"Engine Blueprinting"


The Engine Analysis Program

Part 1

Initial Documentation:

Using the Head clearance gauge that is available from Rossi Sales of America (901)396-7485, carefully measure the stroke of the engine. Also the head clearance of the engine as it comes. Write down this clearance in thousandths. Using a depth micrometer or a good set of calipers (MSC has good digital calipers cheap) ($80.00)(800-645-7270), measure the depth of the head from the flange on the head to the bottom of the squish band (the depth the head protrudes into the liner). Measure WITH the head shims in place. Add the previous two measurements together to get the measurement of "top of the liner to top of piston". This is a primary input item for the program. Using the head clearance gauge

Disassemble the Engine:

Completely disassemble the engine and inspect all parts for machining flaws. Measure the diameter (bore) of the liner with a good set of calipers.

Measurement of the exhaust and intake ports:

Holding the liner in your hand insert the piston and rod into the liner and using a very high intensity light, find the place where the piston closes EACH port. Measure the depth from the top of the liner to the top of the piston at each of these closing points. It will be easy to see when the light goes out, looking through the port and moving the piston up. It is very helpful to have an extra set of hands helping you here, as these measurements are VERY important (ACCURACY!). The exhaust port is usually slopped, so it is necessary to use the light method. Input these numbers into your program and the timing of the engine as it came stock is shown. Remember that the boost port is the intake port(s) opposite the exhaust and the side intakes are the transfers. After you have this documentation it is time to decide what kind of timing you want for your engine. I can tell you my personal preferences. But in the end, you will have to decide what works best for you. There are MANY considerations. How heavy is your model, what is your driving style, etc. My models are always light weight and I like to drive VERY close to the buoys. I use intake ports with timing of 126 to 128 degrees on ALL my engines of all sizes. I use exhaust timing on my .21 engines (183-185), .45 engines (185 -188), .67 engines (183-188), .80/.90 engines (187-192). If your model is heavier, you will want to preserve a larger part of the "low end power" of the engine, thus LOWER the exhaust timing..

On your spreadsheet, set up a line (under the line which you have documented the engine in stock form) to show the engine in modified form. The intake ports will have to be set initially. I input exactly the same measurements on the line below the stock measurements and start changing the top of liner to top of piston measurement, until I get the INTAKE timing I want. The amount I have changed the top of liner to top of piston measurement, is the amount I will have to turn off the UNDERSIDE of the liner flange to lower it to get the intakes where you want them. Note: Be careful that you don't lower the liner enough that you let the bottom skirt of the piston be higher than the bottom of the exhaust port at TDC(Sub Piston Induction). You DO NOT want this condition as it takes away from low end power. In some rare instances, you will have to make a liner shim to raise the liner to get the intake timing where you want it. VERY RARE that you have to raise the liner. This takes care of setting the intake ports....... Next the Exhaust Port Timing and the Shape of the Exhaust Port.

Another FINE source for any serious 2 cycle engine builder is a book authored by Dr. Gordon Blair, a researcher and one of the foremost 2 cycle experts in the world. This is the ultimate technical guide available.
The Blair book & software can be purchased from SAE (Click Here

ENGINE Analysis Software for the Serious RC Competitor



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