I was trying to calculate the compression ratio and after doing a lot of estimating, I had a broad idea where it would be but I realized that there really is no way around actually ccing the head to find a more realistic number. I found that it can be done yourself without spending very much money.


HOW TO: CC YOUR COMBUSTION CHAMBER

Materials

1. Liquid (Best to use something slightly thicker than water and colored)
2. 60 ml Syringe (1ml=1 cc)
3. Petroleum Jelly
4. A piece of plexiglass

I decided to use some water wetter + water since it was laying around.


Clean the subject combustion chamber using solvent, clean shop rag, air pressure etc. before you begin. Install the spark plug you will be using.


Apply the petroleum jelly to the cylinder head surface around the combustion chamber to create a seal with the plexiglass.


Put the plexiglass on the cylinder head and make sure it seals to the surface.


Cover the chamber except for a small amount at the end where you will fill the chamber with liquid.


Fill the 60ml Syringe with liquid to 50ml or any starting amount, making sure you get all the air out.


Fill the combustion chamber slowly. Move the plexiglass around to get any bubbles out if necessary.




Carefully fill the chamber until you can just slide the plexiglass over the liquid with no air bubbles.
Now your combustion chamber is full.


Subtract whats left in the syringe from what you started with and that's the size of your combustion chamber. I would recommend repeating a few times just to verify results. For a more exact result a lab pipette could be used.

Here's a quick Static CR Calc for my particular build. The piston-to-deck height was measured at about 0 so the volume was negligible. In this particular application the head was milled .020" as well. CR should be between 11.55:1-11.65:1.

 

Nice write up.

If you don't have water wetter or coolant lying around. A mixture of water, food colouring and alcohol works very well. The alcohol reduces the surface tension of the fluid. Another hint would be instead of filling it from the side and sliding the plexi over. You could try drilling a hole in the center of the plexi so that you don't have to move it once it's sealed in place. Remember to CC all 4 chambers as they may differ slightly.

 

Nice write up, thanks for posting this. I was searching around yesterday for a good article/post on this. I found a couple but not many with good pics.

 

very good information -- thanks

 

OMG tech....

 

Very nice write up.
Newbie question here. Where did u get the .00025 and the Gasket volume thickness = .74 ?

 

Thanks alot for this DIY
I saved it in my favorites.

 

win.
saving this page for when the internet goes boom

 

Glad this is helpful!




A good question. Since it seems people are going to be referencing the calcs I adjusted them so they are easier to understand. The .00025 I was using is just a condensed version of the area formula multiplied by the cubic mm to cubic cm conversion. ((Pi)*((d/2)^2))/1000=0.00025

Also OEM headgasket range is 0.660mm-0.740mm. I adjusted the thickness to .660mm which would be the smallest crushed thickness. But anywere within that range the CR won't really vary much.


Here is a good compression calculation thread for more info:https://honda-tech.com/forums/all-motor-naturally-aspirated-44/diy-compression-ratio-calculation-2476094/

 

Nice write up!