CC'ing the Cosworth Vega Cylinder Head

One of the key elements of an engine "blueprint" is the matching of combustion chamber volumes in the cylinder head(s).

If all cylinder volumes are equal, compression ratios will be equal, and the engine can be "tuned" for maximum power.

If combustion chamber volumes are unequal, maximum power will be compromised. Different chamber volumes mean different compression ratios and thus unequal power in each cylinder.

Detonation will occur in the cylinder with the highest compression/smallest volume before the remaining cylinders develop maximum power.

The parts and equipment list we assembled to CC our Cosworth Vega cylinder head (Tonawanda # 648) is short:

1 50 cc glass burette

1 6 x 6 x .25" Plexiglas plate

1 electric or cordless drill

2 drill bits: 1/8" and 1/4 ".

1 pint denatured or isopropyl alcohol

1 Pyrex two cup kitchen measuring pitcher/beaker

Red and/or blue food coloring

1 stirrer

1 eyedropper

1 tbs. Vaseline

1 pencil

1 piece of paper

Paper towels


Drill a 1/4 inch hole in the center of the Plexiglas plate. Center the plate over a combustion chamber in the head and mark a location for and drill a 1/8" hole in a "corner" of the combustion chamber. This will be the bleed hole to allow air to escape during the filling process. Make sure that you use the 1/4" bit to chamfer and clean the burrs off the underside of the 1/8" hole, otherwise once the air bubble gets small it will hang up on the burrs and refuse to bleed through the hole.


Mix several drops of red or blue (or both) food coloring with a cup of the alcohol that has been poured into the Pyrex measuring container. Stir thoroughly and set off to the side.

Spread a thin layer of Vaseline around the circumference of the combustion chamber. Gently but firmly press the Plexiglas plate down onto the Vaseline, observing carefully.
Installing the Plexiglass Plate
You will be able to see the Vaseline seal to the Plexiglas, and you will be able to see where air bubbles remain.
Slide the plate around to spread the Vaseline evenly and to accomplish a seal completely around the perimeter of the combustion chamber. You will need to press forcefully in different places to achieve this seal. Once the seal is obtained, break it by removing the plate and wiping away any excess Vaseline that has extruded into the combustion chamber. Then reinstall and reseal the plate.

Next, fill the burette with the dyed alcohol.

The meniscus line

Fill it past the 0cc point, and using the burette's valve, drain the contents back into the Pyrex beaker until the bottom of the meniscus just touches the 0cc line


Move the burette over the 1/4" hole and open the valve to begin filling the combustion chamber.


The nozzle in the burette is tiny, to facilitate accurate measurement (if you want incredible accuracy, check it out ), so it can take up to a minute to fill the chamber. Be patient.
As the combustion chamber fills, you will see the trapped air bubble decrease in size. A helper is handy, but not necessary at this point. The cylinder head will need to be lifted and tilted in order to keep the center of the air bubble under the vent hole. Continue filling through the fill hole just until all of the air has been forced from the combustion chamber through the vent hole.

 Filled Combustion Chambers

Once full, close the valve of the burette and read the new volume, again using the bottom of the meniscus, and write it down.

This is your combustion chamber volume.

Pour the remaining contents of the burette into the Pyrex beaker, and lay or stand it safely and securely out of the way. Do not drain the tip.
Carefully remove the Plexiglas plate by sliding it away from you. Once the liquid is barely uncovered, use the eyedropper to suck it up and return it to the Pyrex beaker. When most of it has been recovered, remove the Plexiglas completely, wipe off the Vaseline with a paper towel, and then use the towel to absorb the few drops remaining in the combustion chamber. You will have to turn the cylinder head over to drain the alcohol from the spark plug.
Repeat the entire process for each combustion chamber.
If you are adventurous, you can cc the piston depressions in your flat top pistons. You just need a plate with four properly spaced 1/4" holes, and a modicum of patience and care

Kevin Connair
"CC'in" The Piston Voids


When you are done with all of your measurements, pour the alcohol back into the original container and store it in your garage. Then wipe out the Pyrex measuring beaker with a clean paper towel, surreptitiously place it in the dishwasher, and maintain an innocent look on your face.