I've preheated engines more lately than I used to, and I notice zero difference. I've never had a rod go.. I had a Caster Grenade (Go 5-port) back in the day, which had extreme pinch, ran it in and for several gallons without ever preheating it. Sent it to the engine guy for a new rod after 4-5 gallons(of temps close to 300 pretty regularly..), and he sent it back saying it wasn't necessary(and not earning money in the process). Sold it off later and it still went fine for the next guy..

Lately I've been preheating less. I just don't believe in it that much. The fad of it took off a few years ago. If you listen to all the preaching about it you'd wonder how engines ever lasted more than a gallon before everybody started preheating.. Reminds me of all the sealing talk back in the day. "You MUST seal your backplate and carb throat etc, or you WILL get air leaks" etc etc... For the most part, overblown, baseless, and unnecessary. Same with preheating, I suspect..

It's a PIA too at a race.. Enough other stuff to worry about..

I'm not saying start it up and floor it from the first tank. Still do a decent heat cycling break-in on it, and go easy for the first half gallon or so. But it's a tremendous amount of effort and energy to preheat an engine (not to mention several..) before every start.., and I just don't think it's worth it, and suspect it's not even really necessary...

(Don't mean to sound argumentative.. Just my random 2c on the subject...)