can you help me find the comp ratio of my engine or tell me how to find it my sckools shop is pretty smaill and we dont have the liqiud tester to find it

bored ,040 block
stock crank and connecting rods (429)
17cc dish pistons
c8 heads
block not decked

 

It is important to "CC" or verify the volume of your heads properly. I just dont rely on factory specs. I have seen heads with a factory 91CC rating in excess of 100 CC's after verification (couple sets of D2's come to mind). If the heads were milled or the seats were ground then you may have some issues that could make your build less than stellar.
Yours should be 96 CC's, but I would wager that this might be slightly different for the above reasons.

Your shop does not have this equipment? Thats easy, make your own. You will need a few houshold items, and some stuff that you can get at your school. Make one or two, and donate one to the school, and keep one for your own tool box. Every engine builder needs one of these precious tools, and you are not any different.

Ok, you will need a sheet of lexan, but plexi glass will work. This will have to be about 6 inches by 6 inches (enough to cover the combustion chamber entirely). Usually a nice thick piece works best, as a thick piece will not flex and can provide a more accurate measurement. Typical thickness is 1/4 inch or better.
This lexan will require a small hole placed on the edge of the combustion chamber itself I like to place them just above the spark plug hole. I do this because centered holes dont allow me to get all of the air out of the chamber. Its often difficult to get the water to flow through larger quench areas anyway, and once you do the air bubble usually splits anyway, and it requires some patience and some startegic tapping on the glass to bleed the chamber. So you have a hole above the spark plug hole, and you will tilt the head at a slight angle to make the hole the highest part of this whole contraption. Only slightly though. It does not take much as the aor will travel to the highest spot in a hurry.
Easy so far right? Sure it is.
Next you will need some way to seal the chamber to the lexan or plexi. Some regular old transmission jelly, or light grease, or even Vaseline. This will be spread around the surface of the head to create a water tight seal once you place the lexan over the combustion chamber.
Next you need some method of measurement. You can obtain a syringe that might carry as much as 140 CC's. These will have graduations on the side and can be accurate enough to accomplish your goal. Where do you get one? Well, you could try an animal hospital. Many large animals can take this volume of medication so this is a good place to start. Mention your intentions so the vet does not think you are doing some bad things that might require this much volume. People tend to go a little nuts when you ask for a syringe. You dont need or want a needle for this, just the plastic syringe so you can measure some volume.
I bet if you head over to see the science geeks, they can offer some form of measurement device that would suit you. You may talk the professor into lending you a burette. This is actually the proper tool for this type of work. This would be the most accurate, but these tend to get broken in a shop environment. They are not cheap, so be carefull. They are nice but not 100 % necessary for this. You can get by with the syringe.

Now you have a flat plate of lexan that the plastics and metals shop made for you. You have a hole in it. You borrowed or otherwise obtained a device that stores an accurate amount of water. You have your Vaseline so you are off to the races.
Seal the plate to the head surface and fill the combustion chamber up. I like to use a level to verify that my head is flat and is not tilted too bad, though we did say that it might require a slight tilt to bleed. I know that I will have to tap on the thing to get the air bubble out, but the level shows that you are paying attention to detail and will impress the chicks. Looks like you really know what you are doing this way.
Right,,,,,,, back on track. Fill the combustion chamber and document how much water the thing takes. Move on to the next hole, and in a matter of 15 or so minutes you will have your data.
Keep a good log because you will be doing it again after the heads have been machined.

Good Luck and see if the shop teacher will give you some extra credit for donating such a quality measurement device..........




Holy smokes. I probably assumed a bunch and probably should add a couple of things.

You will have to work with clean and usable heads. These should be machined and about ready for use. This measurement verification is used to verify that each cylinder is equal. Often times some additional machining will have to be done, and you will again verify that the volume is still correct.
Any carbon or other contaminant will not produce accurate results. You will build a fairly accurate device, but it is only as accurate as your prep work.
Also use a spark plug that you intend to run. This is required to fill the psark plug hole, and since plugs can have a different dimension, you can have a negative affect on your data, so use the same type of plug that the engine will be using.
Same is true for valves etc.
Guess I could have mentioned some of this earlier, but hopefully the instructor can point you in the right direction.