{"id":6625,"date":"2019-03-04T10:26:50","date_gmt":"2019-03-04T09:26:50","guid":{"rendered":"http:\/\/www.checkstar-techblog.it\/?p=6625"},"modified":"2022-11-11T14:46:04","modified_gmt":"2022-11-11T13:46:04","slug":"manifold-discharge-counterpressure-variable","status":"publish","type":"post","link":"https:\/\/www.checkstar-techblog.it\/en\/manifold-discharge-counterpressure-variable\/","title":{"rendered":"Variable back pressure exhaust manifolds"},"content":{"rendered":"
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\"Monza<\/a>
The 'Record Monza' for the Abarth 500, an Abarth-branded variable backpressure exhaust system designed in collaboration with Magneti Marelli.<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n<\/article>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/header>\n<\/div>\n<\/article>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
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The reverse supercharging effect at zero cost.<\/h4>\n

With appropriate exhaust system configurations, a small 'supercharging effect' can be obtained 'for free', which lengthens the engine torque curve and results in longer operating ranges.<\/p>\n

The exhaust system expels gases in the form of pulsations. Analysing the pressure wave and plotting its course on a pressure-time graph reveals that this develops to a considerable peak at the first moments and then subsides as it propagates. The high-pressure peak is followed by a transient phase of negative pressure (depression) that favours the emptying of the cylinders after combustion. If it were possible to channel all the exhaust pulses into manifolds of equal length, an equal distribution of the exhaust pulses would be obtained which, if synchronised with the suction and piston strokes, would be able to help empty the cylinders and aid the intake of the fresh charge.<\/p>\n<\/div>\n<\/article>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

\"exhaust
The graph represents the development of a pressure pulse over time within the exhaust system of a turbocharged twin-scroll engine. Highlighted in blue is the initial pressure peak followed by the depression exploited by the scavenging<\/em>Process of expelling spent gas from the cylinders and intake of new fuel\/air mixture for the next cycle.<\/figcaption><\/figure>\n

This effect is called the 'reverse supercharging effect', more commonly known by the English term scavenging. To make the most of the scavenging effect, it is therefore necessary to have exhaust manifolds of equal length and a perfect synchronisation of the opening and closing of the intake and exhaust valves according to engine timing. The best conditions are dictated by the geometry and performance of the machine, which influence the setting of the valve timing (overlap).<\/p>\n

Overlap is that condition in which, for a certain amount of time, both the intake and exhaust valves are open. During the exhaust stroke, as the piston approaches top dead centre, the intake valve starts to open while the exhaust valve is not yet fully closed: this happens because it is physically impossible to bring the exhaust valve from its closed position to its fully open position instantaneously. This is the reason for the use of valve opening advances and closing delays, which allow the condition of
\ncrossover to exploit the suction effect generated by the exhaust gases leaving the combustion chamber: the outgoing gases in fact draw in the fresh charge which, taking its place, performs a dead space scavenging operation.<\/p>\n

\"BMW
BMW M3 V8 synchronised exhaust manifolds<\/figcaption><\/figure>\n

On the basis of the above, one would say that exhaust pipes should have as small a cross-section as possible in order to speed up the fluid flowing through them, thus favouring emptying. In reality, physics always surprises us, even in this case: narrower pipes generate greater resistance to gas flow, better known as 'back pressure'. When the engine is running at high engine speeds, for which the exhaust gas velocity is very high, the back pressure generated becomes great enough to outweigh the benefits of scavenging, which is why exhaust pipes are only beneficial at low engine speeds. Conversely, exhaust pipes with larger sections reduce back pressure at high revs and increase maximum engine power, but at low revs the exhaust gas flow is too slow to generate scavenging.<\/p>\n

For these reasons, variable backpressure exhaust manifolds were developed. They consist of a series of pipes arranged in parallel with different cross-sections which, through the use of a bypass valve, are crossed or not crossed by the exhaust gases in order to be able to make the most of the benefits of scavenging without running into the problems associated with back pressure.<\/p>\n

\"Variable
Functional diagram of a variable exhaust device. The by-pass valve activates\/deactivates the passage through pipes with a larger or smaller cross-section.<\/em><\/figcaption><\/figure>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

(Source: Technical Car)<\/p>\n<\/div>\n

\"\"<\/p>\n<\/article>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/article>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

The 'Record Monza' for the Abarth 500, an Abarth-branded variable backpressure exhaust system designed in collaboration with Magneti Marelli.<\/p>","protected":false},"author":49,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"acf":[],"featured_image_urls":{},"appp_media":null,"views":1692,"_links":{"self":[{"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/posts\/6625"}],"collection":[{"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/users\/49"}],"replies":[{"embeddable":true,"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/comments?post=6625"}],"version-history":[{"count":0,"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/posts\/6625\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/media?parent=6625"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/categories?post=6625"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.checkstar-techblog.it\/en\/wp-json\/wp\/v2\/tags?post=6625"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}