[Healeys] Octane ratings

[Bob Spidell]

Depends on what you mean by "better off."  In general, you can use the lowest 
octane-rated gasoline that prevents engine knock (the rattling noise you'll hear 
under load--e.g. lugging or climbing a grade--if the octane is too low). 
Knock--aka detonation or ping--can be very damaging to an engine over time; an 
occasional rattle probably won't hurt.  Some Listers get by with regular 
87-octane (R+M/2), some--like me--use premium (in CA, that's 91 R+M/2).  Or you 
could split the difference and use mid-grade.  Make sure your timing is set and 
advances correctly, then try the two (three) grades.  Unless your engine has 
higher than normal compression, premium with no additive will probably work just 
fine; esp. if your static compression is at/under 170psi or so.

Protecting the valve seats is a different topic.  Under normal driving, it's 
probably not going to be an issue; exhaust valve recession has proven to be less 
of an issue than originally thought (ZDDP anyone?).  You can throw in a bottle 
of 'lead substitute,' though I wouldn't bother and just plan on pulling the head 
and installing hardened seats and alloy valves if/when they start to leak.

BTW, you get no "boost" from using higher octane gas.  The energy content is 
actually higher in lower octane gas (it burns faster therefore releases a 
stronger 'explosion').  You only need the higher octane to prevent detonation in 
higher compression engines (which do give you a boost).


bs


Paul Leeks wrote:
> I wonder if I can get some advice re the type of petrol for my BN4.
> 
> Over the last ten years I have used standard unleaded (Octane 95 RON) along
> with Castrol Valvemaster Plus which claims to provide an octane boost.  (I
> have non-hardened valves/seats.)
> 
> So my question is ... would I be better off using super unleaded (Octane 97
> RON) plus the CVP or will this make me 'over-boosted'?
> 
> Many thanks
> 
> Paul Leeks
> BN4
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Bob Spidell           San Jose, CA            bspidell at comcast.net

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