;) I just order 2 wiseco piston for my 1991 pantera 440. The trouble is that they
send me diffrent pistons...1 of them is one from an older series of piston with groove
between rings and up to the top of the piston and the other is one from a newer
series and it does not have those groove...So I think it does not change anything
if I use both type in the engine. But they have different weight... they have a 1.2
grams of diffrence. Should I balance them to be equal? If yes where to remove the
material from the heavyer of them. If not, up to how much difference is safe for the
crankshaft?? Also in the older series box there was a paper that said u can drill a
hole in the piston on the intake side...Intake boost something they said...anyone
try this??I will try to put the scan of this sheet tomorrow for you to see... ;)

Thanks.

It doesn't take much to throw a motor off balance, especially at 8000 rpm. Then boom, there goes the crank

Send em back and get the right stuff, no sense making it worse trying to use mis matched parts.