View Single Post
spuggy spuggy is offline
Registered User
 
Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,831
Quote:
Originally Posted by beepbeep View Post
Seam weld as in weld heds to jugs? Dunno, don't have any expirience with that. Factory used to do it on 4-valve watercooled race engines (beam welded) but it seems a tad too much for a street driven car, don't you think? It would solve leak issues though and maybe relieve some strain on the studs but such engine would be "fire and forget". Never saw welded 2-valve aircooled head though...
According to Frere "This was impossible with the two-valve heads as the larger and more inclined valves cannot be inserted after welding" "Porsche 911 Story" p199.

Inserting the valves is one thing, I have no idea how they compressed the springs to put the collets on those suckers afterwards

Quote:
But as I said earlier, 930 vs. Carrera plastic heat deformation issue is maybe 20-30 degrees apart.
If the alloy used in standard air-cooled heads is really AMS4220 as Bill V suspects in the thread I linked in earlier, then the difference in rating betweem RR350 (aka AMS225B) and AMS4220D is the difference between 600F and 400F according to the specification:

http://www.haley.on.ca/images/Alloy%20Spec%20Sheet.pdf

Which does raise the question as to why, if there were so little difference, did the factory start using RR350 for all 993 heads? Given that it's so much more exotic, expensive to produce and requires special production controls?

RR350 also seems to be specified for use for bearing support housings and other internal parts in more than one gas turbine engine.

And you know those guys would save money if they could use something cheaper.
__________________
'77 S with '78 930 power and a few other things.
Old 12-28-2007, 11:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)