-ed note: I have always given Khiem crap about his overly complicated turbo system and lack of peak power for all the work he did but, I had never driven this car until just before he sold it. I have got to say I have never driven a more refined turbo car in my life from an OEM let alone a tuner car. Well, Khiem is an OEM engineer so I guess that’s kinda OEM. When you drive the car, the boost is immediate and the power is linear. The well-tuned boost-by-gear system at first makes you think the car isn’t that fast until you realize that the rear tires are always slightly spinning giving optimal acceleration. The boost-by-gear system also makes the car super easy to drive in the turns. This is very driveable and easy to modulate power that makes the car a snap to drive slightly tail out. The car doesn’t really feel turbocharged, it just feels like a bigger engine. The engine has zero annoying attributes. This is the S2000 Honda should have built. I can’t believe he sold it!
After all these years, I finally got the turbo setup completed with an initial tune to dial in the timing and fuel. But with turbo cars, the turbo adds another knob to adjust in tuning how the car feels. I have particular tastes and I needed to dial in how the turbo came into boost to suit. It is not just the boost level that affects how a car feels, but also tuning how the turbo spools up. The Hondata KPro has several parameters for boost control to tailor the drivability to one’s personal tastes. It took me some time, but I got the settings tuned for how I wanted the car to feel. I also did some testing to check out the effectiveness of the cold air duct from the bumper to the air filter. Because, you know, cooler air is better for turbos.
If you recall, the cap of the Moroso reservoir had a little brass filtered vent. It turns out with my style of, uh, fun driving, coolant would make its way out of the vent and onto everything around the reservoir. The telltale sign was the smell of coolant. I bought this brass NPT plug from Home Depot to seal up the system. All the components in the intercooler coolant system can handle the pressure increase in the system from the coolant getting warmer and expanding, so no worries about leaks.
I wanted an easy way to switch between low boost and high boost. Depending on the conditions, weather, tire temperature, and who is driving the car, a low boost setting is useful. That said, as the car doesn’t have traction or stability control, it’ll very easily get away from the driver if they don’t know what they are doing in any condition. The cruise control module in the engine bay got ditched to make space for the turbo-related stuff, so I repurposed the main cruise control switch to be my low/high boost switch. I wired the switch in line with the boost solenoid to turn the solenoid on and off. Turned off, the turbo runs wastegate pressure which was about 9 psi. Turned on, the Hondata KPro controls the boost level using the solenoid.
With turbos, typically everyone says it should spool as quickly as possible. There is such a thing as too fast however. In the boost control settings in the Hondata KPro, there are a number of parameters that can be tweaked to adjust how the turbo spools up. One of the first parameters is the ‘Solenoid Activation’ value. I think the default value was around 4psi, but I changed it to 1 psi in order to turn on the boost solenoid earlier to spool up the turbo faster. The higher the duty cycle of the boost solenoid, the quicker the turbo will spool and also the higher the boost level. The KPro has a ‘Quick Spool’ setting that maxes out the boost solenoid duty cycle at 100%. At the bottom of the boost control parameters window is the ‘Quick Spool’ table. Once the boost reaches the values set in this table, the solenoid duty cycle drops back to the values set in the ‘Boost vs Rpm vs Gear’ table. In this datalog, you can see the duty cycle dropped to 25% after the boost went past the 8psi setting in the ‘Quick Spool’ table.
The initial recommended value from the Hondata help files was to set the value in the ‘Quick Spool’ table 1-2psi below the target pressure. So I initially tried out 12psi as my target pressure was 14psi. This caused the boost to way overshoot 14psi and hit the boost cut that I had set at 16psi. I next tried 8psi which was 1psi below the wastegate setting of 9psi. As noted by one of our readers, setting the value in the ‘Quick Spool’ table at the wastegate setting is a good starting point. This worked well if flooring it while in a gear, but doing a pull at full throttle and a quick shift would hit boost cut once in a while in the next gear. I would have tried 6psi next, but honestly, I didn’t like the feel of how the turbo came on using ‘quick spool’. Basically, the boost ramps up faster than throttle position if you’re rolling into the throttle making the torque come on non-linearly with throttle position. This made the car harder to drive in a twisty road situation where torque modulation is critical to staying at the limit of traction. Robin Shute had mentioned the Garrett G25-660 spooled too quickly with the anti-lag on in his Pikes Peak car. I get it now. My old turbo cars, a 2005 Evo 8 and 1996 Nissan SE-R with T25 turbo didn’t have this issue of spooling too quickly. Modern turbos have come a long way.
Therefore, I disabled the ‘Quick Spool’ by setting the values in the table below the boost solenoid activation pressure. I still wanted the turbo to spool up a bit more quickly than running constant duty cycle for a given gear, so I ask for more boost than I know the turbo setup can do at lower rpms in the table. This control strategy was in the tune from Shawn Church. In this plot at ~3750rpm in second gear, I’m basically asking for 18psi of boost which cranked up the duty cycle to 34% even though 18psi is not possible to do in second gear at this low engine speed. As the engine speed increases, the solenoid duty cycle decreases based on the values I put in the tables. With my tire setup, I found 11psi of boost can get just a hint of wheelspin if the air temperature is around 70degF and the tires are warm. First gear, I ask for 8psi which is below the base wastegate spring that gives about 9psi. First gear lights up the tires pretty much all the time. It’s fun. Third gear and above get 14psi target which can drift up to 15psi in colder weather. Remember, the boost control system is a ‘dumb’ system that does not have a feedback loop like a PID controller would do. The Hondata system just runs a boost solenoid duty cycle based on the lookup table. The actual boost level achieved for a given duty cycle will change based on ambient conditions.