It is well published that the 455 Stage 1 engine has slightly larger valves than the regular 455, but does anyone know what the valve sizes are for the 455 they put in the '70 Rivs and Wildcats? Are they the same as the base 455 or are they the same as the Stage 1? If the same as base then how do they get the extra 20 hp to bump it up to 370? Thanks.
Stock valve sizes for the 455 are 2.00" intake, 1.625"exhaust. Stage 1 valves are .125" bigger at 2.125", and 1.750" respectively. There is no way to tell valve sizes from head casting numbers. You have to look at the valves. Some of the bigger cars got Stage 1 valves, some didn't. Again, you have to look. As far as HP ratings, the cams were a bit different between 455 and 455 Stage1 engines. The big car cams were supposedly different as well. I don't take factory HP ratings very seriously.
70 Riviera and Wildcat engines/heads were the usual small valve. The difference was marketing. No change in the engine unfortunately.
