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Old 03-03-2011, 01:46 PM   #1 (permalink)
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EGR with header

I'm building the exahust header for my MGeo with G10 3-cyl,
and wondering what to do about the EGR.

The stock manifold has a little port on one cylinder that runs into a crossover passage through the head to the other side that connects to the EGR valve.

I'm wondering if this is the best way to do this for maximum MPG.
A few issues come to mind.

The EGR comes from one cylinder, I'd think it work better if it came from all 3, so the scavenging effect is equalized.

Isn't the EGR working against the intake manifold pressure, and would be better positioned as a "ram" effect.

The EGR passes through the head, would it be better to bypass this heating of the head at this spot from one cylinder?

Is it best to have the EGR gasses cooler, and thus source them much farther down the exhaust where it has a chance to cool down?

And also, I believe the EGR valve is controlled as an analog vaccuum signal, could I make it a manual switch, or perhaps eliminate the EGR valve alltogether, and have it always on, and just have less power.


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Old 03-03-2011, 02:12 PM   #2 (permalink)
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Quote:
Originally Posted by nimblemotors View Post
The EGR comes from one cylinder, I'd think it work better if it came from all 3, so the scavenging effect is equalized.
It probably would be better.


Quote:
Isn't the EGR working against the intake manifold pressure, and would be better positioned as a "ram" effect.
Mmmm, nope. Exhaust is positive pressure (vs atomosphere) and intake is negative, so EGR naturally flows to the intake.


Quote:
The EGR passes through the head, would it be better to bypass this heating of the head at this spot from one cylinder?

Is it best to have the EGR gasses cooler, and thus source them much farther down the exhaust where it has a chance to cool down?
The head will actually cool the EGR. However, on diesels and the 3rd gen Prius, they are using exterior EGR coolers so that you can run higher amounts of EGR which can have fuel economy advantages. I've been messing around with this idea, but have yet to actually fabricate/make anything to test it.

http://ecomodder.com/forum/showthrea...eage-7358.html


Quote:
And also, I believe the EGR valve is controlled as an analog vaccuum signal, could I make it a manual switch, or perhaps eliminate the EGR valve alltogether, and have it always on, and just have less power.
Having EGR on during a cold start up or at idle is probably not the best idea. It will most likely prevent the engine from running smoothly. The OEM systems do this automatically and should be retained to ensure proper engine operation.
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Old 03-03-2011, 02:22 PM   #3 (permalink)
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Diesels also frequently use EGR coolers, but probably more because of very high EGT.

6.4 and 6.0 Ford Super Duty trucks have had issues with EGR coolers, as they use coolant to cool, and if the cooler fails, engine coolant makes it into the induction system. They have HD replacement options, that you might reference if you decide to build an EGR cooler...
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Old 03-03-2011, 02:36 PM   #4 (permalink)
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Originally Posted by Backtobasics View Post
Diesels also frequently use EGR coolers, but probably more because of very high EGT.
Diesels use EGR coolers almost exclusively for meeting emissions. The cooler intake charge reduces combustion temps. This reduces the NOx produced.
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Old 03-03-2011, 02:54 PM   #5 (permalink)
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Yes, EGR coolers on diesel don't necessarily increase mileage (I should have clarified). However, they do allow you to run more EGR. On gas engines the higher amounts of EGR can be used to increase fuel economy by reducing pumping losses and optimize timing.
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Old 03-03-2011, 02:56 PM   #6 (permalink)
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I also should have clarified. If someone wants to build an EGR cooler, they might consider looking at the style used on the Diesels, that use coolant to bring temperatures down.
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Old 03-03-2011, 03:15 PM   #7 (permalink)
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Quote:
Originally Posted by Daox View Post
Mmmm, nope. Exhaust is positive pressure (vs atomosphere) and intake is negative, so EGR naturally flows to the intake.
What I was trying to say is that if you connect a tube to the exhaust flow, having it point downstream would reduce its ability to extract the flow,
having it face INTO the stream would increase it, I'd think. The stock EGR connection seems to just be a 90-degree opening to the exhaust stream.
I'm thinking of using a U tube bend that is inside the stream.

Quote:
The head will actually cool the EGR. However, on diesels and the 3rd gen Prius, they are using exterior EGR coolers so that you can run higher amounts of EGR which can have fuel economy advantages. I've been messing around with this idea, but have yet to actually fabricate/make anything to test it.

http://ecomodder.com/forum/showthrea...eage-7358.html
thanks for that reference, I did a quick search and didn't see it immediately.
So they route it through the head to cool it? well that heats the head, my concern is it imbalances the heat to that cylinder next to the passage.

The advantage might be to shorten the warm-up time, which we know is important, In fact, I was thinking of routing coolant around the exhaust to heat it up faster, then it could be turned off once the car is warmed up.
For a distance commuter as this car is designed for, warmup time wouldn't be a factor and I don't want to complicate this car, but might consider it for the Boxster.

So it sounds like it would be a good idea to run a long tube down to past the muffler to tap into the EGR source, and by-pass the head passage, and connect it to the stock EGR right now. If I get to replacing the ECU with my own, I might replace the EGR with an electronic controlled version.

Jack Murray




Having EGR on during a cold start up or at idle is probably not the best idea. It will most likely prevent the engine from running smoothly. The OEM systems do this automatically and should be retained to ensure proper engine operation.[/QUOTE]
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Old 03-03-2011, 03:31 PM   #8 (permalink)
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Quote:
Originally Posted by Daox View Post
Yes, EGR coolers on diesel don't necessarily increase mileage (I should have clarified). However, they do allow you to run more EGR. On gas engines the higher amounts of EGR can be used to increase fuel economy by reducing pumping losses and optimize timing.
Actually EGR coolers on a diesel do improve mileage a tad. Cooler combustion temps mean less heat lost on the combustion stroke to the cooling system. However the sole reason for using them is to meet emissions.

Diesel or not, running more EGR doesn't improve mileage. Running the right amount does.

In a diesel often no egr is best because it allows the turbo to make more pressure in the intake than it uses to drive the turbine in the exhaust.
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Old 03-03-2011, 03:39 PM   #9 (permalink)
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I don't think the angle on the EGR inlet inside the pipe will matter. I'd probably keep it clear for a more efficient header. Its the pressure differential between the exhaust and intake that pulls it through the system.

I'm not sure if they route it through the head specifically to cool it or just for space savings. I'm sure it does add heat in near the cylinder its near. However, I'd imagine the coolant negates that effect a fair amount.

The 3rd gen Prius also uses an exhaust coolant heater. There is more info on that here:
http://ecomodder.com/forum/showthrea...very-7107.html

The main problem I ran into when looking into it was how to disconnect the heater from the exhaust once up to temperature.
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Old 03-03-2011, 11:36 PM   #10 (permalink)
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A G10 does not even need a working EGR and it will not effect performance or power. However certain states have emission testing and a functioning EGR would be a must.

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