Physics is the best! I love it.

[Guest Ken]

Physics is the best! I love it.

You must do - your signature photo is a wonderful example of conservation of angular momentum!!!

BTW - Did you know that a Polar bear is an Angular bear that's undergone a coordinate transformation.

[318isCoupe 0]

You must do - your signature photo is a wonderful example of conservation of angular momentum!!!

BTW - Did you know that a Polar bear is an Angular bear that's undergone a coordinate transformation.

Haha, my crazy south african 6th form physics teacher would have found you HILARIOUS

[Guest Ken]

Haha, my crazy south african 6th form physics teacher would have found you HILARIOUS

[will 169]

Haha, my crazy south african 6th form physics teacher would have found you HILARIOUS

is there any other type of south african??

[Guest Ken]

is there any other type of south african??

Some are even worth getting married to!!!