Can someone explain to me the "lower temp thermostat"?

Pete. (l33t FS) said:

In reply to alfadriver (Forum Supporter) :

Intentional afterburn in the exhaust was a lot of the emissions cleanup strategy, to the point that the exhaust manifolds were shaped like burn chambers.  Before 1981, they didn't even need catalysts, but relied so heavily on rich mixture + air that they had a cooling jacket around the manifold.

 

LT1s had a single catalyst mounted very far back from the engine in typical 70s-80s GM fashion, I'm not sure if this would be enough time to prevent the cat from doing all of the heavy lifting.  And, either way, it's all completely conjecture.

 

GM did some weird things in that timeframe.  Pre-OBDII TBI V6s in trucks would go open loop at idle after a few seconds and start adding fuel.  It's been so long ago since I had this explained to me that I've forgotten the rationale, if it was for idle quality or for catalyst cooling.

Back in the 70's and 80s when that kind of reduction was all that was required, sure.  But we are way, beyond that.  Let alone far cheaper and more reliable.

Again, I'm very much separating what was done up to about OBDII- when regulations got tight enough that the "common sense" early solutions were no longer good enough.  Almost none of the pre-OBDII tools are used for their original intent anymore- EGR isn't for NOx, its for fuel economy; air pumps are not for constant catalyst mixture, they are for cold start light off.   And running rich to lower NOx is not an option like it used to be.

Realistically, take an 80's era engine, remove all of the emissions "crap"- put on some good, modern catalysts, and a reasonably modern control system, and the emissions will be 1/10 of what was originally done in the 80s.  And have the additional bonuses of lower cost and better economy.  (assuming the combustion chamber is capable of stoich combustion)

It's almost as if nobody has noticed that we have 500hp cars that are incredibly clean and efficient these days.

In reply to alfadriver (Forum Supporter) :

Yah I get it, emissions systems are different now than they used to be, but this all started with talking about a lower temp thermostat. While I'm sure some people do it, I don't think the context it was being discussed in was "I just bought a brand new modern car and want a lower temp tstat."

It was more of a I just bought a 20 year old car and want to fix known problem areas, so I want a colder tstat. 

How emissions systems are used in 2021 isn't very relevant to this particular conversation, but how they were used 20 or 30 years ago is.

alfadriver (Forum Supporter) said:

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

Common sense is never wrong, however it may not be appropriate for the circumstances.

alfadriver (Forum Supporter) said:

It's almost as if nobody has noticed that we have 500hp cars that are incredibly clean and efficient these days.

They are incredibly clean within the fed testing parameters.

When making 500hp THEY ARE NOT CLEAN!

bentwrench said:

alfadriver (Forum Supporter) said:

It's almost as if nobody has noticed that we have 500hp cars that are incredibly clean and efficient these days.

They are incredibly clean within the fed testing parameters.

When making 500hp THEY ARE NOT CLEAN!

Based on your response, they are a lot cleaner than you think.  I do a lot of testing where WOT is needed, and other than a lot of CO, the HC and NOx would easily pass previous requirements.

But given the direction of this discussion, I'm actually not sure why that's relevant.  Other than super effective emissions controls are still able to let engines make 500hp.

In reply to Opti :

The original question was for an Boxter S.  Which falls into my modern era.  The actual "how" warmed up emissions have been controlled over the last 25 years have not changed- a/f control has gotten better, and catalyst formulations have gotten better.  But relative to the T-stat, it's all been the same.  So what we do now is as relevant as it was 25 years ago when the Boxter was being developed.

The part that has changed the most for emissions is what happens while the catalyst is getting warm enough to work, and that is outside of the scope of a discussion about T-stats and their effect, since it happens WAY before the stat opens up.

bentwrench said:

alfadriver (Forum Supporter) said:

In reply to AAZCD (Forum Supporter) :

It's interesting to see so many internet engineers second guess Porsche's.

I've said it before, I'll say it again- "common sense" is wrong sometimes.

And leave it at that.

Common sense is never wrong, however it may not be appropriate for the circumstances.

I guess I don't understand how common sense is propagated based off of pretty obsolete information.  Most of the "common sense" posted here works for a very small time frame of emissions controls over the past +50 years.  And has obsolete for the majority of that time.  At least for gas engines.

Well this thread got a lot more interesting when it stopped being about making excuses for people you dont even know, even if its still way off the original topic.  Better than the zoom meeting im stuck in for another 2 hours. Time to work on that 123 page cooling systems document..

As usual, discussions no here never seem to end up relevant to where it started.

But that is the fun of this place.