never would I request you to STFU... you present good stuff that makes me think.. like, that time you accused FarmBoy of hitching up to a shopping mall to move it out of the way whilst he worked on it's plumbing..

on a somewhat related, yet way off topic subject about 'burning really fast', is this not the advantage to diesel fuels? is the 'burn' anything more than just a longer, sustained PUSH on the piston that results in stronger sustained push than a gasoline burn?

I've always thought of them as a badly thrown punch (gas), and a well thrown punch with follow through.. or, maybe better compared to a bullet (gas) vs. arrow (diesel)on the same surface (piston face).. the bullet hits with a mighty force and does damage to the absorbing surface, while the arrow strikes with less force but has all that weight behind it still pushing when the tip has stopped, which equals penetration.. (man, out of context this paragraph would be fun, no?).. Gas has a mighty but less sustained push than diesel.. how crazy am I here?


incidentally, I should add to the first post that economy is slightly worse with the cooler stat because more air (denser) is going to require more fuel to make it go (burn really fast) with authority..

 

I've slapped the laptop on my truck and drove it to work, logging the activity so I could learn more about how this works.. All I've learned is that I have a lot to learn..

I have figured this though:

the PCM closes loop around 140*.. it bounces around somewhere around 120*, but finally starts taking poll data from the sensors exclusively around 140*.. well short of the stat opening..

the computer in open loop is running off of tables, but it is NOT ignoring the sensors... it's almost as if it's pre-positioning the information to use when it reaches closed loop.. this is why I think it bounces back and forth between open and closed more than a few times- it is 'sampling' to see if what it thinks is the right trim is actually the right trim before it launches it..

anyway, it closes loop well before 180.. at around 140.. at 140 the PCM is still worried about having misfires, so it livens up the mix (short term curve).. it doesn't back off dumping fuel until EXPECTED operating temperature is found..

the sludgey oil is something else that should be added to the first post.. it is a concern if you never reach operating temperature and do it over and over for a long time.. so would lack of burn off of h2o from condensation in your oil..

 

I am not to sure on this. As a retired marine tech just about all i/os and o/b use a 160 tstat. I have had my hands in 1000's of motors and sludge is only a factor if the motor was not maintained right. I have seen motor's with a small amount of water in the oil and have watched the owner run the motor that way until the water dissipates out of the oil, no more than a half hr at opt. Was this the right way for him to get the water out no. But there is enough heat @ 160 to get rid of the mosture.

Very nice post by the way.

 

Well, it wasn't so much accused him of it... If memory serves I was just pointing out that he had a propensity for embellishment. Or something like that. I'm too lazy to go look.

There's more energy per unit of volume in diesel fuel, and the engines burn more efficiently because they can (must) run at higher compression ratios which result in more homogeneous mixtures. But the big win is in the energy density -- it expands more when you bust up the hydrocarbon molecules, so it pushes harder on the pistons.

Ya might approach it from this angle: It's that 14.7:1 fuel:air ratio that the PCM works so hard to maintain. Colder air is denser, meaning there are more molecules (of nitrogen, oxygen, argon, carbon dioxide, butterfly farts, etc.) per unit of volume, so you need more molecules of gasoline to get the ratio right. And with more hydrocarbon molecules comes more available energy and a lower bank balance.

At least it makes sense to me when explained that way... But people tend to say "huh?" a lot around me so I'm not a good test case.

 

drewactual --

Would you mind elaborating on the tuner side? I ask b/c afaik the 180 tstat seems to ONLY be a necessity for SCT tuners, rather than also OTHER tuners (e.g., superchips). Perhaps I'm completely wrong and hence thinking there needs to be more explanation on this symbiotic relationship.

Case in point is that I have a (old ****) Superchips 3715. It has 3 canned tunes: 87 econ, 91 performance, and towing. Additionally, rev limiter, speed limiter can be removed and lastly tire size input for speedo/tach correction. I'm under the impression that my tuner cannot do fuel trim adjustments like your fancy schmancy SCT big nose tuner. Moreover, what about the other Superchips tuners and brands? I'm only cognizant of SCT and Superchips for 2nd Gens.


I echo that. Talking intricacies of structural analysis in the nuclear/fossil power plants and rocket propulsion leads to:



or



or



extremely limited occasions:

 

 

dang fone wont let me stay login.if the truck hits closedloop at 140 it would be correct to say that with a 180 or 192 0r 195 the truck will run the same up to 180?if it will then your saying it will run rich bc of the 12- 15* difference?for every 10* of temp you can gain 1hp?how much fuel would it take to gain 1.5 hp?wouldnt think much to make the truck run rich would it?what about if the truck has a 195 but never hits 195 only 175 bc of the colder weather would it still run rich?just cant phathom 12-15* have it run rich to loss mileage when in closedloop lean 14.7 ratio?with autoenginuity hit 120 and 2minute timer it is in closedloop.

 

I get what you're saying, and you're right... to a degree.. what you're supposing would be accurate without a tune and only addresses the benefit of cooler temp a+f charges..

a cooler air+fuel charge will account for a few ponies, so long as that is at a 14.7:1 charge.. for every ten degree drop, there should be a pony freed.. however, the tune not only takes advantage of the cooler temperature a+f, it advances timing.. the advancing of that spark is where the real punch comes from, and you can add that directly on top of the benefit of a cooler charge.. without a tune, you're not advancing spark, so you only get a portion of the benefit..

the engine WANTS to run at 195* without a tune.. it will take advantage of the thermostats flutter to maintain that.. once it is achieved, it can take full advantage of environmental conditions to trim the fuel nicely, but it can't advance the spark but so far without a tune telling it to do so.. while it's under 195* (without a tune) it's going to lack confidence it can positively ignite the a+f, so it's going to add more F to the A..

the entire purpose of tuning for a 'stat is to alter the 'expected operating temperature', so that extra catalyst (fuel) isn't added..

the added bonus of using one of HemiFevers tunes is:


Sean, aka HemiFever, walks right up to the edge with advancing spark.. I'm thinking he advances it further than the other tuners care to.. since he is taking somewhat of a risk advancing it to that degree, he needs to take every precaution he can.. If he overshoots his mark, or your engine is running hotter than he expects it to run, you're most likely going to get pre-det.. that is a bad thing.. so, he requests the 180* 'stat, in hopes to keep the temperature low enough that the heat and compression aren't enough to ignite the a+f all on it's own, and before that magic spark hits it..

In short, and because I like to get winded, Sean's SCT tunes push the envelope on ignition timing advances, and he needs every millimeter of safety margin he can get to get your engine to produce the power while NOT pre-detonating..

edited to add:

let's suggest you could slow time, and watch the spark, and stretch it out over a period of two seconds.. when the first bit of that spark appears across the plug, in a cool engine, the a+f may not fully react.. it starts it's burn slowly too- and really starts to burn when the piston slams it in it's entirety into that tiny space.. once the piston pushes the load all the way into the chamber, it is flat out burning.. that burn is going to want to expand- and fast.. which drives the piston down..

when that a+f is being compressed in a hot engines cylinder, it is highly volatile.. it will ignite at the slightest provocation.. the 'flat out burn' may turn into a 'flat out burn' before spark is even applied due to compression and heat.. if that's not dangerous enough, the spark applying may be enough to make it straight up explode instead of burn (as Unreg explained).. that is bad... a few degrees of temperature make a difference here.. a lot of difference.. hence: cooler engine = safer to advance spark..

 

There is an optimum operating temperature range for internal combustion engines. Anyone claiming running and engine colder to be better is trying to put 20lbs of BS into a 15lbs bag -- and failing.

 

Thanks
Great write up and explained well
However, would have came in much more handy a couple days earlier