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Technical Split Exhaust on a Pontiac Flathead 8 (to get V8 Sound)

Discussion in 'The Hokey Ass Message Board' started by leroycash, Jul 13, 2018.

  1. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    A few years ago I read a post claiming you could get a V8 "sound" out of an Inline 8 engine if you split and ganged the eight exhaust ports in a certain way based upon your crank configuration. It had something to do with a 4-4 vs. 2-4-2 crank configuration like on a Packard 8. I have a 52 Pontiac 8 with the standard High Compression head and 2 bbl intake. I'm not sure what to look for with this Pontiac crank configuration as it relates to sound. That's my first question. My second question would be which cylinders should I gang to get that V8 sound? I'm under no delusion I will get much performance out of splitting the exhaust. I just want better sound when I cruise.
     
  2. RichFox
    Joined: Dec 3, 2006
    Posts: 9,281

    RichFox
    ALLIANCE MEMBER

    I would guess you need to put every other cylinder, as they fire, in separate headers. All the even firing in one. The odd in the other. May be hard to do without 8 exhaust ports. And V8s are not usually done that way anyway.
     
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  3. BBFHY
    Joined: May 12, 2018
    Posts: 3

    BBFHY
    Member
    from Texas

    V8 dual exhaust sound is syncopation. Below L is left bank, R is right bank.

    Chevy V8, using firing order -
    LRRLRLLR

    Flathead V8 -
    RLRLLRLR

    Send exhaust to each side of car like that, should get a V8 sound.

    Edit: Looked up Pontiac firing order. 16258374. Plumb odd numbers to one exhaust, even numbers to the other. Should get V8 sound. Assuming you have eight exhaust ports. May not be possible without.
     
    Last edited: Jul 13, 2018
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  4. belair
    Joined: Jul 10, 2006
    Posts: 7,554

    belair
    Member
    1. H.A.M.B. Chapel

    Maybe it will sound like two four cylinder engines.
     
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  5. I'd have to do the math but there's more to it than just one cylinder routed here, one there. It also has to do with the firing intervals which depend on the angle of the V. Simple example, you can't make a parallel twin sound like a V-twin without changing the crank to mimic the V-twin's firing intervals. Maybe the straight 8 already mimics the V8's firing intervals? I dunno...

    That said, "make it sound like" is subjective. What sounds exactly alike to you may sound glaringly different to me. Splitting the exhaust may be worth it, I don't know, but from a theoretical standpoint you may not be able to get there from here.
     
    Last edited: Jul 13, 2018
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  6. jimmy six
    Joined: Mar 21, 2006
    Posts: 3,136

    jimmy six
    Member

    Ford flats had their own sound as the y-blocks and paired cylinder Olds. I'll bet it will sound good anyway you do it. Just remember it will never get the "twice pipes" sound of an inline six..
     
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  7. samurai mike
    Joined: Feb 24, 2009
    Posts: 367

    samurai mike
    Member

    why the hell would you want a straight eight to sound like a v eight?
     
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  8. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 8,461

    Rusty O'Toole
    Member

    I'm with samurai mike. If you want the sound split the manifold and run 2 pipes all the way to the back of the car with your favorite mufflers.
     
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  9. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Good point. Yes, there are definitely eight exhaust ports on the block. I'm wondering if the sequence is a straight alternating pipe-one then pipe-two or if there's something different in the sequence.
     
  10. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Thanks for the response, and wow, that's pretty interesting. Both V8 engines alternate the pattern on each bank in a similar way. I'm going to have to sketch this pattern out with the inline 8 firing order. You've got me thinking.
     
  11. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Ha! That would be disappointing, to say the least.
     
  12. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Good point. By interval do you mean sequence? It seems like the sequence alternating between two manifolds on the inline 8 could be combined similar to the left/right manifolds on a V8. It may look odd.
     
  13. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    I don't know the twice pipes sound. What's that?
     
  14. XXL__
    Joined: Dec 28, 2009
    Posts: 1,203

    XXL__
    Member

    Embrace the engine you have... or if you can't, swap it out.
     
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  15. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Fair question. Right now its just a what if question. It may not make a better sound.
     
  16. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Yes, agreed. I think that's the plan. My only question is which exhaust ports go to which pipe? I may not have that many options given the tight real estate on that side of the engine. But as a hypothetical...
     
  17. RichFox
    Joined: Dec 3, 2006
    Posts: 9,281

    RichFox
    ALLIANCE MEMBER

    V8 or straight eight they both fire every 90 degrees
     
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  18. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    True that.
     
  19. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    Yes.
     
  20. 302GMC
    Joined: Dec 15, 2005
    Posts: 5,153

    302GMC
    Member
    from Idaho

    Split it 5 & 3. The sound is unlike anything else you'll hear - one pipe chases the other as the hydro shifts. Routing the dual side headpipe around the heater is the hardest part.
     
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  21. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,405

    F-ONE
    Member
    from Alabama

    Just run eight pipes all the way back.
     
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  22. leroycash
    Joined: Apr 14, 2011
    Posts: 11

    leroycash
    Member
    from houston

    I never thought of this. Any idea which cylinders you would put on the 5 and which ones on the 3? One thing's for sure, you can't do that with a V8! There's gotta be a quick way to mock this up.
     
  23. 302GMC
    Joined: Dec 15, 2005
    Posts: 5,153

    302GMC
    Member
    from Idaho

    5 in the stock flange, 3 up front. Last one I did, I cut the manifold into 2 parts & plugged the cuts, then used a Gotha weld-in flange in the side to better clear things going down.
     
    Last edited: Jul 14, 2018
  24. firstinsteele
    Joined: Jun 13, 2013
    Posts: 710

    firstinsteele
    Member

    I did this [ 5&3] with a straight eight Buick in the '50s. Awesome sound. My brother still talks about it.

    Ben
     

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