Engine Design

Introduction

Engine design in Automation is very complex, with hundreds of thousands of possible combinations of cylinder count, layout, head types, internal types, fuel systems, aspiration methods, and exhaust systems. This in turn affects different variables and characteristics of the engine, which in turn affects demographic desires. To help explain how the engine designer works, an example using a year 2020, unrealistically basic inline 3 cylinder engine will be used. As of now only 4-stroke gasoline engines can be created, with diesel 4-stroke engines planned for the future. Before explaining the process of engine design, the tab (pictured on the left) will ensure you build a successful motor. This tab shows various engine statistics as a result of your design. From top to bottom: Performance index, weight (measurement scale can be changed in options), reliability factor, throttle response, engine smoothness, engine loudness, engine cooling factor, engine service costs, fuel efficiency factor (in mpg or L/100km), octane rating (affects which type of fuel is best for your engine), emissions factor, material costs, production units, engineering time. These in turn affects demographic favorability towards your car. Knowing how your choices affect each parameter will be the key to a successful design.

Engine Parameters

• Performance Index: affected by the power output and torque ratings of your engine. A higher number leads to a more prestigious and sporty car

• Weight: affected by block layout, material, head design, material, and any additional technologies added on (fuel system, turbocharger etc.)
• Reliability: affected by internal quality (piston, crank, rod materials), power and torque output, and the choice of additional technologies
• Throttle Response: affected by compression, ignition timing, aspiration methods (turbo design) and fuel system choice
• Smoothness: affected by cylinder count, cylinder layout, and piston stroke length. In engineering, the engine experiences primary and secondary motions. The inline-6 engine (and by default the V12 as well) are inherently balanced, and thus are the smoothest in game design. More cylinders and shorter stroke benefit smoothness, as well as the engine's bank degree (in case of V and horizontally opposed designs). The smoothest V/horizontal engine design is calculated by taking 720 and dividing it by the cylinder count. Therefore a 90 degree V8 is smoother than a 60 degree V8 because 720/8 = 90
• Loudness: affected by air intake, turbo-charging, and exhaust design
• Cooling factor: affected by power output and displacement
• Maintenance cost: affected by engine's complexity
• Fuel efficiency: affected by power output, fuel system choice, compression, ignition timing, and turbo-charging
• Emissions: affected by fuel type (leaded vs unleaded), fuel system choice, air/fuel mixture, and catalytic converter design
• Material costs: affected by every choice
• Production units: affected by every choice
• Engineering time: affected by every choice

Creating an Engine Family

The first step is to create an engine family. The engine family determines the cylinder count, layout, block material, size and maximum displacement, head design, head material, and (available after 1990) use of VVL (Variable Valve Lift). Currently, as of September 2018, there are 4 inline setups (I3, I4, I5, I6), 3 60° V setups (V6, V8, V12), 3 90° V setups + 1 DLC/Legacy owner exclusive (V6, V8, V10, V16), and 2 horizontally opposed boxer setups (H4, H6). This has a huge effect on costs (both engineer time and material costs)

• Engine Block: affects cylinder count and layout, which in turn affects displacement, weight, cost, engineering and production time
• Block Material: affects weight, cost
• Family Capacity: affects weight, cost, displacement, valve flow, valve float, RPM tolerance. Modern engines tend to use between 500 cc to 625 cc per cylinder (30 to 38 cubic inches). Remember that family capacity affects only the maximum displacement, which means you can make smaller displacement engines within the same family.
• Head and Valves: affects power output, RPM tolerances. OHV (pushrod), OHC (direct acting) are limited to 2 valves per cylinder only. SOHC (overhead cam) can use 2,3, and 4 valves per cylinder, while DOHC (dual overhead cam) can use 2,4 and 5 valves per cylinder.
  • Each head type actuates intake and exhaust valves differently. The methods they use to actuate the valves create frictions and has a certain amount of mass to it. Lighter and lower friction heads allow for increased RPM limits.
  • OHV: uses a cam in block. The cam spins inside the engine block, the cam lobes push on metal rods that indirectly actuate valves with rocker arms
  • OHC: uses an overhead cam. The cam spins in the head assembly, the cam lobes directly push the valves.
  • SOHC: uses an overhead cam. The cam spins in the head assembly, the cam lobes use rocker arms to actuate valves. Allows for 3 valves (2 intake 1 exhaust) or 4 valves (2 intake 2 exhaust)
  • DOHC: uses two overhead cams. The cams spin in the head assembly, the cam lobes directly push on the valves. Allows for 4 valves (2 intake 2 exhaust) or 5 valves (3 intake 2 exhaust)
• VVL: Variable Valve Lift. Affects power output and RPM tolerances. Cannot be used on an OHV engine or 5-valve DOHC engine. If you dont know what this means, think of Honda's VTEC system, or Toyota's VVTi system

Based on this family, you can now create individual engines suited to different applications

Setting up a new engine Variant

Now that your new family is set up, you can now begin designing a specific variant of your family, which will eventually go into a car. Most modern cars use quick to manufacture cast internals.

Crank: The crank is what transfers the piston's up-and-down motion into rotational motion. Modern cars still use cast cranks as they are cheap and easy to manufacture. Forged and CNC machined (billet) cranks have higher power and RPM tolerances

Conrods: The connecting rods are what connect the piston to the crank. Cast parts are commonly used, although altering casting techniques can produce a heavier rod with higher power tolerance at the expense of RPM tolerance. The same applies to forged rods, but with a more expensive production process. Titanium rods are only used in the highest performance cars.

Pistons: The pistons is a component that causes the engine to run. In a 4-stroke gasoline engine, the piston follows a 4-step cycle: Intake, where it draws in air and fuel, compression, where the mix is compressed (compression ratio = volume of cylinder when piston is at bottom dead center:volume of cylinder when piston is at top dead center), ignition, where the mix is ignited by a spark, and exhaust, where the resulting exhaust gases are pushed up into the open exhaust valves as the piston moves back up to begin the next intake. Pistons of basic vehicles and older vehicles are made of normal cast material, a heavy duty casting sacrifices RPM tolerance for more power tolerance. Forged pistons are made of aluminium, and are good for higher power levels and higher RPM tolerance. Lightweight forget pistons are made for sky-high RPM limits, at the cost of power tolerance. Low-friction cast pistons are like normal cast pistons, however the cylinder walls are lined with a metal such as sodium which reduces internal friction, thus benefit gas mileage. Hyper eutectic cast pistons are just like cast pistons except they are made with a superior casting material (normally silicon-rich aluminium alloys). Hyper eutectic pistons also have an extra benefit: they are better at sealing the combustion chamber, leading to less unburned gasoline getting in the exhaust, which improves emissions. They are currently the choice material for modern piston engines.

Variant Capacity: Determines the displacement of the specific variant of the engine model. Engine families can have different displacements to suit different needs. For example, Toyota's A-series engine had 8 variants with displacement ranging from 1.3 to 1.8 liters (never mind the combinations of different head types, fuel systems, and induction methods). Smaller bore leads to reduced octane requirements and reduced valve float, at the expense of reduced valve flow. Smaller stroke leads to increased RPM tolerance and smoothness at the cost of losing some displacement. Keep in mind, variant capacity barely affects overall engine weight and has no effect on engine dimensions.

Your engine variant has now taken on enough shape to move on to head design

Head and Top End

Compression: Sets the compression ratio. Higher compression is always favorable, as it increases both power output and fuel efficiency. This comes at the cost of higher octane requirements.

Cam Profile: Sets the profile of the camshaft(s). The cams are thin rods that spin at the same speed as the crank. In OHV engines, the cam is located in the block, and uses pushrods that actuate the valves. In all other engines, the cam(s) is(are) located in the head, and use lobes to actuate the valves. A more aggressive cam profile reduces octane requirement, increases high RPM power, and decreases valve float. It also increases idle RPM. A less aggressive profile makes the engine smoother, improves low end power and more fuel efficient.

VVL Profile: Only available in engine families with VVL enabled. This acts as a second cam profile, and is more aggressive than the first cam profile. At a certain RPM (automatically chosen for optimum performance) the ECU of the engine will change which cam lobes are used to actuate the valves. The more aggressive lobes keep the valves open longer, which is better for high RPM power.

VVT: Variable Valve Timing. Another ECU controlled part, which modifies valve timing to suit the engine's needs. Leads to more power and efficiency at the cost of weight, engineering time and cost. In DOHC engines, VVT can be either used on the intake valves only or all valves.

Aspiration

In a naturally aspirated engine, the air intake sucks in air through a vacuum caused by negative air pressure as air is passed through the box into the cylinders for combustion.

In a turbo engines, things work differently

Setup: Inline engines can only use Single Turbos. V and flat engines can only use Twin Turbos. Turbos are a method that force air into the engine via a compressor. The compressor is powered by the turbine, which is spun (or spooled) by exhaust gases. The turbo type affects spooling speeds and maximum boost. Journal bearing turbos are only used in much older turbo cars from the late 70's and 80's. The shaft of the turbo rotates in a larger hollow tube. The shaft slides directly on the tube, and oil is forced between the two, preventing metal on metal contact. This is cheaper and easier to make than a ball bearing turbo. In the ball bearing design, there are multiple little balls that sit in between the shaft and the hollow tube, allowing the shaft to 'roll' inside of the tube. The lower friction of the ball bearing allows the turbo to spin faster and spool quicker.

Intercooler: The intercooler cools air from the turbo before putting it into the engine. Cold air is denser, and more air leads to more power. A larger intercooler can handle more air and cool it better, leading to power gains

Presets: these presets optimize your turbo design for either 3 purposes. F.E. uses a small, cheap, quick spooling compressor and turbine and low boost to increase low end power, with high low end torque. Race preset uses a larger, more expensive, and significantly more powerful turbo to maximize high RPM power and flatten the torque curve. Performance is a compromise between the two.

Compressor and Turbine: The compressor compressor incoming air, the turbine powers the compressor by being spun by exhaust gases. A smaller setup spins faster but reduces maximum power.

AR Ratio: Area/Radius ratio. This has to do with the internal geometry of the turbo, and that is dependent of the purpose of the turbo.

Max. Boost: Boost is the additional air that is provided by the turbo into the engine. It is measured in PSI - pounds per sq. inch (imperial) or bar (metric).

With the engine now having an air supply, it's now time to configure its fuel system.

Fuel System

The fuel system is what gets the fuel (or air/fuel mixture) into the engine. The fuel itself is vaporized before entering the combustion chamber.

Fuel System types:

• Carburetor: The carburetor works by mixing air and fuel before spraying the mixture into the engine. It does this mechanically. The mixture is sprayed towards the manifold, into the engine through small jets which work by the Bernoulli Principle.
  • Single Barrel: The cheapest fuel system. Very sloppy fuel delivery. This was used in most cars of the 40's and 50's, as well as cheaper cars of the 60's, before the OPEC oil embargo and higher emissions standards of the 70's forced manufacturers to switch to more advanced carburetor systems
  • Single Barrel Eco: Also uses single barrel, however it has a more efficient configuration, at the expense of being forced to rely on lean fuel mixtures (14.2:1 is the maximum ratio). It is only suitable for high-efficiency pre-injection engines.
  • 2 Barrel: A more advanced carburetor, that uses 2 barrels rather than 1. The additional barrel allows for more precise fuel control, increased flow for better power output and fuel efficiency. This system was used from the 50's until the 80's when fuel injection became the new standard.
  • DCOE: Also known as a Weber carburetor (named after its inventor). This 2 Barrel system uses a side draft system rather than the downdraft system present in all other carburetors mentioned above. This carburetor was incredibly popular among tuners of its time. It was also the carburetor of choice for sports cars and supercars.
  • 4 Barrel: The most advanced carburetor available in game. It was common in sports and luxury vehicles. It uses 4 barrels rather than 2 or 1
• Injection: Injection systems work by vaporizing fuel through injection. Early electronic injection worked similarly to carburetors, but modern injection systems inject fuel into the engine independently of the air.
  • Mechanical Injection: Unlocks in game in 1965. This was the original injection system, which historically was also used in military aviation for high power piston-engine fighter planes before the jet engine replaced them. It was invented by the same man who invented the V8 engine configuration in 1908. In 1956 the first production car to have injection as an option was the 1957 Corvette C1, using the 283 (4.7 L) V8. Mechanical fuel injection uses mechanical actuation and vacuum lines to control fuel delivery. There is an injector for each cylinder.
  • Single Point Injection: An electronic system. Also known as throttle body injection or wet manifold injection. This system was used in the 80's and early 90's before Multi Point injection replaced it. It uses a single injector positioned above the throttle body, below the air box. It injects fuel into the manifold like a carburetor. It is the most primitive injection design.
  • Multi Point Injection: An electronic system. Also known as port fuel injection or sequential injection, this system was developed in the mid-80's and is still in use today. It uses one injector per cylinder, positioned behind the intake valve(s).
  • Direct Injection: An electronic system. Commonly referred to as GDI (gasoline direct injection) because it already existed for diesel. This system appeared in the early 2000's for common cars. The injector is within the engine block, directly pointing into the combustion chamber. It is the most efficient system, and most expensive in cost and engineering. This system is commonly used in mid-2000's sports and luxury vehicles but has now become a higher end option for normal cars.

Configuration

The configuration of the fuel system depends on your selection and on your engine block design. For carburetors, the configuration affects the number of carburetors. Performance cars tend to have multiple carburetors, such as Chrysler's 440 Magnum engine, which was available with a triple twin-barrel carburetor setup advertised as the "Six-Pack" by Dodge. For injection systems, the configuration affects the number of throttle bodies. Throttle bodies are plates that regulate airflow. Single-point injection can only have a single throttle body. Mechanical injection has the option of either using a single throttle body or individual throttle bodies (throttle per cylinder). Multi-point and Direct injection can use single throttle body, dual throttle body (on V engines only) or throttle per cylinder.

Intake

This option changed the design of the air intake and cleaner. All fuel systems have access to all intake design, except DCOE (DCOE can only use performance or race intakes). A standard intake uses multiple filters and mufflers for maximum reliability and quietness. A performance intake reduces the filtration and sound muffling for increased performance. A race intake removes all filtration for maximum air intake, at the cost of reliability, leading to high performance.

Fuel Type

• Leaded Gasoline: Leaded gas uses tetraethyl lead [(CH₃CH₂)₄Pb] as an additive. Its an anti-knocking agent, which means it bumps up the octane rating of the fuel. However, leaded gas is extremely dirty, as its emission byproduct is a neurotoxin, and is incompatible with catalytic converters due to the lead byproduct. Leaded gasoline was legally banned in most countries by the 80's, and today is only legal in Algeria, Iraq and Yemen.
• Unleaded Gasoline: Normal gasoline. It is produced from refined petroleum. The octane rating is the rating of the gas's resistance to pre-ignition, high octane means more resistance, which in turn means more potential power and fuel efficiency. Higher octane gas is produced by mixing normal gas with ethanol and other high-octane or anti-knock chemicals. Pure isooctane (2,2,4-Trimethylpentane) is the standard used to measure octane rating, 100 octane fuel has identical knock resistance to isooctane. In most of the world, the RON scale is used. RON is calculated by running the fuel through a 600 RPM test engine with variable compression and comparing the results with isooctane. MON is a modified version version of RON. It is calculated by running the fuel in the same engine at 900 RPM, preheating the fuel, and also varying the ignition timing. In North and South America however, AKI scale is used. AKI is calculated using both RON and MON ratings in the equation (R+M)/2.

Fuel Mixture

The fuel mixture is an air to fuel mixture. A rich fuel mixture allows the engine to remain cooler, reducing required cooling and octane requirements. A lean fuel mixture allows the engine to be more fuel efficient, and reduce emissions. A 14.7:1 fuel mixture is considered chemically stoichiometric. This means the ratio is perfectly balanced according to the chemical equation for the combustion of gas, which demands 14.7 grams of oxygen per gram of gas. In chemical equations involving gasoline, gasoline is always represented by the formula for octane (C₈H₁₈). Therefore the equation is: C₈H₁₈ + 12.5O₂ --> 8 CO₂ + 9 H₂O, assuming a perfect combustion and only pure oxygen is present. Combustion imperfection tends to produce other smaller hydrocarbons, and also produce Carbon Monoxide (CO). Also, because the atmosphere is mostly nitrogen, and not pure oxygen, NO_x (nitrogen oxides) are also present in exhaust gas, although nitrogen has no effect on the reaction.

Ignition Timing

Ignition timing determines how late or early the spark plugs are fired off to ignite the combustion mixture. More aggressive timing leads to higher efficiency and power, and also optimizes the engine for higher power peak at high RPM. Less aggressive timing reduces octane requirements and allows for peak power to be produced at a lower RPM.

RPM Limit

Sets the limit at where the engine stops revving. Higher RPM limit can potentially produce more power as long as enough air can enter the engine at higher RPM. Higher RPM reduces reliability of the engine. The physical RPM limitation of the engine's internal components depend on their material quality, and piston stroke length.

With the engine finally producing power, now its time to finalize it with an exhaust system

Exhaust System

The exhaust system is the system which draws waste gases away from the combustion chamber, and out into the world.

Headers: Headers are what draw exhaust gases from the exhaust valve(s) and into the exhaust pipes. Header selection depends on the purpose of the engine. Older mass produced engines and modern cheap engines use basic cast logs, while modern mass produced engines use better flowing but still quite cheap short cast headers. Other header designs are longer and more complex, and built rather than cast in a mold. These headers are lighter, have better flow and promote exhaust scavenging, an effect where areas of negative pressure are produced outside the exhaust valve, which cause exhaust gases to be sucked out. It is worth noting turbocharged engines can only use short cast headers, as the turbo's compressor is part of the header.

Exhaust: Exhaust setup type. Inline engines can only use single exhausts, while V and horizontally opposed engines can use dual exhausts. Bypass valves are usually installed on sports cars and supercars to allow them to meet noise regulations during normal driving but achieve higher performance by bypassing the mufflers when "race mode" is engaged.

Exhaust Diameter: Exhaust pipe size. Larger pipes allow for freer flow which produces more power, but only up to a certain point. If the exhaust is too big relative to the engine, then the exhaust system loses its ability to effectively push out exhaust gases and the gases just hang around the pipe. Dual exhaust setups tend to have a smaller diameter than single exhaust because each pipe is only responsible for half the amount of exhaust gas.

Catalytic Converter: Only available in unleaded gas engines. These seriously reduce emissions, by reacting with unburned hydrocarbons in the exhaust and making them react to completion, at the expense of exhaust flow. Leaded gas will completely clog a catalytic converter and render it useless. There are 3 catalytic converter designs available, 2-way (worst flow), 3-way (better flow), Hi-flow 3-way (best flow). With better flow comes higher costs and longer engineering times.

Mufflers: Used to reduce engine noise. A reduction in engine noise leads to higher comfort at the cost of exhaust flow. There are 3 muffler designs available, baffled with average noise reduction and airflow, reverse flow with high noise reduction and low airflow, and straight through, which has little noise reduction but high flow.

Now that your engine is complete, its time to see what power it can put down and how it sounds like.

Testing

The final window of the engine designer. It displays (from left to right) the information on the engine's displacement, head type, valve count, and block design. The example here is a 1.5 L Pushrod with 6 valves (2 per cylinder) inline 3 cylinder. Below that, all the information that was previously mentioned on the upper right tab during engine design. On the right are 3 gauges. A power/torque gauge (although a power/torque curve can also be seen above), a vacuum/boost meter (naturally aspirated engines will top out at zero at their maximum RPM, turbo engines will top out at whatever boost PSI has been set), and an RPM tachometer. To the right of that is the throttle slide, which can be manually controlled by pressing the bottom Testing button, or, if the top Testing button is pressed, the engine will automatically slowly rise from 0 to top RPM and back. When doing this you can hear the engine's sound, which is affected by intake type, aspiration type (adding a turbo also adds turbo whine and blow off), and engine block (cylinder count and layout - a V12 will obviously sound different from an I3). If you wish to listen all engine sounds, click on this YouTube link to watch a playlist containing all engine sounds (except for boxer engines). To hear boxer engine sounds press here.

Now that you know the basics of how your choices influence your engine's design and purpose, you can go out there and build the best engines! Have fun!