GTA Finals at Buttonwillow 2019
Awesome to get the "band" back together since COTA. We went in hoping to make it a third year in a row of wins at this event. Lots of excitement, with more power and other improvements we expected to be on a very good pace.
Day 1 morning had an open practice session so the plan was to do a systems check and a quick warmup lap then back to pit lane to get tires dialed for the first timed session.
Half way around the track going through Riverside, the highest speed sweeper, the engine cut out and the throttle pedal ceased to work. I coasted to a stop off-line trying to figure out what happened. Engine was idling, pedal just didn't work. I figured out I could limp the car back on idle speed and got around the track at 11 mph in 3rd gear, thankful for the torque of the engine.
Back in the pits we tried to figure out what had happened. First thought was wiring or a bad pedal or throttle body but nothing immediately jumped out at us. The first timed session started with us still in the pits. Suddenly after cycling the power off/on again the pedal was back. I jumped in the car and rushed out, only for it to cut out again at the exact same point on track. Got the car back the same way, first session gone.
During testing last year I had encountered something that manifested itself the same way... but in that case it had been due to a fuel pump sock that had been left in the E85 for too long (should be changed once per year) and it only happened when I was running under 1/2 level in the fuel tank. The result - engine cutting out briefly and losing the throttle pedal - was identical, but here we were running a full tank. Regardless, with that as our one solid lead Greg and I jumped in and pulled the fuel pump fixture and replaced the fuel sock while Moti made setup changes based on the few notes I could come up with from less than one lap. We noted that the fuel sock seemed to be trying to come out of the DW400 pump (this pump is universal, not designed for a Miata pump fixture or sock), so we did some zip tie magic to help it stay put and got it back in.
Afternoon, session 2 - I coasted through the high G areas and made it around the track! Seemed like we had an improvement.
Got two laps in taking it easy through the high load areas and then tried to pick the pace up in the third lap. This was our first year with radio between the car and someone on pit lane. Coming through the first section of the track I wanted to get on the radio and yell to Moti “this thing is really fast!” but the car kept me so busy and everything comes so fast through Cotton Corners and the Bus Stop section I couldn’t even lift a thumb to the push-to talk button. Coming around Riverside, the car stumbled, then going into a hard braking zone it cut completely. I got myself out of the way and cycled the car several times and eventually got the pedal back, but the session was done.
Speaking with others I got confirmation that the cutout and pedal loss is the result of the GM ECU going into limp mode. There was a definite correlation between fuel level and triggering limp mode. The sock replacement had helped, but the car was clearly very sensitive to fuel level. There was just one more session for the day and we hadn’t yet even had a chance to get tire temperatures/pressures. We needed to just get a full lap in and get back to the pits so we could get that data while it was hot. We filled the car completely to the brim for session 3.
Went out for session 3 and the car made it through Riverside! I got a full lap in at some pace without it cutting out, and brought the car back in to get tire temperatures. Track drama from other cars having issues ended the session.
That night we went back and forth over just about everything. The orientation of the sock on the pump fixture was in question but there’s no sure way to check that as once the pump fixture is installed there’s no way see into it. A thank you to Supermiata / 949Racing for some consulting and offering what they knew of the subject, and we spoke to some others who have big power Miata setups who even question the flow rate of the factory sock - they said they found the sock to be a restriction - the problem is that the factory sock is the only one with the right geometry - the aftermarket socks don’t reach to bottom of the tank, so you trade one problem for another. We knew the way to kill it with fire would be a surge tank, but that just couldn’t be done trackside. We scoured the track for anyone with fuel cell foam or hydramat that we could possibly stuff in the tank… we even came up with several squares of fuel cell foam that someone had ripped out of their own fuel cell because they were having starvation issues and suspected the foam was breaking down and gumming the filter. Upon close inspection, the foam was breaking up. We thought better of it.
Based on what we had found on day 1, we figured we could get two solid laps in before the fuel level got low enough that we’d have issues, so the plan was simple. Run full to the brim, two laps, then refuel.
I like to run the full session. There’s a big difference between leaving a margin and pushing the car hard and it takes me a few laps to feel comfortable pushing, especially with this car. I tend to get faster through a session, and similarly, faster through a day. There’s some crossover point when the tires are better early in the session and I’m better later, but always more laps are what I need to find where I can really cut time. Day one I had something like 2 laps at decent enough speed that I had an idea of what the car was doing. This definitely wasn’t how I like to normally do things. Hoped for better in the morning.
Day 2 morning is when temperatures should be ideal. We got filled up and went out for the first session. Naturally, everybody is thinking the same thing; now is the opportunity to get that fast flyer… and so there were a ton of offs, people pulling dirt on the track, yellow flags, etc. Both laps aborted. Back in for fuel, got topped off, and the track was black flagged.
Back in our pits as we were making some minor changes we found the car was making so much downforce it’s starting to warp the chassis, break spot welds, etc. The perils of a 25 year old chassis. Moti jumped into fabricating reinforcements. At the same time, I noticed the passenger side muffler had more movement in it than it should. The bolt holding it in place had come loose and allowed it to flex more than usual, and tracing things upstream I found that as a result of that extra movement the downpipe had cracked ⅔ of the way around.
Greg and I got the downpipe removed and I jumped on the scooter and blasted over to Sevens Only to see if we could get it repaired. They obliged. It’s not the prettiest weld… actually, I’m definitely going to grind it out and reweld it myself later… but it was no longer cracked. Much thanks to them for being available on the spot to glue it back together. I rushed back to the car and we checked the time. 15 minutes to the session. We jammed to get the downpipe back on, I got suited up, and we were on the ground and fired up 1 minute before the session started.
Out on track, we had multiple cars with issues. The track was black flagged, session over, never got one flyer in.
With so little opportunity to get laps at pace in, and distracting issues, I felt I wasn’t getting in sync with the car. I tried to think back to partial laps, brief sections where I had been able to push a bit and feel what the car was doing but it was a challenge. It was definitely harder to drive now than it had been previously. Much more twitchy, and I had to be very gentle with the throttle in a lot of sections where I was previously just rolling into it and full throttle much earlier. We softened the rear sway bar and added some low speed compression damping in the front to try to help.
We had fresh tires on stand by, and the tires on the car until now were older 2017 build dates. It takes at least one session to dial in the tires; ballpark the cold pressures, then take hot temperature and pressure after a session and adjust pressures accordingly to hit your target hot pressures. With the downforce and power this car makes there’s a very large rise in pressure over a session and a large stagger between the predominantly outside front tire and inside rear, so it’s really important to get those pressures all correct. So this was our last chance to put the fresh tires on - use session 3 to get them set right for session 4. We put the fresh ones on.
Session 3 started off well, tires felt a little better than the old set but the balance had changed, I had a little more front bite and a little less in the rear. Sliding through Riverside at 115 mph and catching it juuust at the outside edge of the pavement had my heart rate up and on the radio saying “we need more rear wing”. Despite the tail happy balance I kept pushing and the lap felt OK... twitchy and bumpy, but it was feeling like the best lap of the day.
But then, going over Phil’s Hill and coming down the back towards Star Mazda I was quickly catching another car that was on a cool down lap. Unfortunately they didn’t notice me until too late so instead of staying off-line and slowing on the straight they cruised into the next turn on-line. I set up wide and tried to keep my pace up and go around the outside but found a ton of dirt and debris as soon as I was out there off-line and the car slid juuust enough to pull me off track. The lap was gone. I aborted and got back to the pits for fuel. Back out and the rotrex temperature warning light started triggering, with the numbers spiking up and down. I pushed through the lap but was distracted with worrying about and what that meant and what would cause it. Lap felt OK, but the car was fighting with me and felt really twitchy.
Back in the pits between sessions we figured the only culprits that would cause erratic temperature spikes at the sensor on the Rotrex are either air pockets passing the sensor or a bad sensor/wiring. We got the nose off and topped off the fluid, which was just a hair under the disptick.
We had just the final session in the fading light. We executed our plan; 2 hot laps, in for fuel, then another 2 laps. With less cars on track we had some clear track and I finally got to push the car without interruptions. But it was a real challenge. The car just felt unsettled almost the entire lap. I pushed as much as I felt I could, had one brief off on the outside of Bus Stop but got three solid laps in this final session. Drilled down to a 1:48.0 but couldn’t get much more out of it.
1:48 flat turned out to be good enough for 4th place in a 26 car field. We were just 0.07 seconds off the third place car. SO CLOSE to the podium. But with all our trials this weekend I must say that I’m massively thankful and proud of our team. We busted our butts for two days straight, didn’t miss a single session despite everything trying to stop us, and in the end got things together enough to take a very respectable finishing result home.
I’m not one to say later “we looked at the data and it shows we could do X time”. That means so little. What matters is what you actually put down out there, the rest is just noise. But, what I did find Monday night when going through data and video was a big realization - sitting at home with a clear head I immediately noticed in the video that I was bouncing all over the place, way more than the car usually does. It was suddenly obvious - we were still running largely the same setup as we ran at COTA. Specifically, lower and stiffer than we ever have before at Buttonwillow. My only recent test day on a similarly bumpy track was at Streets of Willow where I was largely engrossed in working through early boost issues, but when I think back now the car was far too stiff that day as well. I should have caught it then.
But, every step of the way I learn, and you can bet I won’t be making that mistake again.
We fought, we overcame, and we come home with a ton learned and a game plan for how to improve. You can’t ask for more than that. There’s a lot of teams who dream of a 4th place at this event. We may have our sights set much higher, but I remind myself to appreciate the struggle, because that’s how we get where we are aiming.