Tim,
I've seen a lot of chatter about high octane gas, but did anyone comment on
your pinging problem?
My '74 is an 18V with a 45D distributor, running at 170 lbs. compression
with a mildly warm cam - and I'm at about 20 deg. BTDC with no ping.
If I had your problem, first I'd check to see if I was just running real
hot. See if you can pick up a cheap temperature gauge at the local auto
parts store. Failing that, you could try to calibrate your temperature
gauge with a meat thermometer driven into the top radiator hose (as near the
thermostat as possible).
Second, I'd check to see if my vacuum advance was not releasing under low
vacuum. You've already proven it has some effect, but I'd check to see if
it's working at specs. Either your manual or one of the Clausager owners
can tell you what that should be, but I think it's generally 0 to 20 degrees
vacuum advance at 5 to 13 Hg for some motors, 0 to 10 degrees vacuum advance
at 10 to 15 Hg for others.
BTW, make sure your "stock" distributor is the correct one. Seems the 25D's
wear out after a mere 25 years and are hard to replace. That's why I had to
swap in a 45D. If you really do have the original distributor, I'll bet
it's pretty badly worn out. That could be your problem as well.
Cheers,
Matt Kulka
Huntersville, NC
'74 B
-----Original Message-----
From: Pearson, Tim [mailto:tpearson@westpac.com.au]
Sent: Wednesday, June 16, 1999 10:07 PM
To: 'mgs@autox.team.net'
Subject: Pinging, compression ratio, and advance....
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
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