Error,

I’ll try to touch upon the three things you mentioned above, please don’t take offense if it sounds kinda simple, I want to word this so anyone else reading can easily understand.

First before we start, the general concept of “cool air is better” regarding an internal combustion engine and power/torque. Cooler intake air is largely preferred since it is generally accepted that cooler air is denser, and therefore contains more oxygen and potentially more extracted energy when mixed with the proper ratio of fuel and ignited at the exact perfect angle of rotation during the compression stroke in order to completely burn the mixture while preventing detonation (this I touched briefly upon in my opening thread).

To address some of your exact questions/statements, let’s take a look at the first:

“I’d not go by the spark advance alone to figure if it hurts power”

This is correct; however, spark advance is directly tied to the general concepts listed above. As the IAT rises, an ECU controlling a fuel injected engine such as ours plays a balancing act of ignition advance and fuel delivery, all while maintaining a stoichiometric burn while avoiding detonation. You’ll see how this ties together with the other subjects as we go along below:

Let’s take a look at your second concern:

“It may simply be that it needs to be pulled a little bit because the combustion is faster?”

Yes (sort of). With higher IAT’s is increased chance of detonation. The ECU pulls spark advance to prevent detonation, and the end result is less power (not only because of the advance being pulled, theoretically if your engine is tuned properly you’re still getting a complete burn, only there’s less to burn due to less oxygen/fuel caused by higher intake temperatures). I’ll touch more on ignition advance as I address your third concern below:

Your last question:

“So it may actually be a good thing it pulls ignition to get more power/torque.”

Sorry, this one completely wrong
Hopefully the above explained everything? If the timing wasn’t pulled you’d “potentially” get detonation which would destroy your engine; however, less oxygen and fuel equals less power and torque, it’s as simple as that
(Section 5.1.1 of the paper linked below better explains the spark retard/power relationship as it pertains to engine knock).
Furthermore, retarded ignition timing (to prevent detonation) in this circumstance results in peak cylinder pressures occurring past the best rotational angle of the downward power stroke, resulting in less overall engine efficiency and loss of performance.

Here is an interesting paper I found on the subject, if you’ve got a lazy afternoon it’s a good read:

https://www.sciencedirect.com/scienc...60128516300764

Of course my comments regarding your three concerns were quite general, there are many other variables involved such as combustion chamber/piston/valve design/fuel type, engine load, etc, just to name a few. Hopefully these explanations make a little sense

PS: I enjoyed reading your engine build thread. Will you be doing the dyno tuning yourself or having someone tune it for you?

 

Yeah - lot's of variables we don't know on the user end.

Fully agree with your comments. Actually that's what a forum is for - discussion.

Would be nice to know why GM decided that it needs the advance being pulled in the first instance.
Whenever I see such things as pulling the advance by just a little bit it gives me the creeps. Sometimes these are indications of an engine being knock limited. Especially in the lean fuel efficient part load area there is the danger of running close to spark knock.

Agree, coldest possible air would always yield the most out of the injected fuel. Interesting field for experimentation to get some figures along the intake. Makes me think to add some ports to the air intake to be used by a second IAT sensor and datalog along the intake.

Once the engine is ready I will definitively be in the dyno room on every run, probably also tuning it myself. But I'll look for expert help. Not going to tune all by myself.