Just finished these up for Jason "seethrough", they are Gen4 Viper heads with our custom stainless 2.125 intake and 1.61 exhaust valves, dual valve springs good for .660 lift, and titanium retainers. Had very nice gains on the intake side, will be a huge improvement with his ~ custom .630 lift cam we ground for him. Exhaust had a moderate improvement, not near as much to get there as the intake side. Keep in mind that when comparing flow #'s, its like comparing dyno #'s, this bench obviously reads on the low side since the stock castings only flowed 305 cfm on the intake side, and the typical #'s I've seen are 15-20 cfm stronger than that. Notice the gains themselves, that's what really matters. The exhaust was measured without a pipe, figure another 20-30 cfm more with a pipe attached. Should be assembling this engine soon, just waiting on the block to come back from the machine shop.