Hey guys, just doing some practice porting on some old junk irons and i have a few questions. First of all this is just the rough cut, only using a carbide bit, i still have alot of stone grinding and sanding. I want to know if i should smooth out the coner transition from the runner to the port as indicated in the pic, and also if i should smooth out the roof out the outer edge. for my first port i think its turning out ok, I was amazed at just how fast you can port with an air die grinder and a double cut carbide bit. and its my understanding that I shouldn't change the size of the runner, is this true?

Thanks, Matt

 

Don't port the "roof" of the port. Just round it a bit so that the air follows the runner into the chamber. Think of air as sticking to metal a bit, in other words it will follow smooth curves but not sharp transitions. Pretty much just smooth everything out. All in all it looks good. I love to see people building a 12A up, they are extremely durable engines and run extremely well with some mild porting, a good header-back exhaust, and a nice intake setup. (I prefer EFI but Weber DCOE carbs work very well for performance)

Here are a few shots of a 12A that I have done. It is very mild as far as timing is concerned and is shaped a bit differently than other streetports but I have my reasons for it.

http://community.webshots.com/photo/...2732275cAcyGZ#

 

here's a comparison shot--you be the judge

 

Definately round it off a bit. Its up to you whether you want to make it knife-edged like that. Somewhere in between will better direct air into the chamber rather than pushing more of it against the back of the chamber in my opinion. There are others who would probably say otherwise and I haven't seen any dyno comparisons either way, I'm just basing my advice on what I have done and my basic knowledge of fluid mechanics and the rotary engine. The best thing would be to take a bit off of the "roof" of the port, in other words taper it a bit, then round the edge a bit to meet the opening of the port. The rounding would best be done with a stone or sandpaper roll to keep from taking too much off or opening the port sooner, just as a precaution.

 

that's not a knife edge. it just looks that way because of the camera and crappy lighting.