I have them in my 63's mild 440 and my sons 400. Both are street cars that get street driven much more then raced. The Dart's 400 has been together since 2004 and my 63's 440 has been on the road since Sept 2006. I drive my 63 alot and have raced it about 6 times in the last 3 years as I go to a T & T 2 or 3 times a year. But we run them hard and the KB Hyper pistons are holding up fine. My son shifts his short stroke 400 at 6700 to 6800 and I shift my .030 over 440 (446) at 6200. You just have to be sure and set the piston to wall clearance and the ring end gaps as they tell you. The top ring is very important to set it as they tell you. They can have some piston slap noise when cold but it goes right away as it warms up. My son and I are also on tight budgets and thats why we used them also. My 440 uses 906 heads and the MP .557 cam and has run 11.50's so far. My boys Dart has hit 11.40's in good air. Any way we have had great results with the Hyper pistons and my brother also uses them in some of his race cars and none have had any piston trouble. Ron