My Megasquirt adventures over the years
Heck of a write up.
This right here gentlemen, is why this dummy-"me" will only run carbs... :lol:
Lol, I know I probably get a bit too wordy at times. I still have a carb on my 71 Vette, and the carb that came on the 318 that was in my Dart when I bought it ran like fuel injection. You could just turn the key and go, no waiting or anything. I never knew a carb could do that, though I also didn't drive it in every weather condition to see the full extent of its tune. I do know that the Hemi did not care for a carb with the ModMan intake though. I tried and tried and put all sorts of different rods and jets and springs and stuff in it, but I never could get it to work. I just don't think the intake was well suited for it, and I probably would have still been messing with it if I didn't get the screaming deal I did on the Megasquirt.
I mostly just wanted to share the success I'd found with it and some of the cool things you can do. There's no doubt the OEM computers are more sophisticated and capable, but they also have to do a lot more stuff than us average shade tree mechanics would care about (like emission control). However, their specialization at controlling things so precisely for a stock setup is kind of their downfall in some regards as soon as you start changing things. OEMs run thousands of hours on dyno with all sorts of sensors to optimize things and meet all sorts of requirements and durability ratings to get those values. It's silly to think I can get anywhere close to that with just some driving back and forth to work every day, but that doesn't mean I'm not going to try, lol. That whole OEM engine controller is basically one big mathematical model of airflow and chemistry (an engine is just an air pump after all, they say). Their model accounts for all sorts of things, so I always cringe a little whenever I'm watching videos where tuners are talking about zeroing out whole tables or setting stuff to constant values or stuff like that. I get why they are doing it, it simplify the process so you have less variables to control. The thing is, those variables were there for a reason.
One of the most recent ones I ran into was a thread on some forums where people were talking about zeroing out the MAT correction table on the MS when you make your base tune, but still having issues with hot starts or idling or it driving different at constant speed vs around town. It generally boils down to bad assumptions, the biggest being that people seem to think the temperature value their IAT sensor reads is the same temp as the air going into the cylinder. My MAT sensor is in the #8 runner and it's wild how much the temperature can change with just some change in throttle. On average, my MAT values are 20 degrees higher than ambient temps at steady state on the highway. That's how much the air heats up just going through the intake, and probably still even a little more after the sensor before it gets to the cylinder. If I roll off the throttle and start coasting you can watch the temps climb 5-10 degrees in seconds. Get back on the throttle and they start going back down. Imagine how much worse it gets if your IAT is all the way up at your throttle body. An OEM plastic intake would probably actually be better than my aluminum one in that regard as I would expect less heat transfer. There's actually a table in the OEM controller that models the heat gain between the IAT sensor and the cylinder if I remember correctly.