EGR, Should I run one

[Dirtfarmer]

Building a new motor for the J10, 401 9 to 1ish compression, Edelbrock performer cam and Intake. Unhooking virtually all the emissions. Will probably start out carbed but would like to go with a TBI at some point. My question is should I run an EGR, will it do any good alone for drivability without the other emissions stuff.

[FSJunkie]

An engine tuned to run with EGR will run great. An engine tuned to run without EGR will run great. If either one is run the other way, problems can arise.

[Southern Gorilla]

EGR is just another emissions device. There's no performance or economy benefit to running it.

[tgreese]

EGR is just another emissions device. There's no performance or economy benefit to running it.

True but deceptive. There is also no performance or economy advantage to removing it, unless you change the air-fuel mixture to compensate.

The EGR mixes exhaust gas with the fuel-air mixture to lower the temperature of combustion. This reduces the amount of nitrates of oxygen NOx in the exhaust. If your Jeep came with EGR, the carburetor mixture is factory-set to work with EGR. You can't change that unless you change the main jets inside the carburetor.

If you keep the factory carburetor and don't change the main jets, there is no performance advantage to removing the EGR system. When and if you go TBI, the computer will then adjust the air-fuel mixture based on the reading from the O2 sensor in the exhaust gas. Then you can remove the EGR and possibly get a slight performance boost ... but the engine will produce more NOx.

[Dirtfarmer]

What about ping? If I end up with a compression ration around 9.5 to 1 and try to run regular pump gas would an EGR help at all with that.

[FSJunkie]

EGR does not operate at full throttle, so no matter if you run EGR or not, you'll still need to run fuel with just as much octane. At 9.5:1, I wouldn't put anything less than 91 octane premium in it. Don't be a cheapskate and try to get away with 89 just because you don't hear anything. Detonation occurs way before you hear it, and will destroy your engine. Maybe not today, not tomorrow, but eventually it'll catch up.

The ignition timing for EGR engines is set to deal with EGR. The initial timing and mechanical advance should not be much different than a non-EGR engine, but it's good to check them anyway. Vacuum advance for EGR is higher than non-EGR, because the diluted fuel charge burns slower and requires earlier ignition. The starting and full vacuum advance is the same, but the total timing the vacuum advance gives will be somewhere around 20-25* for an EGR engine, while a non-EGR engine will need something more like 15-20*. This is where people who have distributors set up for EGR, but disconnect the valve run into part throttle ping problems, they have too much vacuum advance.

The carburetors for EGR and non-EGR are jetted the same or so close to the same that you won't have problems. For proof of this, the Motorcraft 2100 1.21v on a 1968 Ford 360 non-EGR has #55 min jets, and the Motorcraft 2150 1.21v on a 1984 Jeep 360 EGR has the same #55 jets. I am currently running that 1984 Jeep carburetor (EGR) on my 1972 (non-EGR) engine, and it runs better than the factory carb!

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This is an automotive topic, worse yet, it's an emission control automotive topic. Opinions are going to vary greatly, and you have no way of telling who is actually correct unless you do some research yourself. I suggest you check out some books on EGR and engine tuning from your local public library, but those can be biased as well because they are written by self-promoted "experts". Probably the least biased references you can find are called SAE papers, and are based on scientific tests in laboratory conditions. This one should tell you just about everything you need to know about EGR.

http://papers.sae.org/2013-24-0113/

[Southern Gorilla]

EGR is just another emissions device. There's no performance or economy benefit to running it.

True but deceptive. There is also no performance or economy advantage to removing it, unless you change the air-fuel mixture to compensate.

There has to be some advantage, although I'm sure it would be trivial to the point of immeasurable. The recirculated exhaust gas is non-combustible and displaces some of the air/fuel mix. Without that exhaust gas you will have more clean charge in the cylinder and therefor more power. But I'm definitely not going to argue that you will notice the difference. So if we define "advantage" as meaning "noticeable improvement" then I absolutely agree with you.

One thing I'm sure we can all agree on is that the EGR is one more thing that can go wrong. So why have it if you don't need it?

[tgreese]

There has to be some advantage, although I'm sure it would be trivial to the point of immeasurable. The recirculated exhaust gas is non-combustible and displaces some of the air/fuel mix. ...

Not in practice. Since the exhaust gas is introduced to the intake manifold, it does displace some of the air-fuel charge. But the difference would only show up at WOT where the demand for fuel exceeds the supply. There is no EGR when vacuum is low at WOT. All the EGR does is reduce the O2 fraction and reduce combustion temperature at part throttle cruise. If the EGR system already functions correctly, there should be no performance difference if you remove it. But removing it will change the air-fuel ratio at cruise speeds.

Why would you remove the EGR if it works? All you gain is a few less hoses under your hood, and a dirtier exhaust. Seems like a lousy bargain.

[FSJunkie]

EGR does not require different carburetor jetting. For a given amount of oxygen in the cylinder, there needs to be a certain amount of fuel. Exhaust gas is inert and will not change the ratio of fuel to oxygen, nor will it react to combustion, it only takes up space in the cylinder so less of the same fuel-air mixture can be admitted. The ratio of fuel to oxygen remains the same, only there is proportionally less of both. Aside from cooling combustion, the side effect of inert gas dilution is it makes your engine effectively smaller in displacement.

Benefits of EGR:

When EGR is operating, less throttle is needed and this increases fuel economy, though with less burnable mixture, the engine will have less power and the throttle plates will need to be opened further to attain the same output. In that way, the situation offsets pretty equally.

EGR cools combustion, resulting on less stress on exhaust valves, spark plugs, piston heads, and the engine cooling system.

A 1973 engine with EGR produces 1/8 the emissions of a 1960 engine.

EGR is not in operation at idle to maintain idle quality, nor does it operate under hard acceleration or load.


Downsides:

3 vacuum lines for most systems. Oh my gosh, how could we possibly manage!?

Can cause carbon buildup in the intake system.

Valve requires maintenance or it'll gum up and malfunction. "Wait, you mean cars need attention!?"

It's guvment interference in our daily operation of vehicles, which instantly makes it an evil first step towards communism in the minds of scared people.

People don't do their own research about how it works, and believe what the scared people above, or quite simply people who have misconceptions about how it works, say about it. Just because someone has been building engines for 40 years doesn't mean they know how EGR works.

[carnuck]

comparing a '60 with a '73 is misleading because the motor design was changed. REAL world numbers of a motor with/without EGR are a better comparison. I leave the EGR on my motors (that came with one) and unhook the hose and tune to run without it. If I get a bad tank of gas and it pings, I hook the hose up till I get my next tank of good stuff. I really wish we had 85 octane here in Seattle because the crap they add to 87 "regular" here screws too many things up!

[serehill]

no EGR