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What's the reason for the pulsing?

86 people have voted on this poll. You may not vote on this poll

Exhaust manifold design
48 55.81%
Boxer engine design
38 44.19%
  1. Post
    #26
    Mettler wrote:
    I don't think it's a combination of being a boxer engine AND exhaust manifold to make that sound, it's solely the exhaust manifolds. However, the exhaust manifolds being this way is a result of the boxer engine design.
    Yeah, that'd be a better way to word it. Was kinda trying to get at that, but work is doing my head in atm. Hence downtime

    Mettler wrote:
    Now think of this. If a cylinder fires, then another cylinder fires, and the first cylinder's exhaust runner is longer than the second one's exhaust runner, then both pulses will arrive at the collector at the same time (roughly), or within very close proximity to each other, merging together to create a single larger pulse (and sound).
    Presicely what I attempted to draw (lol). But then I wonder, the VWs had a similar sound, but a different firing order. Then again a different manifold so maybe the net result was the same.


    Then just as I was thinking about what you said about the rally evos, I realised that the question was answered. My first thought was "Well what is the manifold design on those, maybe pulses double up due to that."


    In closing, I accept that manifold design is the cause of the sound. But the engine design affects manifold design. A flow on effect. Both are the cause, but one more directly than the other (imho)

  2. Post
    #27
    Jewjew wrote:
    I would have thought that an extra meter or whatever of mainfold wouldn't effect the sound so much, considering its travelling at the speed of sound, but I guess the engine pulse and airflow would affect it greatly.
    Consider that all four exhaust pulses are travelling at the speed of sound, so if they have varying distances to travel, it'll change their merge spacing when running together. It'd be pretty cool to configure an exhaust exactly such that they all merge at the same time and give an engine a "BOOM BOOM BOOM BOOM" single pulse exhaust note


    Worst wrote:
    In closing, I accept that manifold design is the cause of the sound. But the engine design affects manifold design. A flow on effect. Both are the cause, but one more directly than the other (imho)
    Ah awesome But because it's friday, and because I'm argumentative, I'm calling you out on saying the engine design is what's responsible for the exhaust manifolds. Well, I say that's not true, because bolt-on, even length aftermarket manifolds are available for the subarus, which means subaru could have produced those from factory.

    Either subaru were saving money, or they deliberately made their cars sound like that. Either way, blame subaru for creating one of the more interesting sounding 4 cyl sports cars around. ;P

  3. Post
    #28
    Mettler wrote:
    WTF, are you seriously actually attempting to say that a boxer engine doesn't have a combustion event every 180 degrees, but are spaced like... 200 degrees, and then 160 degrees apart?
    lol no. Just that the net result of the cylinder that fires first on one bank, its pulse has further to travel.

    Mettler wrote:
    It'd be pretty cool to configure an exhaust exactly such that they all merge at the same time and give an engine a "BOOM BOOM BOOM BOOM" single pulse exhaust note
    **** yeah!

  4. Post
    #29
    Mettler wrote:
    BTW I'm fairly certain that V4s (boat engines at least) have two cylinders firing at the same time.
    Boat engines, eh? I wouldn't know.

    Car engines don't though.

  5. Post
    #30
    Mettler wrote:
    Either subaru were saving money, or they deliberately made their cars sound like that. Either way, blame subaru for creating one of the more interesting sounding 4 cyl sports cars around. ;P
    Yeah. I'm gonna go with it was deliberate. Just like using a flat four when all the other Jap manufacturers were using I4s for the most part (that's a guess btw). And couldn't you wait till tomorrow to be argumentative bro? I'm sober now but got CC and Dry tomorrow

    *edit* And I'm pretty much a car newb. I know a little, but not really any specifics. That's why I'm in CB&M a bit more these days, hoping some of it will rub off.

  6. Post
    #31
    Good shit, rubbing off in CB&M is a hilarious idea.

  7. Post
    #32
    Whatever gets your motor running

  8. Post
    #33
    im going for exhaust header lengths being un-even to the collectors (sound wave/pulse stuff)

    on a side note, "how does 911 headers workout for lenghts? " they dont really sound like a boxer with 2 more cyls

  9. Post
    #34
    911 ones wont be equal length either, but they have more cylinders so the pulsing isnt there. They still sound unique though.

  10. Post
    #35
    Mettler wrote:
    Either subaru were saving money, or they deliberately made their cars sound like that. Either way, blame subaru for creating one of the more interesting sounding 4 cyl sports cars around. ;P
    It's only WRXs that sound like that though eh? The regular shitbox Imprezas don't (unless it's just because the exhaust's too quiet to hear it?).

  11. Post
    #36
    Egor wrote:
    (unless it's just because the exhaust's too quiet to hear it?).


    There's plenty of NA Legacies and Imprezas driving around going BRRRRR making the same sound, albeit much flatter and hollower due to producing approximately NO power.


    *haxed by Mettler
    Roadskin
    Guest

  12. Post
    #37
    All this Subaru talk reminds me of this:


  13. Post
    #38
    'Eat my poo, subaru'.


    Someone stab me in the eyes, or the ears.

  14. Post
    #39
    WTF LOL

  15. Post
    #40
    I didn't watch it, whored it to death a few years ago when it came out

    Check the nips on the nippon

  16. Post
    #41
    any flat 4 subaru with a loud exhaust makes the rumble including NA. some of which have a symmetrical exhaust system. alfa 33's do it too. if the one in your workshop doesn't, cut the muffler off and it will. it will be a different sound to subarus but will have the low freq pulse. VW's are different again but there's still a low frequency compnent to the sound.


    i've run alfa 33's (and probably subaru's though i can't remember a specific incidence) with NO manifolds and they still do it.

    also consider the exhaust headers of turbo vs NA subarus. radically different yet produce almost the same noise.

    even though i dont understand the phyics of it, i feel the engine layout is the major factor in producing the "boxer rumble".

  17. Post
    #42
    +1 exhaust layout- and thats solely because the boxer design severely compromises exhaust design.

    The 'symetrical exhaust system' is still only symetrical L/R - not F/R so you still have an uneven exhaust note. The only proper matched exhaust system for the boxer engine is the 4-1 aftermarket headers that are annoyingly bulky and make the exhaust note even.


    BTW, there are v-4s that fire 2 cylinders together, like 2 V-twins, and V-4s that fire indivually. Balance is terrible. They also sound like subarus.

  18. Post
    #43
    Alfa 33's have a virtually symmetrical exhaust system, 4-1 - slight bend where it exits onto the rear muffler - but by then they have merged anyway. I've had the manifolds off on one.. Don't sound like Subaru's... Boxer yes, Subaru no..Cylinder head and port sizing anything to do with it?

  19. Post
    #44
    Hi guys,

    As an owner of both NA scoob and WRX (well UK Turbo anyway) can I put my well informed and experimented 2c worth in?

    The turbo motor has the turbo entry just behind one cyl bank, so the manifold is very very short going in to the turbo collector on that side, only about 16", the other bank comes way across the back of the engine and joins the first one, but its length is around 28".

    On the NA, the manifolds are EXACTLY the same length, and with just the manifold and first cat, the two sound entirely different. The NA sounds pussy and normal like any inline 4, the turbo sound just like a scoob is known by.

    Boxer motors, are so called because they "punch" like a boxer, its like swinging 2 cyls down on the crank journal of an I4 till they hang out the bottom instead, then laying it flat, I4's pop alternate pairs of cyls up and down 2 at a time, boxers pop all four out and in at the same time as the crank pins are 180 degrees apart as normal but 2 cyls are pointing the wrong way, get it?

    Boom Boom Boom Boom

    AND having spent loads of time trying to replicate the sound on an NA then finding out it cant do it unless the manifold runners are very different lengths, I built an exhaust out of S/S exactly as the WRX shape, and it worked perfectly. I can even post a sound clip if I can find it. Unfortunately, it diminshed its already puny power output by a good 30bhp.......This is also why the 2L engine makes such crap power without a turbo....uneven exhaust manifold lengths and poor scavenging. Seperate banks with uneven length main runner, absolute truth no doubt about it.

    Been there, read the book, saw the movie, ate the pie AND wore the tee shirt, end of.


  20. Post
    #45
    BTW Subaru are actually Fuji Heavy Industries who made aircraft engines from WW2 onward, and used the flat4 light aircraft engine as the basis for the car. The engine was a flat4 design so the block was kept out of the pilots viewline and increased his forward view from the cockpit by letting the prop be mounted lower down and kept the centre of gravity low too.

    A friend who owns a Subaru garage, actually owns and flies an original subaru light aircraft (now painted in WRK colours and stickers LOL) and it has the 2L Turbo engine in it, exactly like my car did...

  21. Post
    #46
    Cool info scotsman welcome aboard

  22. Post
    #47
    So.. Was Mettler correct?

  23. Post
    #48
    Yes. Try reading the thread.

  24. Post
    #49
    Yup he was

    Thanks for the welcome guys!

    (Now...I was actually sitting thinking, how can I make my new Audi Quattro Turbo sound like the scoob without losing hp.....)

  25. Post
    #50
    Slap a scoobi motor in it?