Mark, I will let a lot of the stuff you say on here slide, but in this case you are 100% wrong. Lean misfire can and will melt a catalyst if there is enough of it. Also, 99.99% of automotive catalysts are not designed to run lean. They are designed to run at lambda 1. Above or below that the 3 way reaction does not occur. And if anything, the catalyst will tolerate rich mixtures much better. Why do you think engines overfuel during heavy load? It cools the cylinders and effectively turns off the catalyst so it doesn't overheat.

 

Do you really know what you are talking about , or guessing. i know the EGTs adn CHTs of lean operation. its strikingly low. very low! now, i would like to hear how a lean misfire, which is basicaly, a non-combustion event, can hurt a cat. Im open to learn about cats here, as I know they get cooked if you are running the wrong gas, or lean mixtures, as in near stoich, due to high EGTs, but how does it hurt the cat if you are running very lean. Now, ALSO , dont confuse the lean misfire with WOT misfires, vs a part throttle misfire under very lean conditions. Im just asking you.

cats run fine , coasting down a hill from 7000feet to sea level with out touching the gas. (i.e. very lean, always for 30min at a low power setting. ) or they run fin at 10 to 12:1 rich, under WOT . so, your statement to us seems to be more flawed than mine. you show me the problem with lean of stoich and cats and ill listen. but, back up your statement that im 100% wrong, which i am not.

now, you say , a lot of stuff i say? really? such as?

I try and keep things real and dispell misconceptions and there a TON of them. nothing i say has not been backed up by a good amount of fact or experience.
many times the arguments or the confusion is when two folks are talkng about two differnet things. this is a good example of this. lean is always thougth to be tied to hot EGTs. it isnt. stoich is. very easy to confuse this . This is why i had such luch with NOS, because if you keep things fat, there is no chance of having heat issues. and REAL lean, is not a problem either. stoich is the enemy most refer to when thinking lean = boom.

 

somethings wrong, i still get 20mph, doing the same thing you are doing. around town, it can slip to 12, but thats having some "fun".

yeah, even if you kill the fuel, i dont like to think some cylinders are running dry, but maybe its ok, if you can kill the fuel, forget about the spark.

Yes, thats the thread! god you guys are SO STUBORN!! i just read most of that discussion. amazing. so many doubing thomas'

Here is the chart found on page one of that discussion


yep, that 2.75 will kill you

even i know we need to mess with coding plugs to do some of this stuff!

 

I save gas by........ not driving a big V8 with a super charger.

My beater 93 Honda Accord gets 34 MPG

 

You read it?? Mark, that was YOUR thread, you WROTE it. And you were arguing with everyone there, also.
And you were also wrong on many points, you just beat everyone down.

I don't think anyone said that high temps were going to be the problem. It is detonation with lean mixtures under load that is the problem. You need to monitor knock-retards with a Sharktuner, or fit a knock-lite, or sacrifice a few chickens to your personal gods, or something. You can't just futz the coding plug, bugger the temp-II sensor and call it "good".

 

Jim,

the 928 (and all others I've tested), will hesitate due to a lean mixture but will not register a knock (or oil ejection) due to lean fueling FWIW.

I tune mine for lean, till I get slight hesitation and then raise it a couple points.

 

So Colin, what is the load point where you tune back to stoich?

Dan
'91 928GT S/C 475hp/460lb.ft

 

Don't catalyst fires happen because of running rich? Misfire causing raw fuel to be dumped into the catalytic convertor?

At least that was what happened to my F150. Nothing like your carpet catching fire while you are driving.....

 

Apparently I can improve my 928 mileage by trailering my car.

Reminds me of aftermarket performance improvers that increase resistance on the temp sensor to get the brain to run rich.

This is a crappy idea because you're relying on the knock sensors and brain to keep the engine from being damaged by knocking to to a lean mixture. Why risk it? Leave that to cars designed to operate in that way.

I've got a pile of cars and pick the one that makes sense. I'd never drive the 928 across country unless it was the car I wanted to have when I got there. Tuned for power and getting sub 15mpg.

Ya wanna improve highway mileage? Drive the speed limit or a few MPH under it. Better yet, follow a Yellow truck. Those are limited to 62 MPH. You'll get great mileage that way.

 

I do it by feel on the MAF system I moniter pedal pressure at cruise and see where it is at on the load points. I then go just a tiny bit above that and leave stoich. This gives lean cruise but good power when needed.

Glen,
Lean burning during cruise will not create knocking, detonation, pre ign, etc. just high NOx

 

Sure. "Partial throttle" but who can resist passing? And punching it on the on ramp? And remember to throw the switch every time?

Change the map in the LH if ya wanna go this way.

 

It's all good!









Attachment 623885

 

Now I understand, and yes I only do it by tuning the LH

 

I thought the cat was supposed to glow red hot ) Too rich or oil burning coats the platinum in the cat so it does not do its job plus eventually clogs it and it overheats.
My experience with running too lean has always been overheating.Think about how you weld. You add o2 to get the hottest flame.Too much o2 puts out the flame then its cool. I ran in lots of club economy rallies and after a 100 or so miles the valves or valve seats were burned and the head had to come off. I once managed 94mpg in a 998cc sprite but a gal in a 911 beat me at 96mpg. Hmmm I cheated ...what did she do?

 

Well, this is the classic response. say how wrong someone is and leave out any example or logic. again, when someone has information and the rest disagree, they are beating them down . really??

you dont get detonation with lean conditions do you even understand what happens with a lean mixture. the misfires are no combusion. not enough fuel to ignite! worst case, with that you have that fuel load, passing out the valves unburned. very similar to what happens in your car when you lift the throttle. still have spark, but not enough fuel. the differerence, is ALL the cylinders are doing this off throttle, not just one during a lean misfire.

so, you didnt read the chart as most im sure didnt. its the same thing in the last disucssion I fight, because some arent using thier heads and are making statements like they know something.

now, lets list those other "points" you disagree with . so far, all i hear is the misconceptinos , that lean burns motors, and thats not true. its stoich that burns motors, or running through stoich, getting detonation , etc.
lean of stoich is safe operation and has been done for 75 years!!

Thank you ! JEEEEEZZZ!!!!!! lizard and i have gone back and forth on a lot of stuff, but he is always willing to bring in the facts, not wives tales!

Yes, right about the cat, it glows and gets very hot. other compounds present can force it to overheat. example, race gas , or additives.
now, you are trying to use logic that has some errors in its foundation. adding 02 to a flame is not the same as leaning out the mixture on an engine. the hotest flame happens at the perfect combustion mixture. its what you get when you are a welder and you tweek back the fuel or lean out the mixture to stoich. in a car, there is not an explosion, its a rapidly propating controlled burn. its very different than your example. go look at the lean of stoich chart i just posted. this is from Lycoming!!! guys have been doing this since WWII in airplanes and its the same for cars, but WE and the country , care about the polution of cars, which is worse when you run lean of stoich. (high NOX)

So, if you were burning valves, you were still too rich! CHTs and EGTS will be lower lean of stoich, which means you COULD have beat your competition if you could have leaned out your mixture a little more. gone farther on a gal of gas and not burned the valves.