How Coolant Temp affects Timing Advance

[strange_trp]

it would logically make sense that higher ECT would result in less ignition timing advance. i mean, higher ECT suggests higher combustion chamber and intake manifold temps. hotter mixture in combustion chamber needs a later spark or combustion will occur early. if the ign timing is still way up there you'll inevitably get preignition.

but as mentioned in this thread, the stat only controls the flow of coolant through the system, not the coolant's temp. the temp is controlled by cooling fan operation.

[SuperRat]

Make peak horsepower with cooler engine. Warmer engine is more efficient "economy" wise. :D

[strange_trp]

cooler engine = greater piston to bore clearance = more blowby contamination of crankcase oil.

also cooler engines tend to sludge quicker than warmer engines, and if you run too cool, you take the chance of incomplete fuel vaporization which leads to cyl wall wash and further oil contamination. i know a lot of guys that run 160 and it works fine for them. and thats cool. i run 180 and i'm sticking with it for the above reasons and others.

if you're looking for more ign timing advance, go with a jet stage 2 or simply slot the mounting hole on your crank sensor pickup so you can move it slightly. i wouldn't do this to my car, but it does work. logging with my autoxray, i've found that the iat mod also gives a degree or 2 more advance, but you'll never see it running 87 octane. the KS will signal the pcm to back off ign timing to prevent detonation.

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by RedbirdV6:
Could this be causing my valve rattling problem I have tried everything and haven't been able to cure it :( <hr></blockquote>

maybe a bottomed hydraulic lifter? or one that leaks down too quickly? possibly excessive valve to guide clearance.

in response to someone's hypothesis that the SES light would come on if the problem was too serious: 'tis not necessarily so. the SES will illuminate primarily if the PCM computes exhaust emissions will exceed expected values by a factor of 1.5. it's basically an emissions device.
the PCM monitors its sensors and actuator feedback circuits and illuminates the SES when it sees a return value outside the parameters it expects. a problem such as excessive valve guide clearance or even a lifter that leaks down too quickly will not usually set a code, because there is no PCM sensor or actuator feedback to monitor this. (except in the case of a bottomed lifter, if the valve fails to open you may get an o2 or misfire code).

good luck. hope it is nothing too serious.

[ November 17, 2001: Message edited by: strange_trp ]</p>

[bluecmaro96]

well i have a 180* stat and the fan switch mod. when i let my temp go up to like 200-210 i get a consitent .1 in the 1/4 as opposed to letting it at 160-170* why is this?? so what would be better leaving the 180* in and letting the car get 200 210 for track or get a 160 and dont let temp go ver 160* at the track? which is better 4 track for u guys

[Magnus]

This is a very technical discussion. Lets keep it that way.

Please do not post silly remarks.
Please ask your questions about your car in a new thread. It will be looked at I promise you.

Lets keep this topic about how coolant temp affects timing advance. It also wouldn't hurt if we discussed how engine temp affects power as well.

<blockquote>quote:</font><hr>Originally posted by strange_trp:
cooler engine = greater piston to bore clearance = more blowby contamination of crankcase oil.<hr></blockquote>

While I believe this to be true with the aluminum LS1, I don't nessesarily believe this to be true with the cast iron L36. Aluminum expands much more than cast iron.

For those of you who run better with a hotter engine temp, have you autotapped the car and checked for knock retard with cool engine temps? I thought Deuce was having KR troubles a while back.

And I believe the Jet PCM achieves its Timing Advance by acting as a MAF Translator. Nothing more. What were your results strange_trp? You just kinda vanished after you did your testing.

[Deuce Bigs]

unfortunately i didn't have obd2 back then but right now with the 180* thermo the max i have is 2.8 degrees of knock. i tried going from 87 to 89 and my knock only went down to 2.6 degrees. thinking aobut doing the knock desensitizer mod. the only thing i have to go on was about a 3-4mpg drop in economy and when i did have it dynoed it started out at 160 and by the third run because of just sitting there had gone up to 210. the hp kept going up as the temperature increased and if i remember right it was about a 5-7hp increase but i'll have to find the dyno sheet to be sure.

[NBMA4V6]

Finally a technican discussion to read about that interest me.....

when i went to the track i was on the stock thermo but had a SLP Fanswitch....during stagging i popped the hood and let the motor cool with the fan switch on high...and it did cool down and when i went to make my best to date run..i figure i was around 150-170 Degrees.....the car felt like it hard more in it and felt overall stronger..

Another point is that when you start the car up on the stock thermo in the morning and then hammer it when you pull out on the highway..it feels good and pulls harder than once it has already hit the 205 mark....i also have the fan switch like i mentioned earlier and if i turn it on high i get a much longer warm up time and the car great until it gets to the 205 mark....thats my observations and because of the differnece that i feel SOTP and the track reslts i attained at a lower operating temp...i am going to get the 160 thermo

Jeff W

[ November 19, 2001: Message edited by: NBMA4V6 ]</p>

[SuperRat]

I have the 180 deg stat and definitely notice great performance when the engine is cold and warming up. The sucka wants to go. Idle will be about 1,000 rpm. So the computer is telling the injectors go rich because the 02 sensors are showing lean until they warm up. 3.4l sensors are non-heated. I know the computer is factoring temperature as well. What happens first? Does the computer read ECT and adjust the fuel mix? Or does the computer receive the 02 input to lean the mixture? Strange? [img]graemlins/burnout.gif[/img]

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by SuperRat:
So the computer is telling the injectors go rich because the 02 sensors are showing lean until they warm up. 3.4l sensors are non-heated. I know the computer is factoring temperature as well. What happens first? Does the computer read ECT and adjust the fuel mix? Or does the computer receive the 02 input to lean the mixture? Strange? <hr></blockquote>

when cold, you're in open loop and the o2's are completely out of the picture altoghether. on your 3.4, the pcm calculates injector pulse width based on map sensor, tps, rpm, trans range, engine coolant temp, and other sensors. only when the o2's are warm and responding does the vehicle go into closed loop operation, where it uses the o2 sensor signals to determine mixture.

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by Magnus:
[QB]This is a very technical discussion. Lets keep it that way.

While I believe this to be true with the aluminum LS1, I don't nessesarily believe this to be true with the cast iron L36. Aluminum expands much more than cast iron.
QB]<hr></blockquote>

i don't recall writing anything silly. i just stated that it was logical that the pcm would cut ign timing at higher ect to prevent detonation. its common sense.

the logic of "cold = more power" has been taken out of its appropriate context. cold AIR equates to more power, because it is denser and contains more oxygen. therefore the pcm may deliver more fuel and the energy transfer from combustion produces more power.
this is not to say that colder engine coolant temps necessarily equate to more power. at a certain point, the fuel will not vaporize before ignition and we all know that liquid fuel does not burn. it sticks around in the combustion chamber to dilute crankcase oil (cyl wall wash).

cast iron or aluminum, both metals expand when they get hot, and the engineers that designed the engine designed it to run at about 200-210. when you have a 160 stat and a fan switch and you run it at 160, the piston to bore clearance WILL expand, regardless of what kind of metal the piston or bore is made of. granted the alum will expand a bit more, but the cast will still expand, meaning you'll have a larger tolerance piston to bore than the engine was designed to run with at normal operating temp. this equates to lost power and oil contamination due to increased blowby. this is why you do compression tests with the engine at operating temperature (even on engines with cast blocks); because at colder temps you lose compression. 180-200, not that big of a difference. 160-200, the difference becomes a little more significant. this is of course assuming that the cooling fans are keeping the ect at 160...

plus the aluminum block of the LS1 still has steel bore inserts which effectively temper the heat transfer characteristics of the aluminum block material.

[SuperRat]

I went for a drive while ago and observed the idle rpm and temp gauge. The idle dropped from 900 to 700 rpm as soon as the temp gauge got to 180. I assume the thermostat opened and the 02s are feeding the computer at 180. [img]graemlins/burnout.gif[/img]

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by SuperRat:
I went for a drive while ago and observed the idle rpm and temp gauge. The idle dropped from 900 to 700 rpm as soon as the temp gauge got to 180. I assume the thermostat opened and the 02s are feeding the computer at 180. [img]graemlins/burnout.gif[/img] <hr></blockquote>

the pcm controls the iac valve to idle a bit faster for quicker warm-up to reduce exh emissions and get you into closed loop more quickly. once you get into closed loop and the engine is warm, the pcm controls the iac with a different strategy. the drop in rpm is not due actually to the o2 sensor, more due to different strategies used by pcm and iac valve for warm-up and curb idle in closed loop. actually on most of the newer 3800's you get into closed loop (o2's responding) around 120-130 deg F.

[Magnus]

strange, those comments were not toward you. They were toward off topic replies.

I believe your point about piston to bore clearances. Not arguing that at all, although I do believe it doesn't make much of a difference in our cars from 160 to 200 degrees.

If our PCM's kept the timing advance the same at 160 and 180, well then you might just make more power at 180. But the fact is as ECT goes up, timing advance goes down. It goes down so much that you lose power.

It might be a good idea to try a MAFT+ and bump up the timing and run the car at 180. Do some Test and Tuning and see how much degrees of advance you could squeeze before knock kicks in. I bet though you would be able to see more degrees of advance with a 160 ECT.

- Keith

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by Magnus:
I bet though you would be able to see more degrees of advance with a 160 ECT.
<hr></blockquote>

more ign advance does not always = more power.
[img]smile.gif[/img]

like i said, if 160 is working, go with it. i know the engine is designed to run at about 200*. i don't mind running 180, mine never really gets down there anyway because i'm not controlling fan operation. i myself am a bit apprehensive of running 160 with fan control. to each his own, right?

honestly, i don't have the time right now to do much logging. i would expect that kicking ign timing up on a hot engine would be futile, because the knock sensors would signal the pcm to bring it back down. it may also increase egr operation to control combustion chamber temps to prevent detonation. this is theory. i haven't seen it work for myself.
but the thing is, even if i do see it on mine here in NC with the autoxray, you might see something completely different on your car where you live, because of different ambient conditions, different pcm adaptive learned strategies, and different amounts and characterics of engine wear between the 2 vehicles.

again, i havent seen it but i suspect that the difference in pcm controlled timing advance between 160 and 180 would be negligable.

[ November 19, 2001: Message edited by: strange_trp ]</p>