Garage - Engine

The engine is probably the most discussed and modified element in a drag racing vehicle. IHRA allows extensive modification of the engine and components.

The engine simulation technology uses a gas dynamics model developed by Motion Software" for their Desktop Dyno" software. The following items can be modified:

Induction: The Induction menu allows you to change the airflow into the engine. Flow ratings range from 300 cfm 2bbl carburetors to 1100 cfm 4bbl or 8bbl (or multiple carburetors) for pre-defined configurations. You can also type in a custom flow.

Manifold: Select from various intake manifold types. An intake manifold is the pathway for the incoming air (and fuel if non-fuel injected). Generally, the smoother, larger and more tuned an intake is, the more power that can be produced.

Fuel: Selects the type of fuel being used. Various types of fuel combust differently and produce different power results. Most dragsters run on racing gasoline or on alcohol. You can also select from Nitrous Oxide and Nitro-methane as fuel additives.

Header: This item specifies the exhaust manifold or header configuration. There are a variety of configurations to choose from. Generally the larger and more tuned the exhaust is, the more power that can be produced.

Head/Port: The head design and porting type affect the way the fuel is mixed and the exhaust is pushed out. For high power, port and valve size should be as large as possible.

Valve Diameters: The Valve menu allows you to choose from several "standard" sizes, or you can have IHRA automatically calculate the optimal value sizes. Valves should be as large as possible for optimal power.

Compression Ratio: The compression ratio is a comparison of the volume that exists in the cylinder when the piston is located at BDC (bottom-dead-center or the lowest point in the stroke) to the "compressed" volume when the piston reaches TDC (top-dead-center or the highest point in the stroke). The compressed ratio can range between 6:1 and 16:1.

Bore/Stroke: This is the size of the engine. You are presented with many pre-built configurations, but you may also select a custom configuration by inputting your own data. The larger the engine, the more power that can be produced.

Camshaft: There are several pre-defined configurations for camshaft type, configuration and timing. If desired, the user can input the valve events in either the 0.050-inch lifter-rise or the seat-to-seat methods.

Advance/Retard: This is an offset to represent the camshaft timing. The timing of the cam can be adjusted to occur later or earlier in the stroke of an engine. You can use this to move the torque and horsepower curve up or down the RPM range.

Lifter: The lifter is the connection between the camshaft and the valves. In general, the roller-type lifter produces more horsepower.


Turbochargers and superchargers are called "blowers," "boost devices," or "power adding devices." These devices work by compressing and forcing more air into the intake system. This allows more fuel to be added and effectively raises the compression and power of the engine. Adding a boost device can easily increase the power output by 50%.

Superchargers are driven off the crankshaft by a series of belts and pulleys or gears. Boost is instananeous and available through the RPM range of the engine. However, superchargers require a significant amount of horsepower from the engine (sometimes up to 40% of the engine's power). Superchargers are also very susceptible to damage from an engine backfire. Turbochargers, on the other hand, are driven by the high-energy exhaust gas that is normally wasted. Because turbos are driven from the exhaust gas and must be spun up to an RPM that allows sufficient boost pressure, there is lag before the horsepower builds. Either device is a quick and fairly inexpensive way to build horsepower.

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