NG headwork - carbon deposits

[JShadzi at aol.com]

Ben, you are right, the valves don't really need to be unshrouded.  As far as 
the carbon deposits, it wouldn't be a bad idea to take your head to a shop, 
for about $150 they can clean up all the valves, lap the seats, and put in 
new valve guides and seals.  This would be a really good idea, especially if 
the head has over 100k miles.  Personally, I would want those deposits off 
the valves.

As far a porting, one of the best tricks I know of, esp. on the NA cars (the 
turbo cars need all the valve seat surface they can get) is to have 1.5mm 
machined out of the ID of the valve seat, which can effectively be like 
putting in 1.5mm bigger valves.  I always go inside the bowl areas and smooth 
them out, and the nub that supports the valve guide can be brought down on 
the sides to make it more elongated when looking from the top.  The "short 
side radius" (where the valve port turns 90 degrees or so) can always use 
work in smoothing, often there are sharp edges here from machining of the 
head originally.  

The exh. port turns exactly 90 degrees to go to the manifold, I always spend 
a lot of time on the SSR here and often it can be a sharp 90 degree bend 
here!  Then, overall smoothing of the ports, I like to finish everything off 
with 200 grit, you don't want any of the area AFTER the injector to be shiny 
smooth, a little tumble will help atomize the fuel.  Port matching the IM to 
the head is probably the biggest gain to be had, and of course, the IM can 
always be polished and opened up more, at least get the 1/8" of grease that I 
always find in there!

HTH, let me know if you have Q's about specific areas.

Javad
www.80tq.com


In a message dated 7/6/2001 6:29:04 AM Pacific Daylight Time, 
BSWANN at arinc.com writes:

<< Any tips on porting or polishing for this specific head would be
 appreciated.  I understand from previous posts, that the valve  seats don't
 need to be unshrouded.  I'm not looking to remove much material, only to
 clean up some casting imperfections, mostly on the manifold side.
  >>