Tony (boatracer572) had great luck with his predator stuff, and he helped me with the 2 I have. My 572 has been trouble free for 64 runs, that's a record. It has run a best of 7.30@183 weighing 1850lbs, in 4800ft air in Boise. Tony says it's a smallish cam for the heads, but I wanted it to stay under 8200 RPM. I think it might run a 7.0 something at sea level, even with the smallish cam and lower than optimal compression. I am finally seeing what he was saying after I had so much trouble initially. They do work. Like others, I wish we had a 5" bore space block to put them on. As far as the SR20 comparison, I have a budy at the track that has an all out SR20 headed 632 in a dragster that weighs 1790lbs with driver, he runs about .05 faster than I do. I think there's a bit more in my 572 with a cam and compression change.