13 Sept

So close. The crack in the #4 primary was real, but turned out to not be the main leak. That ended up being down below the flange where the gasket material had blown out. I don’t blame the gasket itself; I knew that I’d been pushing my luck by reusing it several times, so a replacement and spare are on order.

Thought I understand PID closed-loop control, there’s still a lot to learn when controlling the engine. More early-morning testing is slowly dialing in the boost control loop, gradually getting rid of the overshoot while still maintaining fast response. Just as important as determining the P(roportional) and I(ntegral) terms is limiting the integral value to keep it from “winding up” the loop and causing overshoot. A little is okay, but I was seeing 20-30 kpa, which isn’t acceptable; it’s now down to about 10 kpa and I’m trying for a bit better.

Reintroduced throttle-position-dependant boost, which makes the engine act more like a V8 and less like a boosted 4-cylinder.

Also ordered a replacement hood scoop for the air filter. While I plan to someday make a proper carbon unit, the cheesy vacuum-formed unit had melted somewhat and cracked. Time for another temporary replacement.