For those of you running 85-86mm b series blocks with vtec head, do you have to open up the chambers in the head to match the block to clear the pistons?

 

I don't think you HAVE to as long as your piston to head clearance is sufficient. Might be an issue with GSR head vs b16 head.
I have heard however that opening up the chamber helps due to some deshrouding of the valves.

 

It's called a fly cut and yes it is good for cone flow formation at transition speeds through the port.
Some very radical pistons MAY have a clearance issue with the dome on the divider where it meets the head.
I have had both of my heads fly cut for this reason.
My custom made 1/2 GSR nitrous head. Helps to shape (soften) the combustion event and push exhaust across through the ports at TDC.

 

^^That is friggin beautiful!

Interesting how chamber shape can affect combustion and flow... (off to google)

 

I would say no, honda didn't do it with the b20.

 

Opening up the chambers to de-shroud the valves helps tremendously around your low lift characteristics, it is not something that is done so much for clearance but for horsepower placement across your power band. it is not as simple as just matching the chamber to the bore if done incorrectly you stand to hurt your flow characteristics .

 

What that guy said^^^^

 

i know right!