Hmm, my observation would be that the compression reading is rather
higher than one would expect. This would correlate with pinging. When was
the head off last? You may have carbon buildup in the combustion
chambers. If this is a newly built engine, I'd say you overdid the head
planing and need to consider octane booster additives (or a fat head
gasket). My stock motor '66 (which hasn't been tuned lately, I have to
admit) runs like a champ at 14 deg. BTDC more or less, on 92 octane
unleaded. But I would expect mine would have about 150 lbs compression if
I checked it. Even then, during a period of driving mostly short trips
last fall, it started pinging a little, but so far this year it's mostly
been 40-50 mile freeway blasts at off-peak hours, and it seems to thrive.
Pearson, Tim had this to say:
>OK then gents (& ladies):
>There is always a certain amount of debate over what is the correct timing
>to use to prevent pinging and get best performance. Everyone seems to have
>their own ideas, which can usually be summed up as "advance till it pings
>under load, then back it off a bit"
>I've noticed a lot of people saying they use 15-20 deg BTDC.
>The factor which never seems to be mentioned is compression ratios/pressure.
>Of course, the higher the comp ratio, the less advance you can get away with
>for a given octane rating.
>
>The reason I raise this is :
>66B. 18GBUH engine. Compression pressure = 170. K&N filters, #6 needles.
>Mild cam. Stock distributor. Free flow, single muffler exhaust. NGK BP6ES
>plugs.
>Local fuel here is about 94 - 96 Octane leaded.
>
>Dynamic timed at 700rpm, vaccuum advance disconnected and blocked at carb =
>5-7 deg BTDC.
>And it still pings very slightly under heavy load (like full throttle, 3000
>rpm up a steep hill) when warm.
>
>Now, either I have something very strange with my engine, or I am doing
>something very wrong, or everyone else on this list is imagining things (and
>I'm not quite egotistical enough to believe that!). I've tried disconnecting
>the vaccuum advance; this helped the pinging problem, but introduced
>hesitation on sudden throttle opening (not entirely unexpected).
>
>Comments, anyone??
>
>Tim
>66B rdstr YGHN3-3238
>
>
>
--
Max Heim
'66 MGB GHN3L76149
Runs great,
looks particularly bad since some SUV clown backed into it.
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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