I checked closer, high compression was actually 8.8:1, and low was 8.0:1. It
was by pistons top, flat or dished, and compression pressure is 160 lbs/sq.in
for HC, 130 lb/sq.in for low compression. (Page 47 in The Complete Official MGB
1962-1974, note that data from 18G and 18GA is carried over into later engines,
unless otherwise stated in General Data section for the later engine. I'm not
sure where 18GH fits, I have general data for GB-GG, then it jumps to 18V, and
for 18V high compression is 9.0:1, low is 8.0:1, pressures stated at 170
lb/sq.in reguardless of compression ratio, which doesn't seem right.
Distributor 41228, which you have, is designated for high compression, and
should not give 30 degrees of advance anywhere (except including static of 10
degrees). Your curve should be:
0 - 6 degrees at 600rpm
4 - 9 degrees at 700rpm
7 - 11 degrees at 900rpm
13 - 17 degrees at 1600rpm
18 - 22 degrees at 2200rpm
Vacuum advance will give you additional 20 degrees or so maxium
If you are setting stroboscopically, the book states 13 degrees BTDC at 600rpm
for both high and low compression, so at 2200rpm you should have all the advance
in (with the vacuum line off) and anywhere from 21 to 35 degrees advance. I'd
go with the advance until it pings under load, then back off a little method
(with this much admitted variability on the part of the manufactureer).
Sorry to keep flooding the list with info.
Phil Bates
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