I dont feel like reading all these posts, so I'll put in my 2 cents based on what I see. First I'd say get a printout and scan it and re-post.
Look at what the smoothing factor is and tell us, cause i cant see it. The end of the curve looks like floating springs or spark blowout....its terrible. It drops quick and is extremely jumpy.
What gear was it run in?
It MUST be run in 3rd gear, NOT overdrive (you're getting reverse torque mutiplication in OD), and the TC MUST be locked up. Wire up a lockup switch...extremely easy to do...look through the million posts on here or go to gnttype.org and study how the lockup circuit works. You only need to jump one ALDL (service port under the dash) pin with a switch to a good ground. Find out about the valve springs. Replace them but dont go too high on the pressure. I'd highly recommend some comp cams beehive springs and retainers. They allow you to run light seat pressure without valve float by reducing sprung mass at the end of the valve, which is great for flat tappet cams that tend to go flat with too much seat pressure on the #3 exhaust lobe, if you dont run a good synthetic with plenty of zinc and phosphorous additives (no oil with the starburst symbol on them...go with valvoline SYN, Quaker State "Q" oils, Redline or Royal Purple and you'll have no need for additional additives). Pressurize 1 cylinder with a compression tester tube and some fittings/air compressor, etc , remove 1 intake spring and measure, with calipers, the distance from the spring seat on the heads, to the underside of the spring retainer. Get as accurate a reading as possible. Make sure there are no spring shims on the head when you measure. Re-assemble and then pull the exhaust spring on the same cylinder, and repeat the same measuring process. The 2 wont be the same...dont assume that the exhaust installed spring height will be the same as the intake cause they never are the same...except in rare situations where the engine builder cared about what he was doing. Call comp cams and tell them these numbers, and they will recommend the right shims for you and the springs and retainers. If you're not a guy who feels capable of doing this job yourself, take it to someone who can. Dont experiment with your car if you havent been down this road. Its also a great time to replace the valve seals. That funky deal at the end of the curve could also be knock retard, but without a scanmaster, you wont know if thats happening. If it is, you're losing big power. Also, any oil misting at all in the cylinder can take a 100 octane fuel down to the low 80's so make sure the IC is free of oil, the intake manifold isnt filled with it, and the PCV valve is only flowing in 1 direction. Changing valve springs and seals will also give you the opportunity to wiggle the valves and see if the guides are worn out. That could be a source of oil contamination and resulting knock.
But first I would rule out wiring and ignition issues. Get some good plug wires and assemble them correctly with the right tools. A 500 dollar set of wires are only as good as the guy who assembled them. Ohm check the wires when you're done and make sure they dont vary alot. Also ohm check each coil, front post to back post, on each of the 3 coils. they should be between 11k-13k ohms....that means 11,000 to 13,000 ohms. Denso Iridium plugs are expensive but pretty much rule out all plug related issues, as long as you dont damage them by gapping them wrong and damaging the electrode.
Looking at the graph, it doesnt really look like spark retard, as retard usually shows a smooth drop (unless the smoothing factor isnt set well). Valve float however, tends to be really jumpy, like yours. Check the grounds at the back of the passenger side head and make sure they're tight, do the ignition upgrades and change the valve springs, replace and or adjust as many sensors as you can, replace any suspect hoses and use a clamp on as many as you can, flush the IC out (needs to be removed) and your car will likely gain a healthy amount of power. But I think your issue is valve float. But with me, I tend to think up 20 different possibilities and fix them all at once, and never know what the problem was, but it goes away and the car has a hell of alot more power and driveability in the end. The point is to return the engine to as close as you can get to "like new" conditions in terms of spark, fuel and metering/sensing. Address all those sources and you will always find your problem, unless it has a major mechanical malfunction.
