Ebay item #260338834301


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By Rudder2fly - 17 Years Ago
A good buy or bad buy? Anyone have any experience reducing piston dome height? Maybe I will use that pitted bird block after all! Thanks G.S. 
By 46yblock - 17 Years Ago
The Jahns domed pistons I briefly owned had very thick skirts resulting in a heavy slug.  Required clearance as I remember was .007 or .008, apparently required due to all that aluminum expanding at running temp.  Guys who actually ran them say they produced quite the racket from piston slap until everything warmed up.

The forged dome pistons now offered by JM definitely makes the Jahns obsolete.  I would say bad buy at any price if you were actually planning on using them. 

By mctim64 - 17 Years Ago
Jahns pistons are not the best, the ones I have had experience with where heavy, not very well cast, and the weights were way off between pistons from a supposedly matched set.

Next;  +.125" over is an awful lot to bore a 312 block, they can take it in some cases but check your cylinder walls first. Then you will need a set of "Big Bore" head gaskets, Mummert dose carry them for up to 3.935" bore.

Not trying to rain on your parade but I don't think it is the way to go. Just one mans opinion. BigGrin

By PF Arcand - 17 Years Ago
As I recall the Jahns pistons from years ago, they probably weren't that high in quality & the front edge of the domes were not clearanced at all near the spark plug & in fact would hit long reach plugs in a Y-blk. The current ones that are sold by J. Mummert appear to be a much better design.