I have been racing B1 originals for 12 years now with good results. I've seen a few 600-13's on 655's and they weren't very impressive for the cost. Sure they might make slightly more power than B1 originals, but I would bet B1/Mc's would keep up with them on a 655, although they are not available for a 4.84 bore center block. Now for the Predators....having raced several B1 combos...and even though my Predator combo hasn't transfered the type of power I feel in my pants with it...I will get that baby to fly when I'm done working out the combo. There is no comparison in the power I feel now versus the power in the B1 deal. Not knocking the B1, just pointing out the difference. And the fastest 655 600-13 motor I've witnessed went 7.60's in a pro stock type car that weighed around 2350#'s. That was right before it granaded. I was running 8.30's in my 572 B1 Original 1850# car at the same track. I'm pretty sure my Predator 604 deal will run in the low 7.0's at that track when I get it figured out. And the only reason people might be having problems with the Predatos is, they are new and very few people have them, so just like when the B1's first came out, we are still figuring them out. That is unless you want to call someone like Steve Gill or Ceralli's in NJ. They have it figured out. Oh.....and boatracer 572, he has it figured out. I'm sure others do to....but those are the ones I know unless you want to turbo them....then get ahold of Gogreen!!! Oh, and I'll be building another Predator as soon as I can afford it. Wheatcraft is another one, sorry Chris.