How long does it take to lean burn a 496? I have a 496ho and a bonehead mechanic. Last summer, I noticed the engine was only getting 4300-4400 rpms turning a 25p mirage plus. Usually, it does about 4800. The engine idled a little rough adn the IAC was pretty noisy. I took it to my mechanic who found nothing wrong with it and told me the fuel pressure was fine. After 2 months of the same problems, I eventually lost trust in my mechanic and checked the fuel pressure my self. Turns out I was only getting 24lbs. I replaced the high pressure fuel pump and cleaned out the fuel system, which solved the problem. Now the engine is turning 4700-4800 rpms, fully trimmed. I haven't done a compression test on the engine yet. How robust are these engines? Is it likely that I damaged the engine? I probably put 15 maybe 20 hours on it last summer.

A compression test and leak down test will tell you if you have any cylinder or valve issues. With a good prop on a healthy engine you should be able to pull about 5000-5100 rpms, all things being right.

Best Regards,
Ray @ Raylar

Thanks for the advice,

Jim