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Message: <blockquote data-quote="swampratt" data-source="post: 3399371" data-attributes="member: 15054">The 403 is fine  unless you want to go really quick and turn a lot of RPM.Some of those later Oldsmobile engines 350 and 403's had scalloped main webs and did not like a lot of RPM. If you revved too much it would destroy the main bearings and Block or main saddle flex was the culprit.But under 5500rpm and you are golden for 100,000+ miles easily on a cheap rebuild.Stick a 268H cam into an Olds and you will be amazed at the power.Couple that with some quick bowl porting of the heads and a quicker timing curve and put the hurt on many 350" chevy engines.That was the course of action decades ago.It still does well today.</blockquote>