Modern Engine Blueprinting Techniques. Mike Mavrigian
In a nutshell, run a shorter rod for the street or whenever low-end torque is the priority and run a longer rod where you want peak torque to occur higher in the engine RPM band.
Keep in mind that some rod, crank stroke, and piston CD combinations don’t work or are impractical due to clearance constraints or unavailable piston compression heights.
Rod ratio refers to the relationship of the rod length to the crankshaft stroke. Theoretically, a higher rod ratio produces more torque at peak RPM, and a lower rod ratio produces more torque at lower RPM.
Depending on the type of engine being built, there is a target range for rod ratio. So, a higher rod ratio for racing and a lower rod ratio for street performance seem to make sense.
Here’s the formula for calculating rod ratio.
Rod Ratio = rod length ÷ crank stroke
For example, you have a rod length of 5.700 inches with a 3.000-inch stroke. Using the formula:
Rod Ratio = 5.700 ÷ 3.000
1.90:1
Computer Software
Computer software doesn’t build an engine. Machining and assembly skills are still required for the build itself. However, software related to engine building can serve as a tremendous aid in your quest to design and, in some cases, test a virtual engine build combination. These programs allow you to experiment with various engine component and dimensional combinations. That gives you theoretical performance insight into horsepower and torque via different bore and stroke combinations, cam profiles, cylinder head and intake flow, rocker arm ratios, and more.
Most programs include handy calculations that allow you to plug in various data and obtain quick answers, so you don’t have to perform the math on your own. This type of computer program allows you to play “what-if” games by trying different combinations of components.
For pro engine shops that utilize CNC equipment, highly sophisticated programs are available for digitizing, designing, and machining individual components. This type of program (Mastercam, etc.) applies only to design and machining processes and are highly technical in nature. They are not discussed here.
The following manufacturer list includes programs suited to the needs of the enthusiast. It does not, however, include “games” designed to let you play drag racer, oval track racer, or road racer. I’ve limited the findings strictly to those that apply specifically to the process of engine component selection, engine math, modifications, and dyno simulation. They each have different capabilities. The information here should save you time and aid in your selection of various component and dimensional choices.
Comp Cams
The Desktop Dyno 5 software program is reportedly designed to apply to any four-cycle engine, ranging from four-cylinder to twelve-cylinder applications. It has an interface capability that provides a series of DirectClick menus. This permits the selection of specific components and the ability to enter parts with custom specifications.
A series of built-in calculators includes a CamMath Quick-Calculator, Induction-Flow calculator, and an Air Flow Pressure-Drop calculator. Test combinations are illustrated with detailed graphs that display projected horsepower, torque, volumetric efficiency, and engine pressures. The program’s automated testing tool provides additional support as you attempt to determine optimum component combinations. Another useful feature is a combustion chamber modeling program. Windows 7 compatible.
ProRacing Sim
The DynoSim5 is a Windows-compatible program designed to try out your engine build in a virtual state. According to the manufacturer, this software package allows you to experiment with simulations of a variety of build platforms, including forced induction (turbocharging, supercharging, and nitrous injection).
Additional features include ignition curve modeling and rocker arm ratio calculation. The DynoSim5 is also designed for program updating online. A CamDisk8 supplement provides data applications for more than 6,000 camshafts. A specific cam profile can be selected and added to your virtual engine build for testing and simulated dyno results.
The Dynomation-5 Wave Action Engine Simulation is an advanced engine simulation software. It illustrates live pressure waves and airflow through the cylinders and engine passages. In addition to providing horsepower data for a given combination, the wave action program provides a 3D cutaway engine view that illustrates airflow, intake and exhaust port pressures, and velocity according to the cranskshaft angle.
The DesktopDyno5 offers a host of simulation features. (Photo Courtesy ProRacingSim.com)
This program provides an aid in analyzing intake runner length, volume, and shape in conjunction with cylinder head flow and variations in camshaft profile. Windows 7 compatible.
Challenger Engine Software
Challenger offers three programs suitable for engine design and analysis: Virtual Engine Dyno Professional, Dynamic Compression Ratio Calculator and Camshaft Selection Utility, and Engine Builder 3D. They are only available by purchasing website downloads. All are compatible with Windows 95, 98, 2000, NT, XP, or Vista.
A sample screen display from Virtual Engine Dyno Professional.
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