have you tried phosphoric acid? i recommend alumiprep 33 (available from aircraft spruce). usually, it provides a nice, bright finish.
now, i HAVE noticed with certain parts that cleaning w/ alumiprep leaves the parts grey. as best i can GUESS, porsche has applied some type of anodizing to the block to help resist corrosion. in that case, mild acid treatment will leave a surface coating of antimony, which is grey.
the antimony can be removed with nitric acid (hard to get). alternatively, and i have not tried this, you can use a mixture of phosphoric & chromic acid. keep in mind these things are a little nasty.
once you've done this, any anodization will have been removed. bare aluminum WILL corrode. you can either re-anodize OR use an alodine process, which will leave a nice looking golden finish on the part. i'm getting ready to make some more drop links this week; i'll take photos of the process if you want.
the final alternative is to steam clean the parts. this should leave a nice finish without altering the anodization / surface treatments. it won't be as pretty as bare aluminum, but it may suffice.
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Originally Posted by BYprodriver
Hey Insite, speaking of questionable castings any insite on the alloy used to make M96 engine parts like case, heads,cam covers? Having a hard time finding the best solution for cleaning parts without turning dark grey.
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