There is no vacuum at WOT.


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Posted by Chris Case @ San Diego on Friday, February 29, 2008 at 14:58:15 :

In Reply to: Re: Power Wagons No Vacuum Advance why ? posted by John Dunn on Friday, February 29, 2008 at 11:55:38 :

Or at least not enough to make a vacuum advance work.

What vacs do is to vary the timing per engine LOAD. Less load, less ping, so more advance is useful to get maximum economy.

A typical centrifugal has about 35 degrees, while a vacuum usually has about 10. Adjustments are usually in spring tension, to vary at what speed things advance, not usually the total.

Many vacuum units are adjustable. The ones that have a hex nut at the hose nipple use shims to vary spring pressure. The ones that have a hex-shaped stamping with an integral nipple have a hex nut inside the housing- adjust the screw within the nut by using a small hex key inserted through the nipple.

Centrifugal is usually adj by either bending the ears the spring hooks to, or by turning the eccentric pins with the end of a pair of dikes. GMs need to change springs.

Vacuum advance is a critical part of dyno-tuning for mileage. Centrifugal is critical for horsepower. Engine loads differ with gearing, tire size, vehicle load. All of which is compensated for in modern vehicles by the on board computer chip- something that FFPWs don't have.

A fixed load, like an industrial use, needs only fixed advance. Variable loads, like consumer cars, need variable advance.



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