The headers are too small for the LS1, I found out today that they are only 1.5". I spoke to Sanderson headers today and they have the block hugger in 1 5/8 and 1 3/4. I will try these if they do not fit then I will just take my car to sanderson and have them make me a set. It seems like a waist to put in such a nice motor and then kill some of the power.