Is the 1968 J Code enjine a rare enjine

The J in the engine code corresponds to the month the engine was manufactured. J means the engine was made in October. l am pretty sure Pontiac made lots of engines that month.

The link below explains how to read the Pontiac engine block codes

Also in the engine codes, there was a YJ, which is a 326 cubic inch, 265 horse power automatic. And there was a WJ, which was a 428 cubic inch, 390 horse power, manual. If it is a 428 manual, it may be somewhat rare. l saw these mostly in the Grand Prix.

See the second link

Yes. they are rare.
but making them more valuable would be the car it is in, only 5% of the 68 convertibles had the j-code engine in it.

As has been pointed out, more information is needed to determine if it is a 326 or 428. l can say with certainty that if it is possibly a 428HO manual as had a poster suggested, it is very rare, although the popular application for the Grand Prix is for 1969, not 1968.

Additionally, there is no way to tell how many were installed in Pontiac ragtops, as has been suggested by another poster. Pontiac did not keep these figures, & one would have to go through all the invoices to determine how many were installed in which models & bodystyles. l would be willing to bet most were installed in Catalina fastbacks & Grand Prixs. If u finally determine which engine it is, l can tell u how many they made for all installations . . . & l am almost certain it is about 500 or so.

1968 J Code ... Not enough information

l am thinking you are asking is
does 1968 Grand Prix J car have a rare motor.. Most likely no.. most J is had a 400 4 bl

If it had a special order 428 yes that is rare..

Need the engine code to confrim Rare. Also head codes. center exhaust ports. Motor code right front on block just below head on front.