andrewh wrote: ↑Mon Jul 22, 2019 3:52 pm
OK , well I have now timed the 123 statically to TDC and will put in the curve on the APP. I am assuming that we start at 500 rpm 10 degree advance and go from there. What I am unsure of is what the vacuum advance should be in inches of Mercury. I should have listened more in Physics
The 123 not so helpfully is graduated in kilopascals ( ?)
I had heard that curve 7 on the standard 123 works very well, does anyone have the profile for that, at least before I go off to the rolling road. Sorry this thread has developed into a 123 Distributor thread but I am sure it will be of use to others. Anybody got the book on power tuning XK engines? That may have some useful stuff in it, but I have not been able to purchase a copy.
You're not going to be far wrong if you start with the factory's maximum values for the distributor.
Those values are (in crank terms, not distributor ones):
rpm adv
1050 3
1300 8
1600 14
2500 17
3600 21
4600 21
Your preferred static value needs to be added, as you've initialised the 123 at tdc (so 10 in your case).
They worked alright for me, on a pretty standard 4.2. We (or rather, the rolling road operator) found that you can easily go to maximum advance at 3000rpm. Could probably be earlier than that if you want to experiment.
We also observed that maximum hp started to drop off a bit if we had 32 or more (21+10) degrees of advance. But that is probably just my engine.
As for the vacuum, I don't have the figure I used to hand. But again they are a straightforward copy of the maximum Lucas values.
Simon
