Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION

Robb,


I personally don't care much for tight LSA's on pump gas engines for a few reasons. While a limited cylinder head will respond to a tight LSA vs a good cylinder head, the increased cylinder pressure from the early intake closing increases the chance of detonation on sketchy fuel, and the work against the piston after combustion is lessened because the exhaust valve opens early causing combustion pressure to blow out the exhaust before it is done working. The overlap reversion then dilutes the intake charge, and causes the loss of bottom end power and driveability. Once the rpms increase enough to overcome the reversion and the overlap is actually drawing the intake charge, cylinder pressure spikes, and before you know it, the motor is rattling itself to death, whether you hear it or not.

As Yellow Rose said, the timing events can be moved to where they need to be, but the cylinder pressure spike is going to be more prevalent the tighter the LSA gets. It will also lay down earlier, which is why they are better for a limited head that can't feed the motor at a high rpm anyway. Make the most power you can, before the cylinder head runs out of steam. And more duration won't be much help. Once the port goes sonic, it's done filling the cylinder, and it won't rpm any more.

All of this in the above quote is extremely accurate. I didn't want to GO there 'cuz like you said a book could be written. Very informative post--for those who don't already know this read the above two paragraphs over and over until a light bulb goes on. Thanks, Mike. J.Rob