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Turbo maybe too big?


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Ive got some questions, concerning the correlation between boost, egts, gear and load. The truck in question is a 2004 CV 713 with a AI300/Allison 4500/4.64 rears. We recently did the EGR cripple (E-Tech exhaust manifold/full 5 inch exhaust/427 hp injectors and S467 YTS turbo, Pyro and boost gauges. Im much happier with the power of the truck, especially the initial rollout from a dead stop. When she is loaded, I notice that when she hits top gear and speed levels out (60-65), the EGTs get up to 900ish @ 1400-1450 rpms. If I downshift a gear, rpm and boost both increase and EGTs go down to 700-750 range. At WOT it will drop to the high 600s. Is this indicative of the turbo being too large? When we tag the excavator along (82k gross), we stay below 50 and she runs in the 700s. I know i was told to keep egts below 4 digits would be a good goal, so I downshift, or back out of the throttle a tad  when it exceeds 900. Am i being too cautious at 900? Would a different (smaller) turbo have better flow at a lower engine rpm and keep egts lower without downshifting? 

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well, i'm curious.. because to me it sounds fine, but then again, I am not a good study on this, i just knew when I was running a bit hot and would adjust as I went...  It' been a while.... looking forward to some more comments just caus' jojo

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Sounds to be working the way it should ! Your observations are What I would expect The exhaust temp going up indicates to me that u have reached the point where the turbo is not producing ENOUGH air for the fuel being feed to cyls  taking half a gear is the right thing to do ! if the temp climb is gradual  everything is good But If the temp climb is relatively fast then you may have a boost leak! At this point you should see smoke behind you even when you have your foot right in it!

 

Just my opinion

Edited by fjh
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Running too rich will increase exhaust temps. Also if your exhaust system has too much back pressure then you will experience very high exhaust temps. I had several truck over the years where customers were experiencing exhaust temps being too high and found that the baffle inside the muffler would restrict the exhaust flow out. But with your situation it seems normal.

V

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Yup All relative ! If you have a restriction on the muffler side its the same result as a boost leak not enough air flow in Or out of the engine!  for the most part!

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Your temps are fine. We run a little bit bigger turbo (s475 1.32ar) and have the same temps as you. As long as we keep it above 1400 the pyro stays below 1000. 1650-1700 on a hard pull she's right around 900-950 and on flat ground around 700

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I noticed when out and about in Mrs Mack that on the Pyro guage it says something to the effect of "maximum 600 c°" which is over 1100 f 

So the 900 that was the original question is as we all thought and according to my Pyro guage  perfectly normal and my bog stock 320 coolpower runs at 450 all day which is around 850 and gets up to 600 mark on a long hard pull

 

Paul

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Ok, sounds like she is doing good, i thought she was getting a little too hot, but from the feedback, sounds like she is good. I still may try a slightly smaller turbo to keep the boost up more when she makes the 3-4 and 4-5 shifts, she drops down pretty low and takes a few seconds to build it back on those two, 5-6 isnt bad(smaller step) and your over 50 or so by then and backing out anyway.

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