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

 

I'm interested to know if these dimensions are indeed for a 12a. Could you please verify?

I'm looking into welding my own manifold and would need a DXF for water-jet cutting a flange.
And gaskets are stupid expensive here, so I plan to use the same DXF to cut one from gasket material

 

Hello from 7 years ago

The DXF and dimensions in the above post are for a 13B. I don't have the parts on hand right now to measure, but for a 12a I suspect the 130mm dimension drops by either 5 or 10mm - if you're drawing the part up in CAD and have the engine already, just print on paper 1:1 and double check. Good luck!

 

Just take a 12A gasket and scan it. Take a measurement of the exhaust port as a reference. Import into Fusion360, InkScape or favorite cad 2D and use the measurement and scale to it. I do this when I cut stuff on my CNC plasma table.

 

25.4mm = 1.0”

not 25.6 (from post #1)
.