Video: Blue Performance’s 680ci ‘Secret Weapon’ Pulling Truck Engine

The sport of truck and tractor pulling may seem relatively simple to an outsider; put in a monster engine, send the throttle to the floor, and wait for the truck or tractor to spin out. This is somewhat accurate, but what many people don’t realize is that there is a large of amount of work that goes on behind the scenes in regards to engine development. The engine’s performance accounts for a large percentage of the truck or tractor’s resulting footage at the end of the hook. In this article we’ll have an inside look at Blue Performance’s 680 cubic inch B441 Ford Engine that was campaigned in the team’s “Secret Weapon” Ford F-150 during the 2014 season with the Outlaw Pulling Association.

 

Application Explanation

IMG_0824“The Secret Weapon” is a 6,200-pound modified 4X4 pulling truck; during the 2014 season the truck finished third in points overall and got as high as second in points, right behind its sister truck also campaigned by Blue Performance.  It won several hooks and was successful early on in the season until issues plagued the later part. This truck has been pulling since 1982 and has undergone several revisions and engine alterations through the years to stay competitive within the sporting engine regulations.

The current engine regulations state that the engine block must be able to swing a factory production crank (big block Ford, Dodge, or Chevy), is limited to a bore spacing of 5 inches, and must have two valves per cylinder. The class is centered around naturally aspirated engines; no unnaturally oxygenated fuels such as VP’s Q16 and M5 are permitted.

With these simple and straightforward rules, the competing engines start to resemble IHRA Pro Stock-style mountain motors. Displacements north of 650 cubic inches utilizing Jon Kaase and Sonny’s Racing Components-inspired cylinder heads are common. Mechanical fuel injection is the primary induction choice, with only a few competitors using carburetors. Electronic fuel injection is illegal to help prevent the use of traction control along with other driver aides–this is done by the sanctioning body to promote professionalism within the sport.

Home Made Performance

Fred Blue of Blue Performance machining a custom piston to fit the combustion chamber perfectly.

Fred Blue of Blue Performance machining a custom piston to fit the combustion chamber of the B441 cylinder head.

The engine block is a Carroll Carter Motorsports 4.900-inch bore space, 11.200-inch deck height engine block. Since a pulling truck is not really susceptible to large magnitudes of vehicle acceleration a single stage wet sump oil system is utilized.

The 680 cubic inch Ford utilizes B441 cylinder heads that are CNC ported to optimize air flow. The intake ports flow 580-680 cubic feet per minute depending on valve lift. These heads are similar to what Jon Kaase places on his championship IHRA Pro Stock Mountain Motors. The valve train utilizes titanium valves, PAC triple springs, and T&D rocker-arms driven by a 60mm camshaft. The valve springs are installed at a height of 1.200-inch, which gives roughly 400 pounds of seat pressure in this application.

“When the valve springs get below 375 pounds of seat pressure at the installed height, it is time to throw away the spring,” says Fred Blue of Blue Performance.

With this large amount of spring pressure the overall diameter of the camshaft is extremely important. A larger diameter camshaft requires larger lifters; the larger lifters use a larger diameter roller within the lifter which reduces the magnitudes of stress on the roller.  The concept is similar to that discussed in EngineLabs’ recent article that documented the camshaft specifications NHRA Pro-Stock engines utilize; the only difference here is the camshaft bearing spacing and rocker ratios.

Note that each piston is matched to each cylinder, denoted by the number marked on the domes of the unfinished pistons. When the pistons are finished the domes are coated with a ceramic thermal barrier and the skirts are covered with a dry film lubricant.

Care is taken when it comes to the development of the piston’s geometry. A JE piston blank is ordered and the finial dimensions are hand milled in the Blue Performance shop using a home-made piston vise. The compression ratio is a highly guarded secret and is extremely important when it comes to extracting the maximum amount of power from the engine. After the pistons are milled they are coated to reduce drag at the cylinder walls and protect the hand-fitted domes from thermal events. After the pistons are finished they are mounted on top of Oliver forged-steel connecting rods.

Forged rods are utilized due to their increased reliability, determined through Blue Performance’s research and development in pulling-truck applications. Aluminum rods not feasible in a naturally-aspirated engine in this type of application; their replacement intervals are not feasible, especially when the engine’s total run time for a season is taken into account. For example, the total time that a drag car engine may run per pass is seven to eight seconds. A pulling truck engine can run up to twenty-five seconds at full throttle per pass. In a particular season there maybe twenty to thirty passes made on the same short-block. Due to the events and how they fall on the calendar there may be little to no time to freshen the bottom end. Moreover, this time does not include the passes that are executed on the dyno after the engine is assembled.

Mechanical Fuel Injection for Newbies

Mechanical fuel injection has many benefits when compared to electronic fuel injection, especially in this application. For instance, the fuel injector’s physical size is much smaller than the traditional electronic Bosch style injector. This allows the mechanical fuel injector to be mounted in locations that are off limits to conventional electronic injectors.  Placing mechanical fuel injectors in multiple locations throughout the intake manifold and ports helps improve fuel fragmentation and mixture quality. It is not uncommon to see a mechanical injection system with two to four sets of injectors. The fuel of choice is normally methanol; this requires roughly a .035-inch diameter main injector with one or two .010-inch diameter supporting injectors per cylinder.

The fuel pump controls fuel flow with respect to engine speed, unlike traditional electric pumps. This helps the pump match the fuel volume needed for the engine in order to reduce that amount of returns or bypasses throughout the mechanical injection system. The flow to the injectors is controlled through bypasses or returns that flow fuel back to the tank and a barrel valve connected to the throttle body.

The left photo shows various mechanical injection fuel system components. The center photo is of the main fuel injector commonly referred to as a down nozzle that injects fuel at the bend of the intake port. The photo on the right shows the fuel line that carries fuel to the down nozzles.

A nominal mechanical fuel injection system consists of a low speed bypass that controls the return of fuel at idle, a main bypass that controls the amount of fuel returned at all times above idle, and a high speed bypass that returns fuel at higher engines speeds to help match the engine’s volumetric efficiency curve. When air density changes due to altitude, temperature, humidity, etc, the main bypass’s pill size is adjusted to optimize the flow to the injectors for the conditions. This makes a mechanical fuel injection system effectively a two-dimensional fuel system, fuel flow with respect to engine speed. Only the barrel valve throttles the fuel with respect to throttle position at idle and just off idle which adds another control parameter for low end response.

The fuel system on this particular engine has two sets of injectors; one at the entrance of the intake port, and one located under the valve cover so that the injector can shoot fuel across the port. Placing the injector in this location helps the air negotiate the turn in the port due to its interaction with the mass of fuel–this is done to help improves the air flow performance. Bombarding the air with fuel droplets also helps to further fragment the fuel and improve power output.

Results

Single stage oil pump with the mechanical fuel injection pump driven off the back of the oil pump.

Single stage oil pump with the mechanical fuel injection pump driven off the back of the oil pump.

After the horsepower is SAE corrected, the combination yields roughly two horsepower per cubic inch. Since the power demand of a truck pulling engine is different when compared to other motorsports, maximum power is not as important as area under the torque curve.

Also unlike other motorsports, there is no shifting during the pass. One gear is matched for track conditions. This is where the larger amount of power available under the torque curve makes the engine more useful during a hook. On this particular engine, 1,100 foot-pounds of torque is available from 6,200 rpm to 7,200 rpm. The engine speed ceiling for this engine is 8,400 rpm–after that, connecting rods will start to be the weak link. The 4X4 Modified 2015 season opener is in Ravenna Nebraska the weekend of June 19-21, and the Secret Weapon will be in competition at that event.

About the author

Corey Blue

The first engine Corey built was for his 70cc Honda dirt bike at the age of seven. As he got older, he had the opportunity to work on big- and small-block Fords and Chevys for truck pulling, and modified his 32-valve Ford Modular 4.6 Cobra to generate 900 horsepower. Corey is a graduate of Missouri University with a degree in Science and Technology for mechanical engineering and I interned for Roush Industries working on the 2011 and 2012 Shelby GT500 Mustang.
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