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Old 12-22-2009, 10:45 PM
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Advancing cam timing......

I have a roller cam with 224/224 duration@.050. LSA 112. Lobe centers 107*/117* By advancing the cam 4 degrees....how will this affect idle quailty? What about retarding it 4 degrees? It was installed dot2dot and has 4 degrees advance already in it.
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6sally6

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Old 12-22-2009, 11:16 PM
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Advancing it really isn`t going to effect the idle any, what it will do is lower the powerband by about 200 RPM for better low end responce. Retarding the cam does the opposite, it cuts the low end in favor of top end horsepower. Most cams have advance "ground in" from the factory so advancing it more really isn`t needed.
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Old 12-23-2009, 06:02 AM
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cam

224 @.050 and a 107 deg center will close the intake valve @ 39 deg @.050. Moving the cam advance 4 deg will move the intake valve closing event to 35 deg @.050.

It may change the idle vacuum a very little amount. Sometimes it does, some times it does not. Depends on alot of other factors in the engine.


If you ran a dynamic compression calculation you may gain 3 to 5 cranking PSI with the change.

All-in-all there is very little change to be had with changing valve event timing.

Is there a reason your asking?? Are you have a problem??


Keith
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Old 12-23-2009, 06:50 AM
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Most modern cams are timed 4 degrees advanced on the dot to dot or "straight up" position by the manufacturer to boost lower rpm tq and save us from ourselves by over-camming our engines picking too large a cam - most guys thing bigger is better and like to tell their buddies how "big" their cam duration is, truthfully most folks drive more at low-mid RPM than high RPM, plus a bit of cam advance lowers the tendency of detonation if we get a batch of bad pump gas. With a commercial grind you may want to install at 0 degrees or 4 degrees retarded if you are trying to save power and top end tq.

Here is a good chart courtesy of Grumpy's Performance website regarding degreeing or indexing your cam timing:
ADVANCING / RETARDING CAM TIMING (LCA)will change with any changes in indexing
ADVANCING......................................... ......RETARDING
Begins Intake Event Sooner........................Delays Intake Event Closes Intake
Open Intake Valve Sooner..........................Keeps Intake Valve Open Later
Builds More Low-End Torque.......................Builds More High-End Power
Decrease Piston-Intake Valve Clearance....Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance...Decrease Piston-Exhaust Valve Clearance

Good luck!
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