1966 L36 HIPERF casting code

[Gary S.]

I understand that most 1966 L36 and L72 blocks share casting number 3869942. I don't have many books, but Rick Miller's implies but doesn't explicitly state that in 1966, the 425hp blocks have HIPERF cast into the right bellhousing flange but the 390hp blocks do not. I ran a forum search of HIPERF and came up empty, HI PERF didn't yield anything relevant. Can anyone confirm or deny?

[Philip C.]

Re: 1966 L36 HIPERF casting code

The change from pass to hiperf for corvette was in the late 65 model year on the 396 around april. The 66 all have hiperf casting the machine process is the only difference, two bolt, four bolt and oil cooler plugs. Phil 8063

[Gary S.]

Re: 1966 L36 HIPERF casting code

Thank you, Phil. Are the plugs usually visible when the engine is in the car?

[Ronnie Rains]

Re: 1966 L36 HIPERF casting code

Yes they are visable
RDR

[Philip C.]

Oil Plugs

The plugs are above the oil filter boss on the side of the block. There are three holes on the side of the block on the boss. All 2-bolt blocks have the front hole is 5/16" the center hole is drilled and tapped into the oil galley is 3/8 pipe thread. The rear hole is 1/2" coarse thread. The 4-bolt block the front hole is 3/8" pipe thread drilled into the oil gallery. The center hole is a 1/2" pipe thread. The rear hole has a 1/2" coarse thread hole. So after all that the four bolt blocks have two large holes and two bolt blocks have one. Phil 8063

[Gary S.]

Re: Oil Plugs

Thank you!