8. When it came to heads, we had a choice to make. The GM heads that came with the ZZ4 engine had 58cc chambers, which worked the compression to right around 10.0:1, requiring 92-octane gas. Given today’s gas prices, we opted to go with Summit Racing’s 200cc street/strip aluminum heads (PN 162111, $1,050 pair). These feature 64cc chambers, which will drop the compression ratio to around 9.6:1, allowing us to run much less expensive 87-octane gas if we choose.