Camshafts ADV & RET

[mick taylor]

So you all, i was thinking about the Barra 4.0L engine in the main.

About the cam timing ! regarding the intake Cam

So in regards to how and what goes on with the Advancing and Retarding show that is taking part.

So i have heard that some may at idle advance the camshaft timing 6 Deg then set the Cam at full 6 Deg Retard from 3000RPM ?
Or could set the Cam timing half way = 0 deg at times ?

So by rights the camshaft movement can be 12 Deg all up ?

Then we can start talking about what the Exhaust Cam is doing ? and when and why ?

Now in regards to exhaust emissions, the adjusting Game would have it's part in all of this ?

Now i know that regarding ADR27A Laws, Holden changed it's V8 Cam specs so that the intake and the exhaust valves close later and the reason for the exhaust valve being close later is to put more heat into the exhaust system, their by acting some what in the regards of a cat converter in burning un burnt fuel !
So our Barra 6 may do this as well at some point ?

Now another question is, i have conflicting views on what is Advancing a Cam and Retarding a Cam ?
So lets for argument sake in a old spec talk of a 20/60 Cam i am led to believe that 5 Deg ADV will make a 20/60 become a 15/55 and NEG 5 Degree will become a 25/55 !
But looking on the Net some claim it's the other way round ?

So in regards Spark timing if we ADV to 12 Deg this means the spark is set before TDC and reason for this is that the piston has stopped in fact for how many Deg ? regarding the rod and stroke ratio ? but we can go say 40 Deg Adv spark and the reason why we need more ADV is to do with performance and also economy reasons !

So if we Adv a Cam this is the logic ?

But then again a clock face only Adv and never Retards, so clock wise is Advancing ?