EGR Discussion - split topic

[t70]

damn... now i gott put the friggin thing back in.. well. maybe not.. but I'm glad to have learned what it actually does.. i've removed it on my supra too but it was on one of the exhaust ports and in order to flow match the exhaust ports i had to tig it closed. oh well.. next engine i won't remove it.

[300zxt]

Jason mentioned earlier that he still gets good milage with his EGR removed, unchanged milage even with his a/f ratio remaining the same as before but with the stock ECU I do believe it does richen it a little.

[G-E]

think of it this way..... when cruising at very light throttle, the egr makes your engine smaller

so you'd have the fuel economy and power output of something like a 2L engine, which is fine considering how little energy it takes to keep an object in motion vs. getting it there, and thus it saves fuel without running lean and hot

[Signal 12]

fuck the egr

[got boost?]

copied from Z31.com at http://z31.com/board/read.php?id=140949

There has been some controversy regarding the function and utility of the EGR system in our cars. This post is an effort to clarify these debates by giving factual info upon which to rely.

High combustion chamber peak temperatures (the really short duration high temperatures near the end of the combustion process) cause oxygen and nitrogen to combine chemically and form oxides of nitrogen. To combat this, the EGR system injects a carefully controlled (by the ECU) amount of oxygen deficient (inert) gas. This exhaust gas serves to cool the combustion process (to below the threshold for NOx formation), and also slow combustion (for this reason, advanced timing curves are designed into these systems).

Contrary to popular belief, EGR actually increases the efficiency of gasoline engines via several mechanisms:

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 relatively minor compared to the first two.

EGR is typically not employed at high loads because it would reduce peak power output, and it is not employed at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. The EGR operates from a ported vacuum source and thus is not even capable of actuation (opening)at high vacuum closed throttle conditions.

Early EGR systems were unsophisticated affairs utilizing manifold vacuum as the only input to an on/off EGR valve; reduced performance and/or drivability were common side-effects. However, modern systems utilizing electronic engine control computers, multiple control inputs, and servo-driven EGR valves typically improve performance/efficiency with no impact on drivability. In the past, a meaningful fraction of car owners disconnected their EGR systems. Some still do either because they mistakenly believe EGR reduces power output or causes a build-up in the intake manifold in diesel engines, or because they feel the environmental intentions of EGR are misguided. Disconnecting an EGR system is usually as simple as unplugging an electrically-operated valve or inserting a ball bearing into the vacuum line in a vacuum-operated EGR valve. In all cases, the EGR system will need to be operating normally in order to pass emissions tests.

Because EGR operates under part throttle cruising conditions, it lowers the operating temperatures of the combustion chamber. The ECU is calibrated taking in to account the mass flow of the EGR under these conditions, so the engine can possibly run lean without it. The combination of higher CC temperatures and a slight lean condition greatly increases the chance of preignition at transient part throttle conditions, and also potentially at full throttle conditions (due to higher CC surface temperatures). There are no well demonstrated drawbacks to a modern, properly operating EGR system.

In short, the EGR system is a useful engine control component, which should retained unless new engine control parameters are set (i.e. reprogram the computer).

An informative and easy to find reference (I checked a copy out of the local library years ago) is
Heywood, John B., "Internal Combustion Engine Fundamentals," McGraw Hill, 1988.

[84z31]

you can lower your intake temps just by running a colder plug. i run ngk v-power plugs. i went from a 5 heat factor to a 6 heat factor. i just installed them and i can tell a seat of the pant in power.

i have removed all the emmisions except that idle control thing. which will be thrown away tomarrow. i hadn't thought about adjusting the idle with the throttle cable. damn that was stupid.

i have an 84 NA with 114k. combined driving i get 26 mpg. and i drive the car pretty hard at times. i have a lead foot by birth. i think it came from my mother.

[got boost?]

84z31 wrote: you can lower your intake temps just by running a colder plug.

This might have been an attempt a humor, otherwise:
you don't know what you are talking about. the plug temperature is the temperature at which it operates, it does not affect "intake temps". In choosing a plug heat range, you want one just hot enough to keep itself clean.

[300zxt]

Im pretty sure that article from z31.com is entirely useless in relation to Z's because as far as I'm aware the VG30ET IS has an early EGR system which according to that article were "unsophisticated affairs" and considering prior to that there was no form of EGR system at all in the Z it has to be an early system, no?

I'm sure the fact it's computer controlled makes it more efficient than if it wasn't but only marginally, with the right tuning as Jason mentioned above it's not needed. I've said a few times though that with the stock ECU I imagine it'd richen the mixture a little at most which is better than leaning it!

[G-E]

a "simple" system exists on my k-car.... theres a vac line infront of the throttle body, same as the Z... but there's no solenoid "off switch" so it's always opening when there's sufficient vacuum.... (it's a flapper door much like the heater core door)

and I can tell you having tested different types of intake, including ram air, that the k-car ecu is definately not tuned to deal with a higher efficiency intake, the car doesn't ping or anything but it becomes gruff and feels like it's breaking up, but as the timing is 8 degrees stock on 9.5:1 that could be cured with added timing and 94 octane.... still not much point

the ram air made a huge difference when flooring it at highway velocity, I could actually pass reasonably quickly (read: less than eternity), but the moment I let off and start cruising is would get choppy, touch the gas and everything back to normal except for the unwanted acceleration

in both cases, the Z and the K don't activate the egr idle, the throttle is closed and the vacuum port is outside, only light throttle will create vacuum on the Z and lets say due to the restrictive intake design the K suffers from more vacuum at greater throttle positions

I know how the car breathes, it's almost like a turbo, I have to close it to get some engine vacuum going and pop it open to increase VE to get anywhere, but steady state running will trigger the egr and it can't turn it off..... the Z can

[280Z Turbo]

I eliminated EGR on my 1981 turbo motor.

I don't know if it's this way with Z31s, but the EGR tube on an L28et makes turbo removal absolute hell. Without it, it's fairly easy.

I also didn't like the idea of throwing carbon back into the motor. I could feel a bunch of carbon deposits where the EGR inlet was on the manifold.

[G-E]

egr and turbo are on opposite sides.. and you could always run a catch-can for it, so it acts like a scrubber hehe

even on a turbo car the egr shouldn't operate during any rich conditions so the carbon should be minimal, not to say the car never goes into egr mode after having been rich and therefore still extra sooty...

I would imagine the egr will add less gunk than the pcv will

[300zxt]

That's good to know it doesn't operate at wot, as I plan to be running at full throttle all the time in my 86T lol

[84z31]

heat range from NGK

http://www.ngk.com/charglossary.asp?kw=Heat+range

happy reading

i was actually talking cylinder head temps. i guess i should have stated that. by running a colder plug you can lower temps 70-100*C.

[quote]got boost? wrote:

you can lower your intake temps just by running a colder plug.
This might have been an attempt a humor, otherwise:
you don't know what you are talking about. the plug temperature is the temperature at which it operates, it does not affect "intake temps". In choosing a plug heat range, you want one just hot enough to keep itself clean.

[got boost?]

300zxt wrote: Im pretty sure that article from z31.com is entirely useless in relation to Z's because as far as I'm aware the VG30ET IS has an early EGR system which according to that article were "unsophisticated affairs" and considering prior to that there was no form of EGR system at all in the Z it has to be an early system, no?

I'm sure the fact it's computer controlled makes it more efficient than if it wasn't but only marginally, with the right tuning as Jason mentioned above it's not needed. I've said a few times though that with the stock ECU I imagine it'd richen the mixture a little at most which is better than leaning it!

The Z31 uses a computer controlled vacuum solenoid, it is very much a modern egr system. "with the right tuning" is correct, just removing it is a bad idea.

[300zxt]

We've already established deep into this thread that removing it is perfectly fine. The JDM VG engines didn't have an EGR system at all, Why? Because at the time they didn't have to worry about emissions period and that's the only function the EGR serves, I dont have a problem trusting the engineers who built our cars myself.