Another EGR question
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Race Director
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From: Lake Wylie SC
Another EGR question
Okay, we all know the function of the EGR system is to 1) reduce NOx and 2) to reduce combustion chamber temps. This system was put on engines with OEM cam shafts which didn't have much if any over lap (which allows exhaust gas in the combustion chamber). My question is when using a GM Hot cam in a LT1 engine, is there enough duration to produce the same effect of the EGR as in the LT4 cam? I've just rebuilt a LT1 to a 383 with the GM hotcam and 1.6 rockers and wonder if the EGR system is needed.
Burning Brakes
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From: Ridgecrest Ca
The EGR function (open/close) is done with vacuum. If you end up with too little vacuum due to an aggressive cam then likely the EGR will not function properly but neither will any other vacuum controlled functions like the HVAC blend door etc. Not sure of the later EGRs but my 90 requires the proper amount of backpressure and vacuum to operate correctly.
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From: Lake Wylie SC
Again to further clarify my question, The function of the EGR where it adds exhaust to the combustion chamber for cooling and stopping or reducing ping, it is my understanding that the EGR opens by direction of the ECM which uses many sensors to compute when to open the valve. When using a GM Hot cam, the amount of time, both the exhaust valve and the intake valve are open simultaneously, is increased more than the OEM cam. Does anyone know if this is enough to eliminate the need for an EGR system. What leads me to this question is the LT4 not having an EGR system because of the cam design. I hope so as I would like to remove the EGR system. Yes, I know the ECM will be tuned with this mod. My concern is the temperature of the combustion chamber with our aluminum heads and pistons.
Team Owner
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From: Park City Utah
The EGR function (open/close) is done with vacuum. If you end up with too little vacuum due to an aggressive cam then likely the EGR will not function properly but neither will any other vacuum controlled functions like the HVAC blend door etc. Not sure of the later EGRs but my 90 requires the proper amount of backpressure and vacuum to operate correctly.
OP, The stock LT4 cam apparently had enough overlap to preclude the necessity of the EGR system; the LT4 meets the requirements w/o one. The LT4 hot cam is more aggressive and I assume has more overlap than the stock LT4 cam, so *I* would submit that it would provide an "EGR function" w/o and EGR valve.
OTOH, there is no danger to the aluminum heads and pistons due to combustion temps, with or w/o an EGR function. The aluminum and the cooling system are more than capable of pulling heat away from the surface areas of the combustion chambers. The need to lower combustion temps is not to protect the hardware; it is to meet emissions requirements.
Last edited by Tom400CFI; Feb 10, 2015 at 02:17 PM.
Thread Starter
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From: Lake Wylie SC
Thank you for your thoughts. I guess I should run a poll on the question, but I think I'll be the test case on this one. I lost my cam spec card which would have told me the duration, but I tend to agree with you that an EGR in my case is not required.
Hey Tom, I like skiing around the buoys, too.
Hey Tom, I like skiing around the buoys, too.
Last edited by Strick; Feb 10, 2015 at 02:25 PM.
Thread Starter
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From: Lake Wylie SC
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Drifting
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From: Motor City
I really never thought of this point when considering the never ending EGR vs. no EGR debate on the forums. But, I would also agree that the extra overlap of the LT4 cam (or other aftermarket cams) creating more internal EGR would offset the external EGR from the factory. Good thought 
Intermediate
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From: Tallahassee Florida
I really never thought of this point when considering the never ending EGR vs. no EGR debate on the forums. But, I would also agree that the extra overlap of the LT4 cam (or other aftermarket cams) creating more internal EGR would offset the external EGR from the factory. Good thought
Just to clarify (and ask selfishly) What plugs or parts were used to block system off???
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From: Lake Wylie SC
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^Not answering the OP's question.
OP, The stock LT4 cam apparently had enough overlap to preclude the necessity of the EGR system; the LT4 meets the requirements w/o one. The LT4 hot cam is more aggressive and I assume has more overlap than the stock LT4 cam, so *I* would submit that it would provide an "EGR function" w/o and EGR valve.
OTOH, there is no danger to the aluminum heads and pistons due to combustion temps, with or w/o an EGR function. The aluminum and the cooling system are more than capable of pulling heat away from the surface areas of the combustion chambers. The need to lower combustion temps is not to protect the hardware; it is to meet emissions requirements.
OP, The stock LT4 cam apparently had enough overlap to preclude the necessity of the EGR system; the LT4 meets the requirements w/o one. The LT4 hot cam is more aggressive and I assume has more overlap than the stock LT4 cam, so *I* would submit that it would provide an "EGR function" w/o and EGR valve.
OTOH, there is no danger to the aluminum heads and pistons due to combustion temps, with or w/o an EGR function. The aluminum and the cooling system are more than capable of pulling heat away from the surface areas of the combustion chambers. The need to lower combustion temps is not to protect the hardware; it is to meet emissions requirements.
Racer
Joined: Dec 2007
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Since you're having it tuned it should be adjusted for in the tune, for example the .5 to 1 degree EGR ignition advance put there JUST BECAUSE EGR IS PRESENT can be put back to zero, or whatever the tuner thinks is the right amount in the little window where stock tuning alters the timing advance for EGR.
It's similiar to DFCO, not needed but since it can be added to the computer program why not....
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Race Director
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From: Lake Wylie SC
My opinion is that someone at some point in time said we can just add an EGR system to anything to reduce emissions. Not the other way around, no one said wow this engine needs EGR to cool the combustion chambers.
Since you're having it tuned it should be adjusted for in the tune, for example the .5 to 1 degree EGR ignition advance put there JUST BECAUSE EGR IS PRESENT can be put back to zero, or whatever the tuner thinks is the right amount in the little window where stock tuning alters the timing advance for EGR.
It's similiar to DFCO, not needed but since it can be added to the computer program why not....
Since you're having it tuned it should be adjusted for in the tune, for example the .5 to 1 degree EGR ignition advance put there JUST BECAUSE EGR IS PRESENT can be put back to zero, or whatever the tuner thinks is the right amount in the little window where stock tuning alters the timing advance for EGR.
It's similiar to DFCO, not needed but since it can be added to the computer program why not....
Racer
Joined: Dec 2007
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The two functions of the EGR system seem to be connected. EPA says to reduce NOx so the engineers came up with a way of reducing NOx by decreasing the combustion temperature. Decreasing the combustion temperatures also decreases detonation or "ping." With lower combustion temps, octane levels could also be reduced. So everybody was happy.
I don't unterstand your concern, and I really, I REALLY don't want you to explain it.
You've re-engineered a small block chevy, something thats been done a million times. You're going to have it tuned, I'm assuming dyno tuned. Throw the EGR in the garbage, let the tuner tune it. It's going to be fine.
Whens the last time you heard of someone melting their engine down because they took the EGR off?
Thread Starter
Race Director
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From: Lake Wylie SC
Until engine computers came along, then spark was added when EGR was active.
I don't unterstand your concern, and I really, I REALLY don't want you to explain it.
You've re-engineered a small block chevy, something thats been done a million times. You're going to have it tuned, I'm assuming dyno tuned. Throw the EGR in the garbage, let the tuner tune it. It's going to be fine.
Whens the last time you heard of someone melting their engine down because they took the EGR off?
I don't unterstand your concern, and I really, I REALLY don't want you to explain it.
You've re-engineered a small block chevy, something thats been done a million times. You're going to have it tuned, I'm assuming dyno tuned. Throw the EGR in the garbage, let the tuner tune it. It's going to be fine.
Whens the last time you heard of someone melting their engine down because they took the EGR off?
Instructor
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From: NW Arkansas - usually winter in FL
Strick - -Seems like you are spot on relative to the function of the EGR system - way better than most. As to your question if the new hot cam will replace the EGR gases - I have no idea. Increased overlap sounds logical in itself and increases in overlap usually reduces NOx generation because of exhaust dilution of the intake charge but, well "logical" doesnt always play out in the real world because of all the other varibles which come into the equation. Somebody probably does know - but it's not me - LOL.
Anyway, seriously doubt you will have much change in detonation characterstics - but your cruise NOx will probably increase a smidge.
Jake -
Anyway, seriously doubt you will have much change in detonation characterstics - but your cruise NOx will probably increase a smidge.
Jake -
Last edited by jake corvette; Feb 13, 2015 at 08:44 PM.
Thread Starter
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From: Lake Wylie SC
Strick - -Seems like you are spot on relative to the function of the EGR system - way better than most. As to your question if the new hot cam will replace the EGR gases - I have no idea. Increased overlap sounds logical in itself and increases in overlap usually reduces NOx generation because of exhaust dilution of the intake charge but, well "logical" doesnt always play out in the real world because of all the other varibles which come into the equation. Somebody probably does know - but it's not me - LOL.
Anyway, seriously doubt you will have much change in detonation characterstics - but your cruise NOx will probably increase a smidge.
Jake -
Anyway, seriously doubt you will have much change in detonation characterstics - but your cruise NOx will probably increase a smidge.
Jake -