01-11-2007, 09:49 AM
Andy Wrote:I wonder how VVT works with Pushrods. I assume the cam is still dead in the middle of the motor.
I know for Chevy, the cam is advanced or retarded like a distributor:
GM Marketing Machine Wrote:GM's pushrod VVT uses a spline-type phaser to turn the camshaft relative to its drive sprocket. Given the single cam, intake and exhaust valve timing change at the same rate with a fixed relationship, but GM says the VVT helps improve fuel economy, reduce emissions and optimize the balance of low-end torque and high-rpm horsepower.
But all I can find on the viper is that it "VVT electronically adjusts when the exhaust valves are open and closed according to engine speed and load, allowing the engine to ÔÇ£breatheÔÇØ cleaner and more efficiently." Which doesn't really say shit.
Now, I can think of a couple of ways to do this...let's say you have a exhaust lobe with two profiles. It would just be a question of switching the profile from one pushing on the pushrod to another, like VTAK!. you could vary timing and lift this way, and with the different combustion chamber shape on an OHV engine, maybe you get more power by doing that on exhaust side. (Most DOHC seem to do it on the intake side).
But IANAE.
1987 Oldsmobile Cutlass 442