not a damn thing. I have a stock bottom end...I put a larger cam in with new aluminum heads...1.72's are too big...Edelbrock said go with 1.6's...so I did...the only reason I have these are from a deal they got thrown in...they are from cochese...they are like brand new...I put them into the scorpion 1.6 box...to keep them nice...they are nice and oiled...pic will be up in a few minutes...waiting for cam batteries to charge....this is a smoking deal...no joke...I bought new 1.6's from A&E this morning....these have to go!