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The Terminator
Turbo Cobras
Smoke when letting off throttle?
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<blockquote data-quote="Onelfastlride" data-source="post: 9247167" data-attributes="member: 7298"><p>After speaking with a turbo design engineer he explained to me.......a possible cause for smoke on decel is a insufficent oil drain for the turbo. Keep in mind I have a ball bearing turbo which require less oil then a standard journal turbo, however both require a sufficent oil drain line. </p><p></p><p>He explained it like this........the seals on the turbine side of the turbo are similar to a piston ring. The seal has a gap at the top, if the turbo does not drain properly, on decel when large amount of vaccumm is created on the exhaust side, the excess oil sitting in the turbo is pulled past the turbine seal and causes smoke seen in the cars exhaust.</p><p></p><p>From what I've heard, oil drain lines should be a min. -10AN, -12AN is even better. They should be always on a downward slope to the pan with less then 90deg turns.</p><p></p><p>So........if you have a marginally sufficent turbo oil drain line and then add a little crankcase pressure, you've made the situation worse, and it's even harder for the turbo to drain.</p><p></p><p>By venting the valve covers to atmosphere and it smoked less on decel, you most likely let the turbo drain easier and stopped excess oil from being pulled past the turbine seal into the downpipe on decel. Many will say putting a restrictor in the oil feed line is a band-aid and the solution is a larger, more direct, oil drain line.</p></blockquote><p></p>
[QUOTE="Onelfastlride, post: 9247167, member: 7298"] After speaking with a turbo design engineer he explained to me.......a possible cause for smoke on decel is a insufficent oil drain for the turbo. Keep in mind I have a ball bearing turbo which require less oil then a standard journal turbo, however both require a sufficent oil drain line. He explained it like this........the seals on the turbine side of the turbo are similar to a piston ring. The seal has a gap at the top, if the turbo does not drain properly, on decel when large amount of vaccumm is created on the exhaust side, the excess oil sitting in the turbo is pulled past the turbine seal and causes smoke seen in the cars exhaust. From what I've heard, oil drain lines should be a min. -10AN, -12AN is even better. They should be always on a downward slope to the pan with less then 90deg turns. So........if you have a marginally sufficent turbo oil drain line and then add a little crankcase pressure, you've made the situation worse, and it's even harder for the turbo to drain. By venting the valve covers to atmosphere and it smoked less on decel, you most likely let the turbo drain easier and stopped excess oil from being pulled past the turbine seal into the downpipe on decel. Many will say putting a restrictor in the oil feed line is a band-aid and the solution is a larger, more direct, oil drain line. [/QUOTE]
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Smoke when letting off throttle?
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