[Stan Weiss]

Originally Posted by TransAm 474

Thanks Stan, I appreciate it. That comes out real close to the actual lift that we measured at TDC, within a couple thousands on each anyway, but our I.C. was coming in at 106.125° and 109.125°, so I assume that is where the couple thousands difference is coming from. I believe when we measured at 109.125° Centerline, we had right at .060" on the Intake and .0415" on the Exhaust. At 106.125° we had .0655" on the Intake and .038" on the Exhaust.

With all of the different tolerances in the manufacturing of these cams, I am surprised how close one cam is to another. Remember this is a mass produced cam.

Stan

[70GS455]

Originally Posted by Formulajones

The idea with this intake/exhaust relationship is that as the piston starts it's decent, it's sucking in a cooler intake charge, rather than a hotter exhaust charge, so that when the piston comes back up on the compression stroke, it's a slightly cooler combustion process, and as a result less likely to detonate.

Heat is the enemy.

But if the intake is open too much more than the exhaust, hot exhaust gases get pushed/ sucked (vacuum) into the intake, instead of out the exhaust at the end of the exh stroke, only to be sucked back into the cyl when the piston starts back down

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[Formulajones]

Originally Posted by 70GS455

But if the intake is open too much more than the exhaust, hot exhaust gases get pushed/ sucked (vacuum) into the intake, instead of out the exhaust at the end of the exh stroke, only to be sucked back into the cyl when the piston starts back down

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That's why it's said to shoot for .035" to .040" max.