Austin 850 performance conversion

[DomMINIque]

3) Cylinder volume from the crown to the top of the block = area x measured height (in other words 1/2 bore squared x PI x measured height). For this measurement the head obviously has to be off the block so one can take measurement. I haven't done this on my engine because I use my car as a daily driver. I've taken the measurement on another standard 848cc engine. I'm hoping this will be close enough. In fact if anyone thinks this is a mistake and I should rather take the measurement on the actual motor, I'll have to do that. For the time being, here are some measurement pics

This measurement was 0.017" which is 0.4318 mm. Using the formula above, the volume above the crown up to the top of the block is 1.354 cc

I don't have any experience in engine building so this comes with warning.

But I don't think it would be necessary to actually change to using the actual head as I don't believe the differences between parts would make such a significant difference even if you have to consider manufacturing tolerances into account.

Based on your calculations you've got 1.354cc.

If you do this these are the results:

Lets assume that your motor currently being used as a daily has a slightly greater crown to deck height - lets use 0.5mm for arguments sake. This is 13.6% difference in measurement. This is a rather large difference in terms of engine tolerances from my limited knowledge.

(0.5 x 62.94mm)^2 x PI x 0.5 = 1.555cc

In this case you end up with a 12.92% increase in volume of the area.
Already here we can see that this is a exponential function based on the increase in measurement results in a non equal increase in volume.

Nevertheless we'll test it in the other direction as well.

In a hypothetical situation your daily uses pistons that were made on a Monday/Friday that are 0.1 mm longer than usual resulting in a 0.3318mm crown to deck height. This is a 23.15% decrease in actual measurement.

(0.5 x 62.94mm)^2 x PI x 0.3318 = 1.032cc
This results in 23.78% decrease in volume. Again illustrating the exponential effect but this time due to the fact that it is in the opposite direction the opposite result occurring. Some maths here that everyone always ask when they will actually use this in real life bla bla. (For anyone that is interested go and have a look at the properties of an exponential function)

In summary (and some plain English) I realistically, even with the mini's strange build history, I don't think your measurement between your actual motor and the other you've used to take measurements from is going to be 20% different.
And even if it is so significantly different the result would only really be 0.3cc in error (at a 25% error margin).

This works out to a total of (0.3/848) 0.035% of the total volume. And I don't think this would even affect your compression ratio calculation by even a value of 0.1.

A whole long story to basically say that I personally think the measurement you've taken for this is sufficient and it wouldn't be worth the effort stripping the other motor just for this right now.