quote:Originally posted by Carlo:
Hi, I have a question for the engine experts.
Is the rough idle that is common to many V8s, particularly the older ones, caused by poor mixture quality at very low RPM or is it because of the camshaft design?
I compared the specs of the cam in my Cleveland with those of a '95 Winsor 302 HO and noticed that my cam has slightly more duration but considerably more overlap being 61° compared with 39° of the 302.
Modern V8s generally idle smoother than say, those of the 70's. Is this so because fuel-injection provides a better fuel mixture or is it because of a change in camshaft design?
Cheers,
Carlo
first thing comes to mind comparing overlap degrees is where the measurement is taken, some sources provide advertised duration numbers (seat to seat or near seat to seat) while other sources specify valve event times to a specified lift ie .050" or .020" for some mechanical lift cams. point is make sure you're comparing apples to apples. there's a way to convert differing measurements by math. 61* overlap is not necessarily a raggedy running beast by any means
the first 1/2 of the 70's cars came equipped with breaker point ignition, convert points to electronic and the difference is obvious, smoother idle and low end drivability, improved efficiency evidenced by decreased fuel usage
now add that any early 70's car still a running breaker point ignition likely has significant wear to the lifters, cam and valve faces / seats and that can easily explain a rough or poor idle
'performance' camshafts and their idle characteristics is an entirely different matter altogether