the factory tachometer. Various Pontiac sources have emphatically stated that NO versions of the SD-455 were installed in regular production cars. The SD-455 motor was listed as an option in dealer brochures for the 1973 Grand Am and LeMans GTO(and planned for the Grand Prix as well) although none were produced for sale. Nevertheless, there appears in the October 72 issue of MOTOR TREND, a road test of a 1973 SD-455 Grand Am. 1975 Factory Service Manual lists the SD-455, but the SD-455 did not meet emissions for the 1975 model year and was canceled. Experimental V8s 427 Hemi SOHC This was a project started with the end goal of building a 427 Hemi. Pontiac asked Mopar (Chrysler, Dodge, Plymouth) for help in designing it and making it work. Surprisingly, Mopar actually agreed and sent over several of the engineers that designed both the 392 and 426 Hemi. The goal of making a Pontiac Hemi succeeded but the engine was never produced. Features: Thin-wall, cast aluminum block bore x stroke, 8 cylinders, each having a bore of 4.342 inch and a stroke of 3.75 inch, results in a displacement of 444.21 cubic inches (7,279.34 cc); for the Pontiac OHC 427 Hemi refers to it as a "TOHC" and lists the bore at 4.257 inch—which, with a stroke of 3.75 inch, results in a displacement of very slightly more than 426.99 cubic inches (very slightly more than 6997.124 cc). main bearings Forged steel rods (Ram Air V style) 12:1 compression Mechanical Port Fuel Injection Large-valve heads (valve diameter): intake, exhaust Small-valve high-RPM head (valve diameter) intake, exhaust Splayed main caps, head bolts tie into main caps. Head bolts do not pull on the cylinder wall causing distortion. Cam drive: fiberglass belt Maximum RPM (high-RPM engine): over 8000 rpm Engine weight: estimated complete Dimensions: width , length height Power: estimated at 7500 rpm Pontiac SOHC 421CID V8 Most likely prompted by its development of the Pontiac OHC six, the GM division built three different experimental SOHC 421 CID V8 engines in the early 1960s. According to the engineers who worked on the project, the SOHC 421 engines produced around 625 hp and were capable of turning 7,000 rpm. One version of the engine featured camshafts driven off the front of the engine, another design had the cams driven by gears off the back of the engine. Apparently at least one of these