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How air goes thru your engine.....(basic)

Discussion in 'Technical Chat' started by chris4x4, Nov 30, 2008.

  1. Feb 27, 2010 at 7:34 AM
    #41
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine. Staff Member

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    FlimFlubberJAM
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    I went into all of that in the first version, but it was too long, and I had to shorten it. :( I'll make it a sticky :)

    Thanks :)
     
  2. Feb 27, 2010 at 8:19 AM
    #42
    4low2go

    4low2go Well-Known Member

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    Great post :thumbsup: Smooth flowing manifold runners made a big difference in the old carburetor (and throttle body injection) systems as coarse passages and abrupt angles actually de-suspend fuel from the fuel air mixture, costing power while increasing emmissions. With fuel injection systems, this is a non-issue.
     
  3. Apr 1, 2010 at 3:37 PM
    #43
    DGXR

    DGXR Well-Known Member

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    Makes sense how forced induction just crams more air and fuel into the cylinders, so a free-flow/low backpressure exhaust suits these applications best. Easy to read and understand. Thanks
    EDIT: Looks like someone's been watching "Two Guys' Garage" ;)
     
  4. Jul 14, 2010 at 10:50 PM
    #44
    HBMurphy

    HBMurphy Ban Pending

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    No! Video's that violate do not have validity! :)
     
  5. Nov 13, 2010 at 3:57 AM
    #45
    tacoman05

    tacoman05 Well-Known Member

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    Hi guys. I have a question. My truck is up for a smog Check and I have a trd cold air intake and an aftermarket exhaust. I'm afraid I could have trouble at the smog check place. Do any of u know if that would affect my truck passing the check ? Thx
     
  6. Dec 28, 2010 at 2:13 PM
    #46
    TampaDude

    TampaDude Well-Known Member

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    For normally aspirated engines, exhaust pulse timing and exhaust tuning is critical to obtaining maximum power from the engine. For turbocharged engines, it's a lot simpler...just have as free-flowing an exhaust as possible for maximum power. The ideal exhaust for a turbocharged engine would be a conical or horn-shaped pipe going straight to the atmosphere. While impractical for a street car, you see them on race cars all the time.
     
  7. Oct 1, 2011 at 1:30 PM
    #47
    LifeIsGood169

    LifeIsGood169 Well-Known Member

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    I only read the first page, but the "myth" of engines needing back pressure might have come from 2strokes (first internal combustion engines). A back pressure wave can really help compress air entering the cylinder depending on the exhaust valve location (or open engine hole). I know if I take off the expansion chamber on my 2stroke - it gets absolutely no power in comparison (maybe a 50% drop or more). So 2 strokes is definitely a different story.

    Tuning the flow is right though. After a warm engine, I found about 1/8" bigger helped me get 1-2mph more top end and quicker response (i just drilled in some extra small ventilation holes - ie: not everything has to come out the very end of the pipe). But after only 1/8" + on exhaust size I started losing power. I would've thought 1/2" + or more would do better. Bigger definitely is not always better until you change the cams or turbo, etc.

    The best advice is:
    -just to leave it stock
    -only mod it a little (<1")
    -or keep trying stuff until you find what works right, but this can be pretty time consuming. Took me about 2 weeks on a small motor (tuning the carbs / intake size / etc. too though). I also had to tune while driving, cause it was completely different verse stationary tuning (dealing with 25mph+ i found much different throttle responses compared to stationary). I probably needed a fan on the intake to tune parked.


    I think this is a cool topic, because I see a lot of people immediately jump to the 4" pipes. My buddy with an old Wrangler got the 4" pipes. It's funny to watch him take off in 1st gear. He has to rev soooo much to avoid stalling. It's so bad off road - especially crawling on fire access routes.
     
  8. Jul 7, 2012 at 8:44 AM
    #48
    exchiefi

    exchiefi New Member

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  9. Nov 26, 2012 at 8:40 PM
    #49
    BuildDesign

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    Chris4x4 or any others can explain a smog pump or air injector?

    I believe it's now on 13's
     
  10. Jan 30, 2013 at 3:54 AM
    #50
    tacomarich

    tacomarich luvsoffroading

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    secondary air injection? like in emissions control. fresh air is injected into the ehaust stream to allow a fuller combustion of gases. thank for this great thread. can really learn a lot.
     
  11. Jan 30, 2013 at 7:30 AM
    #51
    DGXR

    DGXR Well-Known Member

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    ^ this, and
    the fresh air injected into the exhaust stream provides oxygen to allow any unburned fuel in the exaust gases to burn. In other words, the exhaust gases are still hot enough that the unburned fuel will combust when it finds this injected air/oxygen, that is the theory.
     
  12. Feb 15, 2013 at 7:22 AM
    #52
    RDtres

    RDtres Well-Known Member

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  13. Mar 24, 2014 at 2:07 PM
    #53
    GotExhaust

    GotExhaust Well-Known Member Vendor

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    Excellent write-up Chris. You could also incorporate the effect of high-temp thermal coatings that are often applied to aftermarket long tube headers. Keeping the heat "in" lowers under hood temperatures and protects surrounding components, which is widely believed as the main benefit. However, keeping the exhaust gasses hot is also very important with a properly sized primary tube diameter for the reasons you have covered.
     
  14. Mar 24, 2014 at 3:51 PM
    #54
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine. Staff Member

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    GotExhaust">
    Interesting you mentioned underhood temps, as I have actually tested that. Seems underhood temps are around 10 to 20* over ambient temps when the vehicle is in motion. When idle, at a stop light for example, temps go up to around 20* less than engine temp. Depending on vehicle, that can be anywhere from 160* to 200*. The vehicles I tested this on were 2001, 2007 Toyota Tacoma, 2005 Dodge RAM 2500, 2006 Honda Accord, and a 2004 Chevy 2500. I haven't had a chance to test with a header wrap, but the ceramic coating didn't seem to influence the temps one way or another. A friend of mine, who has a little more knowledge with using the wraps, seems to think the wraps would make a difference, but not to an extreme degree. The radiator in an engine bay is one of the largest contributors to underhood temps. The exhaust temps are higher, but given the surface area of the headers, vs. the radiator, the radiator wins the engine bay heat war.
     
  15. Aug 31, 2014 at 11:51 PM
    #55
    gray223

    gray223 Well-Known Member

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    So how do you explains something like an air intake manifold spacer. Don't they lower the torque peak? Wouldn't they limit the back flow ,from the closing of valves, from getting to a different cylinder like mentioned in the op?
     
  16. Apr 22, 2015 at 10:08 AM
    #56
    Cogneato

    Cogneato Active Member

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    Ok so with all this said, why would a truck that has perfect fuel trims and timing run lean or rich? I just replaced my exhaust manifold about 3 months ago and I just found out that the new one is cracked. I'm about ready to ditch this truck.
     
  17. May 13, 2015 at 7:20 PM
    #57
    Justn868

    Justn868 Well-Known Member

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    Great writeup :thumbsup:
     
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