Can someone explain to me why the intake valves for Cyl.#1 has to be open by 1.4mm at TDC?

I was reading the FACMAN and I saw this,....

Timing:
intake opens 4deg after TDC
intake closes 40deg after BDC
exhaust opens 36deg before BDC
exhaust closes 4deg before TDC

I am trying to figure this out but it's kinda confusing. Can someone explain the before and after of TDC/ BDC? I mean assuming the engine is moving in the correct direction,... after TDC would be when the piston reaches TDC and then passes it and after BDC would be the same concept? If thats true,... if I set the intake valves open 1.4mm at TDC thats not 4deg after TDC. Can someone explain?

 

2:29PM, and no i don't know but maybe someone else does.

 

Check out the camshaft-lift diagrams on my <a href="http://members.rennlist.com/951_racerx" target="_blank">951 RacerX website</a>.

 

That would be me posting in that last message... <img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />

They say a picture is worth a 1000 words, but in this case, I could easily write 10,000 words on cam-timing. So... I'll leave it to the pictures.... <img border="0" title="" alt="[Wink]" src="wink.gif" />