Does anyone have any nifty ways of measuring the true volume of an engine's cylinder?

[Stretch]

Dear All,

I've just discovered something - the cubic capacity of an engine refers to the sum of the swept volume or displacement volume of each cylinder in an engine. So this is simply defined as the area of the bore multiplied by the stroke.

It doesn't include dished surfaces in the head or the piston crowns.

Timing adjustment methods

http://en.wikipedia.org/wiki/Engine_displacement

But how could I measure or calculate the true volume of each cylinder?

Does anyone know? All of the handy engine calculators on the internet assume that you know the volumes of the dished surfaces in the piston crowns and the head to start off with.

With an engine in bits I could fill complicated surfaces with oil and then measure the volume of the oil tipped out of them - but there would be errors due to surface tension (and probably other things). This would also be a pain in the backside.

I have also had trouble measuring by how much head gaskets get compressed when a head is fitted and torqued in place. I know these parts of the engine are only going to contribute small amounts but all the same I'd like to make accurate measurements if I could.

So does anyone have any tips? Has anyone heard of any hair brain ideas that can do this?

[bobodaclown]

valve adjustment will also have to be taken into account. liquids don't compress, hence bending a valve when the cylinder is filled with a fluid (water/coolant/oil) and is rotated.

[Matt L]

If you know the swept volume and the compression ratio, you can compute the unswept volume.

Valve timing affects how much air actually goes through the engine, but that has nothing to do with displacement or compression ratio. These are computed as if the engine were ideal.

[W124 E300D]

Simple trig is good enough for a good enough approximation.

If you want an accurate measure then you need to make up jigs and start weighing displaced light oil of known density / temperature etc etc

3.14 x (radius squared) x stroke is good enough even for engine machine shops.

edit, cos I wrote Pi x d... doh

[whunter]

Originally Posted by Army

Dear All,

I've just discovered something - the cubic capacity of an engine refers to the sum of the swept volume or displacement volume of each cylinder in an engine. So this is simply defined as the area of the bore multiplied by the stroke.

It doesn't include dished surfaces in the head or the piston crowns.

Timing adjustment methods

http://en.wikipedia.org/wiki/Engine_displacement

But how could I measure or calculate the true volume of each cylinder?

Does anyone know? All of the handy engine calculators on the internet assume that you know the volumes of the dished surfaces in the piston crowns and the head to start off with.

With an engine in bits I could fill complicated surfaces with oil and then measure the volume of the oil tipped out of them - but there would be errors due to surface tension (and probably other things). This would also be a pain in the backside.

I have also had trouble measuring by how much head gaskets get compressed when a head is fitted and torqued in place. I know these parts of the engine are only going to contribute small amounts but all the same I'd like to make accurate measurements if I could.

So does anyone have any tips? Has anyone heard of any hair brain ideas that can do this?

Virtual automotive tools/data
Virtual automotive tools/data






.

[Stretch]

Originally Posted by whunter

Virtual automotive tools/data
Virtual automotive tools/data






.

Thank you very much a great collection of resources.

[leathermang]

You are being ' squishy ' with your wording...and need to tighten it up..
I said in the other thread that ' engine size' is the area swept by the top of the pistion.
That compression is the total combustion chamber volume .. that piston sweep PLUS the amount of space above that ... the max at BDC compared to the total at TDC gives the compression ratio...

but your question about the volume of the head itself... ( assuming some dome ) is that you take it off and turn it upside down.. and titrate water into it... measure the amount of water in the container before dripping into the head... and subtract... ...
This is how equal volumes were produced in race engines.... metal was ground off safe areas until all the head volumes were equal.....

[Stretch]

Originally Posted by leathermang

You are being ' squishy ' with your wording...and need to tighten it up..
I said in the other thread that ' engine size' is the area swept by the top of the pistion.
That compression is the total combustion chamber volume .. that piston sweep PLUS the amount of space above that ... the max at BDC compared to the total at TDC gives the compression ratio...

but your question about the volume of the head itself... ( assuming some dome ) is that you take it off and turn it upside down.. and titrate water into it... measure the amount of water in the container before dripping into the head... and subtract... ...
This is how equal volumes were produced in race engines.... metal was ground off safe areas until all the head volumes were equal.....

Squishy I am - squishy I have nearly always been - it is one of many failings. I'll try and do better!

[Stretch]

I've been doing some calculations to see the effect of my engine rebuild on the swept volume and the compression ratio.

My engine has been re-bored and fitted with over sized pistons. The bores are now 91.5mm

I've calculated the clearance volume of a standard engine using data from the FSM and the information given on wikipedia:-

http://en.wikipedia.org/wiki/Compression_ratio

Here is a step by step re-working of the equation (each new line is a step to obtain the final formula)



Vc is the clearance volume, Cr is the compression ratio, and Vs is the swept volume

Using this formula I got a value of about 150 cubic centimeters of clearance volume.

Using the new dimensions of the re-bore (same stroke!) I've now got a 3038cc engine instead of a 2998cc engine.

Assuming that the clearance volume did not change during the engine rebuild I've come up with an estimation of the new compression ratio => I think it is now 21.26:1 instead of a 21:1

So my conclusion? (Considering it was an inconvenient unexpected engine rebuild)

...Well at least I now have a larger engine with a slightly higher compression ratio!

[layback40]

Originally Posted by Army

Using the new dimensions of the re-bore (same stroke!) I've now got a 3038cc engine instead of a 2998cc engine.

Assuming that the clearance volume did not change during the engine rebuild I've come up with an estimation of the new compression ratio => I think it is now 21.26:1 instead of a 21:1

So my conclusion? (Considering it was an inconvenient unexpected engine rebuild)

...Well at least I now have a larger engine with a slightly higher compression ratio!

Now Army, dont let all the extra power from the higher compression & capacity get out of hand !!!

[Stretch]

Originally Posted by layback40

Now Army, dont let all the extra power from the higher compression & capacity get out of hand !!!

Heady times indeed - I'll see ya at the stop light!

[leathermang]

Originally Posted by layback40

Now Army, dont let all the extra power from the higher compression & capacity get out of hand !!!

Ok.. since we had a some physics stuff in the other thread... and I do know you are kidding.. ( ignore the amount )...
Others should remember that increasing the compression ratio does not increase power...
UNLESS
More fuel is added... and may decrease available power if the heat from compression was already sufficient to completely burn the fuel in the proper time span... you would be talking MORE load ( ... and without added fuel.. less power NET ).....

[Cr from Texas]

Originally Posted by leathermang

but your question about the volume of the head itself... ( assuming some dome ) is that you take it off and turn it upside down.. and titrate water into it... measure the amount of water in the container before dripping into the head... and subtract... ...
This is how equal volumes were produced in race engines.... metal was ground off safe areas until all the head volumes were equal.....

I gave my race engine building friend (currently holds a Bonneville record) a buret out of the lab to do this. But he doesn't titrate with water. He uses oil.

[leathermang]

Originally Posted by Cr from Texas

I gave my race engine building friend (currently holds a Bonneville record) a buret out of the lab to do this. But he doesn't titrate with water. He uses oil.

LOL, easier to clean up using water... if your valves seat well enough to hold water... he may be using oil for that reason....or he just likes the smell of it..?

[Cr from Texas]

Originally Posted by leathermang

LOL, easier to clean up using water... if your valves seat well enough to hold water... he may be using oil for that reason....or he just likes the smell of it..?

The one time I watched, the engine was on a stand and pretty much assembled. He titrated a cylinder with the piston at bottom and rotated the engine so the spark plug hole was the high point. The titration to full gave him the total displacement of the entire volume (including gaskets). I assume he may have had some concerns about rust if he used water.