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Jim (and anyone else interested) here are my advance curves for the car stationary: www.mo-sys.com/mark_eng_adv_curves.pdf I recorded the vacuum with my carb synchroniser which has a scale in cmHg but I don't know how accurate it is. I got the vac adv figure by subtracting the mech only adv at certain RPM fronm the combined adv at the same rpm. As you can see the vac kicks in at about 1600 rpm and rises rapidly to about 2300 rpm, but there is obviously a limit as the actual vac advance seems to max out at about 12 deg at 2000rpm. The scary thing is the total advance figure which exceeds 45 deg with the vac attached at 3500 rpm which seems way too high. I don't know how different that would be in actual driving conditions, but I can't see why it should be any less. The mechanical advance itself is fairly nice and linear/ proportional and maxes out at a healthy 32ish degrees. I did notice that my idle was a little low at 850rpm. I will endeavor to do some more tests with a remote vacuum gauge and tach while driving in various conditions to complete the picture soon. Mark Seaton '73 Fasty London > With a Tee and a gauge in the line, just suck on the hose while you watch the > timing change as the engine idles. Set the timing to TDC statically. Record the > advance, vacuum, and RPM at several points up to max vacuum advance. > > Now, with no vacuum advance, use the throttle to duplicate the same RPM > readings and record the amount of mechanical advance at the same RPMs as your > previous data. > > Subtract the 2 advance amounts to give you the amount which is solely due to > the vacuum advance. (If you're lucky, the extra vac advance won't give you > enough RPM increase to bring on the mechanical advance.) Now you have a vacuum > advance chart, like that in the Bosch lit or the Bentley manual. > > With that chart in hand, you can now do various kinds of driving, and, while > consulting the gauge, tell how much vac advance you must be getting under each > of those conditions. > > Yes, it would be a bit of work and somewhat involved, but it sounds just > interesting enough that I suspect that you'd enjoy doing it. > > -- > Jim Adney > jadney@vwtype3.org > Madison, WI 53711-3054 > USA > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org > > >