EGR question

[mjr45]

I have 2 engines, one in the car (now runs great after a new AAM and electrical connectors) and one that I'm considering rebuilding. Th one in the car has an EGR system and the other none, no pot on the intake and no vacuum line to the throttle body. Which is the better setup? I lean towards no EGR but don't know all the facts.

[5thhorsemann]

What year and model. Assuming 240Z earlier the better. the less crap on the motor, the better it runs.

[FastWoman]

The EGR results in cooler combustion gasses, which I think lowers NOX emissions (??). A properly functioning EGR does seem to improve running in some engines. I know this from having repaired a couple of engines blocked EGR ports (and effectively no EGR). That said, EGR is a relatively recent system ('70's?), and engines ran pretty well before its development. I don't think it's that critical. If restoring a car to run as well as possible during ordinary driving conditions, I'd use the EGR. If restoring a car either to look good under the hood or to race, I probably would ditch the EGR.

I'd also keep the original engine in the car if possible, as matching serial numbers are important for the value of these cars.

Edited April 17, 2011 by FastWoman

[5thhorsemann]

The EGR results in cooler combustion gasses, which I think lowers NOX emissions (??).

The reason for the cooler combustion is the addition of non flamable gasses into the combustion "charge". You are pumping spent fuel into your air/ fuel mix. Strictly a desperate attempt by engineeres to meet govt. mandates for smog control. Just like the smog pumps which add fresh air into the exhaust stream in order to lower the ppm of nudesireable exhaust gasses at the tail pipe. In the trash heap with all of it!

[LeonV]

The reason for the cooler combustion is the addition of non flamable gasses into the combustion "charge". You are pumping spent fuel into your air/ fuel mix. Strictly a desperate attempt by engineeres to meet govt. mandates for smog control. Just like the smog pumps which add fresh air into the exhaust stream in order to lower the ppm of nudesireable exhaust gasses at the tail pipe. In the trash heap with all of it!

EGR is a win-win. For some reason people enjoy demonizing any device seen as "smog control." EGR decreases emissions and improves fuel consumption while decreasing NOx without detriment to performance. It is not a "desperate attempt by engineers" but rather an elegant and effective solution to a problem. Unlike a smog pump, EGR costs you nothing while improving fuel economy.

[Walter Moore]

In the U.S. EGR wasn't required until 1972 I think... so early cars didn't have the equipment. (To the best of my knowledge, there was no EGR on my 71' )

The purpose of EGR is to reduce oxides of nitrogen by lowering the combustion temperature. This in theory makes the engine less efficient, not more efficient. (Research "Carnot efficiency" to understand why this is true... ) But I believe that in practice on the engines of the 1970's they likely need all the cooling that they can get, so without the EGR you MAY need to run a richer mixture, which would be less efficient.

I have read that one of the reasons that some modern cars from Europe get so much worse fuel mileage in U.S. specification form is because our emission laws require the EGR valve, which reduces the thermodynamic efficiency. I am not certain that I believe that, but it is widely repeated. If your EGR is working properly it doesn't really hurt the performance of the car, so why mess with it?

[LeonV]

You are correct about combustion temperatures being decreased but notice that I said nothing at all about thermodynamic efficiency. Instead, I mention fuel consumption/economy. This is essentially a reflection of overall engine efficiency, thus thermal efficiency is already factored in along with fuel conversion, mechanical efficiencies, etcetera.

EGR reduces engine pumping work holding throttle and engine speed constant.

Take the same engine, one with EGR and one without. The increase in intake pressure by the EGR charge reduces pumping losses and raises volumetric efficiency thus improving fuel economy and effectively total engine efficiency. There are other reasons that I can't recall right now, don't have my reference materials on hand.