[ultraflo]

The biggest difference between the two blocks is that the R302 block has siamese bores, and the A4 doesn't... the cylinders in the R-block are connected internally, in that the coolant doesn't circulate between the bores vs. the A4 bores, that allow coolant to circulate between them, like the factory block.

The R302 block can be bored .125 over, and the A4 can be bored .090 over.

Also, the R-block is factory rated to handle more HP than the A4, mainly due to the siamese bores connecting the cylinders together.

-Ryan