> I would like to start an on-list discussion of octane, timing and
> performance.
> I have a stock 1971 TR6. I currently run premium gas, which is
> what is recommended.
I'm surprised at that ... with the lower compression, more modest cam, and
poorer breathing, I would have thought a stock US-spec TR6 would run fine on
regular.
> With all the vacuums, etc attached I time
> it at 8 BTDC.
So your vacuum retard is not working then ? Or do you have a non-US-spec
TR6 ?
> No ping, runs great.
> My understanding is that lower octane gas burns faster and a
> little hotter, but at 20 cents/gallon cheaper it is tempting to
> switch to the lower octane and retard the timing until it doesn't ping.
Should be no problem, as long as you're sure it doesn't ping or knock under
any conditions. I've broken several pistons on an engine that only knocked
at cruise (due to worn valve guides).
> Any thoughts? What are the down sides? Has anyone done this?
Downside is poorer fuel mileage (and poorer performance), also more of a
tendency to overheat. There's also a definite limit as to how far you can
go ... you may find that it takes so much retard to prevent knock that the
engine won't run well at all.
> Am I missing something?
Might be worth pointing out that there are many different methods used to
rate 'octane' or anti-knock properties; and they give different results. I
don't know what method was in common use in the UK by 1971, but ISTR a TR3
manual that specifies "research" method, which gives a higher "octane
number" than the "R+M/2" method used in the US (by law).
Randall
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