I was checking exhaust port and headers matching and saw, that exhaust port (D-shape) is slightly larger than headers tube (round). How did you solve this problem? I thought that maybe I should remove some material from headers flange?

Second problem is that headers round flange (that is slighlty higher) is too small for pushing gasket against head. In some places theres only 1-2mm wide. Is that enough for sealing headers and preventing it from leaking in the near future? Has somebody good solution?

I think many of you have using AFR 190/195 with 1 5/8 headers, maybe somebody have good soilutions.

Thanks!

The hedman headers that you have were probably not designed for a high flow aftermarket head. You really have 2 options to do it right. The first option is to order a new set with a larger primary tube size and better designed flange. The second option ( exactly what I did with my victor jr's) is to order a flange kit and have it welded to your tubes. I had the hedman headers and y pipe on mine and had to modify the collector length and the flanges for them to work properly with the heads and the car. I really think that leaving the header port smaller than the exhaust port on the head will hurt performance a good amount.

Yup, it's yerbasic mismatch.... you're trying to hook up peanut-port headers to large exhaust ports.

Your only option that makes any sense (seeing as how you've now got $1500 worth of heads that you're not going to be able to get much benefit from, since there's still this weenie 305-sized exhaust system strangling them) is to get the right headers.

Hedman makes D-port headers. Maybe you can return the ones you have or sell them.

But all dyno numbers on the AFRs website are made with 1 5/8 headers... What headers are they using? I didn't find any header suggestions in their manual on website. Aren't 1 3/4 headers too big to hurt flow speed? I'm using CC 224/230 hyd roller cam.

Out of all the motors I see on that page, only the minimum couple of packages were tested with 1-5/8" headers. And of course they didn't say what brand; for example, if they used quality ones such as SLP instead of the cheap ones, their flange is the same as their 1-3/4", they just step down to the smaller tubing size about an inch past the flange. So they avoid the fitment problem that way.

You still should get 1-3/4" headers for a 350. The smaller size will cost you HP. It's too bad they don't show similar motors with the 2 header sizes that you can compare, to see how much HP they're giving up; I'm sure it's substantial.