desides visual whats the difference & purpose between 2 vr & 4 vr

 

compression and price.

4vr you can use 8 identical.

2vr you have to have 4 and 4 (they have to go in only one way, dot forward)

4vr will lower compression over 2 vr.

 

Not really. Most 4 valve relief pistons are 4 to 6cc's
5cc being very common. Most 2 valve relief and single trough type relief pistons are 5 to 7cc's.

Some have different compression heights.
(how far down in the bore the piston top is at TDC)

 

Deck height varies yes, and I didn't state that those are the only differences.

We are both right.

I see what you mean about the 2vr having similar cc, one would assume to be to keep compression the same but allow for a higher valve lift.