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

Ben Drinkin said

Ok. So i think i finally got the visual in thick skull (put the bourbon down for a moment).. I've been focusing on exhaust closing/intake opening (overlap if I'm not mistaken). Reading your description, intake closing point seems more important. . Close the intake earlier, make more compression. How does one determine the optimum point for intake closing? If that's not a moronic question...

And you're doing a hell of a good job 'splaining stuff!

Click to expand...

Optimum intake closing really depends on what you want/your application. Ideally you want scavenging (in a naturally aspirated motor). That is overlap that allows for exhaust to draw out all the burnt carbon as it brings in fresh fuel/air. A perfectly designed motor would sense the very last atom of burn carbon on it's way out and close the valve at that exact moment before any fresh air/fuel got into the exhaust. Obviously this isn't possible, so you want to get as close as possible.

Then, you want it to close early enough to build pressure, but not so early as to make so much pressure it causes detonation. You also don't want it to close so early you don't get enough air in there.

What I do to figure out optimum intake closing, is use it to determine DCR. Your dynamic compression ratio. Wallace Racing: Dynamic Compression Ratio Calculator

8.5 max DCR on iron heads with 91 octane. 9.5 on aluminum heads. As a rule of thumb.

I pick a cam based on it's entirety. You want to pick a cam that will fit all your needs on that engine. Whether it be high revving horsepower, low end grunt, or something in between. Intake valve closing will play a part in that. And from that you can determine your DCR.

Pick a cam for it's entirety, not just one part. And remember, a good engine is built around all the parts. And how they work together.