EGR?

[Chero77]

Many people have said that if you remove the EGR valve, the engine will run leaner. Does anyone know why this would be? As I understand it, the EGR valve operates from ported vacuum, thus it is closed at idle and wide open throttle when ported vaccum is low, and only operates at part-throttle when ported vaccum is high.

Also, EGR dilutes the air/fuel mixture with relatively inert exhuast gas. Ok, so if EGR dilutes the mixture when the valve is operating, wouldn't the mixture be a little richer if you removed the valve? i.e. no dilution so you get a richer mixture.

Anyway, I tried running without EGR today and I felt little difference. If anything, it seemed like the engine had more power. But that could have been my imagination.

[Langdon]

As I understand it: the engine is pulling the same volumes of fuel and 'air' with or without egr. With egr, inert exhaust is added so the same amt. of fuel is mixed with a lesser amt. of _oxygen_ = richer mixture. Without egr, same amt. of fuel is mixed with more oxygen = leaner mixture.

:cool:

[Stuka]

You will have more power without the EGR, because your engine is not being fed HOT exhuast fumes. Instead its just getting cooler air from outside.

[ October 27, 2001: Message edited by: Stuka ]

[Chero77]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Langdon:
As I understand it: the engine is pulling the same volumes of fuel and 'air' with or without egr. With egr, inert exhaust is added so the same amt. of fuel is mixed with a lesser amt. of _oxygen_ = richer mixture. Without egr, same amt. of fuel is mixed with more oxygen = leaner mixture.

:cool:<HR></BLOCKQUOTE>

Ok, well I agree with the above to the extent that at least at the throttle plates the engine pulls in the same amount of mixture with or without EGR. However, I am not sure that EGR actually changes the mixture density much. Maybe what happens is that the EGR merely displaces a certain amount (like 10% or so) of mixture in each cylinder (and for reasons I don't really understand, but accept as true, reduces peak combustion temperatures). So if the above is true, then with EGR, each cylinder is filled with 90% mixture and 10% exhaust gas. Thus by disconnecting the EGR, I may be feeling an increase in power because because each cylinder now gets 100% mixture rather than 90%.

Any comments on this, or any other theory EGR operation, are welcome.

Also, I have read (in a Hot Rod article) that stock EGR equipped vehicles have spark advance curves that provide extra advance during EGR operation. However, I can't think of any reason why this would be, rather it seems like an EGR equipped vehicle would have a retarded timing curve.

Any comments or experiences are welcome. My local bookstore has plenty of books that say what EGR does, but not how it does it. None state the interaction between spark advance and EGR. So far as I can see the pros of EGR are that it reduces NOX and that it reduces the possiblity of detonation with lean mixtures. The drawbacks seem to be it reduces power by displacing mixture in the cylinders and of course it makes the engine more complicated.

[reddog]

With an EGR combustion temps are decreased because of the reduction in available fuel matched by the reduction in available O2 in relation to combustion chamber size. The exhaust gas introduced via the EGR is lower in O2 content so the "EGR" carb is jetted to take this reduction in O2 into account via leaner mixture.

When I replaced the non functioning EGR in my 87 (with stock 2150 carb) with a good EGR the pinging I was getting was reduced alot.

Kerry

[Chero77]

Well, I flogged my jeep over hill and dale today with the EGR disconnected. For whatever reasons, without EGR I have noticably improved throttle response and more power. I now realize that the mediocre throttle response I had previously been assuming was a characteristic of carbureted engines was actually caused by my EGR. I did some freeway driving too and did not experience any pinging. My guess is that the EGR valve was diluting the mixture more than its supposed to. Anyway, from now on its staying disconnected. Now that I see how much better the engine runs without the EGR, I suppose I will end up removing all the smog stuff except the spark CTO. I don't think these primitive '70s emmissions controls worked well from day one. Anyway, I've spent to much money trying to get the emissions stuff to work right. Its time for it to go.

[JOECOOL]

Dave just don't toss them. You will need them for the smog checks. I yank off the cr*p same day I get home from the smog chec andstore it till next time.

[Chero77]

<BLOCKQUOTE>quote:</font><HR>Originally posted by JOECOOL:
Dave just don't toss them. You will need them for the smog checks. I yank off the cr*p same day I get home from the smog chec andstore it till next time.<HR></BLOCKQUOTE>

Yeah, have to keep that stuff around. The current plan is remove the EGR valve and the EGR CTO and block them off. Also, I am going to get a second set of exhaust manifolds from which I will remove the air injection tubes and swap them in for my current manifolds. Of course will remove the smog pump as well. Then every two years its swap in the smog stuff, get tested, and swap it back out.

Heck, the only real smog controls on a 49 state '77 are the air injection system which doesn't effect performance one iota (but seems to get in the way of just about everything) and the EGR system, which at least on my rig does adversely affect performance.

My only concern with removing the EGR was the spark advance curve, i.e., would detonaton occur with EGR removed. So far no problem.

[ October 29, 2001: Message edited by: Dave _S ]

[JOECOOL]

I only needed the EGR with a stock lean jetted carb. I pinged when I removed the EGR but I was able to stop it by going higher grade gas. I ended up swapping a holley carb and was able to run the cheaper gas again.
Not really sure on how an EGR works but I only run a stock carb at smog checks so it don't matter.
If you get pinging try jetting up a little or running higher octane gas.

[Chero77]

<BLOCKQUOTE>quote:</font><HR>Originally posted by JOECOOL:
I only needed the EGR with a stock lean jetted carb. I pinged when I removed the EGR but I was able to stop it by going higher grade gas. I ended up swapping a holley carb and was able to run the cheaper gas again.
Not really sure on how an EGR works but I only run a stock carb at smog checks so it don't matter.
If you get pinging try jetting up a little or running higher octane gas.<HR></BLOCKQUOTE>

I am planning on a switch to a Holley 4160. Got one off ebay cheap and got the rebuild kit from Summit. I am looking for another stock phenolic spacer (anyone have one?). I am planning on drilling out the holes to better match the Holley. If that doesn't work (the phenolic material seem brittle - might break when I drill it) I am going to use a one inch open spacer over a stock spacer.

[Bob Barry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Dave _S:
I am planning on a switch to a Holley 4160. Got one off ebay cheap and got the rebuild kit from Summit. I am looking for another stock phenolic spacer (anyone have one?). I am planning on drilling out the holes to better match the Holley. If that doesn't work (the phenolic material seem brittle - might break when I drill it) I am going to use a one inch open spacer over a stock spacer.<HR></BLOCKQUOTE>

The stock spacer does not have flat surfaces on the top and bottom; like the 2150, Jeep used the screwball thick composition gasket on top of the phenolic spacer, which itself was not flat but rather had raised "lips" for each of the throttle bores. From what I recall, it didn't look like there was nearly enough meat to hog it out to fit the Holley's bores. An open spacer above the stock spacer might leave gaping holes; at least it's worth a shot, though, right? You may have a different spacer than my '78 came with.