Increasing compression ratio?

[mox]

While head is off 4 cylinder Series 2 motor, am considering having engine reconditioner shave some metal off to increase compression ratio. Am interested in comments from those who have done this or changed from a head with 7:1 compression ratio to 8:1. Presumably with the latter, should be a small increase in power and improvement in fuel economy. Also, if shaving the head, how far is it worth going increasing compression before benefits are outweighed by problems created including knocking? Keeping in mind that want to use the common 91 octane petrol.

[incisor]

Is it shallow thermostat housing head or the earlier deeper thermostat housing head ?

You can not shave the early head...

[mox]

Is it shallow thermostat housing head or the earlier deeper thermostat housing head ?

You can not shave the early head...

As Australian assembled in 1961 it originally would have had the early type head. Below it what is obviously original bottom end but among notes in workshop manual that came with it, head was replaced in 1975. It also has a Series 3 manifold -which has partly self destructed although probably less inclined to than earlier ones. Future project to look into extractors, which I gather are on your S2. Bought a skirted thermostat for a spare before realising I had the later head and that they use conventional ones.

From talking to a Land Rover specialist who is my main parts supplier, I gather that very little if any can be shaved off the early type heads - apparently because of lack of clearance under where thermostat setup is on them

[JDNSW]

The early 7:1 heads do not have enough metal to safely shave a significant amount off. Later ones can, but check whether it already has been done or was 8:1 to start with.

The distinguishing feature is that the later type head has a square boss about 15mm across cast into the top of the head, outside the rocker cover, and opposite the carburettor. This should (but not always does) have an "8" if it is an 8:1 head. 7:1 heads either have a "7" or are unmarked. The numbers are stamped and may not be very clear. I have seen references claiming that the newer heads can be safely skimmed to 9:1, but I think you would need to run on higher octane fuel for that to work. For 8:1 you may need to run on 95 or 96 octane to avoid having the ignition set so retarded that you lose a lot of the benefit.

A modest increase in compression from 7:1 to 8:1 will give a noticeable improvement in power or a little better fuel economy if you don't use the extra power, provided the ignition timing is adjusted to suit both the compression and the fuel used. There will be a slight reduction in tractability at very low engine speeds.