Measuring Combustion Chamber CC

[Morris]

I wanted to add this to the Wiki, but was unable to register. If any of you can help me in that matter, I will appreciate you greatly. The article follows:

This is a "budget" procedure for measuring the volume of your combustion chamber based on advice given to me by the incomparable Hap Waldrop. Combustion chamber volume is a critical measurement needed to calculate compression ratio. https://www.csgnetwork.com/compcalc.html

Materials you will need:
1) A syringe marked in CC or ML. 1CC = 1ML. Hap recommended a feeding tube syringe, which typically come in 60-70CC sizes and cost a few dollars. The drug store around the corner from my house did not have any, but they gave me a 5ML syringe for free.
2) Wood shims (usually available from the hardware store for a few dollar.
3) A piece of plexiglass (or similar) large enough to cover one combustion chamber. This is also something you can get from the hardware store for a few dollars.
4) Grease or Vaseline.
5) Rubbing alcohol.


First you will need to place your head upside down on your workbench and level it as best you can. The wood shims will help you get the head level. Drill two holes in the plexiglass so that they will be on opposite ends of the combustion chamber when it is covered by the plexiglass. Smear Vaseline or grease on the surface of the head around the chamber you will be measuring (I use Vaseline because it is less messy). Cover the chamber with the plexiglass pushing the plexiglass firmly against the head so that the grease forms a seal. Fill the syringe with alcohol to its measured capacity. Using one of the holes you drilled into the plexiglass, slowly inject alcohol into the chamber until you can see no more air bubbles. If you have a large syringe, simply subtract the amount of alcohol from the amount you started with and that is the volume of your chamber. If you have a small syringe as I did, you will have to track how many times you empty the syringe into the chamber, then subtract the what remains in the syringe after the final injection and add it all together.

 

[SilentUnicorn]

Thanks for the information. I have never done this. Sounds easy enough tho. One question - What do you do if they are not all the same?

m

 

[Morris]

Cry... :wink:

Mine were in a range of roughly 36-37.5. I am guessing that is due partially to the imperfection of the measurer, and partially to the imperfection of the head casting. I guess if I were a perfectionist, I could mill a little off the pistons to get everything equal then re-balance the engine. That will not be happening by the way. Maybe Hap will weigh in on this.

 

[nomad]

You won't have any trouble finding syringe's large enough at a vetrenary supply or vets office. Don't forget the displacement above the piston. Piston dish, distance below the deck, and head gasket thickness.

Kurt.

 

[SilentUnicorn]

Cry... :wink:

..

No doubt there.

The way i see it , if it is off i would look at the parallelism of the head and make sure the head had not been cut at a taper. Or ..can you <span style="text-decoration: line-through">adjust</span> tweek the depth of the valves slightly to compensate? 1.5cc seems like a lot. 1.5cc = 23.129 drops

m

 

[JodyFKerr]

John Twist of University Motors did a video on this recently.

Here:

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Jody

 

[Hap Waldrop]

It's almost impossible to do this with piston dish in the block, because the the block is almost never level on engine stand and the deck height is negative, meaning the piston sticks down into the block.

You can ask for feeding tube syringes, and they will hold alot more volume.

As for pistons dish volume, I try to do that on my piston before they ever go in the block.

This is not terribly hard task, but you may want to double check yourself a couple of times, don't be alarmed is one combustion chamber varies a 1-2 CCs, these engine were never that exact in stock form.

 

[nomad]

I agree Hap, for everything other than the head and piston dish math is the easiest way. It doesn't have to be exact in most case's anyway.

Kurt.

 

[dklawson]

Not that this matters but the home method I have used for years is a little different. Not saying it's better... just different.

I use those shims mentioned above to intentionally angle the head on the workbench. I use a Plexiglas cover with only one hole and I position the hole at the "top" of the chamber once the head is angled on the bench. When you fill the chamber up, the fact that the single hole is at the high point helps get all the air out. I repeat the measurements about 4 times and average the results.

I also do this by putting Vaseline on the valve seats to provide a seal rather than fitting the springs. That way I can easily remove the valves to "touch up" the smaller chambers and bring their volume up closer to the largest chamber.

 

[JPSmit]

This months Practical Classics talks about measuring combustion chambers as part of an article on porting and polishing.

 

[58Custom]

Also, alcohol with some food dye is a much better medium than coffee. Alcohol has very little surface tension compared to water so it's easier to get out bubbles. If you are gonna try to CC a piston in the block, a thicker medium will dome up held at the edges of the dish due to surface tension and give a false enlarged estimate. Coffee has solids so it is thicker and, as clearly seen in the vid coffee gets foamy, which will lead to a false low estimate.

You can get 25mL, 50mL or 100mL syringes without dangerous and delicate needles at any animal supply store.

A single hole in the plexiglass plate is fine. Don't use glass unless you plan on interrupting your progress to clean up broken glass at some point. I mean, how many glass tools do you have in your tool box?

Hey, if I can do it...

 

[Guest]

Cry... :wink:

Mine were in a range of roughly 36-37.5.

You have flat tops?

If so that's ~ 9.5/6-to-1.

 

[racingenglishcars]

fwiw, I used glass, one hole, angled head, but also what I've never heard before, I used antifreeze as a medium.

Morris: "Mine were in a range of roughly 36-37.5."

Is this a typo error. I don't know what head you have. The various head chambers range from 21.4 to 28.3cc and are reduced by approximately 1/2 to 3/4 cc for each 0.010" skimming.

 

[Morris]

1500 combustion chambers are roomier than the cockpit.

 

[Hap Waldrop]

I use green rubbing alcohol, and I do this often, no Acme Speed Shop engine or head gets built without this getting done.

I notice no one has talked about caculating how much you cut off your head once you know what you have. Here's what I do. I first step is get the CC volumes of the uncut head, I run those number with all the data in a CR cacualtor, there are several ones online you can use, then I start entering less combustion chamber volumes in the caculator until I reach near my CR traget, now with the head leveled on the bench , I inject the volume into the chamber the cacualtor told me would get to my CR targer, then I use a depth micrometor, say for example I had 30cc (just round number) on stock uncut head and in the caculator when I entered 20cc (again, just round number) I hit my CR target, I put that amount of liquid inthe leveled chamber, no need for the palxiglass at this stage, I then use the depth mic and slip on the setting extednign deeper to i just break the surface oif the liquid, and then I double check it, say it takes .020" to reach theliquid and after rechecking i see that number repaet, then Ok, i know I need to take .020" off the head to get to my target CR.

OK with all this being said I seen so many novice engine builder mess this up, due to they don't follow the proper sequence, you should have your bottom end built, all your piston dish volume, compressed head gasket thickness,and deck height number salready documented, and then and only then resurface the head the final amount to hit your CR target. One must follow the ocrrect sequence, or you can bet you get into trouble, i seen it too many times from people that were new to this type of performance build, sequence is everything. Building a performance engine is like playing chess you always have to be thinking about next 5 moves, if you're learnign as you go, you real likely to mess up. Most of the higher perofmance novice A serie engine builds I have witnessed have all been tail-chasing exercises, because the buiders were not experienced in the proper sequence of such a project.