Quote:
Originally Posted by Railcarmover
Late model vacuum /mechanical advance distributors were designed with emission control in mind,advancing the spark under no load peak vacuum conditions to lean the burn.This also strips deposits in the combustion chamber by raising combustion temperatures. I'm not so sure the long term effects are beneficial.
|
Well, let's squash that right now, because it is simply not true. Centrifugal advance and vacuum advance were implemented by almost all auto makers in the 1930s, and had absolutely nothing to do with emmisions. Additionally, these advances do not increase operating temperatures, in point of fact, they have the opposite effect.
Yes, in the late 1960s, and even further into the 1970s, additional controls were added for emmisions, and ported vacuum was used with a meriad of other ideas to control emmissions, which had multiple negative effects. The use of the Honda distributor does not include any of these items/controls.
Really, railcarmover, you simply have not been fully informed/educated on this subject, and have made inaccurate statements. While the benefits of the vacuum advance on the model A engine may be minimal, given the archane nature of the beast with limited power output, they are in no way harmful in any aspect other than not looking "original".
Some people think that because most race cars don't use a vacuum advance, cars don't need them. Just think about the face application for a minute. They run with the throttle wide open, hence almost no vacuum. Of course a vacuum advance has no benefit there. But in your street car, vacuum is an indicator of the load on the engine, and the mixture involved at that instant. Remember, lean mixtures burn slower than richer mixtures, and when you put you foot in it, the engine takes in more A/F. The air compresses, but the fuel part doesn't, hence the mixture is denser, and urns faster. This faster burn requires a bit of spark retard to avoid pre-ignition.
The centrifugal advance takes care of having less time from firing off the mixture, until optimal force, which needs to occur at around 15-18 degrees after TDC, when engine speeds increase. The vacuum advance, takes care of allowing greater advance during periods of leaner mixtures, when the engine is under light loads, thus optimizing engine performance and economy.
This is not my theory, it is well established internal combustion ignition fired engine science, and is fact. The model A came out just as these things were being fully understood, and Henry was slow to accept them, but with the V8, he did include these items. Please educate yourself before making incorrect statements like those.