Introduction[edit | edit source]
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 piston gasoline engines can be created, with diesel 4-stroke and Wankel rotary engines planned for the future. Before explaining the process of engine design, the tab (pictured in Engine Parameters section below) 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 Design Theory[edit | edit source]
In order to get the most out of your engine design, you must have a clear goal for it. Different purposes call for different engine types, which all perform differently. After all, you wouldn't want to try to sell a 1000 hp V12 in what is supposed to be a simple economy car, or try to make the best out of a small I3 inside a giant truck.
Theoretically, the perfect engine has a perfectly flat torque line rather than a curve, and its power output rises in a linear fashion in accordance to torque and RPM (using the horsepower equation: hp = RPM×T/5252). Of course, the perfect engine cannot exist, but it is still possible to get as close as possible to the ever elusive flat torque line. Usually, the engine's torque curve appears to be a rounded wave shape, with a hump in the mid-range of its RPM range, and a drop-off at the high end. Naturally aspirated and turbo engines have their differences, but provide a similar shaped torque curve, although the turbo engine has a sharper wave shape with a more defined peak once boost pressure is built up. Where the torque peak takes place is what seperates a run-of-the-mill passenger/utility engine from a performance engine. In a regular car or utility truck, it is best to have a high torque peak in the low RPM range (1500 to 4000 RPM) with a moderate RPM limit. This is done in-game by having a low cam profile and a sightly restrictive, quiet exhaust system. This low torque peak ensure highest possible efficiency and a linear power delivery. It also allows the engine to be only used in the low RPM range, thus improving reliability and fuel economy for the driver. Using a low cam, quiet exhaust, and standard air intake also promote drivability and comfort, due to the lack of noise and vibration.
In performance applications, high power takes a priority over high low-end torque. Because power output is a function based on RPM and torque, as stated in the hp equation, it is best to have peak torque at mid to high RPM range, and the engine's RPM limit itself maxxed out to the highest value the engine can take. To keep high-end power as high as possible, a high cam profile, less restrictive air intakes, and high-flowing exhaust system are used. Drivability and comfort of a quiet, smooth engine is sacrificed in exchange for higher power.
Engine Parameters[edit | edit source]
- 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. When running, the engine experiences primary and secondary motions. These motions come as a result of the pistons going up and down. They can be cancelled out by the inherent cylinder layout and firing order, or by the use of balancing weights and shafts. 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 or 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[edit | edit source]
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 April 2019, there are 4 inline setups (I3, I4, I5, I6), 3 60° V setups (V6, V8, V12), 3 90° V setups (V6, V8, V10) + 1 DLC/Legacy owner exclusive (V16), and 2 horizontally opposed boxer setups (H4, H6). More layouts are planned as either additions to the core game or as DLC items, such the I2, I8, H2, H8, H12, 90° V4, 72° V10 and R1, R2 and R3 (Wankel rotaries). 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 375 cc, 500 cc and 625 cc per cylinder (23, 30 and 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)
- Head Material: affects weight, cost. Higher cost if head material differs from block material.
- VVL: Variable Valve Lift. Affects power output and RPM tolerances. This is done by offering two different cam profiles, allowing the engine to gain a flatter torque curve, optimizing both low-end torque and high-end power. Profile switch-over is set automatically by the game. Cannot be used on an OHV engine or 5-valve DOHC engine. If you dont know what VVL is, think of Honda's VTEC system, or Toyota's VVTL-i system
Based on this family, you can now create individual engines suited to different applications
Setting up a new engine Variant[edit | edit source]
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 and easy 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 torque 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 high end super/hyper 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 torque tolerance. Forged pistons are made of forged aluminium, and are good for higher torque levels and higher RPM tolerance. Lightweight forget pistons are made for sky-high RPM limits, at the cost of torque tolerance. 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. Low-friction cast pistons are like hyper eutectic cast pistons, however the cylinder walls are lined with a metal such as sodium which reduces internal friction, thus benefitting fuel efficiency by reducing friction losses. 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[edit | edit source]
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 camshaft(s) are metal rods with lobes machined on them that spin at half of the speed of the crankshaft. In OHV engines, the camshaft is located in the block, and uses pushrods to actuate the valves. In all other engines, the cam(s) is(are) located in the head(s), 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 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. 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[edit | edit source]
In a naturally aspirated (NA) engine, air is fed into the engine for combustion via diffusion. During the intake stroke of the engine, a vacuum is produced by the piston going down from top dead center. Through the process of diffusion, air rushes in to fill the vacuum, and restore a near-atmospheric pressure within the cylinders. This air is then mixed with fuel, compressed, and the combustion takes place.
In a turbo engines, air is taken in by the intake and fed through a compressor. The compressor, which is powered by the turbine (which itself is spun by passing exhaust gases), compresses air. The compressed air passes into the intercooler, where it is cooled down and further compressed, due to the higher density of cold air. The cooled, pressurized air, is fed into the cylinders, allowing for more air to be used for combustion.
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. 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. Due to game limitations which are to be fixed via a future revamp of forced induction, the most effective turbo tuning strategy in game is quite unrealistic.
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). Higher boost means more air, which in turn means more power. This comes at the cost of higher internal pressure, which reduces the engine's reliability and raises octane requirements.
With the engine now having an air supply, it's now time to configure its fuel system.
Fuel System[edit | edit source]
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.
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.
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.
The fuel type used in the engine can affect various parameters of the engine, most importantly the engine's performance potential. Fuel type itself has no effect on the engine performance. A fuel with higher octane rating is less likely to knock, meaning the engine using higher octane fuel can be pushed to higher limits. Fuel itself, known as gasoline in North America or petrol in Europe and Oceania, is a mix of various hydrocarbons (CnH2n+2), ranging from pentane (C5H12) to octane (C8H18). The difference between lower grade and higher grade fuels lies in the hydrocarbon content, with higher quality fuel being less volative and prone to pre-ignition due to higher percentage of larger hydrocarbons (such as heptane [C7H16] and octane). In Automation game, as of 2019, only gasoline/petrol is available. Diesel is a potential future addition, as a DLC.
- Leaded Fuel: 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 in exhaust fumes. Leaded gasoline was legally banned in most countries by the 80's, and today is only legal in Algeria, Iraq and Yemen.
- Unleaded Fuel: Common, everyday fuel. It is produced from refined petroleum, refined through a process called fractional distillation. 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.
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 usually represented by the formula for octane (C8H18), although it can also be represented by the generic alkane (saturated hydrocarbon) formula CnH2n+2. 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, NOx (nitrogen oxides) are also present in exhaust gas. NOx is produced due to the presence of O2 and N2 in the atmosphere, combined with the high heat of combustion withine the engine cylinders. NOx is not involved in the combustion of fuel.
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.
Sets the limit at where the engine stops revving. When the engine reaches the set limit, fuel is cutoff to prevent the engine from revving beyond this limit. 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 (which is seperate from the RPM limit set by the slider) depend on the weight of the internals, and piston stroke length.
With the engine finally producing power, now its time to finalize it with an exhaust system
Exhaust System[edit | edit source]
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 devices reduce emissions, by catalyzing the burning of unburnt hydrocarbons, and catalyzing a reaction between O2 in the air and CO (Carbon Monoxide) present in exhaust fumes (due to partial combustion). Leaded gas will completely clog a catalytic converter and render it useless. There are 3 catalytic converter designs available. The earliest design, used in the mid to late 70s is the 2-way catalytic converter. The 2-way catalytic converter catalyzes two reactions: oxidation of CO ( 2CO + O2 → 2CO2 ) and the oxidation of unburnt hydrocarbons ( CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O ). The 2-way catalytic converter has the poorest airflow. The 2-way cat design was abandoned upon the advent of the 3-way catalytic converter, in the early 80's. The more advanced, better flowing, 3-way catalytic catalyzes a third additional reaction, the reduction of nitrogen oxides (NOx) emissions into N2. NOx gases are a known precursor to acid rain. The reduction of NOx is a more complicated, 3 step process:
- 2 CO + 2 NO → 2 CO2 + N2 Carbon monoxide and Nitric oxide react together to form carbon dioxide (less toxic than CO) and nitrogen gas
- hydrocarbon + NO → CO2 + H2O + N2 The unburnt hydrocarbon is combusted with nitric oxide in order to form carbon dioxide, water and nitrogen
- 2 H2 + 2 NO → 2 H2O + N2 Hydrogen gas and nitric oxide reacts together to form water and nitrogen gas
The final design of catalytic converters is a higher flowing design of the 3-way catalytic converter. This version of the 3-way cat is useful in performance cars that need free flowing exhaust, but is a useless expense for a common car
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[edit | edit source]
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!