You tune for max power, within the limitations of the available fuel octane. It's a delicate balance of A/F ratio, ignition advance, and engine temperature control, to avoid detonation. Advance the timing too much, or run it too lean, or run high intake air temperature or coolant temperature and you get detonation (knock) and damage the engine.

Why (and how) would the PCM (or the tuner) “slow down engine speed”? No idea what that means. To increase power, you have to burn more fuel. Oxidation of the fuel releases heat of reaction (BTU's). Roughly 1/3 of that heat is converted to mechanical power at the crankshaft. About 1/3 of the heat goes out of the engine in the exhaust. And the remaining 1/3 of the heat is rejected to the coolant. Burn more fuel, make more power, increase the load on the cooling system.


The PCM has absolutely no way to know there is a 160°F thermostat. And installing a 160° t'stat has absolutely no effect on the way the engine runs, (except to slow down the heat up between 160-180°) unless you make the corresponding changes to the fan on/off temps. The thermostat only controls the MINIMUM coolant temp. It holds the coolant in the block until the coolant reaches 160°. Then it STARTS to open. It will not be fully open until 10-15° above the rated temperature. Once it is fully open it has no effect on the flow of the coolant, so once the coolant reaches ~190-195°, the coolant flow is identical to the flow through a 180° t'stat. From that point on, the fans control the coolant temp. So we reset the fan temps on/off to see a lower engine operating temperature. That keeps the heads cooler, which increases the density of the air in the cylinders. Denser air = greater mass of oxygen, so more fuel can be burned = a small power increase.

If you run a 160° t'stat, the TUNER can advance the timing, because the the cooler heads help resist detonation.

Where you get into trouble is with too much ignition advance. We want the burn to start far enough in advance so the peak cylinder pressure is reached (in simplified terms) at TDC. Start the burn too early and you build cylinder pressure too early, and generate unusable heat = overheating and detonation. My earlier comment answered your question about ignition timing causing the engine to run hotter. That comment primarily addressed the extreme case where the cam was not indexed correctly to the crankshaft. Another extreme case would be a screwup by the tuner, programming too much advance.

The last thing you want to do is “automatically bump up timing.....when the engine gets too hot”. Just the opposite.... as coolant temperature increases, or inlet air temperature increases, you want to reduce advance. When the engine gets too hot, you get detonation. The knock sensor picks that up, and the PCM can pull up to 15° of advance (knock retard) in order to eliminate the detonation. Think also about the EGR system. When the PCM sees conditions that increase combustion chamber temperature - example, lugging the engine in the wrong gear at low RPM - it opens the EGR valve to dump exhaust gas into the cylinders to quench the temperature. Wait... how does hot exhaust gas reduce combustion chamber temperature? It displaces oxygen, reducing the burn rate and the amount of fuel burned.

 

Thanks Fred for all the good information, you always have good insight on these lt1s and how they function. I appreciate it.

I did disable my EGR system in the mail order tune and up the timing... Don't know how much degree of timing was added, gotta double check.

​​​​​​You think disabling the egr causes higher combustion temp?

What is the most timing you can add? And what is is a good range it should be at, let say on a mild modded lt1 with a mild cam?

 

How's it going everyone, hope all is well and hope everyone had good Easter with family.

I got some update, thats off topic...
But since we already here might as well just bring it up

So as of late I noticed I been having slow cranks..
Sometime it would just fire up, but most are slow cranks..

Just the other day I was driving around doing errands, I shut it off when I got to the store and went back to start it, really slow crank * after that the ses light comes on.

I scanned it "Code 36" No High resolution? I'm confuse cause I replaced optispark when I installed that cam in September.

Another thing, "voltage dips" I've been dealing with this for awhile and I have talk to Fred about this on another thread. Especially when put in gear voltage will dip and lights will dim out for sec. I pretty sure this involves "Code 36"

I pulled the pcm fuse for 30 sec from the fuse box inside the car. I started it and there was no ses light on the dash... But scanner picked up code 36 with code 51, "prom error" both codes are stored, but say "Current" on scanner.

I do have a MSD blaster coil installed and I heard a lot of bad things about it.. When I think about It i didn't start having these slow cranks until the MSD coil.

I read on some threads that slow cranks can cause code 36 and code 16 to come on in some cases.. It could also be wire related.

I just replaced alternator & battery too.

This car drives real good and still have lots of power.

What you guys think? Especially since that code 51 is back. Can low voltage cause all theses issues?
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Since this is totally unrelated to the original topic, you should start another thread. It helps when people search in the future and they will know what the real subject is when they click on the thread.

 

Ditto... 100%

 

You are right, I'll do that right now