Different valve spring seats in heads

[gttjames]

Just building up a head, swapping the piper springs onto a thicker head I'm going to use and noticed the seats are different. Can the wiser please enlighten me?

http://i15.photobucket.com/albums/a371/sr50james/D395647E-EC6B-4EE7-AB72-4D17867C0E2A-2661-000001CD07DC2B41_zpsc1cd0809.jpg

[greggtt]

Phase 1 - phase 2 ? Just a guess!!!

[Sparkie]

yep thats correct.

[gttjames]

Did think that was a possibility. Is the dished version phase 1? I have seen 5 heads over the last few months and they have all been flat as opposed to the dish version

I would have thought the dished version be better for holding valve spring in place, why did they change to machining it flat out of interest if anyone knows?

[SCHWARTZ]

Possibly something to do with the fact that ph1 didn't have valve stem seals, but again beat to hear it from someone wiser.

[Sparkie]

the answer is here....
http://www.rtoc.org/boards/showthread.php?t=18431&highlight=phase+differences

[Sparkie]

ph2 sits in the bucket - probably to aid the action of the springs at high revs, as they do open out upon compression.