This is a cutaway of a typical...
This is a cutaway of a typical 400 block cylinder wall. Compare the rather restricted route the coolant must navigate with the SHP block photo.
Liner Notes
The original small-block Chevy was designed on 4.40-inch-bore centerlines. Back when the 327 was the biggest small-block Chevy built, the 4.00-inch bore benefited from a very thick wall lining between each pair of cylinders. When the 400 pushed the bore size to 4.125 inches, the only solution was siamesed cylinder walls. But even this trick did little to improve wall thickness for the thrust side of the cylinder wall. The thrust side is the area where the pistons push hardest on the wall. On all V-8 engines that rotate in the standard direction (clockwise as viewed from the front), the thrust sides are inboard of the driver side and outboard on the passenger side. Most engine builders prefer a minimum of 0.200 to 0.230 inch after boring, which is the reason GM 400 blocks should not be over-bored more than 0.030 inch.
Dart realized this and took steps to cast more material around the cylinders on the SHP block to create a minimum of 0.230 inch of cast iron even at the 4.165-inch bore size. Dart also scalloped the outer water jackets to allow freer coolant circulation around the cylinder walls, which eliminated the need for those pesky steam holes and allowed more room for thicker cylinder walls. The bottom line is a more stable bore under power, which means the rings have an easier job sealing to a more uniform bore.
Note how the SHP block coolant...
Note how the SHP block coolant passage is far more direct, which makes cooling easier with fewer flow restrictions.
Drill, Baby, Drill
The small-block Chevy is considered to have one of the best production V-8 oiling circuits, and yet it still comes up short compared with true race engine technology. The small-block lubes the mains by pushing oil down a central oil gallery on top of the cam. Once the oil fills this gallery, it turns 90 degrees and then has to travel around the outside of the cam bearing to reach the mains. This circuitous route creates a small loss of pressure as the oil is forced to make each of the multiple 90-degree direction changes. As bad as that sounds, it's still much better than a Ford Cleveland that has to push oil through the lifters before reaching the main bearings and rods.
Dart's owner, Dick Maskin, has decades of experience in Pro Stock that has taught him the value of what is called priority main oiling. This is what is employed in the SHP block with a dedicated passage from the central oil gallery to the main bearings. The cam and valvetrain are then lubed with a secondary vertical passage. This more efficient lubrication pathway also eliminates the necessity for a high-pressure or high-volume oil pump. It could even be proposed that with a stock production pump, the oil pressure could be reduced when using the SHP block because of this less-restrictive system.
Four-Bolt Mains
One of the biggest expenses involved in building a 400ci production block is converting to four-bolt main caps. The factory four-bolt main blocks are ironically weaker than the two-bolt main blocks because the factory removed material from around the main cap bulkheads. The common trick has been to convert the two-bolt main blocks to four-bolt mains with steel aftermarket caps, which is an expensive procedure. Dart automatically went to the four-bolt main configuration, using the stronger, splayed-bolt approach.