1970 L78 CKO Block from Van Nuys

[Cranberry70SSL34]

Sounds like a l78 all together with the 840 square ports. I definitely like oem stuff myself. If you put 290 oval on a l78 piston with its 101 cc chamber it jumps the compression to over 12 to 1. My piston head is exactly L34 with 10.25 with solid roller cam and auto th400 with 4.88. It works real well. The only minor drawback is the trw oem pistons were not really designed for big roller cams and don't have very big reliefs. Therefore my piston to valve clearance was really tight at the suggested 104 degree spot. I had to leave it straight up at 108 in order to gain proper clearance and was borderline then. Runs super at 108 but would be a little better in heavy car if would have been able to degree it in at 104. If I were to build a L78 I'd prob go in L89 form and try to get compression above 12 with roller cam and try to get it set up at 104 and use the same cam I have in my current engine. I know what you guys mean in order for a 396 to benefit from square ports over ovals you gotta get you gains in the 6500 to 7500 range. Not sure if it is ever all round better than the ovals considering they work so well up to 6500.

[WILMASBOYL78]

I'm not sure if you can use the 290's with the 11 to 1 pistons...I think there would be clearance issues. The oval port heads were designed to work with the different dome design of the 10.25 to 1 motors. Perhaps some of the engine gurus can chime in [img]<<GRAEMLIN_URL>>/hmmm.gif[/img]

That aside, the oval port 290's are more than enough for a strong street/strip setup...the big square ports have the edge on the high end...but, most action takes place far below that.

wilma