Tuning and Modifying Engines Putting together this little slideshow to make it easier for anyone who is trying to build a custom engine and doesn’t know about all the parts and what they do. This will include what changing the values in the sim will do to your engine. This is just to get you started modifying an engine. You will need to delve into the parts files as well to properly modify it. Soon I might write up another one going through the parts library as well. Don’t expect this to be pretty lol, I know engines not how to make a pretty pdf or programming. I’ll try to keep it simple and straight forward. If something is off or hard to understand feel free to dm on discord @damo in the server. Useful Links • Compression ratio calculator https://www.omnicalculator.com/everydaylife/compression-ratio • Tuning exhaust length https://www.musclecardiy.com/performance/exhau st-system-performancemath/#:~:text=Primary%20Tube%20Length&text=Fo r%20example%2C%20let's%20say%20that,%C3%B7 %204%2C200%5D%20%E2%80%93%203). • Exhaust scavenging (cylinder) https://help.summitracing.com/app/answers/detail/ a_id/4794/~/the-scavengingeffect#:~:text=How%20does%20it%20work%3F,of%2 0low%20pressure%20behind%20it. Kohler_ch750.mr Found in assets>engines>Kohler • I’ll start with the Kohler engine as that’s what most people will run into when they first use the sim. • THIS ENGINE WILL NOT BE ABLE TO SHIFT THROUGH GEARS, IT DOES NOT HAVE ENOUGH POWER • Throughout the vast majority of this, you’ll just be changing the number values in the code unless you are crafting a different configuration engine. • Starter torque and speed are used to first start the engine. These will not affect the performance of it once it is running, but in engines with high compression they may need to be increased. • Redline is the maximum RPM of the engine, in this line of code it changes the redline on the gauge in the sim, it doesn’t affect the engine. However, it is also the rpm the dyno will end your run at. Crankshaft • Throw is equal to half of stroke (4 inch stroke = 2 inch throw. Most specs online will give you stroke not throw). However, in this version it already divides this value by 2 with the / 2 at the end of the line so just enter the stroke value here. • Increasing stroke will increase your displacement/size of the engine. • Displacement is the volume of air inside the cylinder that is swept by the piston. Engines are described by the displacement of all cylinders ie. In an 8 litre V8, each piston sweeps one litre of air. • Larger displacement engines produce more torque and more horsepower if set up correctly, but they tend to not rev as high. • Mass is the weight of the crankshaft. a lighter crank will rev quicker in neutral and higher • TDC is top dead centre, when your piston is at the very highest point of its travel, closest to the head and valves. Theoretically when the spark plug should fire. • Light rotating assembly = Quick/high revving Pistons • Here, the mass is just the weight of the actual piston by itself, when it is not connected to the connecting rod. • A lighter piston will be able to rev higher/quicker • Blowby occurs when a slight amount of gas slips past the piston rings into the crankcase. This is for realism in the sim, in a perfect engine you would have zero blowby. • Compression height is the distance from the centre of the wrist pin (connects the piston to the con rod) to the very top surface of the piston. This can be increased to increase compression ratio. • Displacement is whether the piston is dome or dish shaped. A dome will increase compression, a dish will decrease compression. • High compression ratio = More power Connecting Rods • Connecting rods or conrods connect the piston to the crankshaft. • A lighter rod will allow your engine to rev higher. • Dw about the moment of inertia and centre of mass lol • The length of the rod determines the piston speed while the engine is running, which will in turn affect the speed that air is entering and exiting your cylinder. Tuning this is a bit of a science and you are better off to trial and error it or use existing rods found online that suit your engine. • Light rotating assembly = Quick/high revving Cylinder Dimensions • The bore is the diameter of the cylinder that the piston sits in. • Increasing this will increase your displacement slightly and have the same effect as increasing throw. • Deck height is the distance between the centre of the crankshaft to the top of the block where the head bolts on. • Decreasing this will increase your compression ratio as there will be less space between the head and the piston when it is at TDC. • High compression ratio = More power Intake • Plenum volume is the volume of air inside the intake manifold. • Increasing this will give smoother torque across the rpm range and more torque in high rpm. • Intake flow rate is basically how much air can get through the intake at wide open throttle. • More air flow = More power, higher revs • Idle flow rate is the rate of air getting into the engine at idle, increasing will make the engine idle at a higher rpm and decreasing, the inverse. Will not affect power figures but may affect how the engine starts and runs. Exhaust • Outlet flow rate works like intake flow rate. • More air flow = More power, higher revs • Primary tube length is the length of the exhaust tubes before they merge into a collector. This can be tuned to produce horsepower at a specific rpm range. It produces this power through exhaust scavenging. Refer to the useful links to calc it. • Velocity decay is the speed that the exhaust gases slow down in the exhaust. Changing this will affect the scavenging effect of your primary tubes. Not worth modifying. Cylinder Banks • Cylinder bank angle will change the angle the cylinders are in relation to each other. -45 degrees to the left, +45 degrees to the right = 90 degrees apart which is what the vast majority of V configuration engines are, including V8s. Camshaft lobes • Lobes are the sort of oval shaped part of the camshaft that open and close the valves • Duration is the degrees of rotation that the lobe is contacting and opening the valve. • Almost all camshaft specs have an advertised duration and duration at 50 thou • Duration at 50 thou is the degrees of rotation the cam is opening the valve after it is opened 50 thousandths of an inch. • A longer duration cam lobe will hold the valves for longer, allowing more air to enter and exit the cylinder. This can allow for more horsepower, torque and rpm • Lift is the total distance that the lobe opens the valve, allowing more air to enter earlier and later. • Lobe duration and lift require fine tuning and it is worth googling existing aftermarket cam specs to suit your need Camshaft Specs • Lobe separation is the degrees of rotation between the intake lobe and the exhaust lobe. • A smaller lobe separation will cause the valves to overlap (both open at the same time for a very short period). • This takes advantage of the scavenging effect (refer to useful links). • A V8 with larger cams will have a rough idle and lopey sound due having a small lobe separation angle (around 106) • LSA can generally range from 104 to 118 degrees. • In this sim, base radius purely changes how the cam looks when the program is running. It does not affect performance. Heads • Here, the chamber volume is the amount of air that can be trapped within it’s combustion chamber. It is not related to the size, stroke or displacement of the cylinder • Think if you flipped a bowl upside down on a flat surface, the volume trapped inside would be your combustion chamber. • Decreasing this will increase compression ratio. • High compression ratio = More power Timing Curve • THEORETICALLY, the spark should fire at TDC, when the piston is closest to the valves however, that is not always the case. • It takes a small amount of time for the spark to fire and then ignite the fuel which finally needs time to burn and spread. • This all happens in an instant to us but remember the piston is moving at very high speeds • So the spark timing is advanced slightly to allow for this small amount of time • As the piston starts moving faster (at high rpm) the spark needs more time to ignite the fuel so we make that happen earlier and earlier as the piston moves faster and faster. • Eg at 1000 rpm, the spark is advanced 12 degrees and at 2000rpm, it is advanced 20 degrees • This is done with a timing curve. A timing curve is needed for most engines, but in particular, high rpm engines.
