I heard that the A series engines can go at higher rpms than the L series engines and that they can produce more horsepower is this true?

How is an A15 going to make more power than an L20B?

About rpms, I'm not sure ... There are reportedly A12s running 10,500 rpm.

My younger brother once had a 510 with a 1600 in it and installed a sun supertach. He used to run it up to 5500rpm for every shift. He was telling me how good it went but that it sounded like it was winding a lot higher than 5500. I got him to take me for a ride. It screamed and would launch on gear shifts. Later when I had a good look at the tach and installation, found he had it set on 8cyl instead of 4cyl. We switched it over and found it seemed like a dog but that it wasnt screaming anymore. I think that he was actually running 11000rpm instead of 5500rpm due to the tach setting. Wouldnt want to do that for long!

I found the limiting factor engine speed wise on the L series is the lash pads. At high engine speeds the valve springs (340lb on the cam nose 120lb on the seat) were not strong enough to keep the lash pad captive in the lightweight titanium retainers.

A12/13's can run to 10,000 + with the right valve gear and bottom end.