Bad Habit Bird

iTrader: (12)

Ok this is a very simple question and I would like some in depth answers for it if at all possible. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> I have a general idea as to why but would like to have a full understanding of how larger cams effect emission output of an engine.

Thanks,
Sean

<small>[ April 09, 2003, 01:34 PM: Message edited by: Bad Habit Bird ]</small>

ArcticFormula

Well since I'm a novice, all I can offer are my basic thoughts. A "Big" cam will have higher intake valve lift and duration, allowing more air to enter the combustion chamber. One would normally tune the motor to back to optimum air-fuel mixture before the big cam by increasing fuel. The combustion process has a myraid of factors which influnces the efficiency of the burn, but I think its safe to say that the more air and fuel one is pushing through a motor at a given rpm the more likely increased emmissions are a result. Thus the big cam motors suffer in an emmission test.

jimmyblue

iTrader: (11)

Big cams usually have some overlap and this
lets unburnt fuel/air pass through to the
exhaust, at least enough to fail the parts
per million kind of emissions limits for HC.
At high RPM the overlap is your buddy (start
intake before giving up on exhaust, pipeline)
but at low speed there is that intake blow-
through potential.

robertbartsch

Overlap = unburned fuel in exhaust...