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Questions about dumps

Discussion in 'The Hokey Ass Message Board' started by Hellfish, Jul 3, 2012.

  1. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,429

    Hellfish
    Member

    I have a 302/5.0 HO motor with a 4bbl, but otherwise stock. Will dumps add or rob horsepower or torque?

    I read somewhere that eliminating backpressure causes problems and that I would need to lean out the carb... and I've read that there would be absolutely no problem. :) Which is it?

    I'd only uncork them for passes at the dragstrip, and they would probably get placed 12-18" from the end of the headers.
     
  2. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,811

    thunderbirdesq
    Member

    I doubt you'll notice a performance difference with a stock engine. The whole backpressure deal is a myth for the most part.
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 45,660

    squirrel
    Member

    It'll sound faster. But whether or not it will make the car faster depends on a lot of variables....I guess you'll have to try it and see. It's more likely to help if the exhaust system is very restrictive.
     
  4. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,429

    Hellfish
    Member

    The system has a lot of bends in it, but they're nice radiused mandrel bends in 2.25 or 2.5" pipe with glass packs. Not really restrictive
     
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  5. I have only seen a few cars that were faster with open headers. they sound faster like squirrel said.
     
  6. You will find nothing that you can feel from the seat of your pants either way.
     
  7. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,429

    Hellfish
    Member

    "Sounding faster" works to intimidate the other driver, right? :D
     
  8. Throw a cam in it and then the dumps would add.
     
  9. The 14 year old in me sees:

    "...dumps..."
    "...eliminating back pressure..."
    "...nothing that you can feel from the seat of your pants...."


    That aside, some engines actually run better with a bit of backpressure. One of my old trucks when the exhaust fell apart I cobbed a glass pack on it and being cobbed it fell off a couple of times - the milage got worse and I could feel the engine laboring a little at the same highway speeds, it was enough of a difference that before I went home from where I'd gone I went to the parts store for some bits and cobbed it back together.
     
  10. Da' Bomb
    Joined: Apr 8, 2005
    Posts: 438

    Da' Bomb
    Member

    I used motorcycle mufflers with a fiberglass wrap. makes back pressure and still sounds kind of snotty....
    Pat
     
  11. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    tommy
    Member Emeritus

    Dumps will ruin your gas mileage........ You can't help but keep your foot into it and use a lot more gas than a stock exhaust system.

    As far as back pressure helping with HP Somebody would have to prove it on a dyno for me to believe that old wives tale. If you got numbers to prove it then I'll listen.
     
  12. Not to hijack or stray too far off the OP's question, but I always wondered if the use of dumps when they are closed, causes any kind of turbulence in the flow that might diminish power. In other words, if you have say 18" long dump pipes, that exhaust is kinda trapped to some extent when the dumps are capped. Would this cause a disruption in the flow or am I way too over-thinking this?
     
  13. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,429

    Hellfish
    Member

    Yeah, I was wondering the same thing, but figured that enough race cars use them that it can't be that large of an effect, if there's one at all... but that's just a guess
     
  14. I have thought about this also...I figgered(on my set up anyhow) that the exhaust would just go to the deadend and the new exhaust would flow past the tailend of the deadended exhaust...get me?Sometimes I must talk with a drawing...but I look at the deadend as just that and it is just kinda pressurized to the point the where the gas routes to path of least resistance...in other words,the gas is trapped in the deadend and the ex. from engine kinda forces the trapped gas to stay put and just makes the curve to the muffler.I don't think it bounces or turbulates much just looks for the easiest way out...I dunno if I am 'splaining this so others can pick up what I,m puttin down or not....hope so....I would like to know if my theory is close tho....
     

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    Last edited: Jul 3, 2012
  15. ....I understand your explanation completely:) I just wonder if any exhaust companies or muffler companies (or for that matter, some bored engineer) have ever done actual tests to determine how this all might play out in the real world.:confused:
     
  16. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    tommy
    Member Emeritus

    Donnie you need to go back to contemplating your navel.:D

    [​IMG]
    I do set mine up to be a direct shot when they are open. The more restrictive 90 deg. connection is on the muffler connection when HP is not a priority and the muffler is the limiting factor. Really it's just babble for bench racing. BTW I have an innie..:D
     
  17. ....Same here, Tommy, but my innie is farther out than it used to be:D
     
  18. EXracer64
    Joined: Dec 7, 2011
    Posts: 226

    EXracer64
    Member
    from nj

    It will be faster but like .005 faster. Not worth it if it's a good system to start with.
     
  19. II FUNNY
    Joined: Jul 31, 2010
    Posts: 1,827

    II FUNNY
    Member

    I don't know if it makes any more or less power or not, but if your talking about running it at the MELTDOWN DRAGS then I vote for dumps and not the full exhaust.lol

    My uncle said on his old race car they would put on dumps that were around three feet long and then spray paint a line on the dump tube. He said where the paint was not burned off thats how long the pipes needed to be. I think it makes since ,but I aint sure exactly why.
     
  20. If it's a 85-92 era 5.0 w/stock cam it makes 175-225 crank hp I can see doing it it if the truck runs at least low 13's.
     
  21. Someone wants to sound tougher at the meltdown drags? If you have them ready before the meltdown, we have a homework assignment for you. Make a few passes with the exhaust closed and uncorked and report your findings back here.:D
     
  22. von birch
    Joined: Oct 17, 2008
    Posts: 205

    von birch
    Member

    sorry porknbeaner, haha but the post is "question about dumps" need i say more or is the irony obvious?

     
  23. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,013

    Atwater Mike
    ALLIANCE MEMBER

    I always thought they made me at least 2 tenths quicker, on Montague Exp'wy, anyhow.

    Every time I uncorked 'em, here'd come the CHP! When I didn't uncork 'em, it took them a half hour to get there.

    They wouldn't rush out there unless they thought Garlits or Masters & Richter were running... LOL
     
  24. EXracer64
    Joined: Dec 7, 2011
    Posts: 226

    EXracer64
    Member
    from nj

    That's what you do to find out where to put a crossover or h pipe in an exhaust
     
  25. We've had exhaust dumped up front in a OT 1700 hp car, no turbulence.
     

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