So, I'm wanting to go gt40 heads and Im currently running e7's. My cam and piston specs are below however I couldn't find the size of the valve reliefs on the pistons and I couldn't find a site of the manufacture (speed pro) I could only find retailers, summit, jegs, etc. With my cam of .512 lift should do you think I will have ptv issues with the gt40's as where I don't with the e7's or are the gt40 valves that much bigger that I will run into problems? Im ready for the response "one should always measure" before install but I don't want to order a set of heads that most likely will need piston notching since I'll have the car torn apart only to find they are not going to work. It's not like I can run to walmart to exchange em for a different set.... Anyways here are the spces,, thanks for the replies, lately I've only been getting views. Oh and I get it the gt40 head thing has been beat to death but c'mon guys has anything new happened with the 302 in the last 20 years!? Also I think speed pro was bought by china hence the no corporate website. One final question before I let yall go, will springs from an e7 work on the gt40 head? My e7's have better springs than whats offered on the heads and I want to reuse if I can (beehives) Comp 35-440-8 2000 to 5500 operating range 281HR cam grind number 281 duration in (advertised) 281 duration ex (advertised) 220 duration in @ .050 220 duration ex @ .050 . 512 valve lift in 512 valve lift ex 110* lobe sep angle Speed-Pro Hypereutectic Pistons ZH120CP30 Bore (in):4.030 in. Bore (mm):102.362mm Piston Style:Flat top, with two valve reliefs Piston Material:Hypereutectic aluminum Compression Distance (in):1.615 in. Piston Head Volume (cc):+5.00cc Wrist Pin Styleress-fit or floating Pin Diameter (in):0.912 in. Piston Ring Thickness:1/16 in. x 1/16 in. x 3/16 in.