Head Combustion Chamber Volume - CC'ing

[stelz]

Hi Guys,

I'm getting back to the engine assembly and have measured the volume of the head combustion chamber with the following method:

1. valves are installed after grind / lap with springs
2. insert spark plugs
3. invert head and level with spirit level
4. apply film of grease around perimeter of valves
5. apply film of grease around head face to achieve seal to perspex plate
6. place and seal the perspex plate with hole over chamber being measured
7. fill and measure volume of methylated spirits added to chamber (syringe)
8. repeat for all cylinders


What is surprising is that the measured volumes were between 39.0 and 39.6cc which is higher than what I have read elsewhere as standard. I am fairly sure my head is full thickness, but still...

The only things I can think of that may cause these readings are leakage past valves (seems unlikely and I didn't get any drip through), volume in spark plug shouldn't be included (I thought should be included) or valve cut dropping valves (seem ok to me).

Any ideas on this or if my readings are too high?

Cheers,
Ben

[rgh0]

Those readings are pretty normal for a full thickness head at 4.640 inches.
I typically see around 39 cc for a full thickness head and around 36 to 37 cc for a Sprint head ( at 4.600 inches thick)

The readings can vary due to different valve head shapes (how dished they are) and position in the seats ( how recessed they are) and the original machining of the head and combustion chambers.

If there is any significant leakage past the valves while testing you should be able to see it in the ports. I tend to use degreasing solvent or kerosene rather than metho as it has a lower evaporation rate and its coloured so easier to see if it leaks

cheers
Rohan

[stelz]

Cool - I just wanted to check that this was reasonably possible as I am fairly confident in the measurement.

I'll set compression ratio (10:1) off smallest chamber and purchase head gasket thickness to suit from Steve at Lotus Marques.

Ta,
Ben