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Message: <blockquote data-quote="Mad Professor" data-source="post: 3220730" data-attributes="member: 5316">Ohhh. You are one of those cheaters! <img src="/images/smilies/smile.png"  class="smilie" loading="lazy" alt=":)" title="Smile    :)" data-shortname=":)" />The increase in valve size itself should not cause a dramatic decrease in flow velocity anywhere on a 406” Chevy.  I suspect the head was dramatically different in port volume or more likely combustion chamber size. The change in compression ratio can be extreme in a flattop 406.  2 full points between a 58cc and 70cc head. God forbid it was a 76cc or larger head. The 4.155 bore of a 406 also allows a little unshrouding of the intake, more so than a 4” 350. Same with a 358” 4.155 bore engine. I had a really nice set of 292 Angle plug turbo castings with 2.05” intakes on my 400. The chambers measured 59.5 after unshrouding and milling. They were Crane Fireballs” built from GM castings and ported.  I want to say they were made in the late 70s maybe early 80s before the Bowties were released.  A much better head than the 461s we used to search for in the stock head classes. I didn’t have to worry about rules on the street!! LoL</blockquote>