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I’m just looking for a bit of advice on some knock that I’ve run across when starting to tune my Evo 9 (started at VERY low boost levels). Its running and AEM V2 Ecu. I’m using 94 octane pump gas (10% Ethanol). The car had a very rough base map and I picked away at it until the drivability was pretty good (idle, starting..etc) it still needs work, but for my experience level I’m happy with it. Since taking some of the courses on here I thought that I would take a shot at tuning the boosted parts of the MAP. This is where I’ve encountered something a bit odd, at least I think it is. (You can skip to the issue, it’s in the fourth paragraph).
I can go through a modification list, however it’s pretty extensive and I’m not sure if all of it will be pertinent. The car is on a 6466 turbo, ID2000 injectors, forged bottom end, build head…etc nothing crazy just a “standard” issue built evo.
So I have a 6psi waste gate spring in the car. I wanted to start very conservative just to get the hang of things and ensure I don’t bite off more then I can chew. I wanted to dial in the fueling at a low boost level, since with boost compensation once it’s dialed in at a certain PSI it should be pretty close all the way up. Once that’s complete I would simply remove fuel in the lower load areas so I would get a nice taper.
TL;DR - So I started logging the car in 3rd gear. On the 3rd run my check engine light flahes indicating I have knock above my threshold. Sure enough, I check the log and it had peaked at something like 2.34 volts (threshold at that RPM was 2 volts). So I pulled back about a degree of timing and added in a bit of fuel. The car was already running 11.7 in this area, so I got it down to 11.4ish. It seemed to fix it on the next couple pulls, however on the last pull I noticed that the car pulled timing again. I believe I was only running 10.8 degree’s at the time at about 10 psi. At that load I would think I could be running 14-16, however now I need to back it down more? I just find that to be odd. It seems like too little timing to me. Its not like I’ll be running the car at 10psi, I would like it around 20. However, I would like to get this sorted before I start turning up the boost.
I’m going to check my base timing to make sure its good. However I did check it with my original coil set up before I switched to C.O.P’s and it seemed to be bang on from what I could see.
I can attach the actual logs. However, I thought I would just attach pictures for now in case not everyone has the software.
Edit: Just looking through the logs again. It appears at 7300 rpm, not before or after, there's a spike in knock. Even on my other logs it will jump to 2.13 volts for .2ms
From what I've heard, a stock Evo 9 needs to run lower ignition timing numbers compared to a stock Evo 8, or it will knock. I don't remember the exact reason, perhaps it's the variable cam timing and perhaps it's something else about the combustion chamber design. The stock ECU will also run richer than 11.0 AFR in boost, if I remember correctly. Remember that job 1 is to keep the engine healthy, making power is second or third on the priority list. Even when tuning an engine on the dyno, I would remove a few more degrees from the ignition map and target a slightly richer AFR while you get the shape of the fuel table dialed in. Even if your knock thresholds are too conservative and your current timing map happens to be perfect, a few degrees less is not an unsafe thing to do. When the engine hits your (slightly rich) AFR targets consistently, then you can focus on tuning ignition to see which values make good power without knocking. After you're confident in your timing numbers, try a different AFR target to see if that helps power. If a leaner AFR doesn't make better power, the extra fuel might be a good idea to keep combustion temperatures safe. I'm fairly certain everything I just mentioned has been covered in Andre's videos here on HPAcademy, they are really well-done and anyone learning about EFI tuning today is very lucky compared to people who learned about this sort of thing 10 years ago. Even if you've spent a lot of time researching and learning and trying things yourself, it can still help to work with a tuner who is very familiar with the type of car and dyno you're working with. Some people can tell you how well an engine is running just from hearing it make a pull or from seeing how smooth or how rough the dyno chart looks.
I would also check all the spark plugs if you think the engine isn't running right; look for the combustion deposits on the ceramic to all be the same color (to indicate all cylinders are getting similar air/fuel mixtures) and look for any signs of melting or peppering. Reading spark plugs is easier to do on a dyno since you can make a pull and then shut the engine off without spending much time cruising or idling. If you check spark plugs after idling for 10 minutes you will mostly see how the engine was running when it was idling.
Where does that knock threshold come from? How do you know for example that it's 2 volts and not 2.5 volts?