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900 Horsepower From A Supercharged 30-Year-Old Porsche 928 Engine

When you hear the word “Porsche” (“Por-sche”; two syllables), more than likely an image of one of the 911 variants pops into your head. However Between 1978 and 1995 there existed a car in Porsche’s lineup that was not only front-engined, but the very first to be powered by a V8 engine. Of course, we’re referring to the Porsche 928.

In its 18 model-year run, the 928’s V8 engine varied from 4.5-liters (274.6 ci) to 5.4-liters (329.5 ci) of displacement, and came in single overhead camshaft (16-valve) and dual overhead camshaft (32-valve) configurations, with output peaking at a respectable-for-the-time 345 horsepower and 369 lb-ft of torque in 1995. For a frame of reference, the SOHC 4.6L Ford Modular engine was making 215 horswpower, and the DOHC Ford 4.6 cranked out 305 horsepower, from the Mustang GT and Cobra, respectively, in 1996.

The Porsche 928 and it’s engine, while niche, still enjoys a healthy following from everything from general European car enthusiasts to those who have a specific fixation on front-engine Porsches. Leading that movement is the aptly named 928 Motorsports. Not just a retailer of hard-to-find 928-specific components, Carl Fausett and his team are constantly building and developing new hardcore products for an engine that hasn’t seen a production line in 23 years.

One of the biggest impediments of the 928 engine from factory is the OEM intake manifold, especially in a high-performance application like this. 928 Motorsports fabricates their own, very unique manifolds to suit their big power goals.

Building a Halo

“I have always been a big believer in the power of a ‘halo’ product, even before such products had that name,” says Fausett of the current project. “In this case, this is our third 900-plus-horsepower engine. As usual, developments and discoveries are made while building a halo product that trickle down into our related products and improve them as well.”

Originally, 928 Motorsports began this engine program to enter in Open Class competition at the iconic Pikes Peak International Hillclimb. The engine design started with a unique set of requirements, as not a whole lot of other races begin at 9,000 feet above sea level.

“We needed maximum torque for accelerating uphill through 156 corners in just 12 miles from 9,000 to 14,100 feet,” Fausett explains. “The supercharger was added so the engine would not run out of breath as the altitude climbed.”

While at Pike’s Peak, Fausett decided that the engine would also do well in land-speed racing–with a few minor changes. “I knew we had a strong crank and case core, and a good over-square formula. However, for Pikes Peak we needed to favor torque over horsepower, while at Bonneville we needed to favor horsepower over torque,” Fausett says.

“Research into the existing Land Speed records at Bonneville led us to build this 6.54L to fit nicely in the “B” engine class in BGMS (Blown Gas Modified Sports) where we felt we had the best chance of breaking an existing record.” In addition, the engine powers the car in the NASA German Touring Sedan road race series in the Unlimited class due to the car’s incredibly high power to weight ratio.

The Vortech V-7 YSi centrifugal supercharger is the heart of this engine’s airflow. In addition, you can see the unique, complex path of the intake tubing required in the car’s chassis.

The Architecture of Stuttgart

While the original 928 single-cam engine debuted in 1978, the dual-cam model came alive in the 1985 model year, and two years later, the cylinder head design underwent a significant overhaul. This 928 Motorsports-built beast is based on that 1987 revision and sports some serious displacement (by Porsche V8 standards) to help achieve such impressive power numbers.

Starting with a Porsche Alusil hypereutectic aluminum-silicon alloy engine block, Fausett had the OEM cylinder liners replaced with dry ductile-iron cylinder liners to accommodate the 4.125-inch bore (from the OEM 3.93-inch bore). “The aluminum cylinder walls get pretty thin by the time we do this, so we install T-top ductile iron cylinder liners into the block to handle the pressures,” says Fausett.

Fitted into the bore are a set of Arias/CP-Carillo forged 2618 pistons with a dome shape to allow for lower, more boost-friendly 8.5:1 compression ratio. Connecting the pistons to the crank are a set of Oliver parabolic rods, made from E4340 steel. Fausett chose Total Seal Gapless rings for the pistons, Porsche main bearings, and Clevite rod bearings for the combination.

The crankshaft is a custom billet piece, expertly carved from 4340 steel, with a 3.75-inch stroke, up a touch over 3/8-inch more than the OEM 5.4-liter 3.38-inch stroke, for a total displacement of 6.54 liters or right at 400 cubic-inches. For oiling, the OEM Porsche oil pump is used, along with the OEM oil pan, which has been extensively modified with a custom windage tray and crank scrapers by 928 Motorsports.

“I can say that the 928 block and bottom end is wonderfully robust. Designed in the mid-1970’s, Porsche got it right, and built an engine that still holds up, today,” says Fausett.

Up top, the cylinder heads started off life as the revised Porsche four-valve-per-cylinder dual overhead camshaft castings that debuted in 1987, which 928 Motorsports has heavily worked over. Starting at the valve, every port in the head got the transition from back-of-valve to runner reworked to minimize restriction. Once Fausett was happy with the shape, the ports were then enlarged to flow 339 cfm at .500-inch lift on the intake side, and 251 cfm at .500-inch on the exhaust side. That’s an increase of 55cfm over stock on the intake, and 23cfm on the exhaust side.

Significantly oversized intake valves have been fitted into the semi-hemispheric combustion chambers. The stainless 39.5mm intake valves and 33.0mm exhaust valves are 2.5mm larger than OEM on the intake, and the same as OEM on the exhaust. Single 928 Motorsports beehive valve springs control the valve motion, while lightweight hydraulic cam followers translate cam lobe data to the valves.

With the sheet-aluminum plenums removed, you can see the custom-made glass-filled nylon intake runners, along with getting a better look at the DOHC cylinder heads. Notice how narrow the cylinder heads are, compared to other, modern DOHC head designs.

Controlling the valves are a set of four custom 928 Motorsports camshafts with .432 inches of lift and 220 degrees of duration on the intake side, and .398 inches of lift, with 216 degrees of exhaust duration. The cams are dialed in with a 117-degree lobe separation angle.

One of the largest restrictions on a 928 engine is the intake manifold itself. For this project, 928 Motorsports created a custom intake manifold of their own design out of glass-filled nylon runners and aluminum sheetmetal plenums–yes, plural. “To get the kind of air flow we needed, we had to completely design/build our own intake manifold as the stock intake just couldn’t flow enough,” says Fausett.

A 90mm Parabolic throttle body is used, while Siemens Gen III 80 lb/hr fuel injectors, are run by an Electromotive TecGT EFI system. The ignition is also controlled by the TecGT system, with the Electromotive coil-per-plug system, and spent exhaust gasses are routed out of the engine via a set of custom MSDS long-tube headers, which have been Jet-Hot coated. An Aeromotive Eliminator fuel pump inside of a Fuel Safe cell feeds the engine with Sunoco 110-octane gasoline.

The key to the big power numbers is the Vortech V7 YSi centrifugal supercharger. The YSi is a tried and true design capable of moving enough air to make 1200 horsepower and 30 psi of intake tract pressure, leaving Fausett some room, as he is only running 18 psi at the intake plenum through a massive air-to-air intercooler.

Here you can see the flow bench data for stock DOHC 928 heads plotted against the ported versions from 928 Motorsports. More than just opening everything up, Fausett likes to straighten out the runners as much as possible.

“We already had supercharging experience with this motor from our Pikes Peak effort, it made sense to stay with it as our power-adder of choice for Bonneville,” Fausett explains. “I knew that if I went turbo, I would have problems with the heat that the turbo produces harming my exhaust valves, plus finding a way to increase coolant flow around the exhaust valve seats in the heads.”

Also intriguing is the use of an air-to-air intercooler in this application, as opposed to an air-to-water charge cooler. “I have installed both on different race cars and high-performance street machines and, when properly designed, both work just fine. I even favor air-to-water on street machines a little,” says Fausett.

“When we are talking about a racecar, the added weight of a secondary heat exchanger (radiator) just for the intercooler, plus the pump, reservoir, and then the water itself–it all adds significantly to the weight of the system. Plus, the speeds are higher on racecars, and we don’t encounter many traffic lights, so air-to-air works well and is a good, lightweight choice.”

928 Motosrports is in borderline-uncharted territory with this level of engine, often having to create their own parts to handle the challenges being placed before them. “Porsche 928 engine parts for this level of output are non-existent. We have our go-to vendors that assist us by designing the parts with us, and then manufacturing them to our specs,” Fausett explains. “I like to give [the parts companies] a lot of latitude; it doesn’t make sense to me to tell a piston manufacturer how to make a good piston when they do it all day every day. So, I like working with my manufacturer to explain what we are trying to do and what we need, then collaborate with them on the final design.”

Fausett believes that there is another 40 or so horsepower left in the tune, and plans to finish everything up on a chassis dyno. He’s also got an eye towards four-digit power numbers. He should have enough blower left to do it, so we’re interested to see his attempt at that goal.

While the 900-horsepower mark is respectable as all get out from a 30-plus-year-old engine design with an OEM block and cylinder heads, it’s not enough for Fausett. “I’ve got this ambition to make 1,000 horsepower from a Porsche V8 using just air and gasoline,” says Fausett. “I’m sneaking up on it, and we’re getting close – even this engine dyno, although it stopped at 900 horsepower, the tune is not quite done yet and we think there is about 40 more horsepower still in there to be found.”

For the final tuning, Fausett and team 928 will switch to a chassis dyno instead of the engine dyno. “We will be able to spend more time in each load cell and optimize the tune as she goes through that range. It makes for the best finishing touches on the tune and always nets us more power,” reveals Fausett.

“Most importantly, it adds to engine safety. We’ve had our 900-horsepower 928 engines race for five years at a time without needing a rebuild, and this is one of the reasons why. Porsche really built an anvil that I am still pounding on today.”

Watch the 900-horsepower dyno pull below:

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About the author

Greg Acosta

Greg has spent over a decade in automotive publishing as Senior Editor of Race Pages magazine. In his free time, he is a firearms instructor and volunteer in the police armory.
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