With a number of folks asking me how my car (read: Imprezas in general) sounds so distinctive, it's got me wondering why Subaru ended up with unequal headers. It has to be said, the engine note is utterly gorgeous... but if unequal headers are less efficient, why/how did Subaru end up using such a design..?

1) Is it purely down to cost (cheaper to design/manufacture)..? (but everyone would be doing it)
2) Space constraints within the engine bay..? (most cars have the same problem)
3) Constraints because of the boxer layout..? (perhaps this is the reason..?)

Just seems odd, but hey, I'm not complaining!

Jonts.

 

If you look at the Beetle which also had a Boxer engine they sounded similar,They had a bit more space with the engine being in the back(maybe?) so might not be a space related thing....

So back up for a real answer because i would like to know now also.

 

A combination of the three things that you mentioned. Beetle engines sounds similar for the same reasons.

The unequal length headers work at the level of tune the Impreza is at as standard and beyond. Equal length pipework would be more complex, more expensive and harder to package in the engine bay, therefore it was not needed.

 

Certainly makes sense eh.

Jonts.

 

Don't know if this is a red herring or not, but having unequal length headers changes the torque characteristics of an engine, maybe they were engineered to offer a user friendly torque-band rather than maximum horsepower?

 

Ive gone (though admittidly to a more powerful scoob) from uneven to even length headers (both engines standard, though ecu on the classic was a ppp) and the even length ones (242lb ft on the classic to the 356lb ft of torque on the new age) is considerably more drivable than the uneven length one (classic MY00 PPP decat v MY03 JDM STI Spec C).
You have to remember that the engine design was probably "borrowed" from other companies, the enhancements are now showing on (mainly the JDM cars) the newer scoobs, and people dont like it because it kills the sound (shame the sound wasnt there on the standard exhaust system )
Equal is the way to go

Tony

 

It's a trait common to any Vee or flat engine running a single length exhaust (or single turbo). Ultimately its cost and space. And the gain for road use is negligable as the system, like an equal length, can be tuned (in combination to exhaust cam profile and timing) to prevent back pressure pulses re-entering cylinders on exhaust strokes (although over the years, some manufacturers actually wanted this to ocurr for emissions...a crude and cheap form of EGR - this is rarely the case in this day and age though ).

I have never liked the subarus exhast noise...to the trained automotive ear it sounds that the engine is running unevenly and unbalanced, when it isn't. From a engine design standpoint the engine should run perfectly smooth. Anyone else being brought up on straight sixes and v12 with equal length headers know how silky smooth they are - with pefectly timed and sequenced fireing pulses with near perfect balance, which flat 4s should also posses. Unlike single plane V8s and inline 4s twins V twins, v4s and V6s.

Dual plane v8s, like boxers, v12s and inline 6s thanks to counterweighting run smoothly, but the timing between firing pulses is not in regular sequence. Thus the offbeat sound that no header work will cure - it's supposed to sound like that...a flat 4 is NOT supoosed to sound like that

 

I completely agree with that statement, for some reason they always make me cringe when reving hard because my brain is saying "that car sounds rough as a donkey".. It also masks any minor ignition/timing problems.

It does add character though, like the Ducati & Aprillia V twins, they sound ropey but its a beutiful sound, if that makes ANY sense?

 

An interesting read, well posted

 

Surely such things should not be spoken on a subaru website.

Thankfully my ears are not trained . I remember walking home from the pub one light summers evening a couple of years ago and a scooby cruised past me at about 30 mph. It made the best noise I have ever heard on a car and I thought , I have one of those in my garage.

 

Ditto. I was washing my car yesterday and heard a flat 4 rumble/growl approaching, (followed by the pssssttt of the dump valve which I'm undecided on ). I thought "I've got one of them too! "

p.s. rossyboy, "The most heavily modified bedroom cupboard in Scotland...". You must shop in the same furniture store as me because I have the most heavily modified "under-bed-storage" in Wales

 

I'll third that motion. Even if the exhaust design isn't as efficient as it could be, what's refreshing is an automobile which has a unique characteristic. I adore the exhaust note and couldn't wait to get another silencer (yeah, right!) fitted.

With all the other factors taken into consideration, perhaps Subaru used this design to get some free marketing/advertising. Stranger things have happened.

Jonts.

 

Here, here!!!! if it wasn't for the distinctive flat four grumble I would probably have quite happily settled for any other 4-pot turbo. It was the sound of the boxer that ultimately swayed me from buying a straight 4 engined car, and the fact that mine had a nice exhaust (magnex cat back) when I bought it helped.

 

Got to agree with that. The evo handles better but the scooby has more charictor so Scooby was where my money went.

 

Same here swapped from scooby to evo only to swap back because I missed the character of the sub.

 

Not any more. My bedroom cupboard has been emptied and its all lying in the car for fitting this week