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

Robb,

I wish I had more time to get into my opinions and experiences for you, but I would probably end up writing a book, lol.

There is a lot of confusion on this subject, and some of the marketing and "rules of thumb" out there muddy the waters even more. I see a lot of emphasis on one aspect or another of cam selection, but the whole combination of parts is going to determine the cam selected, right down to the size of the tires on the vehicle, if someone is really looking for the best possible choice.

Yellow Rose is not off base, although he is very passionate, and comes off pretty strong with his opinions. Heck, I think he could be passionate about a bowel movement! (Sorry Tim :D) I understand it though. I'm just as passionate about valvetrain geometry, and some people think I'm being a jerk, when I'm only trying to help them. Btw, that plays a huge role in the selected cam working the way it's supposed to. That being said, I'm not a cam genius, and most times I will select a shelf grind that gives me 95% of what I'm looking for, and when the need arises I go custom.

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.

As far as idle characteristics go, the idle will be similar if the intake closing and the overlap degrees are the same, regardless of the LSA. Maybe not exact, but similar. To keep those parameters equal, the duration would have to decrease with a tighter LSA, or increase with a wider LSA, on the intake or exhaust, or both.

Man, I swore I was only going to type a couple lines. I've got to get back to work.
just curious.... if someone was going to build a mild street 360 at 8.5 compression (let's say 350 hp), what LSA would you be marketing for that build???