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muffler question

Discussion in 'Flat Fender Tech' started by Andy4802, Jan 28, 2007.

  1. Andy4802

    Andy4802 Canadian Jeep junkie

    guys i need a new muffler in my flattie... I've got the stock flathead 4. any issue with me putting a cherry bomb (straight through style) on there or do i need something with more back pressure?
     
  2. jeepfreak81

    jeepfreak81 When in Doubt, Pedal out!


    At least in these parts a straight through style is not legal on the trails, I am going to have to have an extra set for the trails around here
     
  3. Andy4802

    Andy4802 Canadian Jeep junkie

    i use mine on both street and trail... i dont think the law will hassle me too much unless its ridiculously loud... im mostly wondering how it will affect the way the engine runs... i've heard that the L4 runs better with a bit more back pressure. any thoughts anyone?
     
  4. BlueFlu

    BlueFlu past owner of some ecj5's

    I'd run a Flow Master myself.
    Can't kill them.
     
  5. 1963cj5

    1963cj5 Member

    get a repo from walcks..you needy the back pressure..repos have the correct baffles in them..
     
  6. Gwillys

    Gwillys 1953 CJ3B

    i wanted to put a glass pack on my 3b 4 cylinder. what does the back pressure do to help the engine?
     
  7. mb82

    mb82 I feel great!

    It gives gas to be compressed along with the fresh air. Or at least thats the theory I have been given. Contrairy to what a lot of people think backpressure to a cirtain point is needed for most motors.
     
  8. 1963cj5

    1963cj5 Member

    Wise man told me it also helps the valves from getting burned out..???
    Makes since but everyone has there own ideas..I have burned valves testing(running) engines without an exhaust system before I have re-built them..
     
  9. CJ-X

    CJ-X Member

    I believe as long as you have a manifold and a length of exhaust pipe you are fine. Exhaust gases will be drawn out properly. The muffler seems insignificant. I have seen flatheads run well with original, glasspack, and mufflerless exhaust. I think some newer computer controlled engines might throw error codes for EGR if there is not enough back pressure for a little exhaust to be returned. Those recirculated exhaust gases do lower combustion temperatures, but that is primarily used at cruising speeds, and many people (myself included) get rid of EGR valves. Engines like cool fuel and clean air.
     
  10. cj-john

    cj-john Member

    I'm going to throw in my 2 cents on this if you don't mind. From what I know about exhaust, which is little, is that running an engine with no exhaust or only a manifold will allow the valves to cool to fast and bend. I think that is why the old timers alway say to run a manifold with some pipe or a header. That is all I've heard about an exhaust system, or the lack there of, damaging your valves. I've never understood the back pressure theory. If you think about what cam and head modifications do for your motor backpressure seems to contradict that. Bigger cams and better flowing heads and intakes move more air and than increases your volumetric efficiency. Your enigine is basically an air pump. Think about an air compressor as it builds pressure. As the pressure goes up in your tank the motor and compressor works harder. Maybe a bad analogy, not sure, I would like to hear some other therories on the back pressure thing.
     
  11. SIDSCJ

    SIDSCJ Jeep addict

  12. cj-john

    cj-john Member

    Hey, I buy that theory. That makes total sense to me. I thought about this more after my post last night. Think about the header designed to produce a "scavenge" effect. That is when one header tube helps pull more air/fuel mix into another cylinder during valve overlap, at least I think thats how they work. Anyhow, this totally bebunks the backpressure idea. Heck, I don't know, maybe each one has its' benefits depending on the engine design. I've already put to much thought in to this. I usually just buy the muffler thats cheap and holds up well. We're talking about a Jeep muffler, not an F1 race car!
     
  13. blevisay

    blevisay Oh Noooooooooooooooo! Staff Member

  14. blevisay

    blevisay Oh Noooooooooooooooo! Staff Member

    Oh and maybe we can con Jerry into commment....I have had several discussions with him in regard to exhaust........he is pretty sharp with it
     
  15. w3srl

    w3srl All-around swell dude Staff Member

    You will definitely feel a lack of bottom-end "oomph" with a straight-through exhaust, not to mention that your Jeep will sound more like a street-sweeper than a Jeep. What works well at high RPM isn't necessarily going to work well at trail speeds. I've run both the stock setup and a "free-flow" setup on my stock '2A and the glasspack setup definitely lost the bottom-end when compared to the stock muffler and pipes. Call it "seat-of-the-pants" engineering. :D
     
  16. cj-john

    cj-john Member

    Once again that points to back pressure as being a load of B.S. Good article, thanks.
     
  17. Andy4802

    Andy4802 Canadian Jeep junkie

    tell ya what guys... I'll be the guinea pig :) . I'm going to install the straight-through cherry bomb... I'll let you know what the results are. And hey, if i blow the motor, we can call it an excuse to finally swap in a 6. R)
     
  18. w3srl

    w3srl All-around swell dude Staff Member

    :toetap:
     
  19. trickpatrick

    trickpatrick Done? LOL

    Racecars and what we drive are not that much alike.
    I think the cherybomb will work but a muffler would be better.
    Not much advice out there for low rpm performance.

    my .02 cents.
     
  20. 51M38

    51M38 New Member

    I have a 51 with the stock L head. I run a cherrybomb on mine with no problem. It runs smooth and I drive it daily. In Virginia as long as I keep antique plates theres no need for state inspections. (cherry bomb's are illegal on newer vehicles???)