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Discussion Starter · #1 ·
There are a couple of WRX's that drive up and down our street (they've got the wings, so they might be STi's). One of them has an aftermarket exhaust and it really sounds like a V-Twin motorcycle. The Impreza has a turbocharged boxer engine. It is about 2 liter, right? So it must be a four cylinder, right (500cc/cyl is a common size)?

So what is the firing order on this thing, because it sounds pretty wierd.
 

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1-3-2-4
2.5L 4 cylinder 4 Valves Per Cylinder with Active Valve Control
 

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I've got the STi motor in my Outback XT and it does indeed have a distinct sound to it. Here's one person's opinion I got from the web:

The Four-Cylinder Boxer Engine's Distinct Sound

or "Why does my new Subaru sound like an old Volkswagen?"

After purchasing a new 2.5L 4-cylinder Subaru, I was curious why the sound reminded me of old rear-engined Volkswagens, and seemed so distinct from inline 4-cylinder engines. Other than the flat-four cylinder configuration, my new Subaru's water-cooled OHC engine had far more in common with any typical inline-four than with the air-cooled push-rod engine in a Volkswagen Squareback.
Yet that's what its sound reminds me of. Most people don't even notice this distinction, and those who do, didn't know what caused it.
Here's one reference to this distinct sound I found in Wikipedia's description of the Volkswagen Vanagon:
This [Wasserboxer] engine is representative of the fact that boxer 4 cylinders produce a low pitch rumble, rather than a high pitch buzz/whine, when running. Some find this aspect of the engine to be pleasing, owing to the dislike of the "sewing machine" sound of I4 engines.​
But why do they sound different? Both an inline-4 and boxer-4 have four even-firing cylinders, so why should they sound so distinct when running at the same RPM? This mystery bugged me for years.
The answer finally came to me while sitting at an outdoor cafe and hearing the cars pass by. I believe the distinct sound is due to the crankshaft and exhaust manifold designs required by the flat-four's cylinder orientation.

The Engines

HowStuffWorks® graphically illustrates the piston strokes of an inline 4 and a flat 4 boxer. rear-mounted VW engine (top view)

front

rear-drive axle
transmission
---------
3 |[]--I--[]| 1
| I |
4 | []-I-[] | 2
---------
Volkswagen firing order: 1-4-3-2
front-mounted Subaru engine (top view)

front
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2 |[]--I--[]| 1
| I |
4 | []-I-[] | 3
---------
transmission
front-drive axle
Subaru firing order: 1-3-2-4
While VW and Subaru have different nominal firing orders, they also number their cylinder locations differently. So in fact they are exact mirror images. Their respective crankshafts run in opposite directions likely due to their transmissions mounted fore versus aft.
So here's why they sound distinct...

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".
 

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Good explanation. I just thought the turbo had something to do with it and it would be cool to sound like that. They (STI WRX) sound badass. The SRT-4 sounds like that because it has no mufflers stock, just resonators.
 

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I was told its more due to the (very) unequal length headers. The passenger side header merges on the driver side.
 

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I was told its more due to the (very) unequal length headers. The passenger side header merges on the driver side.
ding...

http://www.scoobymods.com/forums/showthread.php?t=6772
finally finished my headers today, Equal length, Tuned, Tig welded, 4 into 2 design, the 2 join at at the up pipe turbo flange. Anyways they make a strong power band at 3,800 RPM`s but the down fall I now hate about them is that my car now sounds like a Honda
How's that Honda treating you by the way? ;)

Oh and Sullie is not exactly unique in having an STI engine in his Outback XT.. Anyone who got an XT without the STI motor should ask for their money back :D
 

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Discussion Starter · #9 ·
Oh and Sullie is not exactly unique in having an STI engine in his Outback XT.. Anyone who got an XT without the STI motor should ask for their money back :D
I assumed that Sullie had uprated the stock Forester boxer engine with STi bits.

I guess anyone can make a 1.8T sound like a WRX with a goofy enough header. Hmm...
 

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It's due to the design of the manifold and the air passing across the motor. I believe it cylinder number 3 thats the main coprit
 

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ding...

http://www.scoobymods.com/forums/showthread.php?t=6772
How's that Honda treating you by the way? ;)
The Honduh is good. It's very driver focused, and is predictable all around. Rotates exceptionally well. It could use a little more (okay, a LOT more) front tire for my autocross purposes, but its not as noticeable on the street. The chassis is very stiff, but having driven on stiffly sprung coilovers the past couple years, my butt is still having communication issues w/ the rear tires. :D

Brakes are fantastic. Stops shorter than anything I've ever driven, but they're also cheating a little because its electronically assisted. Gearbox is probably the best in the business. Power is good with the new 2.2L...its torquier than my old KA24DE in my Nissan (sadly enough). Also I'm not sure what's worse, VTEC rollover or turbo lag...because both can catch you off guard at the wrong time.

I think you'd love it...although having two impractical forms of transportation is probably silly. But hey, at least you can take home ladies. ;)
 

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Hello guys,

This is an easy answer. it's due to not only the firing order, but the engine's configuration. Much like an old VW air cooled motor, the subaru WRX motors are opposed engines, also known as boxer engines. Not as in Boxster like the Porsche, but boxer like the dog. Some also call them flat engines or horizontally oposed engines.....

BMW has used this style in 2 cylinder formats on their motorcycle for years, you may notice that it's the style that was on some Honda Goldwings and Valkeries in 6 cyl, and in air cooled and water cooled porsche's for decades (they used flat fours before that, much like an air cooled VW.)

Motors of a similar style generally have similar torque curve characteristics. I6 motors rev long and are torquey, four bangers high and good for hp if not torque, V12's have a torque curve that goes to the moon and HP to match.

Motors of similar types can sound similar as well. Most people wouldn't notice the similarities between a WRX and a VW beetle, but a car guy should. even if he doesn't know why. props to you.

A v12, be it in a Ferrari, BMW, Jaguar or whatever, will all be like and kind. Heck, those V10 F1 engines from last year, although each vastly different, were very similar to eachother as well.

A flat four or six is one of the most distinct sounds of all. And they are interesting to work on for sure, simple for the physics, tough for the plumbing. Anywho, check this out....

http://en.wikipedia.org/wiki/Boxer_engine

it's a fun link to check out and peruse.
 
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