I just recently installed a straight 5 inch exhaust, from my chopped banks exhaust(straight through no muffler) I have a growing concern that my EGT's may have jumped 100+ degrees after the install. Now with that being said my old 4 inch exhaust never had too much trouble with high EGT's, they seemed to stay pretty tame and even getting on it pulling a hill they would be excusable... but now with this exhaust on now it doesn't seem to be have much trouble hitting 900 degrees(every shift) with easy driving... whats going on? Is it the full exhaust that's doing it or am i missing something.

Thanks Ben
Semper Fi

P.s: sorry for the long story, just feel it is necessary to provide all the details!

 

And nothing else has changed besides the exhaust? I find it hard to fathom that changing the exhaust changed the EGT's. That being said, do you always fill up at the same place? I know my EGT's will vary about 50-70* based on where I fill up sometimes. Just a thought.

 

Larger pipe may limit scavenging to some extent. This is a VERY minimal issue with a turbocharged engine since the turbo creates backpressure preventing exhaust pulse scavenging anyhow, but in the event that you let off the throttle fully, then apply heavily between shifts, the draft still existing with 4" may be going away with 5" for the short period when the turbo spools back up after reapplication of the throttle.

If this is what's happening, I wouldn't worry about it. Short lived spikes in temps are pretty tolerable since the heat can be dissipated to the shaft of the turbo and the piston is large enough to absorb some heat before failure. *Sustained* higher temps would be the real issue. Keep in mind, turbos don't get graphed, they get MAPPED. This means two variables affecting a third. Changing nearly anything will affect the map and change the hot spikes.

Having said that, 900 doesn't sound that bad if your probe is post turbo. 900 is only getting toasty for a preturbo probe.

 

as for the fuel stops i always fuel up at the same place....but what you said totalloser makes some sense but I also inquired another cummins buff and he said that maybe they probe could be sticking some how or something, and also noted that soem times to get the turbo to cool down to my preferred shut down temp. I give it a steady throttle then let off and it moves noticeably and then it cools down quicker than when i just bring it to a stop.

 

Sounds like normal operation, to me, but I'm just theorizing so take it in that context.

If you rev the engine with no load, more air passes through the engine and turbo, with very minimal increases in fueling. I often run the engine at a slightly higher rpm for a while to cool the turbo faster after getting off the freeway.

Again, 900 is not really hot if your probe is after the exhaust fan. 1250 is hot for post turbo. 1250 is likely to be a cooked engine for a preturbo reading.

 

As already asked.....was anything else done besides exhaust? And how long had the exhaust been in place before you started noticing the difference in EGT's? I ask because if it was noticeably instantaneous then you could blame the new exhaust but if you just happen to notice after more than a few days but are blaming the exhaust because you cant think of anything else, then consider an incorrect thermocouple or gauge.

I had my gauges in long enough to know exactly what my EGT's should be during most scenarios and when my EGT's started acting strangely hot or not acting like they should, I thought of the obvious first (boost leak, fueling, etc.) but then came to the conclusion that there must be something wrong with the gauge or thermocouple.....and there was. After calling the manufacture and them telling me how to test the components, I replaced the thermocouple and the gauges electronic box and everything was back to normal. Now had I done "anything" else to the truck during that time, I would have had more things to consider or rule out.

 

after reading the your post KATOOM, and gathering some other knowledge Im gonna assume that its the gauge, but im not gonna rule out that the exhaust did it too only because after installing the exhaust I immediately saw a jump in EGT's but tho the gauge didn't act like it used to either.