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General & Tune

Compression ratio

Value
8.2:1
Alt
9.0–9.5 earlier
Applies · US-market 1000 cc, 1980–early ’80s
US-market 1000 cc machines were dropped to 8.2:1 for emissions from 1980, and the 1981 US R100 is the canonical example. Not a blanket rule. BMW's own figures for the US /7 range four years earlier were R60/7 9.2:1 · R75/7 9.0:1 · R100/7 9.1:1 · R100S 9.5:1 · R100RS 9.5:1 BMW-TD77 — so the drop is a 1980-on, 1000 cc, US-market event, not a property of American bikes generally. Market is part of the specification here: European machines of the same model year did not all follow, and later 1000 cc airheads use other ratios again — the R100GS/R100R era is commonly quoted at 8.5:1. Read the ratio for your exact model, build date and market rather than assuming the year decides it.

This is the book's general row. In the book, pick your model and year and this figure resolves to your machine, with the one-page torque sheet, the job pages and the printable booklet.

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