Cam duration
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Cam duration

  1. #1
    Cantard 71hallett's Avatar
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    Default Cam duration

    How much duration can I run in a bbc before it starts drinking water or can that happen?
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    Senior Member crf311's Avatar
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    With logs for exhaust, I was told to stay below 230 duration. Check with your engine builder
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    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    Quote Originally Posted by crf311 View Post
    With logs for exhaust, I was told to stay below 230 duration. Check with your engine builder

    I agree here
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    Senior Member H20MOFO's Avatar
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    I thought having a narrow lobe center/seperation had some(bad) effect also? Like 108*. I guess both add to valve overlap?
    Another Hot Boat refugee
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    It all depends on the exhaust event and how late the exhaust valve closes. You can go up in duration a bit but need to open the lobe seperation accordingly so the exhaust still closes early.
    Straub could explain this allot better than I can, and can probably tell you exactly the duration for a given lobe seperation/installation point.
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    Swollen Member SinisterGrin's Avatar
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    It greatly depends on what kind of exhaust you are running, i.e. stock manifolds, headers (what brand or style), etc. All play determining factors, it depends where your exhaust gases and water meet. Some exhausts you will see reversion as low as 230 @ .50l like stated above and then on some others you can push it alot higher. Lets get some more info on the application and exhaust.
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  9. #7
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    Default cam duration

    I have a stupid question. I thought exhaust logs like a Glenwood or Nicson wouldn't drink water as bad since they are jacketed, and water doesn't enter the exhaust side till it reaches the riser. I have a 427 ford with 258 duration at .50 ground on a 110. I'v been running this combination for 18 years with no problems. I'm working on a simular project with through transom exhaust but a BBC, am I going to have problems with this that I didn't with the FORD. Thanks!
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    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    Better idea






    Run dry headers or Zoomies Like Me!!!!!
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    Quote Originally Posted by cave View Post
    They bout shit themselves when yelled in Messican, "No brakes no brakes."
    I showed them all the sticker on the side that reads "Driver Ricky Bobby" They just looked at me and nodded yes yes
    Quote Originally Posted by Kyle View Post
    Some peeps just build it 1 part, 1 week, 1 paycheck at a time
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  11. #9
    Cantard 71hallett's Avatar
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    Quote Originally Posted by 396_Ways_To_Spit View Post
    Better idea






    Run dry headers or Zoomies Like Me!!!!!
    You know it!! Going to run them dry and get to the point.
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  12. #10
    Senior Member H20MOFO's Avatar
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    Kilowatt , I believe the answer to your question is that it can suck it right from the lake/ or from the water dumps into the snails.
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    Quote Originally Posted by MR. KILOWATT View Post
    I have a stupid question. I thought exhaust logs like a Glenwood or Nicson wouldn't drink water as bad since they are jacketed, and water doesn't enter the exhaust side till it reaches the riser. I have a 427 ford with 258 duration at .50 ground on a 110. I'v been running this combination for 18 years with no problems. I'm working on a simular project with through transom exhaust but a BBC, am I going to have problems with this that I didn't with the FORD. Thanks!
    No, you should not have problems with that either.

    Logs are even "drier" to the exhaust stream than my jacketed headers are IMO. To pull water backwards in a log you have to pull it VERTICALLY up a 2 to 3 inch barier, then pull it from 5 inches to over a foot (depending on which cylinder).
    My headers would have to pull backwards at least 4 to 6 inches up a 45* incline, to pull something into the tube, then go down over 18" to a port.

    I am running jacketed headers, a 240+* duration cam, in a Chevy, 4 years now, and have NO issues.
    Same cam ran 2 years with logs, 2 years with the headers now, this year is year 5.
    The bad boy is the injected header which puts a water spray just a couple inches away from the exhaust valve. At moderate to high RPM, the gas flow blows the water away. At idle, this does not happen and as the piston heads down it CAN "suck" pretty hard for a fraction of a seccond untill teh valve closes. This is one of the reasons why you have to cut water to injected headers at idle, and also why you run significantly LESS water to cool them.
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  14. #12
    Senior Member H20MOFO's Avatar
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    I could be wrong. It just seems like it could crawl up over a snail as eaisly up a header tube. I dunno. I don't think all reversion cones from the injection lines. ??
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    I agree MOFO, but it would (IMO) take more overlap pull to get reversion troubles from a log or jacketed header than from an injected header with excess water fklow (at idle).
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.
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    I just went through all this while selecting a cam for an engine that is being built for my inboard ski boat which has an exhaust below the waterline. Basically you do not want to have any overlap on the cam that will allow the intake and exhaust valves to be open at the same time at the beginning of the intake stroke because that will cause a vacuum which may suck up water. If you know the specs on your cam, the site below should prove to be helpful, it has two simple formulas that can be used to ensure that there is not any overlap using 0.05 duration numbers.

    http://www.empirenet.com/pkelley2/Overlap.html

    Hope this helps.....
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