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Dialing in camshaft timing-or "degreeing"

Discussion in 'Need for Speed!' started by Turdle, February 14, 2008.

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    1. Turdle

      Turdle I bake stuff Staff Member Moderator Elite Explorer

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      What are the effects and results-
      good-bad?

      http://www.explorerforum.com/forums/showthread.php?p=1859704&posted=1#post1859704
      ^^^^^^^^^info here^^^^^^^^^

      lets keep the comments in this thread please-

       
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    3. rookieshooter

      rookieshooter Moderator Emeritus

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      I used to use offset bushings in my cam sprocket so I could advance or retard my cams. Now this was on chevy engines but same principle. It was just a way of rotating the cam in the sprocket while the sprocket stayed in the same geometric plane as the crank sprocket. In other words, lets say that your engine specs call for both timing marks on the cam sprocket and crank sprocket to be exactly facing each other. Cam mark on bottom of sprocket and crank mark on top of sprocket. Now with this offset bushing installed in the cam sprocket, it lets me rotate the cam a few degrees. Either advance or retard, depends on which way I install the offset bushing.

      So now I can have more low end power or top end power, depending whether the cam is advance or retarded. A cam with a lot of split overlap is more designed for higher RPMs. This is where you will get more beneficial air flow as the momentum of the column of outgoing air is pulling (by vacuum) fresh air thru the intake, even before the piston starts it's downward travel. So your now getting some free air as to speak. But now you will have that real lopy sound at idle and may not have as much air in your air booster for brakes. Your vacuum may suffer at low RPMs.
       
    4. malohnes

      malohnes Active Member

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      Old thread, I know, but I'm surprised at the lack of responses from either this thread or the referenced thread. 'Im reviving it in hopes of more activity form those who have experience in cam swapping and tuning their 4.0L OHV engines.

      In my research and understanding a general rule of thumb is: retarding a cam a few degrees will reduce HP and increase torque while advancing cam with do the opposite, that is, boost hp and reduce torque, all things being equal. This isn't gonna necessarily add actual hp or torque so much that it changes the natural hp or torque curves so that they build sooner or later in the rpm's. When you buy an aftermarket cam this effect is all ready calculated in to the profile fo the cam itself, so it can be very difficult to compare the effects of a stock cam advanced or retarded to a aftermarket cam. to further complicate things, our OHV engines dont have adjsutable cams nor aftermarket support for adjustable performance cams. This changes dramatically when Forced Induction comes into play as boost complicates the airflow characteristics and therefore the fuel requirements for proper combustion.

      I personally think that you can change the alignment of the chain and sprocket to achieve this effect, by literally skipping a tooth on the cam sprocket plus or minus so the alignment dots on the crank and cam gears don't line up exactly. A machine shop could custom make an adjustable cam sprocket but I would expect it to be a very expensive mod for few or any gains gains. However, it would be a very educational project to see exactly what happens when one advances or retards our stock cams.
      But, just because you can do a thing doesn't mean you should. I'd rather throw a 410 or 422 cam in and mess with 1.6:1+ rocker arms to gain some actually airflow and ponies.
       
    5. massacre

      massacre Elite Explorer

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      Are the 4.0 OHV engines "interference engines"?
       
    6. CDW6212R

      CDW6212R Hauls the mail. Elite Explorer

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      I never put any thought into the idea of an interference engine. I'm not an engine expert, at all, but I know enough and I can't imagine an engine that if the timing chain broke, the valves wouldn't hit the pistons. Every engine I know of the valves will hit the pistons if the timing chain breaks etc.

      Anyway, advancing or retarding the cam is all about synchronizing the valve timing events to what the intended ideal was, by the cam designer. There are manufacturing variances with any OEM cam, and the best high end billet cams can be a hair off. Race engines will have the closest to perfect cams(least error in manufacturing). Typical custom cams are all billet, and checked more carefully than regular cheaper cams, and rejected if they aren't very close to designed cam specs. That what you get for spending an extra $100(that's for cheap bastards who'll spend $2k+ on an engine but mix and match cams they get a good deal on).

      Advancing or retarding a cam basically will rock the power curve, around the rpm just below the torque peak. So thus you get a little more bottom end, and less top end, by advancing a cam. But it's still a guess, an assumption that the cam isn't ideal for the engine at hand.

      I don't know what is available for the 4.0 V6's, but I'd hunt very hard for a custom cam, before ever considering any off the shelf cam, or the stock parts. A custom cam made by a pro cam designer can gain you power you can feel, at low rpm along with mid range and top end. An OTS cam will never succeed that well.
       
    7. fastpakr

      fastpakr Elite Explorer

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      Lots of engine designs won't make contact in the event of a timing chain/belt/gear breakage. The Lima 2.3/2.5, Vulcan 3.0, Cologne 2.8/2.9/4.0 (OHV) and 5.0 all come to mind. The path of travel of the piston never goes above the lowest point of the valve travel, regardless of time. Within the Ranger family, I'm only sure of the SOHC 4.0 being an interference design. Not sure on the 2.3 Duratec.
       

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