510six Posted July 16, 2007 Share Posted July 16, 2007 http://www.supraforums.com/forum/showpost.php?p=1650426&postcount=7 Surge is an area of flow instability typically caused by compressor inducer stall. It's when the compressor is at a higher pressure than the compressor can generate under it's current conditions. This causes airflow in the compressor housing to back up and stall. As a result, pressure drops allowing normal airflow until pressure builds back up and stall again occurs. Extreme compressor surge is one of the worst things that can happen to your turbo. It results in a sharp and violent oscillation of the compressor wheel which 99% of the time takes out the turbo thrust bearing. Surge is not a good thing. This is the anti surge compressor housing on my T67, it helps to prevent surge at low rpm. http://www.honda-tech.com/zerothread?id=1978506&postid=27803783 Shot at 2007-07-16 Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 16, 2007 Share Posted July 16, 2007 Summing up what we teach our Technicians: Surge is the phenomenon of compressor flowpath instantaneously reversing due to the inability of the compressor to continue making pressure at that given flowpoint. Air delaminates from the blades, slips backwards until pressure comes to a point where stable flow in the normal direction can again occur, and then it will repeat. From there, there are other terms that are used, like 'pumping' whereby the compressor operates in a surge condition continuously. Bad! Microsurging can occur when ambient conditions make the flows or densities marginal for the conditions...you can not hear it in many cases unless you mic up the compressor housing ultrasonically. I digress... "Backspin" or "Pinwheeling" is the phenomenon whereby the turbine is actually driven backward from an air source that has sufficient volume to drive it for a time. This would be very unlikely in a vehicular installation if there was any kind of BOV in the system...mainly because even on lift-throttle the turbine is still getting energy to spin in the correct direction, and that would have to be ovecome as well. In industrial compressors, I have seen failed discharge check valves cause Pinwheeling. But not while the unit is coasting down. It happens after the inertia of the drive is stopped, and then the motive force of stored compressed air starts driving the wheels of the compressor backwards like Turbine Drives...Failure happens almost immediately as the bearings are directional, and speeds come up so fast things just go bad, very bad...quickly. Quote Link to comment Share on other sites More sharing options...
510six Posted July 16, 2007 Share Posted July 16, 2007 I have Backspun a couple of turbo`s from N20 backfires, due to a power wire to a nitrous deticated fuel pump breaking at exactly the wrong moment.The low pressure fuel Hobb switch worked but, not fast enough to prevent engine and turbocharger damage.The reason I went with the anti surge housing is the car is street driven and the S housing with the T67 compressor is pretty large. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 17, 2007 Share Posted July 17, 2007 Yeah, using compressed gasses that have a tendency to explode in the manifold may have sufficient force to overcome turbine inertia well above idle speed! I someplace have nice photos of an impeller that actually had the blades bend backwards enough to score the root of the next closest impeller valley ... before shelling out completely, breaking off, and migrating to the diffuser portion of the scroll, and parts downstream. "Violent Surge" didn't begin to explain it...until the owner admitted he drove into a puddle and immersed the turbine inlet under boost from a stuck throttle. Turbo didn't like to pump water. Oh, that explained it! LOL Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted July 17, 2007 Share Posted July 17, 2007 wizard.. I am not experiencing a backspin .. the surge is slowing the turbo down... a turbo w backspin would be severely damaged Ooops, sorry. What I meant was the OP is experiencing surge. Your description sounds like a tad bit of backspin from BOV flutter. It doesn't actually go so far as to spin backwards with BOV flutter but it does slow it down some and make noise of course. Quote Link to comment Share on other sites More sharing options...
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