HS - 9:1 to 8.7:1?

[ChrisG]

Good day all,

A question, if I may, and apologies if it has been mentioned in the forum before…..

Looking at Service Bulletins in the AOMCC knowledge base, No 109A lists the ‘54 model Scramble HS comp ratio as 9:1 and then No 114, lists the ‘55 model as 8.7:1?

Looking through the manuals, before all the big changes for ‘56, the only combustion space parts to change between 54/55 models, was the exhaust valve/guide and the piston….1661-54 to 1661-55. This later piston was used from then on, and labelled in the parts as ‘9:1’.

I know this is not life changing, and may not appeal to most, but I am really trying to understand the minor differences in the HS models.
So, was this a subtle change by Ariel to assist longevity of components, cylinder bases or fuel quality, etc. or, did the technical department, simply make a typo..?

Any info / thoughts would be gratefully rec’d.

Cheers,
Chris