Porting the Vauxhall C20XE: head limit

[alex new]

Hello,

I 've read in your cylinder head preparation section that a XE head port may have 26mm diameter thru the splitter to give flows more than 150cfm.

My head is the Coscast (Cosworth cast) first type (from Opel Kadett GSi 16v) and has smaller inlet ports than the next generation KS and later Coscast heeds. The difference is about 2mm smaller diameter port for the older heads, but only in inlet side.

My question is what is the maximum safe limit to port the C20XE head thru the splitters without breaking thru, and that limit, in my older type Coscast head maybe is lower because it has more narrow shape design?

Thanks, Alex

[Guy Croft]

26mm is safe in both, though on my full spec GM XE heads I am going to 26.5mm.

The short side radius needs to be very small, blended right up to the seat insert - and the shape of the ramp on the port floor from the flat outer section to that rad is extremely critical. You have to have a gradual curve there.

GC