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the pontiac w72 400 engine

In 1977 Pontiac offered a new high performance engine package for the 400cid motor in the Can Am, Firebird Formula and the Firebird Trans Am. Nicknamed "W72", the T/A 6.6 offered a much higher level of performance than the base 6.6 Litre engine and was capable of low to mid 15 sec quarter mile times at a little over 90 mph in a new Trans Am right off the showroom floor. Here's a detailed look:

1977 T/A 6.6 (W72) Engine Specifications
L78 400cid Block (engine code Y6 if automatic, WA if manual)
200 Net Horsepower @ 4000 RPM (220 in the 1978/79 Firebirds)
325 Net FT.LBS Torque @ 2200 RPM
6X-4 350cid high compression heads with 91 cc's or 93.74 cc's, depending upon which source you believe!
8.0:1 compression ratio (as rated by the factory, although Pete McCarthy says 8.2:1))
Higher performance camshaft (274 degrees intake with .364 or .374 lift (sources vary)/ 298 degrees exhaust with .407 lift; 55 degree overlap.)
800 cfm Rochester Quadrajet carburetor
Special oil pump, delivering 60psi @ 2600 RPM, which ensured sufficient oil pressure during high RPM use.
Special slotted spring pin main bearing caps instead of the standard solid dowel used on the base 400 engine. These special caps induced less stress during high RPM use.
Special harmonic balancer
Chrome valve covers
"T/A 6.6" shaker scoop decal

As can be seen by the list above, the W72 was much more than just a twenty horsepower increase over the standard 6.6 litre engine. While it was installed in the Can Am in 1977 only, the W72 was available in Firebird models for 1977, 1978 and 1979. Minor variations in engine specifications such as a change to a less restrictive exhaust resulted in an increase to 220 horsepower in 1978 and 1979. Given its more desirable performance features, it's important to make sure that this engine is installed in your car, if it was there originally.

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.

Now for the engine codes. The minor problem in this area is that the same codes are used for the base 6.6 litre engine and the W72, but if the codes are correct for a W72 and the VIN excerpt matches, chances are that it is the original engine. On a Pontiac engine, the engine block code is located just below the passenger-side head at the front of the block. A Can Am should have a "Y6" code, as it wasn't available with a manual transmission.

The W72 engine used different heads than the base 6.6 Litre Pontiac motor. The head code for each of these applications is "6X", which can be found by inspecting the area of the head just above the middle two spark plugs on each side of the engine. The W72 heads were actually higher-compression 350 cid heads (91 cc's as opposed to 101 cc's for a regular 6X); this equates to approximately a 8:2:1compression ratio on the W72, versus 7.7:1 for the 6X-8 base heads.

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 temp sensor. From the driver's side, take a small mirror and place it under the outward lip and use a flashlight to view the code. Odds are high that you'll 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.

All '77 Pontiac 400 engines also came with the Rochester Quadrajet carburetor. In order to locate the carburetor code, remove the entire air cleaner assembly. Face the front of the carburetor, and note the vertical "ribs" on the sides of the bowl casting (center section). The rear rib on the driver's side should have some numbers stamped into it. If the carb is dirty you'll probably have to clean the rib first to be able to see them. On a W72 in a Can Am, the original carb code was 17057266. There is also a four digit code near this number; it indicates the day and year the carb was manufactured. For example, "1237" indicates a carb built on the 123rd day of 1977. The W72 carburetor has a different float bowl and throttle body assembly and as a result, it flows 800cfm as compared to the base engine's 750 cfm carb.

This information should be adequate to ensure you have the original W72 engine in your Can Am or Firebird. While this engine isn't a true high performance engine compared to the units manufactured in the 1960's, it is likely one of the best post-1972 Pontiac 400's.

Update - April 2005: John Witzke is the POCI Historian for the 1977-79 W72 Performance Package. He's created an excellent PDF document on the W72 engine that is a lot more detailed than what you've found here. To see it, surf over to the Hitman's Trans Am site by clicking here - a new browser window will open.


The information contained in this article was summarized from a wide variety of sources and Pontiac enthusiasts. I'd like to specifically thank John Witzke, Rich Tucker, Rick Lightfoot and Brad Olson for their contributions. This article is provided for entertainment purposes only and no guarantee as to its accuracy is made, implied or given. Actual results may vary. All brand names used without permission. Original content June 2001, revised April 2005.