We have a member here than has ran his 12:1 Hemi on pump gas, but i'm not sure he raced it on pump. From what i have seen, your about max to race on pump gas also, seems Hemi's are not as sensitive to compression increases as wedges are. Best told me you need 13:1 or higher to really make a difference in power with compression increase from 10.5:1. Between 11:1-13:1 seems to be a bit of a no mans land with Hemi's. That being said, I will be running 12:1 with my 572 because i ordered the pistons before i was told better. Best Machine has made 850hp on pump gas with 10.5:1 compression with a 572 Hemi, so seems there really is no need for higher compression for a street Hemi.