run through the center of each port via pressed-in tubes, in addition to streamlined airfoils over the tubes themselves to improve port shape, and increase flow velocity. The 303 had shorter connecting rods, smaller journals and a solid lifter version of the Ram Air IV camshaft. It shared the bore of the 400, but with a stroke for a displacement of . The short deck engine weighed about less than the other variants and had an 8000 rpm redline. Pontiac's SCCA Trans-Am program was promising, with race-ready engines producing to , however the series’ General Competition Rules required the manufacturer to produce no less than 250 vehicles with the 303. Plans were made to produce Firebirds and GTOs with advertised ratings of and respectively but concerns about emissions, the response of the automobile safety lobby, and the warranty implications of a high-revving street engine led to cancellation of the program. T While the exact total number of Ram Air V engines produced is not positively known, only about 25 engines were produced and about a dozen 428s and 366s. More engines were produced by Pontiac than the other versions - estimates range from 80 to 200 units. Some 400s were dealer installed. Parts for Ram Air V engines are not readily available. The cylinder heads on the 400 CID version had an intake port volume of , nearly twice the size of a typical standard D-port Pontiac head - and flowed in the area of @ valve lift; in the realm of the NASCAR-dominating Chrysler 426 Hemi. Super Duty SD 421 The 421SD was available in 1961 as a dealer option or over the counter then in 62 and 63 from the factory, and was fitted with a list of internal modifications designed solely to withstand the abuse of drag racing. Cam was a #541596 McKellar No. 10 with 308/320 degrees of duration and with 1.65:1-ratio rocker arms and solid lifters, special #529238 forged-steel connecting rods, forged aluminum bore Mickey Thompson pistons, #542990 forged-steel crankshaft with a stroke and diameter main journals. Dual Carter Carburetor #3433S (front) and #3435S (rear) carburetors with manual chokes and mechanical linkage. Factory heavy-duty high-pressure oil pump and eight-quart sump, four-bolt main bearing caps with Moraine aluminum bearings, and #1110976 dual-point distributor without vacuum advance. Two different cylinder-head castings were used for the 1962 model year, both with a combustion chamber volume of to produce