If you’re looking to swap a Honda K-series engine into your S-chassis Nissan, go read Part 1 and Part 2 of this Turn14 Distribution supported series to give you an idea of how we (meaning Vinh at NV Auto) tackled the engine and transmission mounts as well as the subframe and oil pan modifications required to fit a K24A2 under the hood and in the best location in the engine bay for weight distribution and BMW ZF 5-speed transmission positioning in the tunnel.
With the engine mounted, the next big jobs to tackle were modifying the intake and exhaust manifolds and then mating up the header to the titanium Tomei exhaust system that was already on the car. You can buy RWD style headers for the K-series since this is a popular swap into S2000s and Miatas, but we opted for the more budget-minded S2000 header.
To use this header you need a K-series header flange, which as you can see from the picture above has different spacing on the middle two runners.
Once you cut off the S2000 flange from the header, you could try to bend the middle two runners into position for the K-series flange, but we opted to cut them and rotate and weld these runners for a better fit up.
Vinh from NV started this process by bolting the header flange to the cylinder head (which acts as a heat sink when welding to prevent warping the flange) and then tack welding the two outer runners to it.
From there he was able to rotate the middle runners such that they mated up cleanly with the flange. In order to do so, he added in a small section of tubing, as you can see above. From here it was simply a matter of welding up the middle runners and then finish welding all four runners to the header flange.