I want to build a 4-1 exhaust header for my dohc zc , I know that the runner length is dependt on my engine set up but i have not been given a guide line on this. My current set up is: stage 3 cams , 12:1 compression , extensive port and polish , scat rods , lightened knife edged and blanced crank , port matched intake, over sized valves , titanium retaiers and 41kg valve springs. What sort of runner length would you guys reccomend? also when i mean primary runner is that the distance from the flange to the collector or from the flange to the first bend?

thanks - hamish