Building The W72 For Hot Street PerformanceI have a question about the W72 engine, which I want to modify for more power. I want it to run on premium fuel and have a really good drivability factor. I helped do a restoration two years ago on a '79 SE with a W72. The owner went larger on the exhaust valves and ported and polished the heads somewhat, as well as boring and installing a No. 068 cam. I have always heard that the exhaust valves were the holdup on that engine.
His T/A made 276 hp at the rear wheels-if I remember right-when we were at Pontiac Nationals in Norwalk, Ohio, last year. I was thinking of doing similar things to my engine. Good idea? I figured on boring it, then doing some headwork, and adding a cam and an aluminum intake. Do I have a nice combination to make 300 to 300-plus hp at the rear wheels?Doug SchroederVia Internet
Paul Spotts responds:The W72 option in '78-which carried over to the four-speed 400 T/As and Formulas in '79-actually had a completely different cylinder block than other Pontiac 400s of the day. Pontiac brought back the earlier, stronger block (and upped the power rating to 220 hp). The casting code is 481988XX to distinguish the W72 from the '71-'75 castings that have 481988. Pontiac cast XX after the numbers and on the sides of the block.
I predict these W72 cars will soar in value like the desirable musclecars right now. You may have a Bird that will be worth some decent money soon, so keep this in mind before you decide to do modifications.
With that said, your choices for more power are endless. With all the new stroker crankshafts out there, cubic inches can increase if you desire. However, the larger the stroke to increase the cubic inches, the harder it is on the block. Even with studs and four-bolt caps, the block will only live so long with higher-rpm usage. If rpm is kept low, the reliability factor increases, so bear that in mind when stroking an engine. However, stroking the engine to say 461ci and retaining the 6X heads, the torque will increase to tire-frying proportions, and the W72 block will hold up better than the regular late '75-'78 400 blocks since it has thick webs. I've noticed in the later production years, Pontiac's high-quality machining standards diminished. The newer blocks' main caps never seem to be aligned properly.
If you stay with 400 ci, increasing compression has been a popular choice, but it's not totally necessary. With today's modern fast-ramp cams, such as the Comp Cams Extreme Energy Series (XE262H and XE268H grinds), 8.1:1 compression can work. The same holds for the hydraulic-roller series XR264HR and possibly XR276HR.
The 1.66-inch exhaust-valve size in the 6X heads is not the restriction in those engines- it's the exhaust system. Porting the 6X head will still realize a gain in performance, but it's not as important when utilizing 400 ci. Stroking to the larger displacement will make the engine respond to the porting much more.
When I build a set of 6Xs (or almost any stock head), I replace the factory two-piece valves with one-piece stainless valves. Since I'm doing a bowl cut and increasing the valve angles, I change to the larger exhaust valve as a matter of course, but it's not required. In fact, I've heard of tests that showed no improvement in performance with the 1.77 versus the 1.66 exhaust valve, but it didn't hurt either.
Should you decide to upgrade the intake as part of the buildup, the most popular choices are the Edelbrock Performer RPM or the Tomahawk, depending on the cam choice and engine displacement. The Tomahawk will allow the Shaker hoodscoop to work without any mods.