View Single Post
beepbeep beepbeep is offline
Registered User
beepbeep's Avatar
Join Date: Jun 2001
Location: Sweden
Posts: 5,564
Originally Posted by spuggy View Post

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:

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.
Hmm...this is outside of my domain. I got temperature information "ad hoc" and it was more like "don't run the CHT above 220 deg. C on Carrera alloy or 240 deg. C on 930 alloy or you might bugger up the heads" I guess somebody had to test this experimentally

I believe there are also issues of thermal contraction/elongation as well which might influence the longevity.

Why factory decided to use same alloy for all heads? It's hard to say but I suspect economies of scale and common parts had something to do with it. They might have saved money by ordering only one type of heads from subconctractor.

Same happened to SAAB:s. They used to differ slightly in first years but later on turbocharged and N/A engines were almost identical save for pistons/rods.

Thank you for your time,
Old 12-30-2007, 11:43 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)