T/A 6.6 – W72 Performance Package

Starting in 1975, Pontiac began using a lighter 400 engine block (block casting 500557) that were less desirable than the 1970-1974 blocks. In 1977, Pontiac offered a new high performance engine package for the 400 cid motor in the Can Am, Firebird Formula and the Firebird Trans Am. With the UPC order code “W72 Performance Package”, the T/A 6.6 offered a much higher level of performance than the base 6.6 Litre (400 cid) engine. It was capable of low to mid 15 second quarter mile times at a little over 90 mph in a showroom new Trans Am. The 1977 W72 still used the 500557 engine block casting.

Starting in 1978, Pontiac improved on the durability of the 6.6 litre engine by reviving the 481988 block casting, which was beefier than the 500557 used elsewhere. Research shows that all 6.6 litre (400 cid) blocks used for the 1978-1979 T/A 6.6 engines (W72) were cast through November 1977. It appears that the 1978 481988 XX blocks did not have material removed from the web area like the base 500557 400 blocks.

The T/A 6.6 engine shared many major internal engine parts with the base 6.6 Litre engine including pistons, connecting rods and crankshaft. Even though both 400 engines used the same aluminum alloy pistons, the T/A 6.6 engines used molly filled compression piston rings. In addition, the T/A 6.6 engines also used SAE 1016 locked in rod (press-in) piston pins.

Both 400 engines used standard cast Arma Steel connecting rods with Moraine 400 steel backed main bearings. A standard nodular cast iron crankshaft with Moraine 400 steel backed main bearings was used in both 400 engines. All T/A 6.6 engines used a harmonic balancer (P/N 477682) as a vibration damper instead of the rubber floated weight used on the base L78 400 engines.

The W72 engine used different heads than the base 6.6 Litre Pontiac motor. The head code for each of these applications is “6X-4” (P/N 500795). The smaller chambered 350-cid 6×4 heads measured between 91cc and 93cc. The base 6.6 litre used the larger combustion chamber 6×8 heads (P/N 500798) that measured between 98cc and 101cc. The smaller chambered 6×4 heads helped boost the compression ratio from 7.6:1 to an advertised 8:1.

The W72 6X-4 heads can be identified conclusively by the small #4 machined on the bottom of a small ridge that protrudes from the head. It’s located between the front and center exhaust ports directly above the spark plugs, in front of the temperature sensor. You’ll probably have to scrape off the paint, as the “4” is stamped INTO the face of the machined pad. While you’re at it, take a look at the valve covers; all W72 motors originally came with chrome valve covers.

(Pontiac 6X-4 cylinder heads)

At the heart of the T/A 6.6 in 1977 was a new camshaft design with a longer advertised intake and exhaust duration of 274/298, and more aggressive intake and exhaust timing than the base 6.6 litre. In comparioson, the base 1977 6.6 litre engine used camshaft P/N 526793, which advertised less intake and exhaust duration of 265/264.
1977 offered (2) different versions of this cam:

P/N 549112 for block code Y6 with the automatic transmission (identified by green color coding between the 3rd and 4th lodes and a circle stamped in to the distributor end)

P/N 549431 for block code WA with the factory 4-speed manual (identified by orange color coding between the 3rd and 4th lodes and a square stamped on the distributor end)

Although they had the same intake and exhaust durations, they had slightly different valve timing events.

1978-1979 saw only one camshaft P/N 10003402 (identified by white color coding and stamped with a circled ‘A’ on the distributor end) that had the same intake and exhaust duration as 1977 (274/298), but had a few more degrees of intake duration with more aggressive intake lobe lift and gross intake valve lift using 1.50: rocker arm ratio. This resulted in the 1978 T/A 6.6 having 20 horsepower over the 1977 T/A 6.6.

All T/A 6.6 camshafts are unique in Pontiac performance applications, in that they are all ground and installed retarded.

 

 

Physical Comparison Results
549112-’77 Automatic 549431-’77 Manual 10003402 ’78-’79 All
0.050-inch Duration 192/210 192/210 195/211
Lobe Lift 0.243/0.269 inch 0.243/0.269 inch 0.263/0.267 inch
Gross Valve Lift* 0.365/0.404 inch 0.365/0.404 inch 0.395/0.401 inch
*Gross valve lift calculated at a rocker arm ratio of 1.50:1.

 

T/A 6.6 Camshaft Specifications from Pontiac Service Manuals
549112-’77 Automatic 549431-’77 Manual 10003402 ’78-’79 All
Advertised Duration 274/298 274/298 273/289
Gross Lift 0.364/0.364 inch 0.364/0.364 inch 0.375/0.375 inch
Intake Center Line 121.0 degrees 116.0 degrees 118.5 degrees
Lobe Separation Angle 115.5 degrees 112.0 degrees 113.5 degrees

 

 

(T/A 6.6 camshafts Left to right – 549112, 549431, and 10003402)

The T/A 6.6 also used a specific Rochester 800-CFM M4MC carburetor.

 

The T/A 6.6 engines had a higher capacity 60-psi oil pump and used a baffled oil pan (P/N 527503). These internal baffles help reduce oil starvation during hard acceleration, braking and cornering.

(W72 baffled oil pan)

Oil pressure was a problem with the early 1977 code Y6 and WA W72 400 engines. Engines from start of production (SOP) through 90568 needed to have both the oil pump spring and oil pan replaced. Engine serial numbers 90569 through 131040 only needed to have the oil pan replaced.

 

The 1978-1979 XX Engine Blocks:

The 1977 W72 used an engine block with the 500557 casting code. For 1978-1979, Pontiac brought back the stronger 481988 engine block castings. These blocks are very desirable over the the 1975-1979 500557 engine block castings. The 1978-1979 481988 can be distinguished from the 1970-1974 481988 blocks by the addition of a ‘XX’ cast in to them.

These blocks have ‘XX” cast in to the lifter valley (which otherwise commonly contained the last two digits of engine displacement), next to the block casting code, and on the side of the block.

All of the ‘XX’ blocks appear to have a casting date of 1977. None have been found with a date after November 1977.

(This lifter valley has ‘XX’ cast in to it identifying this as the beefier W72 engine block)

(The ‘XX’ cast above the block casting number identifies this as the beefier W72 engine block)

(‘XX’ cast in the side of the block next to the ‘400’ displacement casting)

(Note the 1974 casting year, but the 1977 casting date and the ‘XX’)

The block above is interesting. Remember that the 481988 casting was brought back, and the last year it was cast was 1974. It appears that they reused that casting, but added the ‘XX’ and changed the dates it was actually cast. This then is actually a 1977 block, not a 1974 block.

Matching Numbers – Make Sure it’s a W72:

In restoration circles, a lot of importance is placed on ‘matching numbers’ – that is to say, that the correct components are still on the car as installed by the factory. All major components, such as the engine block, heads and so on have codes that allow you to determine their originality. Fortunately, in 1968 Pontiac also began stamping the last six digits of the VIN on the engine block, so this should be your first step. The serial # of the car is stamped on the lower flat machined surface of the passenger side of the block next to the water pump just above the oil pan. Take a piece of chalk and rub it over the numbers so you can see them.

More Information:

Interested in more research and information on the Pontiac W72 Performance Package? Download John Witzke PDF Document. He is considered an expert and self proclaimed historian of the Pontiac W72 Performance Package.