Of all the iterations of Pontiac’s V-8 engine family, the 428ci version doesn’t get much attention. That’s not without reason, as the 389, 400, and 455 mills were admittedly the “hot ones” to borrow a classic Pontiac tagline.
The block had a casting number of 39792968 and a date code of November 1968. Further inspection and measurements indicated that the block remained at its original bore size. Naturally, the “428” casting also aided in identifying the engine.
The 428 also had a relatively short shelf life, produced only for the 1967-69 model years, which means they are quite rare finds these days. While rated at up to 390 hp, they were designed to deliver low-end torque for the heavier fullsize cars and weren’t installed in the GTO or Firebird. However, numerous dealer-sponsored swaps to the larger engine were made in the traditional muscle cars.
The initial steps in the build involved a visit to an oven-bake followed by a trip to a blast tank to remove decades of accumulated grease and grime from the 428.
At its core, the 428 was a bored-out 421 with the same 4.000-inch stroke. It was replaced by the 455 in 1970, which increased the bore slightly and added a 4.210-inch stroke. The relative abundance of 455-core engines and the more conventional 400-inch Pontiac engines make purpose-built performance versions of the 428 quite rare. However, the interchangeable parts within the Pontiac V-8 family make building one easier and relatively more affordable. By that, constructing one is costlier than a Chevy engine, but not in the same league as the Boss 429 or Street Hemi.
After verifying clearances and measurements, the final honing was completed, and the block was painted in a light Pontiac blue suitable for the 1965 Tempest for which the engine was intended. The bores and bearing surfaces were then meticulously wiped down and cleaned in preparation for assembly.
Locating a buildable 428 is probably the biggest challenge these days, but luck was on the side of Todd Ryden, who knew someone with a 428 block he no longer needed. That set in motion the plans to use it as the foundation for a restomod engine that would power Ryden’s 1965 Tempest. However, achieving that power goal through natural aspiration would require more than a simple camshaft swap and touching the heads, so a plan was devised to bore and stroke the engine to enhance its cylinder volume and, consequently, its airflow capability.
The new hydraulic Comp camshaft (using the cam gear as leverage) is slid into the block. The specifications of 240/246-degree duration for intake and exhaust, 0.507/0.510-inch lift, and a tight 110-degree lobe separation angle will work perfectly on the street when paired with a manual transmission.
A 0.060-inch overbore, and a long 4.250-inch stroke will deliver a 467ci displacement, complemented by a set of Edelbrock aluminum heads patterned after the original Ram Air IV design and a Comp Cams camshaft with over 0.500-inch lift and a relatively tight lobe separation angle. This setup provides enough valve overlap to give the engine an authoritative rumble at idle.
The rotating assembly came from Eagle (via Summit Racing). Understanding that the engine was designed more for street driving than for the strip, a few dollars were saved by choosing a cast steel crankshaft instead of a forged one. The cast crank is robust and provides a 4.25-inch stroke to increase the engine’s displacement. Note the nicely radiused oil passages on the main and rod journals and the larger-than-stock journal fillet, which enhances strength. Additionally, the first and fourth journals are drilled through to lighten the crank.
The big-inch Poncho would also serve as the basis for a side-by-side shootout between Pontiac’s classic Tri-power induction system and a tried-and-true four-barrel carburetor. It’s no secret that a well-tuned single four-barrel will generally outmuscle the six-barrel setup of the Tri-power, but we wanted to see for ourselves with this big-inch displacement—and Ryden was up for the comparison test.
The crank was carefully lowered into position with the main bearings set in the block. A quick spin was performed to ensure there were no interference issues, and afterward the main caps were installed. Yes, four-bolt mains would have been a nice upgrade, but the factory two-bolt mains will suffice for this street engine.
“No matter what the results, the Tri-power will still end up as the induction system of choice,” Ryden says. “This engine isn’t about maximum power. I want some eyeball appeal to go with it.”
The Eagle rotating kit comes with forged flat-top pistons and wristpins made by SRP. With the engine’s selected Edelbrock heads, compression will be around 9.7:1, ensuring compatibility with pump gas.
Agreed. Style counts for a street driver, and the Tri-power setup draws the eyeballs on Saturday morning at the local cars-and-coffee meetup.
At 6.800 inches, the H-beam rods in the engine kit are slightly longer than the stock length of 6.625 inches, which enhances the engine’s rod-to-stroke ratio. This is a crucial factor for stroker engines, as it minimizes the side-loading force on the thrust side of the piston, thus reducing friction.
Regardless of the induction system, it’s worth noting that whether in its stock displacement or the stroker setup of this project, the 428 not only makes a solid starting point for a strong street engine, but most of the parts, including the rotating assembly, are interchangeable with Pontiac’s 455 engine. For this build, most of the parts were sourced from Summit Racing Equipment.
Here, the clearance is checked, and then the wristpin end of the connecting rod is honed to ensure accurate clearance while removing any “flares” or burrs.
So, how did the stroker 467 perform? After priming the assembled engine, it was started, brought up to 2,400 rpm, and held there for about 20 minutes to break in the cam and lifters. After that, the engine was powered through a number of light loads and rpm to season all the mechanical pieces and help seat the rings. Here’s a quick look at some of the finer points behind the dyno setup:
A set of 1.75-inch Hedman Husler headers were used for testing
An MSD distributor was used, and the springs were swapped. MSD assembles their distributors with heavy—and therefore slow—springs. A change to the lightest springs brought the advance in quickly (full advance by 1,800 rpm). Also, before installing the distributor, the gear was coated thoroughly with the supplied break-in lube
After the initial break-in, the spark plugs and valve covers were pulled for inspections—and then given the go-ahead for full-power pulls.
The pistons were installed smoothly—they tapped down into the holes without any issues. Note the position of the valve relief toward the top of the block, which is essential for preventing a potential interference nightmare when the engine is turned over for the first time.
With the engine tuned, warmed up, and put against the water brake, the first couple of pulls netted about 470 hp. Not bad, but fiddling with carb jetting and timing, which ended up with 38 degrees of total advance, raised max power to 492 horses with the 750-cfm Holley four-barrel carburetor. The 500hp goal had not quite been achieved, but the stroked 428 also cranked out more than 550 lb-ft of torque, so there was little to complain about.
All the rod bolt threads were lubricated with ARP’s Moly Assembly Lube, including beneath the head of the bolt. They were then torqued to specifications, which completed the installation of the rotating assembly.
As expected, the Tri-power system came in with less maximum power and torque than the four-barrel: 477 hp and 545 lb-ft. It was still a respectable showing, and the 15 or so horses sacrificed in the name of style won’t be missed with all that torque on tap.
A windage tray was installed due to the increased volume of oil for lubrication expected from a planned Milodon oil pan. This will keep the oil in the pan away from the rotating crankshaft, which could whip it into a power-robbing froth.
Ultimately, Ryden got exactly what he sought—an undeniably powerful engine with plenty of visual appeal. He also proved Pontiac power remains alive and well.
Crankshaft clearance must always be checked against a windage tray, especially in a long-swinging stroker combination. As it turned out, there were some interference issues as the crank rotated. Fortunately, washers placed on the studs served as effective spacers.The oil pan was bolted onto the block with the windage tray’s clearance confirmed. Milodon offers several versions for Pontiac engines, including a few road-race/Pro Touring designs with trap doors for improved oil control during turns. The version used for this engine features a shallow pan design, providing ample ground clearance while accommodating up to 8 quarts. This part can also be found on SummitRacing.com.Next, the necessary double-row timing chain set was installed on the crankshaft and camshaft, completing the short-block assembly.Edelbrock provides several options for Pontiac heads, all made of lightweight aluminum: Performer, Performer RPM (round-port), CNC Performer RPM, and a Performer D-port head. The Performer RPM head was chosen for this engine.Installing an aluminum head is much easier on the back than a heavy factory cast-iron version. Each Edelbrock head weighs only about 37 pounds when assembled. A set of SCE’s “steel back” head gaskets was used with the new heads.The Edelbrock Performer RPM head is based on the round-port Ram Air IV heads and is specifically designed to enhance airflow. It features 215cc intake runners that lead to 87cc combustion chambers with 2.11/1.66-inch valves. Edelbrock states it will flow 264 cfm at a 0.500-inch lift.When installing the heads, the upper row of a set of ARP bolts was set to 105 lb-ft and the lower bolts were torqued to 95 lb-ft—all achieved in three even increments. It is always a good idea to re-torque the heads after initial start-up.A set of Comp Cams roller rocker arms followed. They have an increased ratio of 1.65:1, which mechanically amplifies the cam’s lobe lift by positioning the pushrod closer to the fulcrum pivot point than the valve stem. This combination raises the cam lift to 0.558 inches on the intake side and 0.561 inches on the exhaust side.The engine’s induction setup will be a classic Pontiac Tri-power system, however, its owner, Todd Ryden, also tested it with a single four-barrel. A deal was struck on a 1966 intake and center carb, which provides a performance advantage by offering equal-sized carb inlets. The primary inlet of the 1965 intake is smaller.Experienced Tri-power tinkerer Greg Ryden was called in to tune the linkage and set up the trio of carbs. The largest challenge for ensuring crisp throttle response and maximum performance is getting the secondaries to open quickly enough to prevent a lean mixture. With all that accomplished, the engine made 477 hp and 545 lb-ft.For the comparison test, the Tri-power manifold was replaced with an Edelbrock Performer RPM intake. This high-rise design features a street-friendly dual-plane configuration and will be equipped with a Holley 4150-series dual-feed four-barrel rated at 750 cfm.As expected, the four-barrel induction system delivered greater peak horsepower and torque: 492 hp and 552 lb-ft compared to the Tri-power. However, this engine wasn’t built for horsepower at all costs, and the Tri-power’s more than respectable performance will provide excellent street capability.
