Pretty much every single performance engine manufacturer on this planet breaks in their engines with synthetic oil, as do most builders. There is no reason to go with conventional motor oil unless you just can't afford the synthetic. Rotella T6 5w-40 goes in every single engine I own and there probably isn't a better oil you could buy for the money. BMW and some of the exotic car makers get oil made to their spec and those *could* be better than T6 but it is unlikely.
I've built a few GM small blocks over the years and had a totally insane 700 triple triple that I built in a snowmobile. The SB's were easy with the oil because you just drain it. The sled needed the synthetic oil pumped out of the tank for break in.I didn't read your post before posting my reply a few minutes ago, but I respectfully disagree. When I google Engine break in, the very first link I see from Summit racing mentions the oil. I've heard this and seen it for years. I didn't search this out, or look for other articles, just the first thing that popped up, and I buy a lot of parts from Summit.
Proper engine break-in procedure is critical. The right steps during this procedure can save your engine, your bank account, and ultimately your sanity. With help from the engine experts at ATK High Performance Engines …www.onallcylinders.com
You can do what you want, but I can tell you from first hand experience that one of the best engine builders in our area, who currently owns many NHRA, IHRA, NMCA, etc., class records still uses non synthetic oil for all his break ins, with engine oil supplements for cam/lifter run in. I won't share what brand of oil and supplements he uses, but it's not synthetic. Just saw him do it a few weeks ago. Runs them only a few minutes, then drains, and refills, primes, and runs again. Guy builds motors for a living. No synthetic for a long time in any of his motors. Neither do the other engine builders that I personally know.
Do whatever you please, but I personally know engine builders and unless you are building a flat tappet cam engine, synthetic all the way. Over the road trucks and the top tier racing classes all use synthetic oil, for break in and hard running. Formula One engines have to be filled up with hot oil or they won't even start, still synthetic. Current F1 rules dictate a small number of engine replacements, so synthetic oil is even more important.
There are of course examples that run counter to what I've said, but they are almost all antique or flat tappet cam/lifter setup. In these examples I would still break in with synthetic, but I would spec one that has lots of zinc or add some in.
Ever watch NHRA top fuel guys build an engine? They don't even use torque specs because the engine only has to make one or two 1,000 ft passes. The crew just slams the parts together with air tools and they could probably use vegetable oil and get away with it.
I spent a lot of time during some very boring parts of my military career reading oil sample reports and Bob is the Oil Guy forums.
Ok so let me try this scenario... before all of these posts, I did start breaking the engine in, but because I'm going to dump it out, I used some O'Rileys (sp) cheap 10w-30 and have about an hour in on it. I have been running it at different speeds for random times, working my way up to full throttle (and splitting a little). I let it cool down as I change the throttle periodically.
What if I switched over to conventional oil for a few hours too? Continued to change the throttle and keep letting it get hot and cold. Could I potentially get the best of both worlds here?
How many hours on it? I have a spare engine for mine but my fear is the electric side pukes before the engine does and the new Kohler units are all electronic now.A quick update regarding engine break in. I'm rebuilding a Generac 15,000 watt generator with a 30 horse V-twin horizontal shaft air cooled motor.
While looking up the final torque specs for assembly in the factory service manual, I noticed a section on oil. In there it states specifically that after the initial break-in, it is "then acceptable" to use synthetic oil if you prefer.
But the factory oil is not synthetic on this model, and only after break in does generac consider synthetic oil to be an acceptable option.
How many hours on it? I have a spare engine for mine but my fear is the electric side pukes before the engine does and the new Kohler units are all electronic now.
Why they couldn't leave well enough alone has me scratching my head.