Been a long time with no updates, sorry about that!
But we have kicked off the 2024 season! We travelled just a short way up the road to Traders’ World north of Cincinatti to participate in the Optima Batteries DriveAutoX season opener.
The DriveAutoX events are put on by the same folks that run the Optima Ultimate Street Car series, and feature a lot of runs for the money. This weekend, we had twelve runs on Saturday, another six Sunday morning, and then the shootout began.
These events are a bit different than you’d see with the SCCA. The winner isn’t necesarily the fastest car or driver. The timed runs on Saturday and Sunday are used to seed a bracket. The course is then reconfigured into a loop, and two cars are set up 180 degrees out and set off. The first car to get back to their starting point wins. Hit a cone? You lose. Spin? You lose.
The fun of it is, sometimes the super fast guys are super aggressive, and they hit a lot of cones because they’re trying to see just how close they can get. They do that during the challenge and they’re out, and the more consistent and clean drivers have a chance to win.
I had no illusions about winning this year. The car was completely untested after a turbocharger replacement over the winter. I had no idea how it was going to do. The intention here was to treat this event and it’s huge amount of runs as a test.
And I needed it.
First off: this new turbocharger has turned this car into a monster. It is FAST. But it also surfaced some problems. In second gear, I was hitting boost cut.
On many modern cars, limiters like the rev limiter or boost cut are handled by cutting fuel to individual cylinders to limit power and bring whatever limit you’re exceeding under control. But this car’s fuel system is batch fire (or bank to bank). I don’t have individual cylinder control, so the limiter just shuts off ALL the injectors. The result protects the engine, but it is quite violent and very unpleasant. You can see in the graph above that even though we were above the boost target, the wastegate duty cycle was trending upwards instead of down. This wasn’t what we wanted.
We spent Saturday fiddling with the boost control settings trying to get this under control. The first thing we realized was the distinctive sound of the wastegate opening (the gate is an open dump) was missing. I dismantled the boost solenoid and cleaned it, and the next run I heard the noises I was expecting.
With that fixed, it was time to figure out the boost control. I kept raising the sensitivity, but it seemed to have no effect. The wastegate duty cycle kept climbing even when I was above the boost target. I even lowered the boost targets to see if it would trend downward while seeing a larger delta. It didn’t.
So I enabled “advanced” boost control. This unlocks some parameters that allow integral and differential (as in calculus) alterations. If boost exceeds target, cut duty cycle. If boost still exceeds target or is still rising, cut duty cycle even more. Repeat as necessary.
It worked. Mostly.
After setting this up and fiddlng with it for a few runs, I had it where it was no longer hitting boost cut… but only barely. We’re capping out at 199KPA (boost cut hits at 210). The AFRs are good at 12.2, which is exactly on target. But we are at 105% duty cycle on the fuel injectors. This means we are at the limit of the fuel system in the car.
I have one more opportunity for an autocross to tune this some more. I’d like to get it down to 190kpa. That will give me enough margin to where I’ll be comfortable I’m not going to blow it up. Fuel system upgrades will have to come at a later date, probably after I’ve secured a spare transmission.
But at the end of it, how did I do at the event? Not bad! I finished fourth in a class of six both days. I qualified for the shootout, and I even won my first round. My second round match up was against a modern Supra, so that didn’t pan out for me.
Oh, and what else? This was the first trip with the Truck after replacing the engine and rebuilding the transmission. It worked flawlessly, though it has sprung an oil leak. Engine is still under warranty, we’ll see how that goes.
Stay tuned!