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