Low EGT's with OD Off???
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Low EGT's with OD Off???
Totally confused.
I expected HIGHER EGT's with OD off due to the higher RPM's, but I'm actually seeing the EGT's drop by at 50-80 degrees with OD off.
There is an increase in the boost with the OD off could this be why?
I just don't get it?
I expected HIGHER EGT's with OD off due to the higher RPM's, but I'm actually seeing the EGT's drop by at 50-80 degrees with OD off.
There is an increase in the boost with the OD off could this be why?
I just don't get it?
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From: ARIZONA
as it was explained to me a few months ago,
boost is good, if you can use it, but once you reach the point where you cant your just putting it under greater preassure which generates heat, becuase its not moving through the motor, which then makes in not as effecient - does that sound right, i thought it logical at the time because of the fact that most cant move over 25 psi effeciently with out highly a modified motor/turbo.
boost is good, if you can use it, but once you reach the point where you cant your just putting it under greater preassure which generates heat, becuase its not moving through the motor, which then makes in not as effecient - does that sound right, i thought it logical at the time because of the fact that most cant move over 25 psi effeciently with out highly a modified motor/turbo.
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From: Fulltime RVer
Turbochargers compress the air by increasing the velocity of the molecules. When the air molecules don't move in a direction toward the intercooler (IC), they serve only to heat the air. The more the air is heated above that predicted by adiabatic compression (which is the minimum ideal heating required to increase the pressure a given amount), then the less efficient the turbocharger is.
In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure. For my early 99, I only have 2" boots going to each head (versus the 3" ones on later trucks), and I'm convinced after much trial and error road testing that for me, any boost above 20-22 psi is primarily heating the air and not getting more air into the engine. That's why I use my special boost limiter spring. Later model trucks can probably use 22-24 psi, and mods to improve air flow can probably use a little more boost. But, I also think that any boost over 20 psi on an OEM turbo exponentially increases the wear on the bearing.
In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure. For my early 99, I only have 2" boots going to each head (versus the 3" ones on later trucks), and I'm convinced after much trial and error road testing that for me, any boost above 20-22 psi is primarily heating the air and not getting more air into the engine. That's why I use my special boost limiter spring. Later model trucks can probably use 22-24 psi, and mods to improve air flow can probably use a little more boost. But, I also think that any boost over 20 psi on an OEM turbo exponentially increases the wear on the bearing.
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Thanks for the input guys!
I thought along the lines you guys have suggested.
I've always viewed an increase in RPM would relate to an increase in heat.
For example everytime I lay into the pedal RPM/Boost/EGT's rise.
But by merely hitting the OD OFF button I get an increase in RPM/Boost but a decrease in EGT's. Granted I'm not romping the pedal, but I am giving it fuel to maintain speed. Maybe you guys can try it yourself.
I guess the increase in RPM would be relate to an increase in ENGINE temp, but because of the turbo no increase in EGTs.
I thought along the lines you guys have suggested.
I've always viewed an increase in RPM would relate to an increase in heat.
For example everytime I lay into the pedal RPM/Boost/EGT's rise.
But by merely hitting the OD OFF button I get an increase in RPM/Boost but a decrease in EGT's. Granted I'm not romping the pedal, but I am giving it fuel to maintain speed. Maybe you guys can try it yourself.
I guess the increase in RPM would be relate to an increase in ENGINE temp, but because of the turbo no increase in EGTs.
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You'll notice that if you lug the engine slightly (not truly lug, but run lower rpms where it's on the point of downshifting), that the boost is lower, and thus the fuel isn't burning as much - more smoke and more heat (EGTs). When you get the RPMs up you're into the peak torque/hp range, you get more boost (air) and the fuel burns more fully, less smoke, less heat.
More air burns the fuel more fully, so you get less smoke, and lower EGTs.
More air burns the fuel more fully, so you get less smoke, and lower EGTs.
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From: 21791
Guys if your respoonses were to my question directed at Bigtorque, i know how a turbocharger works and the concepts that were touched on. However what i took from what Bigtorque said is unrelated to higher EGT's due to lugging the engine (Certainly not 25psi) versus downshifting and running a few higher RPM to flow more air in and out of the ENGINE, not the turbocharger. Downshifting from OD to direct drive won't create 25psi unless you are under full load, and by that time you would be in 2nd gear anyway. True over 25psi it will superheat the air and work against cooling the EGT, however i dont see how that is relevant to the situation. 
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Originally Posted by ryaneverk2
You'll notice that if you lug the engine slightly (not truly lug, but run lower rpms where it's on the point of downshifting), that the boost is lower, and thus the fuel isn't burning as much - more smoke and more heat (EGTs). When you get the RPMs up you're into the peak torque/hp range, you get more boost (air) and the fuel burns more fully, less smoke, less heat.
More air burns the fuel more fully, so you get less smoke, and lower EGTs.
More air burns the fuel more fully, so you get less smoke, and lower EGTs.
Next question regarding OD Off....
Is it more fuel efficient to run with OD off at around 45-50mph with RPM's running about 2000?
I know I'm probably using more fuel the higher the RPM's, but with the turbo in the picture, is it actually more effiecient (ie. Less smoke, better burn)?
I really like the quick jump at that speed with the OD off. Then when the RPM's start climbing, click the OD.
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Originally Posted by strokin_it7.3
Guys if your respoonses were to my question directed at Bigtorque, i know how a turbocharger works and the concepts that were touched on. However what i took from what Bigtorque said is unrelated to higher EGT's due to lugging the engine (Certainly not 25psi) versus downshifting and running a few higher RPM to flow more air in and out of the ENGINE, not the turbocharger. Downshifting from OD to direct drive won't create 25psi unless you are under full load, and by that time you would be in 2nd gear anyway. True over 25psi it will superheat the air and work against cooling the EGT, however i dont see how that is relevant to the situation.
I can run 25+ psi for miles on end in any gear including OD, and I did it on a regular basis for many years before I installed my special boost limiting spring. I can still set an over boost SES code in OD even with my spring. I do have a special chip that retards the torque demand downshifts, but even with a stock truck this downshift will not occur if the road speed is high enough, because a downshift would cause excessive rpm. For example, at 71 mph my 4.10 diff rev's the engine at 2200 rpm, a downshift to 3rd at this speed would result in an rpm of 3100, which is almost at the rev limiter.
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Originally Posted by MoreSmoke
EXACTLY what I noticed regarding the smoke as well!
Next question regarding OD Off....
Is it more fuel efficient to run with OD off at around 45-50mph with RPM's running about 2000?
I know I'm probably using more fuel the higher the RPM's, but with the turbo in the picture, is it actually more effiecient (ie. Less smoke, better burn)?
I really like the quick jump at that speed with the OD off. Then when the RPM's start climbing, click the OD.
Next question regarding OD Off....
Is it more fuel efficient to run with OD off at around 45-50mph with RPM's running about 2000?
I know I'm probably using more fuel the higher the RPM's, but with the turbo in the picture, is it actually more effiecient (ie. Less smoke, better burn)?
I really like the quick jump at that speed with the OD off. Then when the RPM's start climbing, click the OD.
Again, you're in the peak torque range, boost builds real quickly, and you just zoom ahead. 
