![]() ![]() Over the course of 40-plus years, MSD Performance has been driving the development of innovative components that helped shape the way our cars race and perform. We continue to innovate and invent components and technology that deliver performance and reliability with products that are easy to use and install. The team at MSD is no different as we strive to deliver the products you need to meet your performance goals. It is not good to have the curve come in at a low rpm, say 1000, because the distributor may not retard when you shut the engine off, and this can cause starting problems.Racers never stop experimenting as they search for every way to wring out more power or handling performance to to gain an edge over the competition. Because of this, it is better if the curve is all in by 3000. The problem with having an advance curve that is all in at 5000 rpm is that you must set the timing above 5000 rpm. However, if you have an automatic transmission and the car launches at 2000 rpm, then you need a quicker advance curve. When should the advance come in? If you run a stick shift and the car leaves the line above 5000 rpm, the advance can come in at any point up to 5000 rpm. However, you must check and set the timing at a high enough rpm so that the advance is all in. The same distributor used in the stock car with 26 degrees mechanical advance and the vacuum disconnected will work. ![]() In this application you need to have about 42 degrees advance, initial plus mechanical. Therefore, you do not need vacuum advance. In this application the engine probably idles at about 1000 rpm, and the only throttle position when the car is accelerating is wide open. Only Delco-Remy vacuum cans are marked with their total advance rate.įor our second example we will consider a car to be run only at the dragstrip, and again with a small-block Chevy V8. As you will discover, aftermarket advance canisters are not marked with their advance rates, but instead only with a generic "B1" code. If you can find a sympathetic and knowledgeable parts man, you can get stock parts for any application. By our previous example, we've seen that Chevrolet makes dozens of different weights and springs and dozens of different vacuum cans. Next, check the vacuum can, and, if it is inappropriate, get one with 10 degrees advance. If you have a distributor that is advance-limited you can elongate the hole, or weld it partially closed if the distributor has too much advance. ![]() In some of these distributors the weights are different and are not interchangeable with the weights in most Chevy distributors. If you have a distributor with 14 or 40 degrees of mechanical advance, get another distributor or another cam for your distributor. Also, the continual metal-to-metal contact could eventually break the weld that holds the pins that the weights pivot on. This plastic sleeve acts as a shock absorber and, without it, the advance might bounce. If you remove this sleeve you will get more advance, but doing this may cause problems. This pin has a sleeve over it, made of plastic or rubber. The mechanical-advance springs found just under the rotor on a small-block Chevy control the rate at which your distributor advances the amount of advance is controlled by a pin that moves in a slot in the top of the cam. There are dozens of variables that affect the ignition point-compression, valve timing, chamber design, and many others-for optimum ignition advance rates. If your engine turned at about one rpm this process would work, but the piston goes up and down 10 times a second at 600 rpm and 100 times a second at 6000 rpm. When the piston gets to TDC you close the exhaust valve, open the intake valve, and the process starts over. When the piston gets to BDC you open the exhaust valve, and as the piston goes up it pushes the burned gas out the exhaust. This causes the pressure in the cylinder to rise and pushes the piston down. When the piston gets to TDC you fire the spark plug, which lights the mixture in the cylinder. When the piston is at Bottom Dead Center (BDC) you close the intake valve, and, when the piston goes up, it will compress the gas in the cylinder. When the piston goes down it will pull in a mixture of gas and air. When the piston is at Top Dead Center (TDC) you open the intake valve. What is distributor advance and why should changing it make your car run better? The basic idea is simple.
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