I was reading someone's thread a while back, and they were talking about basics when dyno tuning. They suggested starting with 2* advanced on intake, and 1* retard on exaust. They said this would increase vavle overlap, and on NA motors, thats what you want. From there, between dyno runs, advance intake more, and retard exasut more till you notice a loss in power, or your prefered power curve start to change for the worst.

My question is that if you advance intake and retard exaust wouldn't you be increasing the time in between intake valves opening and exaust valves opening? Therefore decreasing valve overlap??? You would have the intake valves opening sooner during the stroke, and the exasut vavles opening later during the stroke.

I am obviously confused about something because everyone else on that thread agreed with him. Can anyone explain this to me?

Thanks

 

anyone?

 

unless you have your intake cam advanced like +10 degrees and your exhaust retarted like -10 degrees,you will always have some overlap.Just in stock form,your cams already have some overlap.you dont want too much overlap either.I would say also with a stock or any factory cam,you wont have to move the gears very much anyway to get more power.


[Modified by aeolus, 2:21 AM 5/10/2002]

 

What I think is escaping you is that overlap increased by tightening the LCA, (Lobe Center Angle), is the overlap that occurs at the end of the exhaust valve event & begining of the intake valve event. The exhaust valve closes later & the intake opens earlier creating more overlap.

As a side note, when tuning cams, you should start at straight up, or at least something that keeps both cams advanced or retarded an equal amount. Find what LCA the engine likes, then find what advance or retard the engine wants for both cams @ that LCA.

 

Actually, if you wanted to get rid of overlap, you would want to retard the intake, and advance the exhaust, (widen the LCA). At -10, +10, you would still have overlap. So much so, that your car could not stay running.