Almighty SD-455 -by Chase Johnson

The all-time biggest big block engine
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Every f-body enthusiest knows about the 1976 release of the movie "Smokey and the Bandit". James Bond had his Aston-Martin but Bandit had his Turbo Trans Am! The Super Duty was an engine that for all intents and purposes, should never had seen the light of day, but on March 15, 1973, permission was given to release the engine into production cars. GM produced the Super Duty version of the 455 cubic inch big block engine. The purpose built cylinder heads, engine block, wildly aggressive camshaft profile, and power figures of 290 horsepower at 4000 rpm and 395 lb/ft of torque at 3600 rpm certainly did not fit the mood of the time.

In June 1972 Pontiac stated that they would be producing a Super Duty version of the 455 engine. This engine was slated to be available in the Firebird, LeMans, and Grand Am lines for 1973. The engines would be rated at 310 net horsepower and would be available in the September timeframe. Originally, a camshaft with .480" inches of lift was planned and indeed this engine seemingly passed the emissions tests, as the duration of the tests lasted 50 sec. Pontiac developed an EGR system that would only be activated for 53 seconds of run time, enough of a cushion to allow for production variances. The EPA found out and decided this little variation wasn't quite in the spirit of the law so the approval was revoked and Pontiac set out to re-engineer the SD so it would be legal again. Carburetion changes were required, but the biggest take-away was a new camshaft, now limited to .410 of valve lift losing 20 horsepower, which was not quite what was promissed. Pontiac could have easily given up on this project and the Trans Am would have been without one of the greatest supercars of all time. However as a result the SD-455 project was pushed back to a April 1973 release.

Super Duty engines were coded ZJ and W8 for manuals and XD and Y8 for automatics. Super Duty engines had a choice of transmissions, the almost bullet-proof Turbohydramatic 400 three-speed automatic or the famous Muncie rock crusher close ratio four-speed manual with a Hurst shifter. Either transmission was mated to a limited slip rear axle with a 3.42 ratio when ordered without air conditioning and a 3.08 gear when equipped with air conditioning. The automatic version was capable of propelling the T/A down the quarter mile in 13.54 seconds at 104.29 miles per hour as reported in Hot Rod Magazine in the June 1973 issue.

On the outside, the shaker hood scoop was merely a reminder of what was. It still shook but no longer scooped. Changes in external noise regulations took away the solenoid actuated flapper and replaced it with a permanently sealed block off plate. Perhaps this should be rephrased because as soon as these cars were shown to the press, they had in print just how easy it would be to merely drill out three rivets and pitch the plate. The air cleaner now had to rely on cold air being picked up by a hose whose opening was tucked away behind the left front fender. This colder air could be worth 15 to 20 horsepower.

Of course with every SD-455 came the branding on the hood scoop and for an extra $55 the giant size hood phoenix AKA Screamin' Chicken. Pontiac Trans Am production were divided, 180 were coupled to the smooth shifting Turbohydramatic 400 and the remaining 72 SD-455's were matched up with the rock crushers.

1973 Trans Am
Production Numbers

Engine	Trans	# Built	Total
455 -Base	4-Man	1,420
455 - Base	3-Auto	3,130
Total 455 - Base			4,550
455 SD	4-Man	72
455 SD	3-Auto	180
Total 455 SD			252
Total Trans Am			4,772

Color & Trim Codes

Exterior Colors	Code		Interior Colors	Std Trim	Code	Custom Trim	Code
Cameo White	11		White	Morokide	321	Morokide	421
Brewster Green	48		Saddle	Morokide	331	Morokide	431
Buccaneer Red	75		Black	Morokide	361	Morokide	461
			Burgundy			Morokide	471
			Beige			Cloth & Morokide	551

Engines

CID - Version	Code	Trans.	HP@RPM	Torque @RPM
455 - Base	WT, WW, ZZ, ZE	4-Man	250@4000	370@2800
455 - Base	X7, XE, XL, XM, YA, YC, YD	3-Auto	250@4000	370@2800
455 SD	W8, ZJ	4-Man	290@4000	395@3600
455 SD	XD, Y8	3-Auto	290@4000	395@3600

Transmissions

RPO	Speeds	Code	Useage
M20	4-Manual Wide Ratio	UA	400
M22	4-Manual Close Ratio	FC	All
M40	3-Auto	PG	400
M40	3-Auto	PQ	455-All

Rear Axle Availability

Code	Trans	Ratio	Availability
GYG	3-Auto	3.08	All w/ Air Cond
GYG	4-Man	3.08	Base 455
CMG	3-Auto	3.42	SD 455 wo/ Air Cond
CMG	4-Man	3.42	SD 455 wo/ Air Cond