Magnums have closed chamber heads with small 62 cc chambers so unlike LA engines, they are between 9-9.4 to one from the factory. The variation depends on jjust how far down in the bore the pistons are. If you have a .070 engine you will have right at 9-1 and if you have a .040 you will have closer to 9.5-1. Machine tolerances account for the difference. People typically run .028 head gaskets to get to 9.5-1 from an .080 in the hole engine. Half a point of comp is not going to make more than 10 HP on a 400 HP engine. As IQ52 posted in another magnum thread, a stock 5.9 with 216 @.050 .505 lift 114 LSA cam made 400 HP with not much more than an Edelbrock AG EFI intake, that cam and a pcm flash. If you put a good cam in your engine, you will have smae power if properly tuned.
