MM54

I was given a header when I bought my car which was said to be a racing beat one for a 12a, but when I unwrapped it, there were O2 sensor bungs making me think it may be for a 13b. This simply meant I had to measure the flange to see which it was for - 12a or 13b. This turned out to be difficult, since I couldn't find any sort of discussion of the actual dimensions for the flange (other than 13b is 10mm wider than the 12a). Hopefully this post will help out anyone else having the same difficulty in the future.

I was able to find a DXF file in the thread linked below for a 13B flange, but when I opened it, it was clear this had been scaled up to look nicer or something, because while proportioned right, the units were way off.
https://www.rx7club.com/2nd-generati...nsions-934598/



I went out to the garage and measured the vertical distance between the bolt hole centers, and halved it to get 62.5mm - If 62.5mm in the real world is 1600 in that drawing, than it's been scaled up by 25.6x - so if we divide the shown dimensions by 25.6 we get pretty close to the real-world measurements, including the horizontal distance between bolt centers of 130mm. See below for the actual measurements.



Of course, you could always just go get a gasket and compare to that, but if you don't have one laying around and it's late, this hopefully will help.

In case you're curious, I measured 129mm on center, so I believe mine's not for a 12a after all - but I'm still going to pick up a gasket for my 12a to double check