Hey

I'm looking at powering up my 245 six - but have had a couple conflicting opinions about how I should go about it and I'm hazy on the theory.

I understood a bigger valve is pretty much always better - bigger flow etc.


Now I'll be milling a bit to increase compression in either case, but I'm looking at modifying either the 245 head or putting a 265 on top.

The 265 has larger valves.

Apart from that a major benefit is being able to cut quite a lot off to push the compression as high as I can on 118 octane, but keep at least 245 displacement.

One guy I know has suggested the smaller 245 head would be better - higher velocity through the valves and better mixing. Another has said just go big.

My question is this:

Which do you think would be better?
Would the pumping loss from the tighter 245 offset the greater velocity and mixing?

CR is looking to be at least 10.5 and likely pushing 12 with a couple other tweaks - at this rate, the better mixing from the 245 might be academic... What do you think?

Any advice would be appreciated!