true, ports too large will mess up low rpm airflow. you can also work on matching the ports to the gasket and the manifolds, there is often a good bit of overlap that can't be good for flow at any speed.

Big ports aren't everything

Mine are large but not huge on my H89
I can't find my measurements however

I have gone larger but not huge
I wanted to keep airspeed up

does anyone have the specifications of there ported head? How much taller and wider can i make the inet and exhaust ports?

I wonder if your H89 heads are similar to our H95 A15 heads in the US? The H95 has the heavily shrouded "swirl" oval ports. If the H89 is similar, I can tell you that I tried porting mine and it was looking good until I poked a hole in the shrouded part next to the guide. I was trying to make the port look more like the standard wide open oval port in the H72 head. I thought maybe the extra material added to build up the shroud around the guides was solid but it isn't. There's water in there. Here's a pic of an intake port bowl in an H95 A15 head before porting:




After porting below:




Here they are side by side:




This one is from my H72 head after porting. No shrouding here!




Mike

Hey guys
Just want to know how far out i can port my stock H89 A15 head? Does anyone know how many millimeters i can safely port away?or the demisions of your ported head?
cheers