exhaust port pitting

[wmunchovie]

Hello all: please review this picture of a 76 930 turbo head. I just finished cleaning and blasting lightly with walnut shells. My concern is the deep pitting that is in the exhaust port –

1. Anyone else have this problem?
2. Anyone know what could cause the pitting of the aluminum?
3. Should I get the high speed grinder after it and smooth it out?
4. Should I open up the port size by removing some of the meat where the indention stops ( open up the inner diameter to match port diameter ) ?

Thanks!
Munchovie.

[Mo_Gearhead]

I do not have long term experience with P-car heads, but I would assume that the pitting is probably normal (high mileage, air cooled/alum. head).

Is it just the ONE port or all exhaust ports?

Unless you are building a race car engine, any porting will be, at best, minimally effective ... and at worst, detrimental. Not a 'do it yourself job' unless you know what you are doing. JMO

[Nitrometano]

maybe can be caused buy the walnut blasting that you use.

You can take the grinder and smooth it. I use the air grinder with a metal stick with sand paper. I use a sanding belt that I cut in 1 inch strips. I always buy some grits from the coarse one to me smoth one. I use first 80, 120, 180. Because is the exhauts port, you can polish to a mirror finish, this will help to avoid the carbon build up.

[rsrfan]

Munch,
don't know how I missed this one. If you have the time and patience take a look at this thread by Kevin at UMW regarding DIY head porting for our turbos:

http://forums.rennlist.com/rennforums/showthread.php?t=192483&highlight=head+porting

JP

[A930Rocket]

I'm surprised the walnut shells would eat into the aluminum. More likely, it's the casting marks.

Here's a pic of one of my intakes after opening it up for a 3.2 intake.

[304065]

I think it's corrosion caused by moisture in the carbon buildup.

Not QUITE as bad as this but you can see what water will do to a head.

[3.2 CAB]

+1 with John Cramer, it does appear to be from corrosion build up and moisture creating almost an acid and it started to "eat" the surface metal. Good luck!!