I got answers on my questions regarding calipers and how to find the correct
ignition timing, and thought I'd post them for the eddification of those who
care...
Girling AR and NR, and apparently other XR calipers have a large port on the
side, and the manual helpfully states that it's installed with a special
process during manufacturing and the caliper will explode if you remove it.
Sources tell me that it's actually sealed with a rubber O-ring at the bottom
of the recess. dimensions will vary with the type of caliper, but a bearing
supply house can probably match what's there, and you have to be careful to
get an O-ring that's compatible with brake fluid.
On the ignition question, I got a few replies from the list but nothing that
I didn't already know, so I surfed on over to Superflow's web site. They
have a "ask Harold" button, so I did just that, and asked Harold my question
(how to determine the right ignition timing on a dyno), and lo and behold,
he replied the next morning! Harold is a Senior Vice President at
Superflow, and his reply is attached...and I'm seriously impressed that he
did in fact reply, as my note to him made it clear that I wasn't even a
customer, although my engine guru is!
Cheers, Brian
(EGT's are exhaust gas temp's)
[harold bettes] Brian, I love these types of questions because
they are the real essence of engine testing and development.
A) EGT's are better suited for checking for manifold
distribution instead of an indication of rich/lean conditions or spark
advance requirements.
B) On all engines tested on a properly instrumented engine
dynamometer, many tests need to be done, but RBT, LBT, and MBT must be
done.
Description of critical tests on engine dynamometer
RBT = rich best torque, LBT = lean best torque, MBT = best
torque minimum advance
Test for RBT/LBT is essentially where the engine is at a steady
state of RPM at each data point and the air/fuel ratio is varied until
there is a loss of power.
The LBT point is the leanest that the engine will run at max
torque output (for that RPM). RBT is the rich end of the scale. All
these tests require a good test fuel for baseline comparisons. MBT is a
duplication of the test above, except that the spark is varied until MBT
is found or 1% loss in torque is observed (at that data point).
Because of the odd things that occur in combustion chambers, do
not assume that the timing requirement for MBT to necessarily follow
logic. It may be that an engine would respond to 38degBTDC at 5500 and
42degBTDC at 6000 and 40degBTDC at 6500, etc.
Remember that back in the 60's engine dyno instrumentation and
timing lights were not as good as is available now. Also, there is not
much telling of exactly what fuel they ran. So, proceed with caution and
remember that it is safer to be 5% rich than 1% lean. Timing changes are
typically done 2deg at a time until MBT is identified.
Best of luck.
HB2
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