The big difference is in the camshaft, the 12/52/52/12 cam being fitted GA1HE - GA164889HE (and for some strange reason, GA177973HE - GA187000HE) and a batch of GB1He - GB2700HE. The later 18/58/58/18 cam gives 48bhp (or 51bhp in the 12/50 with better exhaust manifold and downpipe and was also fitted to Mk1 Spit giving 63bhp on twin SU's and 9:1 compression ratio) in 1147cc engine, and is the one used in 1296 Heralds as well. (And Toledos, Dolomite 1300 as well I think).
Haynes also suggests a change from 8:1 to 8.5:1 CR in 1200 engines from GA190341HE, but some of their number overlap, so I'm not convinced there were 8:1 engines with later camshaft. Certainly no different power output was quoted between 39 and 48bhp. (But then Triumph didn't advertise this power upgrade in the Herald, nor the significant improvement in Vitesse 1600 output in mid 1965!)
Just about all other 1200 Herald engine components are the same, including distributor and carb jets, so changing the camshaft, or fitting a later engine if you need one, would give a useful boost to your Herald. A 1200 estate will never set the tarmac alight, but the extra power can help to NOT be an embarrassment on a motorway. (Fitting the 12/50 manifold and downpipe is also a useful upgrade, making the car less strained above 60mph as it revs a little more freely).
Chris Taylor, 16-Sep-2006, 01:11pm on TSSC
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