EGR block-off

[Tricked-T]

This may have been covered here but didn't really turn up anything in a search.

I see this modification floating around the GP and regal sites alot but never fully explained.

I hear some guys removing the EGR, Blocking it off and having the code removed, but what are the benefits of this? Also what are the downsides to this? Is it worth doing? Anyone care to explain a step by step on how to do it?

[xX3800Xx]

If your going intercooled get rid of it. you dont want it dirtying up the core. otherwise keep it you wont really notice any difference if you remove it.

[willwren]

Exactly. Mine is blocked for the intercooler. The EGR actually LOWERS combustion temps if it's working properly. Removing it can actually cause problems.

[Larz01]

Its just a piece of steel with a bolt hole and you put high temp rtv on it to make a seal. You'll have to delete several codes related to the egr as well as bump up your timing, since this modifier is no longer used.

[Tricked-T]

Well there is no plan, atleast anytime soon to go IC so i will just keep it. Thanks guys.

[1fatcat]

Exactly. Mine is blocked for the intercooler. The EGR actually LOWERS combustion temps if it's working properly. Removing it can actually cause problems.

I'm not calling you out here buddy, so don't go banning me or anything, but why couldn't an EGR delete be tuned into the PCM? The only reason it lowers temp is because is chokes the charge with stale air...right? If a PCM was programmed to do so, couldn't it compensate for the lack of EGR by running a different fuel & timing curve? I realy don't know myself, as I have never delt with custom tunning.

[willwren]

It's not as simple as something that displaces combustibles, and there's a lot more to it than just emissions. There are other benefits, and asking a question on this Forum never got anyone banned the last time I heard. Lack of an EGR can raise combustion temps to the point that it causes pinging and knock. Especially bad on a boosted L67 with a very high effective compression ratio, or an L36 with a naturally high compression ratio. Here are a few excerpts to better explain what it does and how it benefits your car, not just in terms of emissions:

As long as the EGR system is functioning properly, it should have no noticeable effect on engine performance. But if the EGR system is leaking or inoperative, it can cause driveability problems, including detonation (knocking or pinging when accelerating or under load), a rough idle, stalling, hard starting, elevated NOx emissions and even elevated hydrocarbon (HC) emissions in the exhaust.

EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. This means the heat of combustion is less, and the combustion generates the same pressure against the piston at a lower temperature. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.

Reduced throttling losses. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.
Reduced heat rejection. Lowered peak combustion temperatures not only reduces NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke.
Reduced chemical dissociation. The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC, rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.

EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. The EGR valve also cools the exhaust valves and makes them last far longer (a very important benefit under light cruise conditions)

[Jrs3800]

GM had no EGR on the 3300 starting in 89... This engine ran through 93... The L27 had no EGR for the 91-92 models... The reason they did not have an EGR is that GM found the 3800 passed emissions without it.. But they were finding that the 3300's and 3800'd without the EGR were cooking exhaust valves and cracking exhaust manifolds pretty early in life..

For the 1993 Models the 3300 never got the EGR again as this engine was being dropped... The 3800 OTOH was going to continue so GM added the EGR to the engine to fight the issues they were having with Burnt valves and Cracked Manifolds... They did not do this for emissions purposes, it was done to simply aid in the issues they were having... The side effect was somewhat better emissions...

I have seen the 3300's 89-93 and the 91-92 3800 with burnt exhaust valves, it was not a common occurrence, but once in a while we'd come across one.. Have the heads done and exhaust valves replaced and reassemble... Most were well over 100k when the issues happened, some as early as 60-80k..

The EGR in these cars does help aid in the reduction of combustion temps...

[2000Silverbullet]

My EGR has been blocked off for many years.....not so many miles......and my top end runs cooler with no noticeable increase in exhaust manifold temperatures.

I have chosen to trade off the benefits of longer lasting exhaust valves for the benefit of a 1% hp gain for every 10F drop in intake charge temp. I don't run an intercooler. I can cool more by using water injection.

Think about the heating effect on your SC when injecting even a small amount of 500F exhaust gas.

Bill has the thermal analysis that clearly shows the red heating precisely at the injection location point on the bottom of the SC inlet.

Keep it cool baby!

[LeSabre in Buffalo]

On the flip side of things, if you want good fuel economy on a highway trip it's beneficial to have your EGR functioning, and your engine using as little gas as possible to keep the car moving.

If you aren't out for performance yet, I'd keep it on there. Your wallet will thank you. Once you get pretty deep into the "go-fast" mods, then block it off.

[willwren]

Bill has the thermal analysis that clearly shows the red heating precisely at the injection location point on the bottom of the SC inlet.

Keep it cool baby!

Absolutely incorrect, Paul. My thermal analysis shows the inlet of the supercharger is hottest where the restriction in the inlet is the greatest. You assumed it was at the EGR injection point at the bottom because you forget the Series 1 injects 90 degrees opposite that point on the front of the supercharger, not the bottom like the Series 2. Natural heat from compressing the intake charge builds up far hotter than the injection point of the tiny amount of exhaust gasses the EGR uses. Look at the injection point on the Grizz for reference, then look at my thermal analysis again. The EGR heat effect is so negligible, it's not even part of the equation. The EGR orifice is TINY. A very small fraction of the EGR stovepipe diameter, and the valve isn't even open full-time.

The risk you take is not a long-term risk I would suggest anyone take, especially in light of all the benefits of the EGR system I posted above.

[2000Silverbullet]

2000Silverbullet wrote:

Bill has the thermal analysis that clearly shows the red heating precisely at the injection location point on the bottom of the SC inlet.


Absolutely incorrect, Paul. My thermal analysis shows the inlet of the supercharger is hottest where the restriction in the inlet is the greatest. You assumed it was at the EGR injection point at the bottom because you forget the Series 1 injects 90 degrees opposite that point on the front of the supercharger, not the bottom like the Series 2. Natural heat from compressing the intake charge builds up far hotter than the injection point of the tiny amount of exhaust gasses the EGR uses. Look at the injection point on the Grizz for reference, then look at my thermal analysis again. The EGR heat effect is so negligible, it's not even part of the equation. The EGR orifice is TINY. A very small fraction of the EGR stovepipe diameter, and the valve isn't even open full-time.

Ah yes sorry Bill, you're partially right, the EGR injection point on the Series 1 is on the side not on the bottom like the Series 2.

I still do not believe that the heating effect of 500 cfm of air moving thru the 3.5" throttle body will have a significant effect on heating the SC.
The majority of the heat on a SC is generated after compression.

I do believe that the +500F EGR does heat up the entrance point significantly.

I have measured a direct drop in temperature without it operating. Not a drop in combustion temp, but a drop in SC housing temperature.
There will be a direct relationship between SC housing temp and air charge temp.

[willwren]

My thermal analysis says otherwise. Even discounting the tiny amount of exhaust gases injected into the inlet in comparison to the massive volumes of incoming air, the analysis clearly shows the restriction of the supercharger inlet is the primary source of heat. This takes into account the typical coolant temperatures entering the passages, and the ambient LIM temperatures after warmup.

I know it sounds odd, but my analysis closely matches that of a college engineering group as well. I have their data also.

[1fatcat]

Care to share that data?

[willwren]

It's posted. If you can't find it by the time I get back on here tomorrow, I'll dig it up for you. Paul (silverbullet) has seen the test parts and hardcopy versions of the analysis personally on several occasions. I based my intercooler design on all of that.

[1fatcat]

the analysis clearly shows the restriction of the supercharger inlet is the primary source of heat.

I don't follow? Restricted inlet making all the heat? It's the act of COMPRESSING air that produces heat...and large amounts of it. Why do you say the majority of heat is produced on the inlet side of the compressor?

[willwren]

Because two independent sets of data from computer models show it.

[willwren]

Keep in mind this screen capture doesn't have the EGR ported and set for temperature yet (I'm still digging for that one), but it showed only a bit of yellow (similar to the SC outlet). The lower portion of the inlet is far hotter than coolant temperature. I don't recall the exact numbers I used for this model, but for the most part, the lower part of the blower was constrained at typical LIM temps (measured on both of my cars), and inlet flow was 60°F. I don't recall what RPM/flow rate I had the 'charger set to. I still have the model around here somewhere to run some more tests on.

The major point is that the lower part of the inlet gets far hotter than the coolant, which is actually having a cooling effect. Some of the heat in the LIM (same temp the bottom of the SC is constrained to) is created from compression, yet the inlet of the SC gets hotter than the LIM and the Coolant.

Older data with a far more simplified model, showing the inlet as the hottest part of the supercharger (I found this older data about a year after I did my own analysis, and briefly traded emails with one of the guys who worked on it):


Back on topic, even though this particular set of data doesn't show the effect of the EGR, I did test that, and it's insignificant. Given some spare time, I can run that model again and post the results, but it wasn't very hot at all in comparison to the sheer volume of ambient air it's mixed with. Given all the other benefits of the EGR posted in this topic, it's pretty clear to me that deleting the EGR should only be done in the case of intercooling, where the heat exchanger is in between the SC and LIM, in order to keep the core clean.

[Nexuscocker]

Sorry about the side note:

Is it for effective to port the inlet of a M90 rather than the outlet? Based off that data I would think that porting the inlet would lessen the heat that was created, but in not and engineer.

[2000Silverbullet]

The major point is that the lower part of the inlet gets far hotter than the coolant, which is actually having a cooling effect. Some of the heat in the LIM (same temp the bottom of the SC is constrained to) is created from compression, yet the inlet of the SC gets hotter than the LIM and the Coolant

Bill, you know I highly respect you and don't mean to question your extensive data collection and knowledge but when something doesn't make sense I have to.

The discharge side of any compressor will be hotter than the intake side. The heat of compression is a law of physics.

The heat gun and temp probe proves to me that removing the EGR and TB coolant cools the intake by a significant amount.

Porting is done to decrease the friction losses and improve flow.