We've had issues with the red cap repros from a few years ago with the smaller sealed battery inside. It would crank my 8.5:1 440 super slow when the engine was warm, and a separate battery (same version) did the same in a friends stock 426 hemi. We needed less than 15* of timing to get them to start. I have a new engine in the car (11:1 440) but haven't tried the repro battery on it yet. Probably going to have to beef up the internal battery. I love how they look but not happy with performance for the price. Other people seem to have better success. I'll give it a test in the next week or two again.