Ok here's my delima I bought a new set of bare heads and I need to put valves in them.
I've looked at Manleys and they use the same part number for their severe and extreme duty intakes which are a NK-844 material, their extreme duty exhaust is XH-432 material which is supposed to be quite a bit better than their severe duty which is a XH-428 material.
To confuse myself even more I've looked at Ferrea competition plus super flo series which are supposed to be great.
I've used Manley and SI before and never had a problem with either of them but I'm open for ideas. I'm using these on a NA engine for my flat that will see some rpm (7500ish +/-) and might have a decent roller cam this time around so what brands are holding up the best and have good quality these days?