Why is running open headers bad...

Discussion in 'Fox 5.0 Mustang Tech' started by 87GT 306, Oct 26, 2005.


  1. 87GT 306

    87GT 306 New Member

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    why is running open headers bad for exhaust valves? Ive heard this before and Im just trying to figure it out. No I dont run open headers, nor would I want to. Just curious
  2. srothfuss

    srothfuss Last night I stabbed the same guy 7 times in a row

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    Because once you turn off your motor the much colder ambient air travels up the pipe and cools off the valve seals too fast...? That is my guess
  3. Lyncher

    Lyncher New Member

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    I thought it also had something to do with a lack of backpressure or something :shrug:
  4. bynummustang

    bynummustang Seen my other Jackstand?

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    I thought cops just said that to make you put mufflers on...
  5. MustangPunk302

    MustangPunk302 Founding Member

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    Wraps or cracks the valve, though for that to happen your talking some extremely cold air... We've run open header's on most of our racecar's with no problems at all, and even bring them to operating temp many times in the winter. Though before I put the 347 in my convert. I ran around with open headers on a stock 5.0, for ****s and giggles. It was loud of cousre and ran fine, and the next day I took it out again ran fine and right as I got home it started running like ****. It died out in my driveway and wouldn't start lol. It had no compression, I toasted the exhaust valves... It's all up to the engine.. lol
  6. Lyncher

    Lyncher New Member

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    :lol: ...its a conspiracy!
  7. gt40_2003wes

    gt40_2003wes I did sound a wee bit gay there.

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    i always thought it was because with open headers u have no back pressure.
  8. I_AM_CANADIAN

    I_AM_CANADIAN Member

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    sort of. I'm not the best person to explain this, but I'll give it a try. The best way I can describe it is for you to think of the exhaust exiting in pulses. The first "pulse" will begin, which will have a low pressure behind it. With the next pulse behind it, the low pressure will "pull" the pulse to the exit. So it all works like a mini vacuum I suppose. Hopefully someone will chime in and clarify even better.
    :canada:
  9. 65ShelbyClone

    65ShelbyClone Founding Member

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    I thought it was because usually when someone just opens up the headers, they dont rejet for the extra airflow and run lean. I'm just taking a stab because I really dont see how the open exhaust alone can do it when so many drag racers run "on the edge" powerplants and open headers with no problems. Also, everyone in this thread came up with a different answer.
  10. -=Red5.0GT=-

    -=Red5.0GT=- New Member

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    i always thought if you run open headers you have to fab some holes for the o2's unless your using LT, other than that you should be fine. btw long tubes and open heads are sick.
  11. slow5poh

    slow5poh Senior Citizen

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    i alwats thought that it was a bad idea cause you might attract the police.........
    :cheers:
  12. bobbys9350

    bobbys9350 New Member

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    The reason is because your valves cool off to quickly after every exhaust stroke causing the heating and cooling of the valves resulting in valve seat wear, etc...
  13. ja1919

    ja1919 Member

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    sooo..i have a gutted h pipe on my 92 5.0 with no mufflers after the h pipe. i have been working on the car the last two winters. Last winter i would start the car once in a while. So this summer when i took off the mufflers, they were filled with water. the condensation built up in the mufflers after starting it during the winter. so this winter iam not putting the new mufflers on till next summer...Is this gonna be bad if i start the car with just a gutted h pipe in the winter???
  14. Michael Yount

    Michael Yount Advanced Member

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    ja1919 - with winter starts, it's always a good practice to run the car long enough to evaporate all the condensation. It takes a good long while if you can't actually drive the car. Remember - there's not just condensation in the exhaust system -- it occurs in the crankcase as well. That water mixes with oil -- and it's important to get the enigne up to oil temps above 210F to boil all the water off. So if you're gonna winter start -- you need to let it run for a good long time, preferably drive it for 20-30 minutes. If you can't do that, it's probably better not to start it at all.

    As for open headers -- well, how do I put this gently. There are probably literally hundreds of thousands of racing cars, bikes, boats, snowmobiles, etc. that get cranked up and raced every week across the globe all with open headers. Some just have a short collector on the header to tune the exhaust (helps with scavenging) -- some without, some with short dumps or side pipes, some with expansion chambers and the like (2-stroke crowd). I don't think the majority of them are chasing burnt valves related to cold air coming up the pipe and warping things --- just a guess. I NEVER had a problem with it during my racing days.

    Loud as hell? Yes. Attract attention? Yes. Could a properly tuned exhaust be a bit quieter and make just as much power? In some cases yes, others no. But I wouldn't worry too much about my exhaust valves.
  15. ForceFed70

    ForceFed70 That's why they call it "dope" Founding Member

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    There's nothing wrong with running open headers.

    Lack of backpressure may hurt low end torque a little, but it won't wreck anything or cause the engine to run poorly.

    I don't buy the "valves will cool off too quickly" arguement. 1/4mile cars proove this wrong often as much as 20x a day. They go from red hot to off right away...can't get more extreme than that.

    Fast cooling doesn't cause problems anyways... it's uneven heating/cooling that causes warping.
  16. srothfuss

    srothfuss Last night I stabbed the same guy 7 times in a row

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    It was just a guess... I haven't a clue what would be bad about running open headers on a race car. Obviously the noise is the biggest issue on a street car.
  17. Euphoric306

    Euphoric306 New Member

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    modified mustangs had an article "The Anamtomy of a Header"

    they explained exhaust as golfballs being pumped through, low pressure after one golf ball pulls the next one through, and as they hit an expanse (collector, or a big fart can on imports) they slow down, creating a wave of backward force that eventually hits the engine (exhaust valve?) i dunno if that has anything to do with the open header question, but it explains backpressure in an understandable way

    maybe the constant backforce of the "golf balls" hitting open atmosphere hitting on the exhaust valves make them go bad?



    plus... with OH u cant run oxy sensors
  18. SmockDoiley

    SmockDoiley New Member

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    You could if you welded them in. Also, you people are using race cars as examples for your valve theories. I seriously doubt a 1/4 car can accurately depict the temperatures the valves are seeing since it doesnt drive up hill, sit in hour long traffic. I dont know what to think about the exhaust valve jumbo since no one has properly tested the theory. But I do know that 12 second blasts aren't going to tell me yes its ok to drive 12,000 miles a year with open headers. Its probably not good as a daily driver because it kills so much low end torque, plus the noise and law problems.
  19. Michael Yount

    Michael Yount Advanced Member

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    Smock - exhaust valve temps even in a 1/4 mile car get at LEAST as high as a street car would see in traffic (that's one of the EASIEST scenarios for an exhaust valve actually) or 'going up a hill'. Besides that, you seem to think all race cars just race the 1/4 mile. In road racing mine routinely cycled from 4500 to 7000 in 3rd, 4th and 5th for 40 minutes to 24 HOURS at a time. We like to think the drag racers are quite easy on their motors.
  20. bluevenom867

    bluevenom867 I will have images of molesting stuffed animals in

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    Yea,and thats also why most serious racers can tuner with EGT.Although you can use the o2 sensor with an open header.

    Street rodder just cant run them,there to loud for the street.Now if you had a really poor flowing head...then they wouldnt be so loud :D but that defeats the purpose.

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