W72 T/A Cam - 1977 vs 1978/79
 

I've been wondering why Pontiac used a different cam in the 1977 W72 T/A than the 1978/79 W72s.

The differences in specs are modest but meaningful, with the 1978/79 cam being slightly more aggressive:

Cam, AID, AED, ID@050, ED@050, IL1.5, EL1.5, LSA, OL, CL
1977 549112, 274, 298, 190, 213, 0.365, 0.41, 114.5, 55, 116
1978/79 10003402, 273, 289, 200, 213, 0.41, 0.41, 113, 54, 118

Did Pontiac undershoot for 1977 on purpose? Emissions standards certainly didn't get less stringent in 1978 yet they went to a more aggressive cam. It would seem they left power on the table in 1977.

Curious if anyone knows the history or rationale there. And also why they didn't go with the 067.

Where did you get those specs from?

This article by Rocky shows different specs.

Cam Quandary
An In-Depth Look at the '77-'79 T/A 6.6 Camshaft Specs
https://www.motortrend.com/how-to/hp...-cam-quandary/

You could also look at this thread
W72 cam vs. Pontiac 068 cam?
https://forums.maxperformanceinc.com...d.php?t=386047

Stan

I don’t think anyone really knows why looking back on it today, but my guess is this.

Pontiac new in 77 that the 78 400 would be the last Pontiac V8 other then the 301 with a resemblance to a classic Pontiac motor.

They also really still wanted to stick it to Chevy since there motor would carry on in the GM, and Pontiac was likely pissed about that!

The extra effort put into the Cam change for the TA motors really made the 78 and 79 Z28 look like Grandma’s motor with its meager 185 hp rating as compared to the TAs 220.

Honestly everywhere I look the specs are slightly different. The specs I posted are very close but not identical to the specs in the back of Rocky's book.

That sounds like it makes sense to me. That said, I wonder if they knew they were leaving power on the table with the 77 W72.

The single cat on the 77 cars might have been part of the reason for a different cam for the 78-79 w72s, IRC, the later w72s in 78 had dual cats.

78-79 still had single cat but had dual mufflers vs single crossflow.

Thanks Skip. I had forgot it was just the dual mufflers versus the cross flow. I was think it was suppose to be an improvement over 77s.

That large Cat was supposedly a high flowing unit ( for its time). I installed a test pipe on my car. Saw no increase in performance or MPG’s, that I could tell. I still have my old converter.

Are you saying that you bypassed the cat with no discernible power increase?

Yes...

I don’t know if all those late 400s had the same cat? I assume all the 77 400s used the same cat?. The cam in the 180 HP may have been small enough that the big cat didn’t hurt it much. My brother removed the factory cat on his 76 180 HP corvette and it made a notable difference, but I bet it had a smaller cat that what Pontiac used on these engines.

My 77 4 speed with 3.23s had the factory type single transverse to dual system on it and someone previously removed the cat. Comparatively a friend had a 78 w-72 that was completely stock but had 3 tube headers and 3.42s. My 77 seemed like it was stronger on mid range, no question his 78 had more charge on the top.. For the most part I think the biggest thing that made the 78s quicker was the 3.42 gear offering, followed by the cam, then the exhaust changes. The nose on the 79 cars really slip thru the air, those 79 4 speed W72s in 79 are likely the quickest of all of the W72s. I recall on 79 road test back in the day clocked the top speed at a little over 130, and they mentioned that the top speed RPMs were well past the 5K redline on the tach. Pretty sure my 77 4 speed engine would have done before that if it with it’s cam, and it’s top speed in 77 was just over 120. I never took mine past 5000 rpm. I typically stopped at 4600, could tell it was done before 5K.

78 180 HP had the single muffler only the W72 220HP got the duals. I missed getting the W 72 by 1 month when I got mine.

I bought a 20,000 mile, used W72 Gold 1978 T/A in the spring of 1982. I removed the cat, richened the carb, quickened the ignition curve and opened the scoop. It made a world of difference. I was beating a lot of my friends "faster cars". They were surprised that my T/A ran that well. It ran really strong. Most people used to laugh at the T/As, calling them the disco cars. I stopped a lot of those comments when I beat their cars.

78 TA 6.6 cars were quick. Do the mods Jerry455 mentioned and you were running mid fourteens. That is what the 5.0 Mustangs ran with a good driver years later.

I read in a couple of magazines, that the TA's got the same Cat as the Corvette. Maybe it wasn't high flowing. Seemed like all Cats looked like those, back then I do believe that the inlet on the Cat was bigger than the outlet. The outlet dumped into a 2-1/4" pipe on a stock 180 HP TA exhaust (the transverse muffler). I'm an expert at nothing. Just repeating what I read...there was fake news back then....too...:caked:

Can confirm that a 78 Corvette has the same cat as a 77-78 Trans Am. I took a test pipe I had from a 78 Vette and installed it on a 77 TA. Direct fit. Cats look identical.

Both were slow as chit. Fixed the Vette by building a 6.0 LS for it, and kicked the TA down the line.

My 78 180 HP and the 2.56s ran high 14s-barely in 3rd.

I want to know details now Skip. That is blistering fast for a base L78 with 2.56s. That is awesome..

The old DIckinson track that the Gays used to race at.

John Witzke has a W72 pdf that has a lot of info on the W72 from 1977 to 1979.

W72 Technical Information

:)

One thing missing from your comparisons is that there were 2 Pontiac 400 engines offered at the time. The 180 HP had the 6X-8 heads which were around 100 cc head. The 220 HP had the slightly more aggressive cam and the 6X-4 head that advertised closer to 92 cc head. This is where the performance boost came from. Not the type of muffler or cat used. However, the 220 HP did use the dual resonators instead of the transverse muffler because of the need for a little better flow. I haven't searched the in depth info on the difference in the cams between the two engines as it's never been something I've needed or wanted to know. I'd imagine they did use different cams though.

Can you tell us a little more? Was it stock? Thanks

See if you can track down on line the Sept 2006 issue of High Performance Pontiac magazine.

In it they had most detailed article on the 3 Cams that were used from 77 to 79 in the 400s that one could hope find.

That was stock. Convertor everything. I had Glenn Tinsley's shop (that leased John Clegg/HO's 74 TA) add a228/228 @0.050 Cam Dynamics and it went a little faster but had to add a little pusher electric fuel pump as top of second would run the Q jet out of fuel. Stock Q jet even with an HO Racing rejet kit was lean in the idle circuit , eventually fixed with n SR 73 SD Qjet.

Very nice!

I have a stock '78 L78 that needs exhaust and one manifold gasket is blown. Was curious what to expect, or what potential it has basically stock once it is up and going.

From the article in HPP that I posted about above here is what the program from an engine Analyzer predicted for power out of the 3 different cams used in the W72 motors.

Unfortunately I believe the L78 motors had less compression so you will fall short of these numbers if your heads have not been milled.

Very cool, thanks for finding that!

Sounds like the summit 2800 or something similar would be a nice upgrade as far as aftermarket.

A pypes exhaust system should give a nice power bump, which I need anyway because everything behind the converter is pretty rotten.

Here is the dyno session on a '78 W72 400 with the Summit 2800 cam...

Dan had a good dyno session today with the W72 400. He rebuilt the original numbers matching engine with .040" over Icon forged pistons w/4.5 cc valve reliefs that were .006" out of the hole and with .045" x 4.328" Felpro head gaskets to provide .039" quench depth. The 6X-4 heads were minimally cut for trueness and measured 92.45 cc's average for a final static compression ratio of 8.75 to 1. Dan replaced the cast rods with forged Eagle H-beam rods. New 1-pc valves (2.11/1.66) with CC dual springs were installed. A Summit 2800 cam (204/214/112 @ .422”/.444”) with new 'old' Crane hydraulic lifters along with a new Melling 60 psi oil pump. The one modification was the use of old factory D-port ram air exhaust manifolds with the 2.1" outlets with Pypes 2.5" mandrel headpipes. The original 17058263 Q-jet on the factory cast iron intake with the EGR system and plumbing were reinstalled.

The base runs were made with 42 degrees total timing in by 3000 rpm, 45 primary rods/74 jets/CH secondary rods on an I hanger. The 3rd (and best) base pull made a corrected 360.3 hp @ 5000 rpm/456.1 lb-ft torque @ 3600 rpm (351.2 hp/444.5 lb-ft uncorrected). The correction factor was a low 1.026 as the weather conditions were very good...low humidity, high barometer, and very cool temperatures (65 in dyno cell). After rejetting the carb to 40 primary metering rods/72 jets/DA secondary rods on an 'I' hanger (same total timing at 42 degrees), employing the 'big' dyno room dumps for the headpipes, and installing the air cleaner base, the max hp jumped to 371.4 hp @ 5000 rpm/459.2 lb-ft @ 3600 rpm (362.0 hp/447.6 lb-ft uncorrected) on the final pull (#14). The highest torque reading was on pull #13 at 460.3 lbft.

Dennis

I did the exact same mods to my wife's gold '79 400 4 speed car. The car ran 16.1 at 86 mph all stock. Felt WAY faster with the mods but my BIL wrecked the car before I could run it at the dragstrip again

I have the 2801 in a low CR 400 and idles smooth.

Damn brother in law, they can't be trusted. That sucks.

He spun out on a damp road and put it backwards through a fence and the rear of the car stopped against a tree. He compressed the back of the car so much that the trunk lid was crumpled up and he had to climb out the window because the doors wouldn't open. Wife took the insurance money and bought a Mitsubishi Eclipse 5 speed. That was a sad day.