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In this section we will take a look at what happens in the combustion chamber. This will include valves, cams, pistons, etc.

Combustion Chamber Volume
Static Compression Ratio
Amount to Mill

Combustion Chamber Volume

The only way to legitimately measure the size of your combustion chamber is to "oil" it. And again, it is imperative to get all the combustion chambers as close as possible in size.

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Static Compression Ratio

First on the agenda is Compression Ratio. What is it and how do you compute it?

Compression Ratio is the relationship between your cylinder volume and the volume in your combustion chamber. If you actually cc'd your engine at Top Dead Center (TDC) and Bottom Dead Center (BDC), you could compute your Compression Ratio from those two figures.

The basic formula for computing the Compression Ratio is:

                           Displacement  times  Combustion Chamber Volume
   	  Compression Ratio =  ------------------------------------------------
                                     Combustion Chamber Volume
      

Click Me to compute YOUR Engine Compression Ratio

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Amount to Mill

The most common way of altering your compression ratio is to mill a certain amount of material from your head. This formula is based on the relationship between the stroke of your engine and the old and new compression ratios. As we already discussed, compession ratio is based on the stroke of your engine and the combustion chamber volume. If you mill your head, you alter the combustion chamber volume therefore changing your compression ratio.

Now, from examining many computer simulations, we have found that one of the biggest bangs for your buck is to increase your compression ratio. One other important note here is that if you change your compression ration to much, a change in gasoline octane may be called for. That issue will be dealt with in a future addition to this page.

For example, our '71 Triumph started life with a 9:1 compression ratio. With the Morgo 750 kit, this is increased to 9.5:1. The compression ratio we would like to achieve is 11:1. The stroke of a Triumph is 3.23 inches.

Using the above data and the necessary formula, we find that we need to mill 0.080 inches from the head.

One final note. PLEASE make sure that any machine work your have done on your head is done be a competent and experienced machinist. Mistakes here can be VERY costly!

Click Me to compute HOW MUCH TO MILL from your head to change compression ratio

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