Re: new top mount manifold
Originally Posted by Whitey
Actually, yes. Stolen from here:
Originally Posted by Joey
Substantially constant pressure turbocharging.
Groupings of cylinders/banks of cylinders in such a manner that two or more exhaust events overlap (substantially). Characterized by constant, elevated mean exhaust manifold pressures. The up side is the turbine is fed with a constant supply of exhaust pressure/flow/energy. The down side is the high ambient exhaust pressure hinder the flow of exhaust gas and heat out of the combustion chamber/head. Turbine efficiency is high, runner efficiency is low. When set up correctly they work well-ish. Typically through the use of two things: long runners and precision merge collectors. The runners are expansive, to mute exhaust pulses, and long to prevent the exhaust pulse from bouncing off the turbine and returning to the originating exhaust valve before it closes (thereby foulling the chamber as the valve closes with a backwash of inert exhaust gas, and heat). A correctly designed merge collector reduces restriction where the runners merge; despite Full Rice Geoff's imbecilic blatherings about these being high tech and his invention, it's been common knowledge since before his birth that a shallow convergent angle of entry greatly smooths disparate flows together. It is appropriate to note at this point, that in some circles the verdict is still out on long vs short runner lengths in constant pressure turbocharging. I concur that the bulk of the gain in the refines constant pressure turbo systems is from a smoothly transitioning merge collector, but posit based on an ed-ju-muh-cated guess that tuning runner length and diameter to suit desired power band will result in some gains. Keep an eye on harmonics, and the relationships of EGTs, exhaust flow speed, speed of sound as affected by temperature, etc. Pressure wave aka shock wave turbocharging. Like, OMG! Groupings of cylinders/banks of cylinders in such a manner that no two exhaust events overlap (... substantially...). This *drastically* lowers ambient exhaust manifold pressure, which ensures excellent scavenging and flow of exhaust/heat from the combustion chamber at all loads and pressures. However, since each pressure pulse builds and is for the greater part spent before the next exhaust valve opens, the turbine is not fed a steady supply of pressure/flow/energy. Turbine efficiency is low, runner efficiency is high. When correctly done, port diameter is kept small to keep pulse strength as well as velocity high. Runner length is as short as possible, to avoid excess volume for the exhaust pressure to expand into as opposed to spending itself across the turbine. Spool time is enhanced, part throttle power and efficiency is enhanced, but WOT power suffers from inconstant pressure to feed the turbine. This is alleviated somewhat by the advent of split scroll turbines, but... no free lunches. So, yeah, I've been screaming that horseshit- er, horsepower, per psi is irrelevant for some time now. This is a good example of this. So you have to "turn the boost up" in order to hit the power levels of a properly refined constant pressure turbocharging system... mean exhaust manifold pressures have decreased dramatically, and exhaust manifold pressure for the bulk of any particular cylinder's exhaust event is decreased even further. Less heat and less stale exhaust gas is left in the chamber, and for a given setup running a particular flavor of fuel more power is made before knock sets in. This is seen a lot in diesels. Groupings of no more than three cylinders, with no more than 240 degrees of exhaust cam duration, in such a way that no two (sets) of exhaust valves are open simultaneously. This is also how the EVO 8's OEM manifold is constructed - that should give pressure wave turbocharging the riceboy stamp of validity. It's right up there with VTEC as the hot thing! Although this actually has some affect on performance instead of annoying exhaust noise. Sorry. Pulse converters. Pulse converters are, quite simply, ejectors or (DeLaval... heh...) nozzles that accelerate pressure waves before reaching the turbine. The idea is to convert an amorphous wave into a burst of focussed kinetic energy. So? Constant pressure application first: flow is accelerated, and the transmission of a particular pressure wave to an adjacent runner is prevented. Have you ever heard of an anti-reversion chamber? When used with pressure wave turbocharging, WOT turbine efficiency is greatly enhanced. At the cost of some runner efficiency under part throttle conditions - no sir, still no free lunch here. Afterword: Make your fancy-pants (insert Brand Name here) tubular manifold with cylinders 1 & 4 and 2 & 3 tied together, and feeding a split scroll turbine housing. Install ejectors as needed, if worried about hp/psi numbers, to impress magazine reading friends you will be kind enough not to introduce me to - unless they wish to race for money. Or you can use a valve (spare wastegate, hmm?) to marry the two collectors/scrolls at WOT or after a certain psi and have your quick spool and hp/psi at the same time. |
Re: new top mount manifold
I'm also whoring it up on the HT thread.
God, I hate DSMtards. |
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