There are several aircraft that can give the SpitV a hard time in a turn fight (Either Zeke, FM2, Hurricane and the Ki-84), but the N1K2 is not one of them, unless you are not using the Spit to its full capability.
My suggestion is that you visit the TA and look for an experienced pilot to play with. Any of the trainers will help out and you can find Badboy, Inyo or any number of MA regulars there almost on a daily basis. Before you fly a SpitV, fly the N1K2 against Spits first. This will aid you in seeing it weaknesses firsthand against the SpitV.
A common problem I see is that many people don't turn long enough to gain the advantage. They make flat 90 degree turns, and then do those silly little slow rolls, which does nothing but allow their pursuer to re-establish a gun solution.
I suspect that you may be concentrating more on being defensive, rather than offensive. Many years ago, when I began competitive boxing a trainer gave me the best advice I ever received. He said, "stop worrying about what the other guy is trying to do to you and start thinking about what you are going to do to him." In simple terms, fight your fight and not the other guy's fight. Think offense, not defence. Take the fight to him whenever possible. In the case of the N1K2, you need to do what Slapshot recommends, force him into a low-speed maneuver fight, where the SpitV will dominate. As anyone who has good ACM skills will tell you, the secret is as simple as equalizing E states. Again, as Slapshot stated, there is nothing as dangerous as a Co-E, Co-alt SpitV.
It's possible to write pages on how to accomplish equalizing E, but the best way to understand this is to watch flims and to actually fly. That is why I suggest the TA, which I prefer to the DA because mistakes will not result in time wasted getting another fighter. In the TA, you simply disengage, separate and re-engage again. You can do this until one of you runs out of ammo and/or gas. Film every fight. Review the film and watch it from the other guy's plane. You will be better able to see your errors from that vantage point.
One final point. Keeping the enemy in view is extremely important. Concentrate on keeping the enemy within your field of vision. If you lose sight of him, you will probably lose the fight.
A typical example of this happened last evening. One of the MA regulars dropped by the TA to practice after getting clobbered in the MA. He flies the Yak-9U almost exclusively. So, I grabbed an F4U-1 and we squared off. On the merge, I went below his nose, then pulled a vertical reverse, using flaps to really tighten it up coming over the top. He never saw me, having lost sight almost immediately. By the time he finally spotted me, I was 400 yards behind and pouring fire into his Yak.
Having mentioned the F4U, let me deviate from the topic a bit.
I have a nephew who lives with us while attending a nearby State college. He became facinated watching me play Aces High and asked if he could try it. Sure, why not? So, he spent some afternoons after classes in the TA, learning the basics of flying. In the MA, he tends to stick to gunning, buffs and GVs. When he does fly a fighter, he usually gets his butt handed to him. Since he uses my account (for now at least), I can't take him to the TA and tutor him. I usually coach him, sitting alongside at the desk. A week ago or so, he took up an F4U for a Jabo sortie and got shot down before he got anywhere near an enemy base. Basically, he did everything wrong from tower to tower. In fact, the only thing he did right was to turn on the film recorder. First, he took the F4U-1. This fighter can carry only one bomb. Therefore, he had little choice but to take a lot of gas, 100% in this case. Nothing degrades the F4U like excessive fuel does. Next, he flies a route that will take him over a friendly base under constant attack. That surely means that there will be enemy fighters there. Finally, the slow climb rate of the F4U-1 means that he will pass this base without much altitude.
So, climbing thru 8k, a Knit 109 shows up, probably up at 15k or higher. However, my nephew doesn't notice until the 109 is nearly above him. Instead of dumping his bomb, and establishing some speed, he turns towards the 109 and continues to climb! Well, the 109 flies over and reverses. So, my nephew now makes a flat, right hand turn. And he stays in a right turn! He dumps the bomb (finally), but continues the turn, around and around. This 109 turned out to be a 109F-4. A light F4U-1 can turn fight it, IF the pilot of the F4U has some skill. But, a heavy F4U, flown by a noob without a clue was a dead duck. I believe the 109 pilot was Drediock, a frequent and worthy adversary in the MA. My nephew's right-hand spiral prolonged the mismatch far longer than I expected. The 109 could not gain a shooting solution until the F4U ran out of altitude and had to dodge trees and hills. At that point Drediock got him.
Reviewing the film I could see his mistakes. Most of these where typical of a noob. Tactically, he did everything wrong. He also failed to simply dive down to the friendly base, just a couple of miles away from the outset. When the fight slowed down to below 250 mph, he didn't use his flaps. Like the P-38, the F4U can use flaps to great advantage. I also saw very little looking around. Only twice did he look to see where the 109 was once he began turning.
Unfortunately, my nephew deleted the film, or I would post it. There's much to be gained by watching lousy flying too.
My regards,
Widewing