The Last Trans Am Engine
By: Patrick Smith
“Look what happened Grand maw!” Overheard in the Bleachers at Daytona Beach, 1957, as Pontiac took 1st place.
The W72 Engine, Some Codes and Numbers:
By 1977, it must have seemed as though muscle cars were dead and gone in Detroit. The 455 Pontiac Trans Am was history. Chrysler’s 440 big block was checking out for the last time at year’s end and Chevrolet’s 454 was just a truck engine. For those who looked hard, performance was still around. You just had to know your way around the option book. Pontiac for instance, introduced their new high performance engine package in 1977 Trans Ams, Formulas and select Can Ams. It was called the W72 high performance package.
What Pontiac did was create a new casting number for their 400 engine block and added some nice pieces to improve the engine. The W72 package engines were cast in Engine Plant 6 and assembled in Pontiac plant 9 which was a state of the art facility with precise machinery. Both were in Michigan. The builders were also trained with the latest in reliability and quality control standards. The engines weren’t hand assembled or blue printed, but they were better than average castings with better tolerances.
The W72 engine had satin chrome finish valve covers, used special 350 cid Pontiac cylinder heads with smaller combustion chambers to increase static compression ratio to about 8.2:1. The pistons also received chrome moly for upper compression rings instead of the regular cast iron rings the L78 400s got. W72s had unique camshaft grinds for automatic and manual transmission usage and their own distributor with better vacuum and mechanical advance timings. The oil pump was a 60 psi unit paired with a baffled oil pan to control violent surging against the walls during cornering which could leave the pump dry. The vibration damper was unique, weighing a bit more than the standard L78 piece. One odd thing about W72 engines is they were all cast during the same one year period at the foundry. It doesn’t matter if your car was a 1979, 1978 or 1977. The W72 engine used was cast between September 1976 and November 1977. The actual casting numbers changed for 1978 but the blocks were all cast at the same time. The unsold castings at the end of 1977 were used for selected 1978 and 1979 W72 cars only.
W72 cylinder heads used 350 cid big valves, screw in studs and 6X4 casting code.
Production totals for W72 Firebirds aren’t accurate for 1978 due to flawed record keeping. It is known that 26,177 Firebirds had the option in 1977. For 1979, the W72 sales are mixed with L78 numbers and 1978 is harder still to figure out due to the bundling of W72 with WS6 suspension package through part of the calendar year. Eventually the W72 engine was made available separately. For a complete up to date accounting of actual W72 figures and more, see John Witzke’s dossier on the package available at 78ta.com website. Witzke is a Pontiac Oakland Club International Judge and is a recognized W72 expert.
For 1878, Pontiac improved the W72 by changing the specs on their camshafts. Essentially, they added more duration and added 1:50 ratio rocker arms. The cams were also installed slightly retarded to spread the horsepower across a wider rpm range. In cam tests, the W72 grind was every bit as good as the fabled 067 Pontiac grind. Half way through 1978, the automatic transmission version of the engine was cancelled. In 1979, the W72 was heavily promoted as journalists lined up to test ride the last of the 400 powered Firebirds. Dealers experienced a rush on orders. The Trans Am and Formula bodies were given a facelift that year that carried them successfully to the end of their 12 year run. The new front end eliminated the grille and pushed all radiator ventilation under the one piece molded nose. An air dam and two turn signal lamp grilles fed cool air to the rad. The tail lamp system was given a dramatic black out treatment of the entire bezel under normal operation. When the brake lights went on, the whole deck lit up. It was sensational, flashy and ate light bulbs for breakfast, lunch and dinner. The Tenth Anniversary Trans Am package was produced using a 403 Olds as the base mill and W72 TA motors with four speeds as the top mill. The W72 was the last Pontiac high performance car engine.
Pontiacs' last high performance engine was a genuine high 13 second runner with minor work.
Let’s look closer at a Pontiac W72 engine and the codes that separate it from the regular 400 V8. People restoring Trans Ams have learned it’s a special mill but many have no clue how to recognize or what parts to look for when restoring one. We’ll go through some of the major pieces and show you what to look for.
The Block: Since all were cast in one half year run, the actual year stamp will be either 76 or 77 at the back of the block near the distributor hole. The casting number was 500557 for the 1977 series of engines. The 1978 blocks used XX481988. The 1979 blocks used the same casting. A partial VIN is stamped in the usual place on a machined surface between the water pump inlet and outlet. You can see why that is important since the date code of the block will no longer work for most W72 cars due to the single batch casting program.
Suffix Codes: For 1977, Pontiac offered an automatic and four speed version of W72. The automatic option was dropped during 1978 and all orders were converted either to four speed cars if the owner insisted on the package or converted to the base 400 engine. Y6 is for automatic, WA is for four speed. In 1978, the codes were X7 for automatic and WC for manual. In 1979, only four speed W72s were available, all were coded PWH. W72 blocks differ from their L78 brethren by having some cool pieces added for endurance and power. The camshafts are special grinds, one for automatics, one for manuals. The main bearing caps used slotted dowel pins instead of solid ones to reduce crankshaft thrust stresses at high rpm. The oil pump is a high capacity 60 psi unit. Having said that, early W72s were made with the 40 psi pump and I own a numbers matching 1977 engine with that set up. The oil pan was also upgraded at the same time with a baffled unit. Once again, early W72s got a non baffled pan.
Note the slotted dowel pins, a W72 exclusive. Engine rebuilders frequently add these.
Cylinder Heads: The W72 engines used a specific 350 V8 head casting called 6X 4. Not to be confused with the 6X 8 version . The L78 engines used the 6X 8 heads which featured larger (90-101 cc) combustion chambers. The 6X 4 heads used smaller, (91-93cc). It’s good for a little extra horsepower with a static compression increase. Look for the small ‘4’ stamped on the square boss as depicted in the engine side profile picture. Another cool feature on these heads are the screw in studs and push rod retainer plates. Camshafts were also W72 specific with an automatic and manual transmission version. Originals will have paint daubs on the metal between the lobes. The end of the cam shafts were stamped with either an X or 0. My 1977 W72 block has the 0 stamping which is PN 549112 or the W72 automatic cam. PN 549431 is for the manual transmission.
As a side note regarding the cancellation of the automatic W72 engine, GM used a specific TH350 transmission for that engine. Since production was cancelled by March, 20th, 1978, finding one of these if yours is missing will be a challenge. It used a specific governor, valve body and vacuum modulator. Essentially, it was a shift kitted version of the TH350 with a smaller torque converter.
The smaller combustion chambers ( 91-93 cc) makes these heads desirable for 455 engine build ups using modern pump gas, one reason why they're hard to find.
A FEW DETAIL ITEMS: W72 6.6 Liter engines also had special distributors. It used GM’s HEI unit with the best vacuum advance curve available for the entire Pontiac range. The paint daub code for the W72 automatic distributor is bright yellow and marked on the milled base where the distributor cap locks on. The distributor number is 1103271 followed by a date code. The internal module is black GM plastic with a yellow circular paint daub. The batch code is stamped in white ink for dates. The water pump for the engine used a cast iron impeller with raised fins for improved fit between baffle and water pump body. I don’t know if all the W72s got this, but mine did. Over all, lots of unique parts and better than average performance made the W72 one of the last true Pontiac Performers ever made. In modern engines you can use preventive maintenance software to check if there are any issues with your vehicle. The proper software can keep your car running smoothly.
A nice video of a Pontiac 455 engine rebuild Part 1.