9. Getting in the Way: The Anti-Shudder Valve and EGR Valve
In an ideal world, the boost air would be allowed to flow completely unimpeded from the intercooler, along the silicone and ceramic piping, into the inlet manifold. However, just prior to the inlet manifold, in the path of the boost, sit two additional devices, namely the anti-shudder valve and the EGR valve. Both these devices present an obstruction to flow. The AMF engine combines these two devices into one component, as shown in Fig. 9.1. The blue arrows represent the flow of boost air.
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The anti-shudder valve is only used to stop the engine. It’s possible to stop a TDI engine from running simply by cutting its supply of diesel. However, this causes the engine to shudder to a stop rather than stopping smoothly. The solution to this problem is to also starve the engine of oxygen as well as fuel. This is achieved by introducing a butterfly valve into the flow of boost air, as shown in Fig. 9.2. When the engine is running, the butterfly valve angles itself so as to present as little obstruction to the flow of boost air as possible, shown on the left. When stopping the engine, a vacuum actuator pulls a lever on the right of the anti-shudder valve upwards, as shown on the right. This causes the butterfly valve to rotate, thus completely blocking the flow of boost air and bringing the engine to a halt.
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Directly behind the anti-shudder valve is the EGR valve. EGR is an abbreviation of exhaust gas recirculation. EGR involves taking a portion of the exhaust gas, mixing it with the boost air, and sending it through the cylinders for a second time. It is a method of reducing the amount of polluting nitrogen oxides emitted by the engine. Fig. 9.3 shows how the EGR valve works. A small branch of the exhaust system is fed to the EGR input, directly beneath the EGR valve. When vacuum is applied to the EGR actuator, the EGR valve lifts upwards, like the lid being removed from a cauldron, causing exhaust gas to mix with the boost air.
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Whilst the objective of EGR is unquestionably commendable, it has a number of undesirable consequences. Firstly, it causes the boost air to get hot. Having invested so much in getting the boost air as cold and as dense as possible, it is totally counterproductive to mix it with hot, oxygen-depleted exhaust gas just prior to entering the cylinders. This dilution of the boost air, accompanied by the obstruction to flow presented by the EGR valve, causes decreased performance and increased fuel consumption. EGR also causes a gradual build-up of sticky tar in the inlet manifold, cylinder head valves and the EGR valve itself, as shown in Fig. 9.4. This introduction of abrasive contaminants leads to increased component wear and increased engine oil acidity, both of which reduce the longevity of the engine. EGR also increases soot and particulate matter emission, meaning that its positive environmental consequences are counterbalanced by a negative environmental consequence.
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I intend to keep my A2 forever. Whilst I believe that EGR has a net positive environmental impact for those with a disposable attitude towards their cars, the same cannot be said when a vehicle is destined to be eternally cherished and maintained. As such, I have decided to completely eliminate the EGR system. It is my choice based on the pros and cons. Others are, of course, welcome to disagree with me, but I’d rather discussion/argument about this topic be conducted elsewhere.
The AMF engine combines the anti-shudder valve and EGR valve into one component, which means that removing the EGR without also removing the anti-shudder valve is a challenge. Whilst the BHC and ATL engines split these devices into two separate components, making the removal of just one very easy, the standalone anti-shudder valve is unreliable. Graham – forum stalwart Spike – devised a clever solution to this problem, allowing the EGR valve to be removed from the combined unit, leaving the more reliable anti-shudder valve intact. Fig. 9.5 shows that the EGR input has been capped with a blanking plate. The additional black component attached to the anti-shudder lever is the vacuum actuator, as mentioned in reference to Fig. 9.2.
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However, there’s more to this blanking plate than first meets the eye. Graham has painstakingly removed all the internal components related to the EGR valve, meaning they no longer present an obstruction to air flow. Fig. 9.6 shows that the blanking plate has been precisely machined to fill the hole left behind by the blanking of the EGR input and the removal of the EGR valve. The result is that the internal wall is completely smooth, aiding air flow, and no evidence of the EGR valve remains.
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Fig. 9.7 shows a comparison of the old unit compared to the new unit made by Graham. Only the anti-shudder valve remains, presenting much less obstruction to the flow of boost air.
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Graham, I shall remain eternally grateful to you for making this unit for me. It has allowed me to eliminate the EGR system without compromise. I’m delighted to have a piece of your engineering as part of my project. Fig. 9.8 further demonstrates what a gifted and inimitable gent Graham is and what an asset he and his knowledge are to A2OC.
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