I have a 2004 mk 2.5, It was originally turbo,d I have converted it back to na. My problem is a blanking cap on the manifold.The manifold is a cobalt 4-2-1. I cannot find the thread size I took a guess at an M20 this did not fit. I think it may be an imperial size. Any info where I could get a blanking cap or the thread size .Any help would be appreciated.
This info seems remarkably elusive.
I found a miata.net thread which states the '99-'00 thread size is M22 x 1.5mm (http://forum.miata.net/vb/showthread.php?t=260171) but unfortunately it also says the 2001+ design is different.
I was a bit surprised that it was a metric thread to be honest. Even though all the fasteners on the car are metric, pipe fittings seem to be stuck in the past using NPT threads so I thought it would be one of those.
It would appear that Flyin’ Miata will sell you the cap you need, but they don’t say what the actual thread is. http://www.flyinmiata.com/index.php?deptid=&parentid=&stocknumber=06-96100
Was the M20 too big or too small? It could be M18x1.5. I’ve used an old EGR pipe, cut it short and folded and crimped the end before to blank off an EGR pipe.