Best Lift Kits for Chevy Silverado – Expert Review and Guide.Best Lift Kit for Chevy 2500HD – Expert Review and Guide.Looking for a Good Shocks for Chevy Tahoe? Read the Article Below…. It will become a valuable guide when setting up the curve for your particular combination.Real advice - performance, mods & accessories. Take the time to sort through the timing maze and be certain you record all changes in the notebook. In any case, you can adjust where the advance starts, the rate of advance (slope), as well as the total amount of advance. As mentioned earlier, some engines will "like" more initial timing than others, while some combinations will want more total timing. What you have to obtain is good throttle response along with detonation free timing. Trial and error plays a major role in the selection of a proper curve. You can also graph the results by checking the timing at 200-rpm intervals (correlating the advance shown on the harmonic damper to the engine speed). Increase the engine speed and make a note of the speed at which the curve begins along with the speed at which the curve ends (where the curve is "all in"). Then make a note of the spring combination in the distributor. When playing with the curve, set the initial. By using a separate starter and ignition switch, you can overcome adverse starter load by spinning the engine first, then clicking on the ignition switch. Automatic transmission cars use more initial advance than stick shift cars. Here are a couple of extra curve tips I've come up with over the years: - Automatic transmission cars almost always need a quicker, but shorter, curve than stick shift cars, however, the total timing should still be the same. The bigger the bushing, the smaller the amount of advance. The amount of advance is controlled by the advance bushing. The stiffer the spring, the slower the advance curve. How quickly the centrifugal advance (slope) comes in is controlled by the spring stiffness. The starting point of the centrifugal advance curve is controlled by the installed length and tension of the spring. Start the centrifugal advance just above the idle rpm. Use as much initial advance as possible without encountering excessive starter load or engine kickback. MSD also offers the following tips on selecting an advance curve: At idle, a spark ported vacuum system has no vacuum advance (in contrast, a manifold vacuum advance might have as much as 12-degrees extra timing). This is completely opposite to manifold vacuum. This is called "spark ported vacuum." Spark ported vacuum is lowest at idle, and then increases as the throttle is opened. The vacuum source was changed from the manifold to the carburetor venturi. As a result, there is no chance of detonation (or pinging).In the mid-'60s, vacuum advance mechanisms changed to suit emission requirements. This means the vacuum mechanism does not advance ignition timing. When the engine is operated at wide-open throttle, manifold vacuum is low. This advances the ignition timing under those conditions and improves fuel economy. During idle and part throttle operation, manifold vacuum is high. This meant that the vacuum was most often taken from a location below the carburetor throttle body. Early, pre-emission vacuum advance units were typically linked to a manifold vacuum source. All vacuum advance units operate on a system where the diaphragm reacts to the difference between atmospheric pressure and induction pressure. Vacuum advance arrangements are more complex.
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