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On 3 May 2004 at 22:03, Mark Seaton wrote: > Jim (and anyone else interested) here are my advance curves for the car > stationary: > > www.mo-sys.com/mark_eng_adv_curves.pdf This looks about right. Most of those which were sold here topped out at 10 degrees, so the extra 2 degrees may be why you get a different part #. > 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. There is a definite stop. You can actually see it if you look at the vac can pushrod. There's a cutout in the rod which determines the amount of movement that's allowed. > The scary thing is the total advance > figure which exceeds 45 deg with the vac attached at 3500 rpm which seems > way too high. The thing that no one ever explains is that the 32-34 deg limit is the full load limit or the limit that the racers have to worry about. When you're cruising along at 1/5 throttle at 50 MPH, you can tolerate MUCH more advance, and the result is better gas mileage. You won't find this mentioned in any of the high performance books because it's just in an operating area where they never go. > 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 difference is that there is no load on the engine in the tests you've run. When you're actually out driving you'll have load, so you'll have to open the throttle more, with no increase in RPM, so the air velocity past the vacuum port will be less, and the vacuum will be less. I suspect that you'll find that you almost never see any vacuum until you reach your desired speed and can let up on the throttle. > The mechanical advance itself is fairly nice and linear/ proportional and > maxes out at a healthy 32ish degrees. Can I assume that includes the static advance? > 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. That will be very interesting. Do you have a Bentley manual? It would be worthwhile studying the distributor curves and coming to some kind of understanding of them and what they're doing. What you're doing is just trying to produce the appropriate curves for your dist. When studying the Bentley curves, note that they are all in distributor shaft degrees; to get crankshaft degrees you have to multiply by 2. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org