[Stuart]

The Motor Trend website reprinted a copy of that article from the October 1970 issue of Hot Rod Magazine about the experimental 427ci overhead cam engine. It's too bad it never progressed beyond the experimental stage.

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Experimental Pontiac 427ci V-8: Lightweight, Hemi-Headed … and Beautiful

Pontiac’s 427 experimental V-8 has all the right stuff for showing or going: aluminum block and hemi heads, direct port injection, overhead cams, main bearing girdle—and the package is wrapped beautifully.



When Steve Kelly wrote his deep-dive on Pontiac's new experimental dual-overhead-cam Hemi V-8 for the October 1970 issue of HOT ROD magazine (actually two engines!), performance was a moving target. Unleaded fuel was still in the future (check out Steve's comments on stellite valve guides and valve seats!) as were the wide use of fuel injection and aluminum castings. By 1970, Pontiac's division head, John DeLorean, had already moved on to Chevrolet and, despite much promise from Pontiac engineering, there would never be another breakthrough Pontiac V-8; like most of GM's other divisions, Pontiac would transition to Chevrolet power. Today, technology like fuel injection, aluminum blocks and cylinder heads, and dual overhead cams are ubiquitous and it's fun to read about the contemporaneous efforts to integrate those technologies way back in 1970! —Johnny Hunkins



Steve Kelly's feature on Pontiac's experimental 427ci hemi engine found its way onto the cover of the October 1970 issue of HOT ROD.

This latest Pontiac experimental engine project, with its innovative interior and exterior design, is highly provocative. Because it is unique visually, it can only make one wonder why automotive powerplants were never "styled" before this time. Racing engines, especially those connected with drag racing and street rods, have repeatedly been styled by individual owners and builders. But there were—and are—limiting factors to this task. Custom and race car builders have been forced to live with casting marks, odd configurations, and the fact that appearance cannot disturb function. When Pontiac engineers first conceived the idea and a workable plan for their latest experimental V-8 project, the Advance Design group, headed by Hulki Aldikacti, proposed a style job on the engine and agreed that if they were allowed to do this, they would not disturb the function of the engine. The project goes back several years, and when it was initially drawn together, four design parameters were established. The first was mechanical development. This includes die-casting the entire cylinder block, as well as working up entirely new attachment procedures and new methods of powering external accessories. The second parameter is a well-known one right now to all auto manufacturers: thermodynamics—in other words, reducing inherent emission problems of an internal combustion engine. The third guide established was adaptability of design breakthroughs on this engine to other Pontiac powerplants, either new or existing. The fourth parameter set down was the application of styling to an engine.



Full cutaway shows thin-section, sand-cast block and cavernous valley area between intake and block. Note the "zero-length" pushrod between OHC lifter and rocker.

In one way or another, all of these parameters have been met in the package seen on these pages, but this doesn't indicate it is what might be considered a finished engine. It will never be completed, for this is a total experimental project. There is no telling whether such an engine will ever be produced for assembly-line installation. That's the idea behind an experiment like this; and that third parameter, adaptability, may be the most important phase of this endeavor. It costs a lot to tool up for a new engine, but if it becomes an evolutionary process whereby bits and pieces from this engine find their way onto existing engines, then the cost of manufacturing is reduced, and within a period of five years or so, complete refinement is accomplished. It is more likely we will see this approach taken rather than the introduction of an entirely new engine.



Front-mounted drive belt has a 3-inch-diameter idler pulley, and center-mounted ring gear is adjusted by cam action for uniform tension without disturbing timing. Overall width is 32 inches, height from pan rail is 24.6 inches, and length is 32 inches.

If you've checked over the pictures carefully, you've noticed this is a hemispherical-combustion-chamber engine. Each bank of cylinders has its own camshaft mounted within the head. Unlike other OHC engines, the rocker or cam following arms don't work directly from cam to valve. There is a hydraulic lifter placed in between. This was done to make serviceability easier. In other words, if this design was adapted to an engine used in a Grand Prix, you could hardly expect a typical GP owner to adjust the valve lash every four or five thousand miles. This would be a definite drawback in trying to merchandise such an engine. The lifter acts on a small, sliding fixture attached to the rocker arm. It works in the same manner as a pushrod, and the round bottom side of the fixture fits into a corresponding concave opening in the top side of the lifter. This prevents binding of the arm or lifter as the valve opening reaches its maximum. Rocker arms are stamped steel items and are retained to the head by screw-in studs. The shape of the combustion chamber is not a perfect hemispherical configuration, yet it is close enough to having a fully rounded dome to be considered a hemi. It certainly isn't a dome. The centerline of the exhaust valve is 60 degrees away from the centerline of the intake. Intake valve diameter is 2.40 inches on the large-valve engine, and 2.190 inches on the small-valve, high-rpm design, while the exhaust measures 2.00 inches across its face in both cases. Intake stem diameter is 0.3723-inch, and exhaust is 0.3718-inch. Valvesprings are inner and outer types, and the valve guides are cast-iron alloy, though stellite is being evaluated. The cylinder heads are aluminum, and because of the chance of flex with this material, cam towers and rocker stand attachment point are beefy and well-braced. Rocker stands are joined together by a single span running the length of the head. This also ties-in the cam supports. Intake and exhaust ports are round, and in the low-speed engine, intakes measure 2.08 inches in diameter; they are 1.90 inches on the high-speed design. Port diameter is 1.73 inches on the exhaust for both test V-8s.



Finned aluminum oil pan could be eliminated with a dry-sump system, which is fairly easy to adapt with the oil pump design used here.

The 90-degree V-block is thin-wall and die-castable all in one piece. This isn't exactly a new process, but it hasn't been used in great numbers (except for the '71 Vega four-cylinder) because of high cost. With a single-unit die casting, there is no practical way to seal the tops of the water jackets around the bores. Any sealing job would require something in addition to the casting, which would add to the cost and weight. Cylinder water jackets are exposed, and sealing is done with a steel, compression-type head gasket. Head bolts are a departure from the norm. They are exposed, and the top five run into what would normally be the lifter galley and thread into the block at the very base of the bore opening. The outside, or bottom, row of five bolts are also exposed and penetrate through the block and attach to the malleable-iron girdle at a 45-degree angle. The extreme length of the rod bolts allows a tremendous amount of stretch to be applied, and because of their extreme retention qualities, only ten bolts per side are required. Each bolt is SAE 4135 cold-rolled steel (GM-300M), and specs on the 14 short bolts are ½-13 x 8 inches. The six long outside bolts are 9/16-12 x 14 inches. Each bolt is torqued to 95-105 lb-ft.



Measured with airbox on, engine height is 32.7 inches, and air inlet is meant to stick through hood.

An internal-external gear pump is fitted to the rear of this engine's crankshaft and is a truly positive-displacement pump. Because a small oil sump is utilized, there is a pickup line to the pan, but the eccentric design and its rear position on the crank makes use of a dry-sump lube system possible without alteration to the pump. Valving on the current experimental engine produces 100 psi oil-pump pressure, but 300 psi is possible. It now pumps three gallons per minute, and this could be increased. The position of the oil filter is unique: It is directly over the oil pump, in the rear of the "galley" area. This is a good position as far as channeling is concerned, but this is the one marginal item on the engine as far as serviceability is concerned. Being that far back on the engine, and concealed beneath the intake, means it might be impossible to see or reach if the firewall were close by. Even without this interference, the inverted position of the filter means oil would drain out all over the engine once the filter was loosened. The '52 DeSoto had one something like this, if I recall correctly from my gas station days. This same "open" area between block and intake is meant to be used for accessories on later developments with this project. Aldikacti, the Turkish-born mechanical engineer, explained that because the engine is a study in aesthetics, in addition to other subjects, it would be a crime to hang a power-steering pump or an air-conditioning compressor on this engine. Besides the appearance factor, the width of this engine squeezes most engine rooms on present-design Pontiacs, making it close to impossible to increase external dimensions and still fit it in a car. Within this valley beneath the manifold, there is enough room to plant pumps and compressors, though one intriguing idea is to use this void for a central hydraulic system which would drive a great many accessories, including air-over-oil suspension systems, power windows, and the pump and compressors already mentioned. Here again, this would offer a central point for serviceability, the only drawback being that it is covered by the intake manifold. Removing the intake is a minor job when compared to problems encountered on a lot of present-day cars, so this idea definitely holds possibilities.



Oil filter in rearmost part of valley could be troublesome for servicing. Caps atop rocker covers hold wiring for injectors and spark plugs.

There are two experimental fuel induction systems on this engine. One is by way of a multiple two-barrel carburetion setup on a plate containing all linkage and throttle plates made up by the Rochester carburetion division, and the other—and more promising—is a fuel injection system. The fuel injection is more promising and offers a reduction in emissions because it is a metered-flow design. Both use nearly identical intake manifolds. That is, they both have individual runners with relatively long lengths. The fuel injection is driven and timed from the backside of the front-cover-mounted capacitor-discharge ignition. The timing of the injection metering is in direct line with the ignition timing, since the fuel pump can be driven from the same shaft that spins the distributor rotor. Injection metering and firing impulses are directed through a common wiring loom, a solid-state affair that merely snaps onto the top of the rocker arm covers. The rocker arm covers are prewired from the spark plug to the top of the cover, and the caps on each side merely snap into place. The leads from the caps to the fuel injection meters are inserted at the base of the inlet ports. Impulses registered from the spark plug timing transfer to the injection meters and release fuel only on demand. This metered and timed method of fuel injection is an optimum way of reducing emissions, because there is no excess flow of fuel into the chamber on deceleration and during idling. Within the inlet stacks for each port injector there is a throttle plate actuated by the accelerator. Various types of commercially available fuel injection units have been tried, and no commitment has yet been made to any one particular design. Fuel injections, when applied to street-operated vehicles, generally only present problems for idling. But a metered system is the best way of overcoming this problem, and at the same time it gives a clean-burning low-speed engine.



Hemi head plug location is offset, but there's plenty of room to add another plug for each hole if need arises. Compression-type steel head gasket is key to sealing open-top chambers. Two shafts on front of this block were used to test drivetrain dynamics on Pontiac dyno.

The front cover-mounted, horizontally located distributor is much different from previous designs aimed at production-line use. A degree plate directly behind the distributor's single adjustment bolt makes it easy to get an accurate setting. The specially built Delco-Remy CD ignition is driven by the rubber-and-glass-belted cam-drive belt, and because of its location at the topmost part of the front cover, tying in a fuel pump, injection metering, or even a mechanical tachometer, is a simple job.

Aluminum blocks present certain advantages and drawbacks. The one-piece casting is light, its sections can be made very thin, and the walls have high density. Because of the narrow sections and open bores, a certain amount of flexing is possible and must be controlled. On the '61-through-'63 GM aluminum blocks, the iron crankshaft contributed a great deal to the rigidity of the block. But this high-speed V-8 is capable of running at speeds in excess of 8,000 rpm and was designed with this in mind. A malleable-iron girdle supports the entire bottom end of the motor, and the long-reach outside row of head bolts ties the upper half of the engine into the rigid lower end. The girdle includes main bearing caps, and there is a vertically arranged row of half-inch-diameter main bearing cap screws in addition to the long-reach head bolts. In essence, this gives the engine a four-bolt main-bearing-cap provision, with the outer retaining bolts splayed out, which offers much greater rigidity than merely doubling-up on vertical main bearing bolts. The crank journal size is 2.9988 inches nominal diameter, the connecting rod journal measures 2.250 inches nominal diameter, and the rod bearing width is 0.980-inch. Main bearing diameter on the current Pontiac 455 is 3.25 inches, although the rod journals measure the same as on this experimental V-8. The crankshaft is forged from SAE 4615 steel, and the rods are forged SAE 4340 alloy steel. Rod length is 6.625 inches, which is the same as on current Pontiac V-8s. Pistons have a high dome, as is common to hemispherical-shaped chambers, and are forged aluminum.



Sand-cast aluminum heads have been made with various sizes of valves and ports, with small-dimension intakes giving driver best rpm.

This engine has an exceptionally good bore/stroke ratio of 0.88, with a nice, fat bore of 4.257 inches and a stroke length of 3.750 inches, which rounds total displacement out to 427 cubic inches. Pontiac's current large-displacement engine has a stroke greater in length than the measurement of its bore diameter, which is contrary to a good performance engine. With the experimental design, piston travel is reduced considerably by comparison to the 455, and while this can improve performance, it can detract from a low emission reading. But the use of fuel injection can greatly reduce the chances of raw gasoline striking a cool bore surface. Use of a long stroke serves to reduce the amount of "cold" bore surface open to raw gasoline, which generally is ushered out through the exhaust without full combustion. Of course, a long stroke not only warms up the bore surface, it warms up everything else too, and heat can lead to wear. Compression ratio on this powerplant is now rated at 12.0:1, though this would certainly drop down were this design worked into a production item. Nonleaded fuels are mandatory in tomorrow's engines, and in line with that, there have been accommodations made on the cylinder heads here for stellite inserts on the valve seats, though the present seats are cast iron alloy, the same as the valve guides.



Parts layout, left to right: 12.0:1 aluminum piston, forged rod, intake valve, 9-inch-outside-diameter 1-X oil pump, main bearing girdle, cam-belt-driven distributor, and forged crankshaft.

In its present experimental form, the complete engine weighs 550 pounds, give or take a few pounds, depending on what and how much equipment is on board. One of the more important points in lessening exhaust emissions involves mass weight; the less there is, the easier it is to operate an engine over the full range, and by fuel consumption being reduced, economy is enhanced. A racing application also benefits by reduced weight. Pontiac's chief engineer, Steve Malone, points out that the 1971 GTO is almost identical in size and weight to the 1964 Grand Prix. He indicated that the intermediate is going back to its old size, or at least to where it should be. But to do this means trimming weight in all areas, and all the cars they build are going to get the same kind of fat-trimming. An engine is a good place to start.

Estimated horsepower of the hemi-head Pontiac is 640 hp at 7,500 rpm. There are fewer than a dozen of these engines in existence, and they are being used to evaluate all kinds of questions, ranging from practicality of design to how well they fit engine compartments. Pontiac hasn't tried experimenting with this engine on a dragstrip, but it would be like a gift from heaven for Pontiac racers interested in being competitive in Pro Stock. It wouldn't be at all bad for a Grand National stocker, and that dry-sump adaptability would make this a natural for a marine engine.

The multifaceted development of the 427 Experimental V-8 employed a system known as Latin Squares. This isn't a new process, but it isn't well-known outside of most engineering brain-centers. It involves assigning each major function of an engine, or any element, substance or problem, a letter. The letters are listed across the top of a square, down one side, and within the columns. The number of columns is the same as the number of letters, and no element occurs twice within the same column or horizontal row. From this, a statistical investigation can be done, and each element becomes relevant to the one next to it, below it or above it. Using this method, carburetion (for example), is as relevant to piston speed as it would be to manifold design. No one part of the engine which is considered a major element would be hidden from another. It isn't an earth-shattering solution to problems, but by following the Latin Squares pattern, one is forced to plot out a means to an end in a different pattern than his own logic or habit dictates.

The styling aspect came off very well, as the photos show. The air cleaner and/or induction system is meant to protrude through the hood of whatever car the engine eventually fits. There is full symmetry to each portion of the "styled" metal, and each side is identical. The front cover encompasses an ellipse. When we asked the Pontiac folks to paint the engine a different color for a cover shot, they agreed at first, then reneged. Turns out that this engine looks good, sophisticated, classy, or whatever might be an apt description, when finished off in black crinkle finish. After personally viewing it, we can only agree with their decision. At first sight, this tastefully designed engine is definitely provocative, as we said earlier, but if you look at it long enough you become aware of the fact that this shape could fit anything from an orbiting space station to a 21st-century high-rise. Looking at the overall project from an objective view, it parallels (sort of) the X-15 rocket-engine "airplane," and because of its completely experimental status, the Experimental 427 might have the same future as the X-15, but like that supersonic missile, there are sure to be direct rub-offs from this project to future powerplants.

An undertaking like this one is always a stimulant for those connected with it, and Pontiac personnel are no different. Anyone we met who had anything at all to do with bringing this engine to life, from general manager Jim McDonald all the way to the security guard posted at the base of the stairway leading to the advance design studio, was quick to brag about the end result. And, as it should be, no one person even hinted at taking credit. No one could, but they all have reason to be happy. There are, no doubt, a great many Pontiac owners who could be happy with this engine reposing in their engine compartment. And the racers? There's no need to ask.

[RocktimusPryme]

I think that was at the nationals this year in one of the tents. It was either that or something like it.

[Cammer-6]

one of my favorite Hot Rod Magazine covers

[Stuart]

Originally Posted by RocktimusPryme

I think that was at the nationals this year in one of the tents. It was either that or something like it.

That's interesting - I'm not an expert but I haven't heard before of any evidence that it still existed.

[Tom Vaught]

COULD HAVE BEEN THE MALCOMB MCKELLAR ENGINE STOLEN OUT OF THE CAR GM GAVE HIM AT HIS RETIREMENT.

May very well be the engine has surfaced. Someone said the owner was asking big bucks for it.

Tom V.

[sdbob]

I remember that article when I was in college and the 2nd gen Firebird article earlier. I thought man styling and performance. Some us think that Pontiac had 'it all' and certain people (even today) did not want that ruining there 'baby'.I thought that was a' paper mache ' non running engine. I thought Mckellar got the over cam running engine.

[RocktimusPryme]

Originally Posted by Stuart

That's interesting - I'm not an expert but I haven't heard before of any evidence that it still existed.

So it’s not the same looking back at it but it’s a Pontiac based OHC V8 experimental engine. I had a picture of it, wish I had taken a picture of the plaque now. Someone else on the board I’m sure knows more about it than I do.

[Stuart]

I agree with Tom V., the engine you saw was the overhead cam engine that had been given to Mac McKellar when he retired. He had it in a 1963 Grand Prix, but after his death it got separated from the car.

[RocktimusPryme]

That sounds familiar. I feel like they had said 63 grand prix in the tent too, but I wont swear to that.

[thepontiacman]

I have that magazine with the 427 Pontiac experimental engine on front cover.

Sent from my moto g power 5G - 2023 using Tapatalk

[Half-Inch Stud]

Some excellent points: Solid valley for the Vee block. Intake runners are dead-straight shot. OHC layout, but the lifter-rocker deal needs a closer look at the Slider-ball in the Rocker; probably okay. Upgrade to roller Rockers without mods.

long outer Head bolts anchored into the Main Cap Girdle. Inner Cap Bolts would keep bottom end put, while doing head rework.
Oil Filter is fine: simply upgrade to a canister-Lid like Mercedes diesel. A minor development.
Looks like ignition could be modern quad coil plates.
Fuel inj could have evolved into sequential elec. Think we all would like elec. Carb (dual carbs) option could happen.

Cons: big exhaust valve, stems. but head could evolve into todays parameters, implementations.
Opportunity: develop Front plate & Mid plate mounts, stainless exhaust headers
I missed the coolant pump details.

[mgarblik]

The 427 engine featured in this thread is a different advanced engine project from the Mac McKellar SOHC engine and the DOHC engines he was developing. Although some features were used on both engines, they were radically different. The McKellar engines were more top end adaptations utilizing OHC-6 style technology in a V-8 format. I was fortunate to hear that engine run at a car show. Smooth and quiet. Wonderful. I have never seen in person any of the 427 aluminum engine bits and pieces featured here. Was a little surprised to read that nearly a dozen copies of the major components were cast. You just have to think a few super rare pieces are still around somewhere.
So many of the design features in this exercise have ended up in other GM production engines. The first that comes to mind is the Northstar Cadillac V-8. 1. Open deck. 2. Aluminum die cast block 3. Super long head bolts, external, tied into the bottom of the bores. It's a real shame that the nothing is developed in a cut and try method anymore. Must have been really fun to be an engineer in the 1960's.

[tom s]

Mike,George Delorian told me they never made less than 12 castings.Because of core shifts and casting voids they wanted at least 12.Also im told Macs engine and car will be reunited.Tom

[Tom Vaught]

between the disappearance of the Mackellar Engine and the photo posted of the engine on the grass.
Mrs Mackellar should have received the money for that car/engine (when they were together) vs the engine being removed and as
the picture shows displayed at a Pontiac Parts swap meet.

Tom V.

[mgarblik]

I hope you are right and the 63 GP and it's one of a kind OHC V-8 engine can once again be together and the car ends up in a museum where it belongs. It's a very important part of Pontiac history and should be preserved.

[RocktimusPryme]

I can’t be the only on who saw that motor. It was that the Pontiac Nationals in the feature tent a few months ago. I would think someone else on the board would have more pictures of it including the story board that was with it.

I just took the picture to compare it to the Cammer Fords of the era.

[RamAirBirds]

This was THE Motor and THE car that were sitting together in the tent at Norwalk. The 2 will definitely be 100% re-united in the near future.
The car was found and bought by this gentleman and soon after the motor was located...Still very close to its original home and a deal was made. A lot of stories about how the 2 were separated in the first place. The original separation was no doubt somebody taking advantage of an older person later in life. Once that happened and motor was sold to the individual that sold it to the cars new owner. The trail is clean from that sale on to this last sale to the cars current owner. The first Purp maybe should be the only one that should not sleep well at night. That party may also be deceased at this point...not sure. A lot of tid bits here but just setting record straight that all the recent parties involved in the car coming back together had nothing to do with the original separation.
Summary. The motor AND the car were together that you saw...and by all accounts will remain so for the duration.........

[Mr_GTO]

Notice injector placement on that engine? Exactly the same on the LS1 engines. Pointed right at the back of the valve. Very cool article.

[hurryinhoosier62]

Originally Posted by Tom Vaught

COULD HAVE BEEN THE MALCOMB MCKELLAR ENGINE STOLEN OUT OF THE CAR GM GAVE HIM AT HIS RETIREMENT.

May very well be the engine has surfaced. Someone said the owner was asking big bucks for it.

Tom V.

I thought Mac’s was one of the 421 SOHC engines.

[Jeff Hamlin]

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