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hello everyone , i picked up a box thats got 6 brand new 580 5 port pistons ..all of them have two 1/4 inch holes drilled in the intake side underneith the wrist pin about an inch apart ..just wondering what the purpose was ..im thinking extra lube ..?? ..will they work in my 3 porters i have 5 port pistons in every one of my motors i dunno if it helps but i always put them in there ..i dont see where the holes would bother anything ..thanks ..

Dome's are different.

yes sir i do no the domes different ,thats why i put them in my 3 port motors for more compresion cuz im to lazy to weld them up ...but sometimes i weld and grind down one of my old 3 port pistons and keep testing the squise till i get about min .009 to max .012 or so clearance with clay .i just got done instaling a full circle kit i found two brand new ones in packages so i used one ..welded dome,ported and polished the whole motor inside and out window cut piston ,eboxy all transfer ports and deflector ,.thinned all rip ports ..welded up stuffer for max fill ,cut the flywheel,if i did my math right its 10.73 to 1 comp.i was just wondering why they drilled all 6 these pistons only thing i can see is extra lube to cyl.. ??..

Do they open into the exhaust port or intake port when piston is at TDC?

exhaust ...there in each botton corner of the wrist pin releif ..

So do the holes let the intake charge escape into exhaust port?

That was called "free porting" or I have heard it called "freak porting". It was used on open pipe engines to add more of a charge to the exhaust. Don't make any sense to do that to a 580 WB...... I have never tried it myself. I'm sure others know more about this than I do.

Just reduces power by letting a portion of the crankcase charge escape out the exhaust. In ye olden days, it was common to add holes to the skirt to improve oiling-then they discovered that it was harmful to do so without making sure that the added holes weren't in line with the exhaust.

ted .do you mean intake insted of exhaust ..?? .i guess i dont understand why they wouldav done it ..im thinking about welding them shut ..but if there not gonna hurt nothin ill leave them ..so your sayin the kinda turbo out the exhaust ..??

OK its time for a picture of the alleged pistoin in question...