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Discussion Starter · #1 ·
Hi guys!

I have a '75 Duster with a mildly built '77 400 4 barrel. I am currently running the stock intake manifold on the engine and I recently installed a stock EGR valve (looks a lot better than the block off plate). The issue I am having is that there is a very slight hesitation at light throttle tip in when the egr valve opens. I know the factory eliminated this by using ported vacuum for the EGR and running a vacuum delay valve to low the opening of the valve. I installed this and it did help, but there is still a slight hesitation there. My other thought is that if the vacuum advance comes in at the same time as the EGR, it may offset the drop in engine rpm from mixture dilution and completely eliminate the hesitation. My vacuum advance begins to come in at 10 in. of vacuum (adjustable can, but that is the soonest it will come in), but the EGR valve begins to open at about 2 in. of vacuum.

Is there any way to either amplify the vacuum signal to the vacuum advance or further delay the EGR valve opening rate so that they both come in simultaneously?

Thanks!
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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I have installed vacuum delay valves before. An example:

 

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Most of the aftermarket EGR valves come with a bag of washers with various holes. You could try using smaller holes.

Also, make sure you're not getting EGR until the engine's warm. You can plumb it into the CCVS for that. Use ported vacuum. I've actually had pretty good luck with both those tricks.
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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I think that gasoline quality is much better these days than in the late '70's. We were dealing with engine ping and hesitation on a daily basis back then.
In the warmer weather, it was worse with the vapor lock tow-ins. Of course once they cooled off, they would start right up.
Leaned-out carburetors and advanced spark timing were great for fuel economy and emissions, but had a tendency to ping. Carbon build-up in the combustion chambers would raise combustion pressures and aggravate the ping.
EGR would help combat ping and lower the NOx emissions. Distributor vacuum advance delays (OSAC valve) and EGR coolant temperature vacuum switches (for EGR disable when cold) and vacuum delays were important to improve driveability.
 
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Discussion Starter · #6 · (Edited)
Thanks for the replys!

Running the EGR valve is kind of an experiment to see if I can integrate factory type emission controls without sacrificing performance or driveability. Also, the intake manifold I have on it currently has provisions for EGR, and the block off plate looks weird to me.

AHBGuru, my EGR valve only came with the valve and gasket. What do the washers look like and how would you install them?

Thanks!
 

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Thanks for the replys!

Running the EGR valve is kind of an experiment to see if I can integrate factory type emission controls without sacrificing performance or driveability. Also, the intake manifold I have on it currently has provisions for EGR, and the block off plate looks weird to me.

AHBGuru, my EGR valve only came with the valve and gasket. What do the washers look like and how would you install them?

Thanks!
If you buy an aftermarket EGR, it may come with an assortment of washers. When you look at the base of the aftermarket EGR, there is a recessed place where the washer will fit. The washers have different size openings allowing one aftermarket EGR to service more than one OEM valve. If I remember correctly, there is a chart in the instructions that tells what ewasher to use for the OEM part numbers covered by the replacement valve.
If you have a factory EGR, it may not have a provision for the washers.
 

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Other than the washers for the EGR itself, which should cure the problem, think about the distributor mechanical advance. Big blocks do not like fast advance, but, if the springs haven't been changed, once a big block has been "improved" over stock, a heavy spring and a medium spring, usually works pretty well to allow the advance curve to improve a stumble.
 

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The rule of thumb was the valve color denoting rate of delay. A good start would be a generic valve meant for EGR delay:


Automotive tire Gas Rim Auto part Cylinder


Gas Plastic Auto part Fashion accessory Cylinder


Material property Gas Plastic Circle Rectangle


Hand Automotive lighting Eyelash Fluid Liquid


Gas Font Plastic Skateboarding Equipment Electric blue
 
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Discussion Starter · #12 ·
Good info. Thanks. The one I have on there now is the orange one, which apparently gives a 2 second delay. I just ordered a pair of NOS gray and black ones, which will supposedly provide a 10 second delay; when they arrive, I will swap one in and see if that solves the issue, then go from there.
 

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Discussion Starter · #13 ·
Dana44, I was running a two stage factory type curve with the initial set at 10 degrees btdc. I ended up dialing in more initial to smooth the idle and make it snappier off the line, and when I did that, I went to a single stage curve with somewhat heavier spring for simplicity.

I remember posting a little while back about my "poor man's hei" conversion that I did, and once I did that and recapped the plugs wider, it wanted less total timing and seemed to want it later. Possibly faster burn from the wider plug gap?
 

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That sounds reasonable, HEI is known for being pretty stout in the spark department. Big blocks, both B and RB are known for wanting slow advance, and 10 degrees btdc is not unreasonable, full advance of 36degrees at 3500rpm is pretty ideal for them.
 
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Discussion Starter · #15 ·
Wanted to post an update: I received the new delay valves and was able to install them yesterday. When I tested them individually with a handheld vacuum pump, they did not seem to provide a significantly longer delay than the orange valve though, so I installed both of them inline to increase the delay time. This seems to have done the trick, although I will need to drive it more to really make sure. Sadly, I am putting the car up for the winter a little early this year because I broke something in the rear end. I will be pulling that apart over the winter though so I can put some more miles on it in the spring. Thanks for all the replys!
 
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