tirod wrote:
I just picked up the latest Pop Rod "Engine Masters" magazine, it has a lot of good teardown info. Lots of the trick stuff isn't in the crank and rods so much - in fact these guys are buying off the shelf to cut costs. Apparently the devil is in the details - using heavier forged nitro pistons, combustion chamber porting, optimizing carb tuning, 1.9 ratio rocker arms with flat tappets and almost stock springs, or completely massaged intakes with matched spacers. Lots of extensive dyno time.
Yeah I love that stuff, like I was saying if those guys can get 500-600hp and 400 to 600 pound feet from 300 to 400 CI engines we should be able to coax out way more than the 250-260 we are. The breathing mods porting and intake modification are indeed some of the more visible things.
The key really though is to think of it as a system, They do knife edge and smooth the crank. And they hand mirror polish journals etc.
However there's a lot to be gained from tight oil tolerances, and near Perfect bores, (within .02" roundness) and tight oil clearances makes power by reducing bearing friction. Boring and honing with a torque plate is the only way to get the bore so close to perfect. These guys are getting power from building to extremely demanding tolerances as well.
I was reading my newly acquired "Mopar Jeep Engines" book which is purely about race modifying Jeep engines, over one third of the book is straight 6 (mostly 4.0 with some 4.2). There's a lot of stuff in this book that is not commonly talked about around here.
For example Mopar says you will make more power with a block that actually HAS some core shift, if it makes the cylinder walls thicker on the passenger side (tested by sonic checking) and thinner on the driver side of the block. Apparently this is due to the passenger side taking the brunt of the force. The thicker wall on this side will cause less deformation (flex) of the bore meaning rounder walls during the power stroke, which means less friction. A block with no core shift has more uniform wall thickness but less meat on the passenger side. Meaning it will actually deform more on the power stroke than a block that has core shift favoring that side.