Next up, you need to locate the cam angle sensor CAS which is held in place with a bolt in this case a 12mm. Loosen the bolt by no more than a turn to ensure that you have free movement of it when using the timing light. On the MX-5 image below, the longest timing mark line represents the factory pre set. All you need to do now is to tighten the cam angle sensor bolt back up and check that the angle still reads 14 degrees.
Remember to do your research before changing the ignition timing of your car, including locating your cam angle sensor, crank pulley and timing marks and diagnostics box. Change your ignition too much and your engine could suffer from knock, which ruins the combustion and could fry your motor! Take a look at this detailed guide on MX-5 Nutz for more information. Please confirm you agree to the use of tracking cookies as outlined in the Cookies Policy. Sign in or register.
Alex Kersten 6 years ago. Whenever you carry out any major changes to the engine, you may also need to implement the necessary changes in the ignition timing.
The engine-makers normally punch the timing marks on the vibration damper at the front or on the flywheel at the rear of the engine. At times, these marks are located on the crankshaft pulley or the largest radius that rotates at the speed of the crankshaft. The older engines used the timing light for setting up the ignition timing. You can set the ignition timing at the correct point of firing while the engine rotates. However, it has to be exactly a few degrees before the Top Dead Centre TDC , which could advance with increasing engine speed.
Modern engines come with a crank angle sensor that directly connects to the engine management system. The crankshaft's timing marks must also match with that of the camshaft for achieving the correct valve timing. There is a certain delay called the 'Ignition delay' to start the combustion after the spark is fired.
The spark must occur before the moment at which the cylinder reaches the maximum pressure. Ignition Advance is the difference between this moment and the occurrence of the spark. The timing advance occurs when the ignition occurs earlier in the compression stroke, i. However, if the spark advances too much, then the combustion will complete even before the piston reaches the TDC. Then, the crankshaft and connecting rod would have to force the piston to move upwards against the compression stroke pressure.
In such a case, this force might not be sufficient enough to overcome the compression pressure. As a result, the engine could stop or stall. An advanced spark may also cause the fuel to explode or detonate midway to produce an audible knock. However, the timing advance is necessary when the engine operates at full speed.
Thus, it allows sufficient time for burning the air-fuel mixture. If the canister is not disconnected, the readings will be a combination of initial, mechanical, and vacuum advance.
Now we can introduce vacuum advance into this system. The more enlightened way to look at vacuum advance is to view it as load-based timing. It's worth a peek down the rabbit hole of the combustion process to understand why load-based timing is important. Let's use the example of a typical carbureted small-block cruising down the freeway at 70 mph at 2, rpm on level ground. The engine could be pulling anywhere from 12 to 18 inches of vacuum. As mentioned before, high vacuum means low load and a nearly closed throttle.
A little known fact is that most mild street engines cruise down the freeway pulling fuel from the carburetor's idle circuit. That's not a misprint. Engines with long duration cams or cars with tall overdrive gears in overdrive might transition into the main circuit but most mild street engines with high vacuum at cruise will actually be running on the idle circuit. With a minimum of air and fuel entering each cylinder, this means the mixture is not tightly packed.
Here's where things get tricky. The common perception of the combustion process is as an explosion—the spark goes off and boom—combustion occurs like a bomb. That's not what happens.
The reality is the spark plug fires and it takes a generous period of time for the combustion gases to burn completely across the top of the piston, much like a prairie fire across a large valley. The more densely packed the grass is, the faster it burns while sparse areas burn more slowly.
We can apply this prairie fire analogy to the combustion space. At WOT, the air and fuel are tightly packed and burn quickly so we don't need as much timing. At 2, rpm at WOT, 32 to 34 degrees of timing could be just about right for a typical pump gas street engine. However, at nearly closed throttle inches of manifold vacuum , the air and fuel are far less densely packed in the cylinder.
In order to make the most power possible at part throttle, we need to start the combustion process much sooner—perhaps as much as 40 degrees BTDC or more depending upon the engine's individual demands. But we only need this much timing when the engine is under very light load. Since manifold vacuum is a great indicator of load, early engine designers used a small vacuum canister attached to the distributor to advance the timing under high manifold vacuum to create a load-based timing curve that would be in addition to the mechanical advance.
We've created two graphs that illustrate very simple mechanical and vacuum advance curves. Mechanical advance is totally dependent on engine speed while vacuum advance is solely controlled by engine load. We need both because on the street we can have low load at very high engine speeds—say 6, with the throttle barely open—or very high load WOT at very low engine speeds like 1, rpm. These two situations have very different ignition timing requirements.
Now let's introduce the critical variable of cam timing. Let's use an extreme example with a small displacement engine like a carbureted Ford 5.
Even with 16 degrees of initial timing, let's say our engine barely idles at 8 inches of manifold vacuum and it is backed by a tight torque converter because it also has nitrous.
Even with 9. This engine would respond to more vacuum advance at cruise speeds at part throttle to improve its drivability and throttle response. Our experience shows that connecting the vacuum advance to a manifold vacuum source will add timing at idle and improve idle quality in gear with an automatic transmission. Milder applications can also benefit from this idea but will require some experimentation.
Several companies like Crane, Moroso, Pertronix, and Summit Racing offer adjustable vacuum advance canisters that allow you to customize the advance curve to fit your engine's requirements. Let's put these ideas into action with a specific example. We dropped a very mild ci small-block into an early El Camino pushing through a TH trans and a very tight inch converter. With 16 degrees of initial timing and a properly adjusted idle circuit in the Holley carburetor, the engine struggled to idle with the in-gear vacuum dropping to below 8 inches Hg.
The distributor was fitted with an adjustable vacuum advance canister, so we merely connected the can to manifold vacuum, which added 14 degrees of advance, creating 30 degrees of advance at idle.
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