I have always taken ignition timing from manufacturers with a grain of
salt. These are chosen such that the worst case stackup of tolerances will
not cause detonation. Each car is different and almost all cars can
benefit from added advance.
This is especially true for U.S. spec cars built after 1968 and before
computer control. In these cars, settings were not chosen for performance
but for emitions control. One of the worst offenders is the infamous
vacuum retard that is attached to many post 74 LBC's. I am not sure
exactly what ill this was supposed to fix but I believe that it is to keep
combustion temps down for NOx and exhaust temps up for HC's. It also helps
keep the idle slower with all of the air leaks introduced by the emissions
crap.
I was just getting into engine tuning in the early seventies so I have
spent a lot of time trying to keep these Rube Goldberg devices working or,
at the least, not destroying how the engine runs. One of the "on the
street" hot tricks was to advance the cam timing one tooth. We did this
on our '74 International pickup truck and it did seem to help. In any case
I believe that most of the cars of this time frame do have the cam timing
more retarded than typical. I believe that this is to keep the intake
opening later so that there is less scavenging of raw fuel into the
exhaust. Whether MG's fit with this is beyond me but maybe someone else
knows.
Even without emition issues, most cams are installed in a slightly retarded
condition. This is because engine performance falls off more slowly with
retarded cam timing than it does with it too far advanced. The number that
stick in my mind is that small block Chevies have their stock cams
installed 4 degrees retarded from the factory. Again, how MG's fit here I
don't know but, given the history of the British auto industry, I doubt
that they had better control of specifications than GM. They were probably
using the same tooling to build these engines in the eighties that they
used when the assembly line was set up in the- well I am guessing the
fifties but it may have been much earlier. I read somewhere that Jaguar
was still using the tooling Lyons bought from Standard right after the War
to build the last XK engine in the eighties. This tooling was originally
developed to build flat head Standard engines in the thirties.
So what's the point of all this? Once again I have wondered off the
original topic. Screw what the manual says. Advance your timing until it
runs best and doesn't ping too much or kick back against the starter. If
you can, buy a degree wheel and time your cam right to get the best
performance. I did not do this when I assembled the A because I am lazy
and was pressed for time- I needed the car for transportation while my
other car was at the body shop. Other wise I would have probably bough a
cheap degree wheel, a cheap dial indicator and magnetic base, and found out
where I was. Someone sells offset bushings for the cam gear or offset keys
for the crank gear to adjust the cam timing without one of those wonderful
but very expensive adjustable cam gears. If you take the time to get
everything right, your engine will run better. Usual disclaimers apply.
If you can't hear the detonation or go lean and burn holes in your pistons
Then I will deny any knowledge of this e-mail, this list, or MG's in
general. This e-mail will self distruct in 10 seconds, 9,8...
Regards,
Bill Eastman
61 MGA who has not seen a timing light since she followed me home and has
no holes in her (still original) pistons.
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