[ROVERNET - UK] Re: Rover P5 compression ratio and fuel

Aidrian Bridgeman-Sutton smokeandsteam at gmail.com
Fri Aug 10 17:13:53 BST 2007

> > I believe the 8.75 ratio is more common on the LHD export MkII 4spd and
> > MkIII's, but I'm not sure of that.
> >
> > If the pistons have been replaced, then the compression ratio may have
> > changed...
> >
> > 8.75 pistons probably require 89 or 93 octane depending on where the
> > spark is set.

IIRC Rover expected premium (100 Research Octane ) fuel for the
3-litre, but retarding the spark will let it run on what passes for
premium these days

The big issue in the long term will be that they were intended to run
on leaded petrol and valve seat recession may be an issue unless you
do something about it. Unfortunately the F head makes it a bit more
complicated than just whipping off the head and adding hardened
inserts; a fuel additive might be a worthwhile investment


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