You are correct, Mark, Minimizing or eliminating laminar flow next to metal - in other words causing the laminar flow in the boundary layer to become turbulence does promote heat transfer.  It also increase skin friction and drag.  However, if the turbulence gets to the point of causing air flow separation then that hurts both cooling and the drag factor.  So like most other things involving aircraft - compromise is called for.

 

My cores are slanted - but, only because I could not fit them in the space I had allocated for them any other way.  Otherwise they would be perpendicular to the air flow.  Clearly slanted cores do work and most of the time we install them in that orientation due to space constraints or aesthetics as Pat Panzera indicated in his response.

 

Paul Lipps has seen great performance gains with his unique propeller design when bolted to his Lancair 235 and the Phantom Biplane, both of which have very streamlined cowls.

When he tried it on a stock RV6, it seems that too much of the cowl frontal area blocked thrust from the propeller.

 

It’s like if you had a 60” diameter prop bolted to a 72” diameter radial engine.

 

If you are not familiar with Paul, his plane or his prop, here’s an electronic copy of an issue CONTACT! Magazine that has the information.

http://www.contactmagazine.com/Issue79/Issue79.pdf

 

Pat