Here's a write-up on the function of EGR:

From Car Craft mag August 2004, Whats Your Problem help column

Increased Efficiency Through EGR?

I enjoy reading your column and just wanted to pass on some additional info on a question I saw in the May issue entitled "Pinging Imp". While I dont disagree with your response, there is something involving the EGR and spark knock that is far more influential than any impact the slightly lean condition due to lack of EGR flow would cause. EGR is added to the intake charge as you describe to lower the combustion temps to reduce the formation of NOx. Older systems that just had EGR tacked on without any electronic controls caused driveability and fuel economy penalties with EGR and gave EGR a bad rap. Later systems, like the one on the Impala SS described, actually used EGR to improve economy by adding a lot of spark advance when EGR is enabled. A very rough rule of thumb is that for every single percent increase in EGR, the spark calibration is increased 2 degrees to offset the slower burn due to the dilution effect of EGR on the charge. So, if an engine is running 10 percent external EGR thru the EGR valve, then the spark is increased 20 degrees roughly to compensate. The engine will actually be more efficient like this than without EGR, as the EGR is "throttling" the engine and reducing the pumping losses slightly by reducing the intake vacuum. It works- trust me. In any case, there are multiple spark calibrations and tables in the OEM PCM for "EGR on" and "EGR off" spark operation. So, if the EGR is supposed to be on, the spark advance is increased dramatically over the "normal" "EGR off" spark levels. If the EGR is not flowing because of a failed valve, restricted EGR feed port, loss of vacuum signal, or so on, the engine will likely detonate or spark-knock heavily due to the fact that the spark advance is being advanced considerably by the PCM, although there is no accompanying EGR flow to dilute the charge and slow the burn rate. That is why the Impala SS is likely detonating, not just because of the slight lean condition caused by the EGR fuel compensation and lack of EGR. At part-throttle, the closed -loop control will pretty much correct for the fueling difference anyway, so I suspect that the reason the detonation is there is because of the extra EGR spark advance in the calibration without the accompanying EGR flow.
Al Cline
General Motors Powertrain
High Performance Vehicle Operations
Pontiac Engineering Center
Pontiac, MI

I don't think you would want to increase EGR much beyond stock tuning. I've never tried it, but would be careful if you decide to do so. Remember that at lower RPM's, the engine's "self-EGR" due to valve overlap increases, especially with more aggressive cams.

 

Remember that at higher RPM's, the engine's "self-EGR" due to valve overlap increases.

This reminds us of the LT4, which has no EGR, but since EGR is most used at lower rpm (like part throttle, closed loop), and any given cam has more overlap at lower rpm, wouldn't the self-EGR be more effective at lower rpm? In fact a cam can cause the engine to run out of breath because the overlap it has isn't enough at higher rpm, where it was fine for lower and mid rpms. I would think intake reversion and anything that would want to pull exhaust back into the cylinder would be strongest on a bigger cam at lower rpm.

the 96 computer runs the egr via pulse width modulation correct
how much dc should i be looking to run

When the EGR duty cycle is at 100%, you are already flowing the maximum EGR that the physical design will allow. You can't add more by calibration. From what I've seen on my 95, it doesn't spend a whole lot of time between 0 and 100. It's either on or off, most of the time.

I'm starting to see stuff like electric power steering on cars instead of old school hydraulic systems like ours, that might be an interesting mod.

We also see variable speed electric water pumps and even variable flow oil pumps (BMW). Another idea I saw recently is to turn off the alternator during acceleration. Not sure what you'd use as a definition of acceleration in this context but the idea is if you want more speed, temporarily remove the alternator drag from the powertrain, then reconnect it at cruise and maybe aggressively charge during coast/braking. Not sure our cars could be modified like this because it seems like you'd really need to develop the electrical system with this in mind from the beginning. Our cars would lose a lot of ignition power alone going down to 12V. It would also be harder on the battery depending.

 

This should get it done..

 

I think forcing the EGR to an on state would be a bad thing, as the PCM needs to be aware of the EGR situation, and add spark accordingly...it also will need to change how much EGR you're seeing based on RPM/load...stock EGR tuning seems pretty good...I'd probably make sure the spark it adds is correct (disable it and get the main spark table in the low load/cruising/mild acceleration areas as optimal as you can...then enable EGR and have it be as agressive with spark as it can without losing efficiency as well)...

Tweaking the DFCO settings can help a lot...I forgot to mention in my other post on your other thread in here, I did tweak DFCO quite a bit (both with the auto and with the T56) and noticed quite a benefit from it, in the cars fun factor and the MPG it got.

 

are you saying an egr force switch is bad because it will not incoperate a change spark advance that is needs with egr

what is the correlation between spark and egr

the 96 computer runs the egr via pulse width modulation correct
how much dc should i be looking to run

 

Thats the thing...you're simplifying it too much...the PCM controls it based on RPM and load (sorta...goes by MAP readings)...just switching it on...will not get you the results you want, and just picking a duty cycle, also won't...there are situations where EGR will see 100% duty cycle.

I think the PCM in your car is far more advanced than you realize...your first step, should be NOT "having it tuned"...you need to get the software and hardware necessary, and start doing it yourself...it takes HOURS spread over DAYS spread over WEEKS of tweaking to really make a tune in a cars PCM be perfected...I've been tuning cars for almost 10 years now...I used to get tired of working with the LT1 because it takes 5 minutes to flash a new program in, and it is always scary wondering if the PCM will survive...but my LS1 in my Camaro...I've been tuning for 18 months now, and it takes 20 seconds to put in a new flash, and I tweak it a few times a week STILL...it's not perfect...I might never consider it done...but it always improves...NOBODY would have been able to do what I've done via a "tune" I could have paid them for...every car is far too different in how it responds, there are far too many manufacturing tolerances in the sensors and drivetrain parts for the same exact numbers to work in all of them...for a rough tune, yeah, the same flash "works" in most of them...for perfecting it though...EVERY car is different.

 

i understand what you are saying .. i think

pcm = complex
time = money
pcm tune = ballpark calibration
pcm tools = learning curve
learning curve = time again
since money cant by time
and all women are evil

did i pass the audition

 

pcm = complex
pcm tune = ballpark calibration

Maybe you could pay Mike to do it for you. He seems to be very experienced in this area.

 

Logic would dictate that the EGR function is optimized from the factory. There is absolutely no reason for it not to be.

I think you would get better results optimizing your fuel trim. A matched set of stock-sized or even smaller injectors would allow a tuner to tune the fuel tables closer to optimum. Stock injectors flow about +/- 10%, meaning you could have a difference of up to 20% between your fattest and leanest injector; matched sets are generally matched to within +/- 1%. This would require a dyno tune in addition to the injectors, too.

Where you want to look in general is in areas where it would either be too expensive for the factory, such as the matched injectors, or not pass federal emissions or noise standards, such as a performance exhaust.

I'm starting to see stuff like electric power steering on cars instead of old school hydraulic systems like ours, that might be an interesting mod.

Everything you can do to lighten the wheels would certainly help. You mentioned you have 29 inch tires, how big are your wheels? The lightest wheels are going to be 15 inch aluminums, along with the narrowest tires that will support the car to reduce rolling resistance.

Maybe venting the crankcase? Racers sometimes run lines from the valve covers to the exhaust and use Bernoulli's principle to vent excess pressure from the crankcase. Makes the car faster, maybe it would help with mileage?

What could you do to reduce internal friction? A set of roller rockers, while they won't increase torque at that low rpm, would reduce friction.

I don't know if increasing oil control at that low rpm would do much or not, and putting a windage tray in the oil pan is a huge pain anyway - you have to lift the motor up to get the oil pan off.

Well, that's all I can think of for now.

 

stonebeaker

that is an informative list of usefull concepts

enough information has been aquired for 9C1 revision #1

 

http://autospeed.com/cms/A_110577/article.html

 

Better AutoSpeed Atricles ...

Tweaking the EGR, Part 1
Tweaking the EGR, Part 2

I'll guess, that at low loads - loads you'd see at or below 15% throttle, which is all it takes to maintain illegal highway cruising speeds - see how much
additional EGR
spark advance
leaner Air/Fuel Ratios
you can get away with?

Would there be any profit to 'actively' cooling the EGR circuit?

 

Would there be any profit to 'actively' cooling the EGR circuit?

a water to air cooler could be plumbed in easy
as the heater hoses are right above the EGR feet tube

 

sorry Stonebreaker but I think that PCV is used at cruise with engine vacuum to aid crankcase venting. The WOT guys would aid in Bernoulli's principle due to low engine vacuum.

 

That would certainly be the way to go while you're researching things.

Maybe instead of an egr valve, use a ball valve or something similar so you could vary the amount of egr easily?

However... once you figure out how much egr you can get away with, I'd still suggest going with a custom cam.

The more I think about it, the more convinced I become that you're not going to achieve much with the egr modification. This is a system that the factory would have optimized - there's no reason for them not to, since testing would be cheap.

I think the most promising area is modifying the cam. Here's my reasoning: The factory has to build a car to please the majority of people. That means a car with enough power to keep most folks happy, but also with enough economy to keep most folks happy (including CAFE). Here on this forum, most of us doing motor mods fall in the "too much power is never enough" camp. We mod the engine with the goal of increasing horsepower.

You fall at the opposite end of the spectrum - you're willing to give up performance in order to achieve maximum fuel economy. It seems to me that if we know what mods make more power, we ought to be able to figure out some mods that improve economy.

Anyway, back to the cam. I was originally thinking you could hold the exhaust open into the intake stroke and load the bottom of the cylinder with exhaust then open the intake and fill the top of the cylinder with fresh charge, but with the excellent tumble and swirl of the stock heads, it's going to mix things pretty thoroughly, so that probably won't work.

Instead, you'd probably want an optimum economy cam - anything labeled "towing" is going to be optimized for low speed operation. I'm a little frustrated because I lost my hard drive to a virus, and I don't have Desktop Dyno any more - otherwise I'd be playing with cam specs right now. But you don't necessarily need to find an off-the-shelf cam. Check through the cam catalogs and find the smallest cam for a V8 you can, and then have the grind duplicated on an LT1 blank.

Comp Cams has a lobe that has only 178 deg duration at .050. That would make a pretty good intake lobe. I'd leave the stock exhaust lobe alone.

One head mod I'd look at would be to install a bigger exhaust valve. You want the cylinder to blow down as quickly as possible on its own to avoid having to use any of the available energy to pump out the exhaust.

A real, real good place to start, I think, would be to look at the LS cam phased engines. See what its cam specs are, and find out where the cam phaser has the lobe centerlines at your target rpm. That will give you a pretty dang good starting point to design an ultimate fuel mileage LT1 cam.

 

Google Miller cycle:

Miller-cycle engines improve fuel economy by reducing the amount of energy needed to compress the fuel-air charge during the engine's compression stroke. It's done by leaving the intake valve(s) open longer than a traditional 'Otto-cycle' engine, allowing some of the gases to escape the cylinder during the piston's upward motion. But less gas in the cylinder also means a less efficient burn and less energy from combustion during the expansion or downward piston stroke, which is why Miller-cycle engines have traditionally been paired with a supercharger to pump in extra air after the intake valves have closed to boost the fuel-air pressure right before ignition. The whole process can also be thought of as postponing compression until as late as possible and then making up for the delay by using the supercharger to rapidly pump in extra air to replace the gases pushed out during the earlier energy saving portion of the stroke. And because the gases are igniting later in the compression stroke, they are also under greater pressure, resulting in a better fuel burn.

A Miller-cycle engine's disadvantage has been that the cost and complexity of adding the supercharger has outweighed the cost savings from improved fuel economy. It also generates less torque in the low-RPMs - a critical miss in a truck application where low-end torque is craved for towing and hauling.

The Silverado Hybrid doesn't use a supercharger, though. This is where the new Two-Mode Hybrid transmission assists by managing more than just gear swaps. Two electric motors placed fore and aft in the transmission stand-in as 'digital' superchargers to provide extra power and torque, so the engine can burn fuel using LIVC / Miller-cycle combustion.

 

Or perhaps I meant Atkinson.

http://en.wikipedia.org/wiki/Atkinson_cycle