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.
For the exhaust side, a set of reproduction Ram Air exhaust manifolds-or better yet, 131/44- or 171/48-inch primary headers-twin cats and true 2.5-inch exhaust will free up some power.
As always, good machining is key. Spend more on quality machine work than bolt-on performance parts. This is the opposite of what most hobbyists do!
Fun For 301I'm not new to owning Pontiacs, having had three Grand Ams and a sweet little Fiero, but I've never built one up for show. I have a '78 Grand Prix that I would like to rebuild, but I'm not sure what other Pontiac parts will interchange with my 301ci engine. Will the intake off a 389ci fit on my smaller engine? What about heads? With a 4-inch bore and 3-inch stroke, the 301ci should turn a fair number of rpm.
I have an idea of building my Grand Prix with a GTO Tri-Power setup on it for fun and for the local car shows-something different but still cool. Please don't tell me that I should change the motor out for something bigger. My 301ci is in sweet shape, and I really would like to keep it.
I love your magazine and buy it whenever I can find it on the newsstands. Tony ZatkovicVia Internet
Rocky Rotella responds:The 301ci engine (along with its 265ci brethren) is often considered the redheaded stepchild of the Pontiac-engine family. While it was fairly reliable when operated within its intended range and a decent performer in the right application, the engine was designed for maximum economy, which severely limits performance. Starting with a low-deck block, engineers removed enough material from it and a number of other conventional engine components to just meet minimum durability standards. The end result was a complete engine that weighed just 452 pounds, or anywhere from 150-200 pounds lighter than a traditional Pontiac engine.
While the 301ci configuration may look decent on paper, it was never designed to be a high-rpm engine. The cylinder heads contain small, siamesed intake ports that don't share a traditional common dividing wall. This also carried over to its low-rise intake manifold, which doesn't contain port dividers in the runners as they progress from the plenum. Couple this with the relatively narrow cross-sectional area of the two components, and higher-rpm airflow is greatly degraded, resulting in an engine that doesn't rev much beyond 4,400 rpm.
Installing a Tri-Power or any other conventional Pontiac intake manifold onto the 301ci isn't feasible for the reasons stated above. It might then appear that simply installing a pair of cylinder heads from a larger engine is the answer. While such castings will certainly bolt on, the low-deck design of the 90-degree 301ci block brings the cylinder heads closer to the crankshaft centerline, which in turn requires an intake manifold with shorter runners to maintain proper port alignment. Since aftermarket intake manifolds aren't available, you'd have to modify a conventional Pontiac casting considerably or fabricate another from metal or a composite material.
Should you decided to move forward with the cylinder-head and intake-manifold swap, crankshaft issues would likely prevent you from safely turning the rpm required to achieve maximum performance with the 301's relatively short 3-inch stroke. As part of the weight-saving effort, engineers removed the two central pairs of counterweights from the crankshaft, leaving just one larger weight on each end. This shed nearly 25 pounds but greatly increased the chance for failure at excessive rpm.
With all that said, you are probably wondering what options you have. You may not want to hear it, but these reasons are only a portion of what make replacing an original 301ci with a traditional Pontiac engine so attractive to hobbyists looking for performance boosts. Others, however, are determined to retain the 301ci and want to safely extract as much power from it as possible, and this can be accomplished with a few simple bolt-ons and some careful tuning.
If your Grand Prix's 301ci wasn't originally equipped with a four-barrel intake manifold, installing one and a matching Quadrajet with proper jetting is a must. Have the HEI recalibrated to provide around 24 degrees of mechanical advance by 3,000 rpm with an additional 14-16 degrees of vacuum advance, and set the initial in the 12-14 degree range. A set of 1.65:1-ratio rocker arms will effectively increase valve lift, and if you can remove the heads, have them milled 0.060 inch to boost compression.
Combine all of this with a 2.25-inch dual exhaust system and a 3.23 rear-axle ratio, and you should notice a healthy performance boost from your Grand Prix. And if you remember to keep the revs under about 4,500 rpm, your 301 should provide many more miles of reliable performance.
'70 GTO Axle-Bearing WoesI'm trying to replace the rear axle bearings on my '70 GTO and have hit a dead end. I tried GM dealers, bearing warehouses, auto-parts stores, and none have listings for my bearing size. The rear is a 10-bolt and I'm sure it's original.
I bought the car in 1976 with 52,000 miles on it. The bearing measures 1.378-inches id, 2.558-inches od and 0.670-inch-wide od, 0.765-inch-wide id. The outer race is narrower than the inner race. This is a single-piece, nontappered roller bearing. The bearing isn't RW-507-CR or set No. 9, which is what everyone tries to sell me. I hope you can help me on this.John T.Spokane, WA
Quint Stires responds:In 1970, Pontiac was transitioning over to other designs of rear bearings and guts. The great thing is that you know what you're looking for and you have the dimensions. I'm impressed. So often, I speak with GTO owners who don't know what they have and think everything is in a book or manual as if it's a dictionary and part numbers are as easy to find as windshield wipers.
To find your bearings, I called Shannon LaFave from Ames Performance (www.amesperf.com), and he knew exactly what you needed and explained in length about the mid-year change. Feel free to call him at the number in the company's ad or any one of the Pontiac specialists advertising in this issue. For whatever it's worth, often parts stores have great information but don't always have the most up-to-date or change-over information. It's the companies who specialize in your car or its issues that know the best way to solve the problem at hand.
Oil-Pressure GaugeWhere is the best place to hook a mechanical gauge for oil pressure? I have a '74 455. Bret SnyderVia Internet
Rocky Rotella responds:Bret, it seems the most common location to plumb a mechanical oil-pressure gauge into a Pontiac V-8 is near the distributor hole on the driver side of the block. There you will find a 31/48-inch-diameter pipe plug with a recessed 51/416-inch square opening. The plug covers a direct path used during initial machining to bore an internal oil passageway that was subsequently tapped and sealed off during production. Because of this and its close proximity to the instrument panel, it makes an ideal location for accurately retrieving an oil-pressure reading.
The pipe plug is commonly removed during engine rebuilds to access the internal oil passageways for cleaning and is typically replaced with a new unit. If your 455ci has been rebuilt in the past, the plug may come out easily. If the engine hasn't, you might find the original plug very tough to break free, possibly rounding out during the attempt. To prevent this, I suggest heating the plug for a short time before hand, it typically makes removal much easier. This assumes, however, that your engine isn't in a vehicle and you can fully access the plug.
If your engine is installed and you don't have plans on removing it, an alternative source for an accurate reading may be the oil-filter adapter. Simply remove the existing electric oil-pressure sending unit, and connect the mechanical gauge's hardware. A drawback to this location, however, is the lengthy distance required to plumb the gauge into the passenger compartment. If going this route, be sure to securely route the gauge's oil line away from the entire exhaust system to prevent burning the line and causing an oil leak.