Looking for a number

[Plechtan]

I have been through the FAQ section and can't seem to find the amount of combustion volume you lose for rvery .010 you mill of the head. It should probably be added to the head FAQ. So does anybody know?

[tomcat]

let's assume the head's diameter is 4" and not a dome for "easy" math.

4" x .01" = .04 cubic inches
.04 inches is 0.1012 cc's

6 cylinders give you either .24 cubic inches
or
.6072 cc's

that, or i am way wrong

[eastin82]

*For each 0.010" milled from the block deck (or taken from head gasket thickness) to reduce quench height, the combustion volume decreases by ~2.0ml and the CR increases by ~0.2*.
thats found on dino's stroker page
http://www.jeep4.0performance.4mg.com/stroker.html
not sure how that converts to cc's but i hope it helps

[PolloLoco]

1cc = 1ml

2cc is correct.

4in diameter = 10.16cm diameter
pi * (10.16cm/2)^2 = 81.07cm^2

0.01in = 0.0254 cm
81.07cm^2 * 0.025cm = 2.06cm^3 or cc

2.06cc * 6 cylinders = 12.36cc = 0.75in^3

Now that 2.06cc is assuming a 4in diameter, which is only for the gasket. IIRC the head is somewhere between 3.905in and 3.935in (I remember that because boring 60 over makes the cylinder bore larger than the opening of the cylinder head). Doing the math for a circular cylinder head with a diameter of 3.91in I get 1.97cc. So let's just say it's somewhere around 2cc per cylinder.

tomcat:
You need to find the area of the circle first (pi * r^2), multiplying in by in will only yield in^2, not in^3.

[SIXPAK]

I think Pete is asking about the cylinder head milling not the block or head gasket here. The combustion chamber is not round so you will not loose as much for every .010 removed from the head as compared to the block or head gasket. Maybe I'm wrong about what he is asking though.

[Plechtan]

The combustion chamber shape is not a circle, it is more oval, and not 4" in either dimension. I think it is about 3,9" across and the width varies from about 2.5" to probably around 2". You can't use the area of a circle to calculate this. I would have assumed that somebody has a kind of a rule of thumb, like the combustion chamber is 66% of the size of a 4" circle,

By the way CC and ML are the same thing,, so if taking .010 off the block reduces the volume by 2ml ( 2cc) and the combutstion chamber is 66% ( for example) of the area of the cylinder, than milling the head .010 would only reduce the volume by 1.3 CC. I have no idea if the 66% number is close or not.

For now we can say that the number is more than 1CC and less than 2CC

[John]

Peter, I think you will find .007 removed from the head will reduce the chamber volume 1 CC.
John

[tomcat]

tomcat:
You need to find the area of the circle first (pi * r^2), multiplying in by in will only yield in^2, not in^3.

mmmmmmmmmmmmm pi





on the right track though

[PolloLoco]

The combustion chamber shape is not a circle, it is more oval, and not 4" in either dimension. I think it is about 3,9" across and the width varies from about 2.5" to probably around 2". You can't use the area of a circle to calculate this.

For now we can say that the number is more than 1CC and less than 2CC

That's why I assumed a circular cylinder head of 3.91in, it makes the math easy. A lot of engineering is assumptions and approximations.

Yeah, I should have made it clearer, my mind tends to think things that I don't say. Between 1cc & 2cc per cylinder seems to be a good approximation.

Isn't there a way to measure the volume that involves mineral oil? Maybe you can tell us the real answers before and after.

[Cheromaniac]

Peter, I think you will find .007 removed from the head will reduce the chamber volume 1 CC.
John

That's right. If you shave 0.010" from the head, the combustion chamber volume is reduced by 1.4cc.

[John]

Thanks for the back up Dino
John

[shockcocker04]

my math says 1.4cc as well

[1bolt]

The reason there's no agreed rule of thumb around here Pete is almost no one is actually trying to ADD compression, most builds are trying to keep it managable for pump gas.

I wonder if you'll have to remove so much that as you get closer to your compression goal you'll reach area's of the combustion chamber where the cross section is dramatically smaller? You should probably cc the head before and after the first couple cuts to make sure you're somewhere around 2.8 less cc's then cc the head again if you get close enough to the roof of the chamber that the cross section is smaller with every cut. Of course I say this not knowing your piston/dome.

[Plechtan]

I will be using a flat top piston, 0 deck height. My combustion chamber is about 62 cc right now. Many of us seem to increase the chamber size when putting in oversize valves, so even on a standard stroker it may be desirable to reduce the size back to 56 cc or so.

I was also thinking of what Rick Mudge told me, that the smaller the combustion chamber, the more power you will make. His thoughts were that you should dish the positon more rather than increase the size of the chamber. He says he proved this with the Hill dragster.

It would be interesting to build a pump gas stroker, and try this out, I am not sure how much you can take off the stock head without getting into trouble.

[John]

It would be interesting to build a pump gas stroker, and try this out, I am not sure how much you can take off the stock head without getting into trouble.

Conversation with the folks at Hesco put this number at .125, and they do not recommend removing that much.
John