CVF,
What you are saying sounds like a very logical defense to me. To those who choose to argue. Look at the big picture...what do engines need to create that explosion in the combustion chamber? FUEL and AIR. EGR's just add unnecessary chemicals to the combustion to lower emissions and in doing so, lowering horsepower. I hate arguing over a computer but in CVF's defense, I makes perfect sense to me and if you have ever blocked off you EGR, you will notice a definite horsepower increase and in my case, an increase in MPG too.

 

CVF, for somebody who knows as much as you do, seems like you could figure out why your 400 uses oil. No?

 

I agree with bill for the most part. If you knew how to do a good tune up then you most likly wouldnt feel the difference. Now I have all my EGR disconnected on my truck and the only thing that I have gained is more midrange power and a loss of fuel milage. Remember that this system was designed for 2 things 1 being emissions and the other fuel economy. If you left most of the EGR hooked up and just changed your vaccume line routing then you might be able to go halfway. If you notice that you vaccume advance is hooked up to a temp sensor in the water neck. Just connect it direct and that should help with the timming. Also play with you timming it makes a big difference. Oh remember your Fuel curves as it is directly related to timming curves. You cannot just change it and guess. You need dyno time and 100° weather.

 

CVF's arguments while vociferous are based on illogical assumptions and a lack of understanding of chemistry and physics. I am sure he spent time in mechanics classes but that will not make up for higher education at the university level.

Please read what Bubba said above, it is right on. I would only add a couple of minor tech details re combustion temps etc but they have been covered in EGR discussions here b4 and can be found thru the search function.

 

In a perfect world where there was a 100% complete burn of the A/F mixture there would be no O2 at all in the exhaust gas that ends up back in the combustion chamber but this isn't a perfect world so CVF is correct in saying that there is some O2 in EGR gas. However the percentage is so small as to not even be measurable and certainly not enough to affect the A/F ratio.

To say that oxygen (O) which has already bonded with other elements such as carbon (C) or hydrogen (H) will "throw off" the A/F mixture is ludicrous at best. As Eric said it shows an ignorance of basic chemistry and physics.

Bottom line, if you do nothing but disconnect the EGR on an older 351M/400 motor you will end up filling the cylinders with additional lean A/F mixture which will heat up the combustion temp, possibly give you a little bit of extra mid range power (the EGR doesn't function at idle or WOT), probably cause the engine to ping, reduce your gas mileage and prevent you from passing the smog inspection in your state if you have one.

 

Unfortunately, you could apply that same reasoning to opening a massive vacuum leak. It will stall the engine, which would pretty much prove that air is detrimental to combustion? The logical flaw is obvious, even though your conclusion is correct.

I'm sure that sometime in your professional experience you saw vehicles with "leaky" EGR valves that caused driveability problems. Stalling at idle and rough or slow idle without stalling are both symptoms of that.

In our engines, the only part that would ever see temps approaching 2500F is the combustion chamber, and then only for a very brief moment during the combustion event. By the time exhaust gas exits the cylinder, it has already cooled down to about 1700F (max), and within a few inches downstream from the exhaust valve, it cools even more. Running lean, with high combustion temps, the highest exhaust gas temp in the manifold and EGR passage is about 1400-1500F. In stop-and-go city driving, exhaust gas temps in the manifold are closer to 1000-1100F. A few minutes of testing with an EGT sensor will demonstrate this.

Chemically, exhaust gas (from which atmospheric oxygen is depleted) acts the same as CO2 (or any other inert gas, such as helium, etc.) in a combustion reaction; it does not participate.

The reason CO2 puts out fires has nothing to do with its temperature. Cold, warm, or hot, CO2 will extinguish combustion when it displaces sufficient atmospheric oxygen (O2). This is analogous to injecting EGR above the carb. In that event, O2 in the intake airflow would be displaced, but the carb would meter fuel based on the flow of "air" through the venturi(s). That would, in fact, alter the mixture (ratio of fuel to O2) because only one of the combustion reactants (O2) would be displaced by the inert gas, not both.

Your analogy is good, but your analysis is not. The percentage of alcohol by volume is an example of a ratio, in this case, total beer volume to alcohol volume. Is the percentage of alcohol by volume different in a full glass of beer and 3/4 glass of beer? You certainly have less beer when the glass is 3/4 full, and you certainly have less alcohol in the glass, but the percentage of the beer that is alcohol (the ratio) is not changed by the amount of beer in the glass.

You can't have it both ways.

The oxygen atoms in CO, CO2, and H2O molecules are not available for combustion, and therefore, those molecules do not participate in the reaction. (Hint: CO2 and H2O are both commonly used to extinguish combustion.)

The boiling point of CO2 is -109F, and the boiling point of nitrous oxide (N2O) is -127F, so N2O isn't that much colder than CO2. However, you are mixing up the effect of temperature on the intake charge with the basic chemistry of combustion.

You can get more power using N2O because it provides more oxygen (about 2.5 times that of air at sea level), and more oxygen allows you to burn more fuel, and burning more fuel is what makes more power. Injecting N2O into a fuel/air mixture alters the mixture (ratio of fuel to O2) because it changes the amount of one of the reactants, and not the other.

So why does the mixture burn hotter when you lean it with air (O2)? There's less fuel to burn, right?

I'm afraid you are stuck in your misunderstanding. You are arguing on both sides about whether the exhaust gas is inert or not, and your reasoning on fuel/air ratio is faulty, even though you come to the right conclusion on the subject of EGR impact on power output.

If you've read any technical papers on the subject of EGR, you know that fuel/air ratio, EGR rate, and ignition timing are all independent factors (i.e., changing one does not affect the other), and they can be adjusted both individually and together to produce various results in emissions, fuel economy (BSFC), and power.

And finally, no, my EGR is not hooked up. I disabled EGR on my 351M (along with several other minor modifications) to improve the power output.

The modifications required to compensate for disabling EGR on my engine were enriching the stock fuel/air mixture at all open-throttle positions, and changing the stock ignition timing advance curve to provide less vacuum advance at low-to-mid throttle and more mechanical advance at 2000+ rpm.

To realize the benefit of removing EGR, you must alter carb metering and ignition timing. If you don't make those changes, removing EGR from an engine calibrated for it will cause severe pinging, mostly because of the carb's overlean metering.

Mixture and ignition timing are adjusted automatically by closed-loop ECMs. The mixture is richer on your newer cars with disabled EGR because the ECM detected the overlean mixture that was produced with the injectors running at the "normal" pulse width without EGR. You have mistaken the result (enriched mixture) with the cause (more O2 available in the intake charge because it is not displaced by exhaust gas from the EGR).

All of the changes I made to my engine's stock calibration were tested on a gas analyzer to optimize combustion efficiency and determine the effect on emissions.

I also run a Thermactor AIR system and catalytic converter, and with the mods I've made, including disabling the EGR, my tailpipe CO emissions are about 20% of the limit and my HC emissions are about 12% of the limit. State-mandated testing for my truck does not measure NOx, and I have not tested for NOx on my own.

With the mods on my 351M, horsepower is up more than 25% and torque is up almost 10% over factory specs, based on chassis dyno testing. My average fuel mileage is down about 10% from what it was before the mods.

 

Yun's guyz r 2 entellijent 4 me. 2+2=4

 

way to go bill, eric, and bubba!!!

 

The reduction in pinging with EGR vs without EGR is partly due to the timing requirements of the mixture. With EGR the mixture does not burn as fast so more advance is required. The same timing advance used with a non EGR mix will therefore ping. This is why we have to make calibration changes when the EGR is disabled.

The EGR system has been very effective at lowering combustion chamber temps with a lean mixture which reduces the amounts of NOx produced. The reduction of NOx is the whole idea behind the EGR system.

 

So dispite all the arguements we all agree that the EGR does it job It lowers emissions at the expence for mid range power.
The ways or reasions may or may not all be understood, but they do not change the effect of the EGR just the way we can compansate for it as we all search for MORE POWER.
As I see the jewel of this dissusion for those will and able to weed through the heated emotions is the wealth tech info that was used to prove the points.
thanks to Bubba, Bill, and even CVF for your willness to share your time, knowledge, and experance with us. Is this not why this board is here.

"just my $.03"
Jason

 

"Mid range power" may not be the right words to use. Part throttle cruise may be a better term. No matter what rpm's you are running if you open the throttle and ask for power the EGR system shuts down. Your engine always has full power available at any rpm. So there isn't any reduction in power available. There is no reduction in emissions at the expense of mid range power. The EGR is almost a win-win situation except for the added complexity. It allows you to run leaner mixtures without pinging or overheating and at the same time it reduces NO2 emissions under the conditions that produce the most of it. It was kind of a stroke of genius from whoever figured it out.

 

to lower combustion temperature? Why not use an enrichment device that introduces high octane fuel to mix with the intake charge? Propane, Methanol or Toluene. Use a knock sensor to activate it

 

Easy answer FUEL MILEAGE... And if you think the EGR system is complicated try using some of the $tuff you mentioned. Plus the HC emissions would go up which is not good either.

I am actually thinking about using EGR on my engine rebuild but I would use the system used on Wheezer engines with the external passages rather than passing exhaust gas thru my intake manifold.

 

This is a good conversation!

Based on my experience CVF has got it right.

Remember by operating at a lower temperature you will not get as complete a burn as you would at the higher temperature because the exhaust is an inert gas. The carburetor doesn’t know that the EGR valve is open or shut its just providing fuel based on the air flow thru the venturi. The carb was designed to meter "X" amount of fuel to supply "Y" amount of horse power and Torque at "Z" RPM.
When the egr is on, the inert gas flows into the intake manifold. Each cylinder only has a specific volume, if some percentage of that volume is exhaust gas that dident have to be pulled thru the carb then the carb will be metering less fuel to the cylinders. Less fuel means less power. (There are no free lunches)

Just my two cents.

 

This thread has been a thoroughly enjoyable read! I'd rather trust the wordings of Bill, Torque and Bubba because they've clear, concise and nonconfrontational discussions. CVF's deduction is incorrect, although the conclusion is correct (as described by Bubba).

The only recommendation I will afford is that CVF provide a more sociable conference on the forum. The words we read influence the opinions we create.

How's them wurds fer us edumacated folks!?

Chris

P.S. lose the caps!