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Old 02-19-2010, 11:24 AM   #1
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Default on crank trigger wheels

Originally Posted by Savington View Post
Jason, J_Man mentioned you guys are going to try a non-OEM wheel to make the OEM cam sensor work - is that just for fun or does full advance on the VVT make the sensors lose sync?
The 96+ crank sensor wheel won't make the AEM lose sync over the VVT range.

My interest was a higher resolution crank trigger wheel. The AEM cannot time off of all crank teeth if they are irregularly spaced - so it has to "throw away" 2 teeth and time off of 2. Some say that this lack of resolution can cause timing errors during transients, such as during rapid engine deceleration. During rapid engine deceleration in theory the next spark could be a bit too advanced because RPM is now significantly lower than the previous cycle.

This is probably worst at low RPM because the effective sampling is slowest. The one situation I can think of of low RPM rapid deceleration is when you abruptly get on the gas at low RPM and the drivetrain windup oscillates (you know, where the RPM goes boyoyoing, for lack of a better term )

At higher RPMs and loads one detonation event may in theory cause a slight deceleration, and misfire would be the worst. I have seen arguments regarding this but not actual numbers (i.e. experimental results).

Regarding the AEM, the highest resolution crank trigger wheel it can handle is 12 teeth. Because of how the AEM syncs, and because the VVT range is 47*, the AEM needs to use a 12-1 trigger wheel to work with VVT. The missing tooth is so that the AEM can tell which of the 12 "teeth" is TDC. With such a wheel, the missing tooth needs to always fall between cam pulse edges regardless of VVT position.

Last edited by JasonC SBB; 02-19-2010 at 12:17 PM.
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Old 02-19-2010, 11:32 AM   #2
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Have models drawn as per our discussion. Parts are out for qoute. Must solder more COP kits. Time has been sparing sorry for taking a minute on this. Will update when I have something new.
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Old 02-23-2010, 12:54 AM   #4
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The largest and fastest decrease in engine RPM is likely to be at the end of an upshift. How bad that works out will depend on how fast the shift is and how much boost is still in the manifold. Could be really bad with a no-lift dog box (just like the one I have -right). If the BOV is keeping anything like full boost pressure in the intake path and the throttle opens simultaneous with or just before the clutch is released, it could go either way depending on the various response rates.
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