Torque convertor and detonation
AJ, I guess I had the wrong idea here, I though that a low-compression motor would take lots more timing then a high-comp, race motor, not vice versa? And that more initial, like 16-18* would be better... it sure feels and runs better, what gives? .
Is it working for you?
Spark plug heat range is on the hotter side, autolite 985, they are clean with no sign of detonation or overheating, again the problem is only with pedal to the floor between 2000-2300 so I doubt it would show on plugs without a chop.
Is it working for you?
Your engine does NOT care about any timing until it hits the stall. Below stall, you can make up for some to most of the timing shortfall with Vacuum advance (which can be modified to get 22 to 24 degrees). Sure; you can use timing to band-aid the loss of low-rpm performance due to low cylinder pressure; but how's that working for you? Not very good right? Really, you need more cylinder pressure; your 262 cam actually makes LESS pressure than the stocker.
ExcessHeat in the chamber is the number one reason for detonation. In order from most likely too least, the reasons for this are;
1) too early an ignition spark,
2) running lean,
3) Hot-spots in the chambers ....like....a hot sparkplug electrode ..... for example
4) the Inlet Air Temperature temperature,
5) the coolant temperature
As for #1;
this is a double whammy, cuz if the spark is too early, the resulting high pressure spike may try to drive the piston down onto the crank, POW!, hammering the bearings; instead of driving the piston down the bore.
Then, because the gasses started burning early, they finish burning early, and the pistons end up pushing them out of the chambers, costing you power, twice.
As for #2;
this can overheat the intake valves, cuz the fuel passing over then is one of the ways they are cooled. If the intake valve has carbon on it, perhaps a circumstance will arise that the carbon becomes a hot spot, which may ignite the air/fuel charge before it's time. If the resulting pressure spike is much too early, the expanding gasses may dry to drive the piston back down the bore, on the wrong side of TDC! This type of spontaneous ignition is called Pre-Ignition, and if left unchecked, usually blows a hole in the center of the piston.
As for #3;
This is usually a spark-plug electrode; but could be a hot valve, carbon, or sharp or pointy thing in the chamber
as for #4;
Above hood air, when the car is in motion, is at or close to ambient, in the range of 50 to maybe 100 degrees F.. Underhood air is from rad temp to header temp and higher. Temps can hit over 400*F. How do you tune for air that is constantly changing density due to Inlet Air Temp? Answer, you cannot. So there will be times that the AFR will be rich and times that it will be lean......... all due to the fluctuating underhood temp..... and lean-running is #2 on my list........
Idling, your headers, before the first bend could be running NOT less than ~350*F.. At WOT, it could be triple that. And the air around them will not be much less. That air is about 1ft from the air-filter house. Do you really want extremely-HOT air getting inside your engine?
The air coming thru the rad is gonna be about NO LESS than 15/20*F (average), less than the coolant temp at the stat.
The oil in the pan. the power steering fluid, and the Auto-trans fluid; are all gonna be close to the coolant temp... or higher, and any/all of them could easily hit 200/220 and more.
Heat gets radiated in All directions, but Hot Air RISES...... up, up, up and straight into the air filter house.
This all is just so much bad news to your AFR.
As for #5;
The coolant temp is actually your smallest problem. From 160 to 195 is just 35 measly degrees.
As for other;
As for slightly late timing, below stall, there are two/three downsides;
1) a really TINY bit of WOT power-loss.
2) The engine may run a little hotter as the fuel may not finish burning in the chambers. In your case with a 262 cammed 360, probably not. But if that happens; the burning AF charge will pass heat to the water-jackets just above the ports.
3) A noticeable drop in throttle-response. This is what you can really feel. But with your very modest cylinder pressure, this is to be expected, expected, expected.
> IMO: You are trying to make something from what is not there. You can just get a piece of it, and then you get detonation. You cannot normally hit the low Power-Timing number at stall that I mentioned, when starting from 16/18 at Idle. If you had a computerized timing control, then you could do that.... but you didn't mention having such a tool. Besides, there is NO GOOD reason to run those numbers at Idle in your set-up; it will just mess up the Transferslot to mixture-screw synchronization. You will end up fighting a tip-in hesitation, which you may be able to cure with excessive pump-shot, which you will activate every time you step on the gas, burning vast amounts of fuel. In a Daily-Driver, you want to tune the pump for as little activity as possible.
>As for slightly late PowerTiming;
At peak power, if you are within 2or3 degrees of optimum, you might experience a loss of power in the range of, 2% to maybe 4% ; so on a 250hp 360 maybe 7or8 horsepower; probably less. In most cases you will never know this by seat of the pants; because in Second gear, with 3.23s, the power may not peak until near or over 80mph. In First gear, you are burning thru the power peak in just a couple of seconds, so no way to tell. The only way to be sure, is to do a timed run from say 4500 to 5500 rpm, and you will need a datalogger.
That's the best I got.
BTW
At Idle, your engine may like 25 to 30 degrees of timing ...... But with the factory advance mechanisms, you cannot drive it like that, because as soon as you put a load on it, it will begin to detonate. Want proof, just pull the timing in until the rpm quits going up, then reduce the idle-speed; then put a Timing-light on it.
But it will take 10 or 12 at WOT right off idle. Now if you V-can has 24* in it you can access that beginning at about 1600rpm on the sparkport with no load on the engine. If your mechanical is up to 16* by 1600, that would total 40 degrees. If by stall of 2400, the mechanical is up to 22*, then 46* , until the vacuum starts to drop out, with load. That's how you get your PartThrottle-Timing back.