Keeping the EGR?

[Gary Sullivan]

Anybody have thoughts on the merits of keeping or ditching the EGR on stock 75's.

[RallyBob]

Originally Posted by Gary Sullivan Anybody have thoughts on the merits of keeping or ditching the EGR on stock 75's.

It reduces NOX emissions. If they don't test 1975 vehicles for smog in your area, then the only merit to keeping it is your own conscience.

Bob

[Gary Sullivan]

Thanks Bob. I haven't tested it to see if it is still in order. It was my experience with some of the systems on earlier Opels weren't designed well and were difficult to keep operating.
Your point is well taken.

[soybean]

This subject brings me to ask the question as to why couldn't it, (EGR tube) be used to exhaust the valve cover? I believe this has been asked/answered before too, I just can't find the answer using the search function.
Thanks, Jarrell

[kwilford]

Originally Posted by soybean This subject brings me to ask the question as to why couldn't it, (EGR tube) be used to exhaust the valve cover? I believe this has been asked/answered before too, I just can't find the answer using the search function. Thanks, Jarrell

Because the exhaust pipe where the EGR connects is at a greater pressure than the engine crankcase, so if you did, you would get exhaust gas inside the valve cover and pressurize the crankcase

[soybean]

Thanks Keith, Makes sense. I was just wondering because when we used to dirt dragged 4WDs many years ago, people would hook up each side of the valve cover to the headers. Way off the original topic now, but thank you. Jarrell

[kwilford]

Originally Posted by soybean Thanks Keith, Makes sense. I was just wondering because when we used to dirt dragged 4WDs many years ago, people would hook up each side of the valve cover to the headers. Way off the original topic now, but thank you. Jarrell

Hmm, now you have me thinking...

I am "pretty" sure that the back pressure at the exhaust manifold caused by the pipe and the mufflers would be greater than the crankcase pressure. I know that one of the "emission" techniques in years past (about 1968 in Opel years) was to use an air pump to pump air into the exhaust stream, thereby adding excess oxygen to help burn up as much unburned hydrocarbon as possible. And it was a "pump", which tells me that it took at least a BIT of pressure to force air into the exhaust stream.

And in an EGR system, the exhaust gases are controlled by the EGR valve as they get injected into the intake manifold. While there is a bit of vacuum to help suck the exhaust gases in, I am pretty sure that there is sufficient pressure in the exhaust to force the gases into the intake.

Yea, I am still pretty sure that an EGR connection to the vale cover would pressurize the crankcase.

[soybean]

I should have added that they were open headers, and not going through mufflers etc, that would create back pressure. Thanks again, Jarrell

[GTJIM]

The pressure in exhaust systems varies from positive to negative - that is how exhaust gas 'scavenging' works to improve performance.

With a PCV valve (Basically a one-way check valve) in the pipe from rocker cover to exhaust then vapour from the engine would only flow when the pressure inside the motor was higher than the pressure in the exhaust.
Why Opel does not use a PCV valve in the rocker cover vent line escapes me ....
Though the standard system vents into the intake manifold ofcourse ...

[Opelkurt]

Originally Posted by GTJIM The pressure in exhaust systems varies from positive to negative - that is how exhaust gas 'scavenging' works to improve performance.

That's quite right. BMW used this principle on their twin-opposed motorcycle engines in the 1980's. They ran a line from the air box to each exhaust port that required no pump at all. The flow of the exhaust drew in fresh air to combust the un-burned hydrocarbons.

-Kurt