The Great 455 Swap

Two engines cannot occupy the same space, so out came the stocker. It’s a 215ci underachiever that’s based upon the venerable Chevy six. We counted five separate oil leaks before pulling this beast. The amount of grease on this pig should give some idea of the cleanup necessary on the engine compartment.

We spent no less than a day’s work, 13 cans of brake cleaner, half a bottle of Simple Green, and three cans of the Eastwood Company’s Pre-Paint Prep before we had the engine bay degreased. Then, we masked off the painted body areas and sprayed the firewall, core support, and inner fenders with Eastwood’s Underhood Black. It dries quickly to a semi-gloss finish. We gave it 20 minutes to cure, masked those panels off, and shot the frame with slower-drying, epoxy-based Chassis Black. We unmasked everything and gave the frame two days to completely dry (it was cold outside). The higher-gloss frame is a nice contrast with the rest of the engine bay. Well worth the time spent.

Swapping out the six-banger meant changing the frame pedestals on the crossmembers. The scummy six-cylinder originals (left) don’t look anything like the proper ’64-’72 Pontiac A-body V-8 pieces. To the best of our knowledge, these pedestals aren’t being reproduced, so we pulled ours from a junkyard ’69 350ci LeMans, bead blasted ’em, and fogged ’em with Eastwood’s Detail Gray paint. Matching factory-style rubber motor mounts from Year One bolted to the 455.

Pontiac pulleys and accessory brackets are complex and just plain ugly. We recommend you pull everything off one donor car, as the brackets tend to be application-specific. Although we scored all the parts we needed–even the A/C compressor mounts—from a 350ci ’76 Grand Prix, we opted to convert to manual steering for a cleaner engine bay, simplifying the pulley arrangement. This used ’64 Chevelle SS steering gear liberated $60 from our wallet. Keep in mind that your centerlink and idler arm might not work (both 7/8-inch and 13/16-inch centerlinks were used on the A-body platform).

McLeod recommended we use its 11-inch raised-cone diaphragm pressure plate and sintered-iron Soft-Loc disc behind our torque monster. Sintered iron’s superior grip allows milder pedal pressure without sacrificing holding power, but the sprung hub is very streetable. Pedal pressure is similar to a brand-new stock clutch. ARP bolts secured the pressure plate in place.

Future canyon-carving plans and the bang-shift coolness factor sold us on keeping the original Muncie M20 four-speed in service. Off came the flexplate, in went a roller-pilot bearing (Year One PN 47392N), and on went a McLeod 30-pound steel flywheel. It’ll fit either the 2.49-inch or 2.75-inch crank register diameter by using a trick press-fit insert. Our crank’s 2.75-inch register didn’t need it, so it was carefully tapped out with a brass punch. Because this motor is externally balanced, the crank is drilled with an asymmetric bolt pattern so the flywheel only goes on one way. ARP bolts were coated with their assembly lube and torqued to 90 lb-ft.

Pontiacs used two throwout bearings that differ by about 5/8 inch in height. We assume high-performance GTOs with Borg and Beck clutches got the short bearing, and the low-performance models with low-reaching diaphragm pressure plates received the longer bearing to take up the slack. Year One sells both bearings, and both long and short versions of the pivot-ball stud that supports the clutch fork in the bellhousing.

We played around with different bearing/stud combos and found that the long bearing (PN 2106N) and short pivot stud (PN 904N) gave us good fork geometry. The clutch fork is perpendicular to the input shaft, with the bearing seated against the diaphragm cone.

A stout oiling system is cheap insurance against starving bearings, and since we’re building the car to accelerate and turn hard, Milodon’s Road Race oil pan made sense. It’s built with two trap doors to keep oil at the pickup under forward, rearward, or lateral acceleration. Milodon recently redesigned the front of the sump to work with the A-body chassis. It’s still a tight fit, though, and we saved some scratches, dents, and headaches by installing the engine without the transmission.

Maybe the only limitation of the Edelbrock Performer RPM heads is the round-port header requirement. Combined with the added complexity of the clutch linkage, we wondered if we shouldn’t just run stock manifolds on this thing. But we’d heard that Doug’s Headers for this application fit great, and speaking with Mr. Thorley himself confirmed that. Naturally, though, we had a few reservations when Doug told us they’d “drop right in.” The headers themselves are a work of art. Between the heavy-gauge flanges, 17/8-inch primaries, full-flanged 31/2-inch collectors, and brilliant ceramic coating, they almost look too nice to install. We had Doug’s weld oxygen sensor bungs in each collector (arrows) to accommodate an anticipated EFI conversion.

A V-8–style throttle cable and bracket (PN RZ647 and TB17) came from Year One, but we soon found they wouldn’t bolt up to the high-rise Edelbrock Performer RPM intake on our engine. Out came the engineer in us, and we fabricated an aluminum plate with a milled-out recess to relocate the cable bracket and lock it in place. Then we noticed that Year One offers a throttle adapter bracket for Edelbrock intakes (PN A39) for use with the cable bracket. That probably would’ve been easier than mooching machine time from the aerospace fabricators next door to our shop.

We had the best luck lifting the passenger-side header in place from underneath the car with the engine raised up about 6 inches. The oil filter adapter (arrow) was removed before attempting this.

The driver-side header was installed from underneath with the engine already bolted in place. The rear lower A-arm frame bracket required some radiusing to clear one of the primaries (arrow).

When finally installed, we had about 1/4-inch clearance between the steering flange and No. 1 cylinder pipe (arrow), which we felt was enough. We were especially impressed at how closely the collectors fit to the floorpan. Speed bumps are a non-issue.

Running the powerful multi-spark MSD 6AL was a no-brainer, and proper mounting and wiring will keep the box running happily. After relocating the battery to the driver side of the car with a tray and cables from Year One, the void left on the passenger side was a perfect place to mount the ignition box. Not wanting to drill holes in the core support, we bought a 7x11x0.125-inch aluminum plate, mounted it using two holes left behind from the battery tray, and secured the MSD directly to the plate. A 10-gauge wire runs directly from the battery to this trick enclosed single-stud terminal block we liberated from a junkyard ’89 Riviera. This block provides convenient high-current 12V power for the MSD and any additional accessories we choose to add in the future.

We were sure running out of room on the intake, but found room for the MSD Blaster 2 coil on the passenger side behind the carburetor. We cut and bent a bracket from aluminum strap to mount the rear of the coil to an intake bolt. Check out the trick stock-appearing fuel line setup from Year One. Although it’s made to fuel any dual-feed Holley-style carburetor, we had to adapt its 5/16-inch inlets to the Demon’s 3/8-inch ports using brake line adapters from the auto parts store.

Gauges are a good idea if you care about your motor. We can trust these Auto Meter 2-1/16-inch Sport Comp instruments, and their compact size cleared our stock console with room to spare. We like that they’re subtle enough to retain our stealth sleeper image. If you’re running a mechanical oil-pressure gauge, consider upgrading to Auto Meter’s copper or braided stainless tubing kit for reliability and temperature resistance.

Our clutch linkage was worn and sloppy from years of grocery-getting, so Year One suggested replacing the wearables with their accurate repro linkage rods, Z-bar components, and rubber boots for the clutch fork and clutch pedal rod. There’s a dramatic difference between old and new, and the six-cylinder Z-bar (left) and the V-8-style Z-bar (right) also have noteworthy differences. Doug Thorley told us only Z-bar PN 9776376 will work with header installs on ’64-’65 LeMans/GTO models. We bought a good used Z-bar thought to be correct for a ’65 GTO, but it flat out wouldn’t work. We couldn’t verify a part number, so it’s assumed we had the wrong one. Meanwhile, we made the stock six-cylinder Z-bar work after bending the lower lever arm 30-degrees outward (away from the engine) to clear the starter. It’s not pretty, but it’s functional, and that makes it a good temporary solution.

Using the reducers supplied with Doug’s header kit, we installed Flowmaster’s 2.5-inch, mandrel-bent American Thunder exhaust kit. The kit fits so well that we were able to get this nearly perfect fit installing it ourselves with the car on four jackstands. A car hoist and fancy power tools are definitely not needed. Look for an upcoming article for the skinny on the full installation. It’s impossible to describe how awesome it sounds, but we’ll try anyway. The throaty sound can be turned on and off at will, depending on how much throttle you deem necessary. The 50-series mufflers should have kept things quiet enough to dart past Officer Friendly, but our lack of hood and valid registration tags got us nabbed anyway.

Always prime the oil pump with a cordless drill before starting a dormant engine. Remember you’ll need to reverse the drill direction to operate a counter-clockwise-rotation Pontiac oil pump. Our Milodon high-volume pump gave the drill a workout, showing impressive oil pressure; we only had to prime it for 30-40 seconds before oil flowed from the rockers. The MSD Pro-Billet distributor was set up for 26 total degrees of ignition lead, all in by 3,000 rpm.

With Year One’s expert advice, we pieced together a cooling system that should work for all ’65-’67 vintage 455 retrofits. The heavy-duty four-core radiator (PN FJL15) works with a late-style water neck (PN 9435N) and upper/lower radiator hoses (PN ID436/ ID591). Don’t forget a filler cap (9004N) and drain petcock (5372N). A five-blade fan and thermostatic clutch (PN 6500N/9189N) and fan shroud (PN F94) keep the big-cube 455 rock-steady at 180 degrees. We modified our light-duty radiator brackets to work with the new, thicker-core radiator, but Year One’s kit (PN FP20891) achieves the same thing, only more easily.

The poor car. With its Hurst-shifted Muncie four-speed, buckets and console and factory tach and gauges, it looked every part of a ’65 GTO minus the telltale “6.5 Liter” badges on the fenders. Its fenders, instead, bore odd “PMD 6” emblems, which gave away the sickly, smoking 215ci inline-six underhood, a mill better suited to hauling hay than hauling tail.

From the start, we intended to change that. No, we never planned on cloning a GTO; we wanted something far more capable than a stock 389. As luck would have it, we’d already built a 501hp Poncho 455, which had been languishing at our dyno shop. That fit the bill perfectly.

What we thought would be a basic bolt-in deal turned into several months of parts searching and modifying. Using modern speed parts often requires accommodating or modifying other components. But we wanted to do things right, which always takes way longer than slapping the whole mess together. And we think you’d agree that installing a $6,000 engine in a car you love is worth the extra time spent.

The beautiful thing about Pontiac V-8s is their common external packaging—so don’t call this 455 a “big-block.” That meant we were able to use many stock ’65 GTO pieces from Year One, as most of these parts can’t distinguish this motor from a 389. A huge benefit of working with Year One is having a one-stop shop at your fingertips. Being able to order everything from a complete cooling system to clutch linkage from a single catalog saves an incredible amount of time. We opted to install a McLeod clutch and flywheel, a Milodon oil pan, Doug’s headers, Flowmaster exhaust, an MSD ignition, and a set of Auto Meter gauges to complement the torque-monster motor.

Was all the extra installation time worth it? When a new motor roars to life on the first blip of the ignition, runs smoothly, doesn’t leak, drives effortlessly, and sounds killer, we think it’s time well spent. With almost 600 lb-ft of torque on tap, though, driver input to the worn-out stock suspension is more of a suggestion than a certainty. In the meantime, we’ll get by smoking the tires from a 50 mph roll.