EGT Probe question - page 2 - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• #15 by larry104 on 15 Nov, 2006 20:43
• Quote from: Slave2School

  No I personally have not.  However just because I haven't doesn't mean that I don't have reasons based on facts such as the turbine sucks vast amounts of energy (heat) out of the exhaust flow to believe that the readings are virtually useless post turbine.
  
  The only application I know of where a EGT probe(s) are used post turbine are jet engines which run in a vary narrow power band and have all the variables already calculated by the manufacture of the engine.  The temperature limits are therefore useful since the engine max temps are meant to be measured post turbine.  
  
  In our case the turbos all have INLET limits so unless you mount a probe pre in addition to post, map out the difference between the two under all conditions (for each set up you run) and run a calculation in your head based on the difference...the post results will be totally useless for being used a gauge of turbo health.
  
  To each there own but other than the slight chance of breaking off my 1" long probe (rated to 2100F) there is no reason not to have it pre turbine and actually read the proper temperature.

  
  
  I rest my case.
• #16 by Slave2School on 15 Nov, 2006 20:44
• You rest your what?  Total lack of understanding...ah I see.
• #17 by larry104 on 15 Nov, 2006 20:52
• Quote from: Slave2School

  You rest your what?  Total lack of understanding...ah I see.

  
  
  I asked if you have measured egt pre and post turbine. You haven't. And telling me that a turbine absorbs "vast amounts of energy" doesn't answer my question.
• #18 by Slave2School on 15 Nov, 2006 21:01
• How can you think that it's the same or if you can't even estimate how much is absorbed?  Therefore post temps are absolutely useless.  No other way to put it.  You could be running close, maybe it's 100F difference, maybe it's 350F difference, but how do you know?  Why bother having a gauge if you have no  idea if the data it throws in your face is anywhere close to accurate or is questionable at best.  Seriously if someone wants to give me $50 I'll order another EGT probe the same as I have and mount it in the down pipe on a toggle switch so I can determine what the difference is on my setup with my turbo.  It'll be useless numbers for your set up though since the variables such as turbo efficiency are not the same.
  
  If you think you need an EGT gauge it should be done so it actually shows the actual factual EGT.  If you can't see that there is no one size fits all formula by now there is no point in continuing the conversation on pre vs post.
• #19 by 745 turbogreasel on 15 Nov, 2006 22:21
• Quote from: larry104

  
  I asked if you have measured egt pre and post turbine. You haven't. And telling me that a turbine absorbs "vast amounts of energy" doesn't answer my question.

  
  I have.  Only because I got a truck that already had a probe in the downpipe.
  
  Slave is right.
  You should not go pre turbine because it is a waste of your money.
  Akin to buying a Ferrari and only using third gear.
  Unless you got your guage for free, and don't give a crap about your engine.
  Here's why:
  
  A) Aluminum melts at 1450F and your pistons are aluminum.
  B) High EGT will burn the tips off the hot side turbine.
  C) EGT damage is cumulative.
  D) It costs more and take loger to replace a piston than a turbocharger.
  
  Post turbine measurements are about 300% slower than preturbine, and may read low by more than 25%
  
  So when you leave the line, and your EGT hits 1400F(danger) your guage may read 1000F(looks hunky dory) twenty seconds later.  I like to think most of us can get fairly far down the track in 20 seconds.  Climbing a hill is even more dangerous.
  
  I asked my Dodge expert(20 yeas as Cummins tech) the best way...He drills the manifold on the car.  If you drill carefuly, the shavings are all small enough to pass harmlessly through the turbine.  I was afraid, and removed the manifold anyway(also had to replace a broken bolt).  Still, he did it in his 7000+ LB daily driver that runs low 12s, I think his turbo is fine.
  
  With the probe being encased in stainless steel which takes much higher temps than most of the other componens, risk of disintegration is pretty negligible.  
  
  In short, POST(edit) turbo EGT guage is a waste of dash space.
• #20 by Turbinepowered on 15 Nov, 2006 23:11
• Quote

  
  .....
  .....
  .....
  
  In short, pre turbo EGT guage is a waste of dash space.

  
  
  Duuuuuude.... nice sarcasm!  
• #21 by larry104 on 16 Nov, 2006 06:10
• Quote from: Slave2School

  How can you think that it's the same or if you can't even estimate how much is absorbed?  Therefore post temps are absolutely useless.  No other way to put it.  You could be running close, maybe it's 100F difference, maybe it's 350F difference, but how do you know?  Why bother having a gauge if you have no  idea if the data it throws in your face is anywhere close to accurate or is questionable at best.  Seriously if someone wants to give me $50 I'll order another EGT probe the same as I have and mount it in the down pipe on a toggle switch so I can determine what the difference is on my setup with my turbo.  It'll be useless numbers for your set up though since the variables such as turbo efficiency are not the same.
  
  If you think you need an EGT gauge it should be done so it actually shows the actual factual EGT.  If you can't see that there is no one size fits all formula by now there is no point in continuing the conversation on pre vs post.

  
  
  What I am saying is, nobody, including yourself, has provided compelling evidence that there is not a functional and useful relationship between pre-and post-turbine temperature. On the other hand, I've read several places that pre/post delta Ts are about 200 - 300 F. If you were really that concerned about egts, you'd have a probe at each cylinder exhaust port proximal to the exhaust valve. What you are measuring downstream pre-turbine is the integrated temperatures of all cylinders minus losses to the exhaust manifold. Then there is the issue of TC lag. A TC has thermal mass and doesn't respond instantly to temperature changes; spikes get integrated out. For all these reasons, and the possibilty that a probe could break and be ingested by the turbo (just because the TC is rated to 2,100 F doesn't mean it can't mechanically fail through fatigue), is why I locate my TC post turbine.
• #22 by HarryMann on 16 Nov, 2006 06:13
• I think replace pre with post in that post 2 above...
• #23 by saurkraut on 16 Nov, 2006 06:15
• Will some one do a search to see if there is any evidence of pre turbo probes snapping off and destroying the turbo.
  
  I spend way too much time stairing at diesel crap on the internet.  I have yet to see any evidence of preturbo thermocouples disintgrating and wreaching havoc on poor defenceless turbos.
• #24 by larry104 on 16 Nov, 2006 06:29
• Quote from: 745 turbogreasel

  
  Post turbine measurements are about 300% slower than preturbine.
  

  
  
  Really? If post-turbine measurements were just 100% slower, they wouldn't be changing at all.
• #25 by HarryMann on 16 Nov, 2006 06:36
• I have been offered one here in England,
  
  300458 Westac EGT sender 1/2" tip
  
  That requires an M8x1 thread in the manifold and protrudes 17mm
  
  Does this seem a reasonable size compared to the ones that Aircraft Spruce offer ?
  
  Is 900C high enough, or would it be best to see 1000 or more?
  
  Thanks for any answers  
• #26 by saurkraut on 16 Nov, 2006 06:57
• 900c is 1652f, so it should work.
  
  VDO has pyro kits.  i like them because you get everthing for the install, and their black face gauges match the VW stuff
  
  http://www.egauges.com/vdo_mult.asp?Type=Pyrometer&Series=Vision&Units=E
• #27 by Slave2School on 16 Nov, 2006 07:34
• If million dollar jet engines have the TC PRE turbine section in many cases I think I'm safe with the VW diesel and the probe pre.  If you size the TC appropriately it won't fatigue from vibrations.
  
  There is only 1 case I know of with a pre turbine TC failing and it was bent up like a pretzel so it could be used in an EGR block off plate on a TDI.  It would have been ~4" long.  something like that certainly see exponentially more vibration than a 1" long TC.  The lucky Fin that it happened to said the VNT vanes stopped the TC from going through the turbo since such a large chunk of it broke off.
• #28 by 745 turbogreasel on 16 Nov, 2006 10:07
• LOL I typoed.
  Post turbo takes 3 times longer to react.
  
  while you are protecting you engine from those little probe peices, you probably should get rid of the glow plugs too right?
• #29 by larry104 on 16 Nov, 2006 10:26
• Quote from: 745 turbogreasel

  LOL I typoed.
  Post turbo takes 3 times longer to react.
  
  while you are protecting you engine from those little probe peices, you probably should get rid of the glow plugs too right?

  
  
  Hmmm...How do you make a "typo" between the % sign and the word "times?" Glow plugs are a necessary risk. The car won't cold start without them. A pre-tubine EGT probe isn't.