Some motorsport competitions are able to compare engine output objectively and remove any differentiating factor such as driver skill, tyres and chassis set-up. Dyno shootout competitions, such as the Engine Masters, pit engine builders against one another – they turn up with an engine ready to run on the dyno, run them and their performance is measured on a common dyno.

The rulebook for the Engine Masters is refreshingly thin. It is clearly aimed at making the competition about practical skills and building a good engine, and the rules outlaw several avenues of engine and component development that would be so costly as to discourage many competitors. One major area of development that is banned is the use of power adders, so no boosted engines or nitrous oxide are allowed.

The variable stack length function. During the dyno pulls the stacks would be fully extended to make more torque down low, and as the rpm increased the stacks would retract and make higher top-end horsepower (Photos courtesy of Nick Smithberg)

The competitors are a mix of companies with good budgets and experienced teams of engineers and engine builder, with some keen amateurs thrown in. Smithberg says, “Everyone in this event either builds engines for a living or are a hobbyist trying to see how they fare against the pros, so this is always a side thing for most people with limited time.”

The engine was actually a collaborative effort, sharing skills, effort and expense. Top-end expertise from Smithberg Racing, based in Nebraska, is combined with the bottom-end build skills of Gene Adams Performance, in California. In this way, both companies benefit from being closely involved with a successful engine.

Even with significant restrictions on development and an eye on costs, these engines can be expensive. Smithberg notes, “With our rules we need to use what is commercially available, and expense becomes a factor, especially with a tight budget. This was one reason why Gene and myself partnered up to share the expenses and also worked with manufacturers to seek sponsorship or discounts to afford the effort.

“Our engine cost somewhere in the region of $50,000-60,000 to make it competition-ready. Some items were shelf stock pieces and others were custom. Another reason behind some of this is that many times these engines will be featured in a magazine, so they want the readers to be able to buy the same parts to build a similar engine.”

The engine is a 410 cu in (6.72 litre) V8 Hemi based on a 1954 OEM Chrysler cylinder block, but with some very modern ideas and clever thinking applied. The use of production heads and blocks makes for a heavy engine, although this is no detriment to a dyno engine. All the major castings are cast iron.

For a low-budget competition, some surprising development items are allowed. Variable-length inlets are a feature of the Smithberg engine, but surprisingly are banned from much of the top levels of motorsport.

As regards how the competition is judged, Smithberg says, “The goal is to produce as much average horsepower and torque for the given rpm range, which is typically 2500-6500 rpm. To level the playing field for different-sized engines, the average horsepower and torque are divisible by the cubic inch of the engine. There is an equation used to create a score in points. The highest points wins.”

Dividing by capacity makes gives torque per unit displacement, and this is a measure of the ‘efficiency’ of the engine, multiplied by a constant gives the BMEP, which is a common metric to compare widely differing engines.

As most readers will know, power is torque multiplied by rotation speed (and is a constant, depending on the units of speed and torque), so the power element in the scoring rewards those who can hang on to good BMEP throughout the measured rev range. Framing the rules to reward BMEP discourages entrants from simply building the biggest possible engine.

The rules seem to be agnostic to engine displacement, but Smithberg notes, “We did see a trend, with a sweet spot for cubic inch being around 400.”

The rule book states that many of the components must be commercially available, but certain areas allow for significant development on the part of the competitors. This applies particularly to inlet and exhaust.

Smithberg says, “From my experience, the induction and the exhaust system are critical. With the peak rpm being a conservative 6500, you need a very fast airspeed port with as much airflow as possible, using the largest intake valve you can fit into your given bore size.” In a two-valve-per-cylinder engine with a modest bore size of 4 in (101.6 mm), fitting the largest intake valves is essential.

An engine designed for this type of competition is not necessarily what you would build for road or race use. Smithberg says, “These engines are very unique in design, so you really wouldn’t see them in much use outside the dyno competition.”

Teardown at Engine Masters Challenge to verify the engine is legal as per rules and claims

A lot of thought went into the engine specification on the critical elements of inlet and exhaust, with Smithberg noting how important it was to correctly calculate the proper port cross-sectional areas needed, wave tuning with proper harmonic lengths on the intake and exhaust tracts, flow demands and so on. ”I learned a lot about manipulating the exhaust collector length; it shifts the power around and can help or hurt your average power,” he adds.

Variable inlet

Smithberg’s secret weapon is his use of a variable-length inlet system, such as that used in Formula One until early 2005. Such systems offer clear advantages in that the engine can have the optimum inlet length (within the given range of adjustment) depending on engine speed and possibly on other parameters too.

As engine speed increases, the time that the inlet valve is open decreases inversely in proportion to engine speed. As pressure waves travel at a fixed speed, the number of wave reflections travelling from one end of the inlet system to the trumpets and back changes in the time that the valve is open. By varying the inlet length, advantages can be gained by having helpful pressure waves arriving back at the inlet valve at the correct time, helping to maintain high volumetric efficiency over the engine’s working range.

It is a normal part of engine development to find the trumpet length that best suits a particular engine to give the best performance. With Smithberg’s system, it is in the gift of the engineer to effectively have the correct trumpet at each engine speed.

There are various options for such systems. The simplest are effectively a binary choice of long or short inlet, and these usually change length at a given engine speed. That engine speed is where the torque curves for the short and long inlets cross.

Racing and production two-stroke engines from the late 1970s onwards took advantage of similar controls with devices to raise and lower the exhaust ports to give the same effect. Formula One systems had more complex control, precisely controlling the actuator at every engine speed and load condition to provide the optimum length.

Smithberg’s system uses a single 12 V linear actuator to directly lift a single block of eight machined trumpets. The actuator comprises a small motor driving a leadscrew via small gears, and has an optional feedback potentiometer that allows precise control of the inlet height.

The actuator  has a stroke of 3.5 in. With a minimum inlet length of 13.625 in, the actuator gives an operating range of more than 25% of the minimum inlet length.

The single actuator is a very tight squeeze in between the fuel rails, but it fits and functions well. It is able to move the inlets for both banks of cylinders without a linkage because all the inlets are parallel and vertical. The lower, fixed part of the inlet is formed from thin-walled tubes, and the upper sections are machined from aluminium.

Pistons, rods and crank

Another area of open development is pistons and rings. Smithberg turned to Ric Panneton of CP Pistons for piston and rings, and the result was a modern competition piston design being used in an old engine.

Luckily the bore size allowed a forging for a modern competition piston with a short, narrow skirt to be used. The reduced skirt area is good for friction reduction, as is lower weight, as it leads to lower bearing loads. Although the piston uses three rings – two would give lower friction but possibly at the expense of less efficient sealing – Smithberg says, “We use a modern ring pack to reduce friction as much as we can.”

Crankshafts can be as fancy as you like, but they must be commercially available to competitors. Unlike a track engine whose characteristics need to include transient responsiveness and good pick-up, there is no advantage in a dyno competition to having a really low inertia crankshaft.  

Smithberg notes that the choice is quite limited. “With an early Hemi in particular you only have two options, an OEM forged crankshaft or a custom billet crankshaft, as no aftermarket forgings are available for this engine,” he says.

With that in mind, he opted for a Sonny Bryant Billet crankshaft, which in this case was a 0.625 in stroker for a 331 Hemi, which has a 4.250 in stroke. “We chose the eight-counterweight option, centre counterweights added, and went to a Big Block Chevy rod journal size for bearing and rod availability and options. We also chose Molnar Technology B Beam Big Block Chevy rods in a 6.800 in length, as it was a stock part.”

With a 4.25 in stroke and the engine running to 6500 rpm, the mean piston speed reaches 76.7 ft/s (23.4 m/s), which is pretty high for such an old engine.

Nick Smithberg (left) and Tony Turner, long-time customer and early Hemi enthusiast

While most American V8 engines have traditionally used a cross-plane/cruciform four-pin crankshaft to produce low-vibration engines with a distinctive sound, those seeking maximum performance are often prepared to deal with excessive vibration to take advantage of the better tuning behaviour offered by a flat-plane crankshaft. Smithberg says, “If I had an unlimited budget I would have loved to try a flat-plane crank with the stack injection. Potentially there could have been more power there.”

Preparation and competition

The unique concept of building an engine for a dyno shootout is just one part of the challenge. The engine has to be compatible with a dyno at someone else’s workshop, and the time to install the engine is tight.

It is the competitor’s responsibility to ensure that the process of installing the engine is quick, and that the necessary connections to the engine can be made swiftly. If the engine doesn’t fit straight away, there is no time to rework parts; you have lost your place in the running. The host dyno staff will install the engine but competitors must be on hand to assist.

Once installed, the competitor has only 35 minutes to get the engine running, warmed up, tuned and to perform at least three full-load dyno pulls. The average of the best three pulls is used to calculate the score.

“Your goal is to likely make small weather corrections in the tune-up and knock out three stellar pulls,” Smithberg explains. “Most people will make a pull, shut the engine off, open the dyno room doors to cool it down, close things back up, and make the next pull.”

Smithberg Racing Street CNC program (hand-finished), showcasing the custom intake gaskets made by SCE Gaskets

With so little time to make adjustments on the dyno, the aim is to have the engine well calibrated beforehand. “All the testing is done weeks before, so you hope you have everything ironed out before coming to the event,” Smithberg says. “It’s not uncommon to see sparks fly from some people thrashing right up to the event with very minimal testing.”

The competitors benefit from giving careful thought to what they might need to adjust and swap on the dyno. The Smithberg engine has a board mounted on one end of the engine which carries the ECU and coils. They are easily accessible and importantly, they remain cool which helps with reliability and eases adjustment/replacement. Although the aim is clearly not to need access to such components, with limited run time, every moment is precious if adjustment is required.

Summary

The result of Smithberg’s hard work was a peak torque of over 600 lb-ft (813 Nm), and with a displacement of 410 cu in, this gives a BMEP figure of 15.2 bar.

The formula to calculate BMEP for a four-stroke engine is:

To give some comparative figures, I turned to Jack Kane’s research into Formula One and NASCAR Cup engines (RET 29, March/April 2008). In that article, he found that these engines produced 15.18 and 15.12 bar BMEP respectively.

Of course, the engine built by Smithberg and Adams is a true competition engine, and although it is not expected to last hundreds of laps of a high-speed oval NASCAR race or be subjected to the twisted and turns of Monaco and Spa, it is surprising that a 1950s two-valve Hemi is so evenly matched with some serious competition engines used in the top levels of motorsport from around 15 years ago.

The Smithberg Hemi is not performing at this level because of low mean piston speeds – the 23.4 m/s peak speed of the Hemi engine is not too far away from that of the NASCAR engine, whose mean piston speed at maximum rpm is only 6% higher.

ANATOMY

The Smithberg Engine Masters Challenge Chrysler Hemi engine is a 90º V8 designed to compete in the Vintage class of the Engine Masters Challenge, and is based on a 1954 Chrysler Hemi engine.

The engine’s main structure is cast iron; a gasket forms the block-to-head seals. The aluminium piston carries three rings. Conventional split steel rods and plain big-end bearings run on a steel billet crankshaft.

The inlet system features port injection and butterfly throttles. Unusually, the rules allow variable-geometry inlets, and the inlet length is varied over a 3.5 in range using a 12 V linear actuator.

The cylinder head features two valves per cylinder: 2.125 in inlet and 1.8 in exhaust. Each valve is closed by two concentric parallel springs retained by steel retainers. The valves are actuated by pushrods and roller rockers.

The cam runs in the cylinder block and is chain-driven from the crankshaft. A mechanical oil pump and electric water pump circulate fluids.

SPECIFICATIONS

SMITHBERG CHRYSLER HEMI

Engine Masters Challenge

90º V8

3.917 x 4.25 in = 409.7 cu in/6714 cc

Pushrod valvetrain

Distributorless ignition

Port injectors, eight injectors

Linerless

Aluminium pistons

Naturally aspirated

One spark plug per cylinder

Gasoline, VP HP101

Cast iron block and crankcase

Aluminium pistons, three rings

Steel piston pins

Steel con rod

Chain-driven steel camshaft

Steel crankshaft, four pins

Two valves per cylinder

53º included valve angle

Valve angles undisclosed

2.125 in inlet valves, 1.8 in exhaust

Butterfly throttle, one injector per cylinder

Plain bearings

12.1 compression ratio

Maximum rpm, 6000

SOME KEY SUPPLIERS

Block castings: Chrysler (1954)

Head casting:  Dodge (1954)

Block and head machining: Gene Adams Performance/in-house

Sump pan: Stef’s

Crankshaft: Sonny Bryant

Rods: Molnar Technologies

Rod bolts: ARP

Pistons: CP

Piston rings: CP

Piston pins: CP

Main bearings: King

Big-end bearings: King

Thrust bearings: King

Circlips: CP

Valves: undisclosed

Valve seats: undisclosed

Valve guides: undisclosed

Valve springs: PAC

Spring retainers: Comp Cams

Cam drive components: Mopar

Camshafts: Comp Cams

Cam followers: Crane

Pushrods: Manton

Pushrods: Smith Brothers

Rockers: Rocker Arms Unlimited

Cylinder head seal: Cometic

Fuel injectors: Deatschwerks

Ignition and engine management: Megasquirt

Data acquisition: undisclosed

Sensors: Ford

Throttle bodies: Smithberg

Throttle bodies: Hilborn

Water pumps: Meziere Enterprises

Oil pumps: Mopar

Oil filters: undisclosed

Air filters: undisclosed

Exhaust: Andrew Calkins

Fluid lines and adapters: undisclosed

Wiring loom: Andrew Peterson

Steel materials: undisclosed

Aluminium materials: undisclosed

Other materials: undisclosed

Fasteners: ARP