by lh7018 » Sun Jun 27, 2010 11:47 am
The best way to do this would be to actually fill it with a known volume. By that I mean remove the head button, install a glow plug, and turn the button bowl side up. Support it the best you can to ensure it is level. Get a small piece of clear Lexan (sometimes called Perspex) big enough to cover the combustion chamber and drill two small holes, one in the center and another about 2-3mm away from center, each hole about 1- 1.5mm or so in diameter. Put a very thin film of grease on the O.D. of the bowl and place your Perpsex on top. The grease film is to seal the Perspex to the bowl. Next, get a small graduated syringe with a total capacity of around 2 cc's, fill it with alcohol or even model fuel, and bleed the air out. Then, with the syringe, slowly fill your combustion chamber through the center hole you drilled in the Perspex until all the air is pushed out of the second hole (which will be acting as a vent) and the combustion chamber is full. Looking through the clear Perpex it will be easy to see when there is no more air (bubbles). Once the chamber is filled, read the graduations on your syringe to see the volume it took to fill the chamber. That will give you the combustion chamber (head button) volume. It obviously will also include the glow plug volume so you will get a more accurate compression ratio calculation once you plug the numbers into your program. This method works for all button shapes and sizes. It's probably best to repeat the procedure about three times or so to confirm your results. Hope this helps.