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On 24 Jun 2003 at 9:32, Greg Merritt wrote: > On Tue, 24 Jun 2003, Shad Laws wrote: > > > _All_ 009's run too retarded at cruising conditions - only at WOT are they > > "okay." They need a vacuum advance canister to do anything more. > > Shad -- do you actually mean "at high rpms" (or maybe "at high > rpms + WOT") rather than simply *any* wide open throttle conditions? Or > do you mean something more complex, where it's good to have the timing > relatively retarded when you have any high throughput or > near-atmospheric-pressure conditions at the intake (i.e. wide open > throttle)? He's just pointing out that you need (or can get away with, they're really the same thing here) more advance if you're not using WOT. The usual max advance that everyone quotes is the max RACING advance, which means WOT. For most of us, our cars spend a lot of time at reduced throttle, which means less charge in the cylinders which burns slower. Thus more advance is required to get the most out of what's there. Look at the advance curves in the Bentley manual. Using mech advance alone you'll get ~30 deg of crankshaft advance once you get the rpms up. The vacuum advance gives you about 10 degrees more. This does NOT mean that the VW engineers disagree with the 32 deg of max advance rule of thumb, it just means that they recognized that you can do just fine (and get better gas mileage) with 40 deg as long as you're not doing WOT. The vacuum part of the dual advance distributors gives max advance at med/high rpm and med throttle: cruising. This vac advance does nothing at WOT or at idle. In the Bentley, note that the degrees are dist shaft degrees. You have to mult by 2 to get crankshaft degrees. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org