Off to AZ to take the car to UMS Tuning. They weren’t the closest option for me, but that wasn’t my priority. I wanted to put the car in the hands of someone who I knew understood what I needed and would do the job right. Tony knows we aren’t looking for a number to brag about or just a full-throttle tune to get me down a drag strip. It needs to drive smooth, be predictable at partial throttle and in transitions, and be reliable.
I had already been consulting with Tony on configuration details, tapping into his experience with tuning modern GMs so that the ECU would be happy with everything and give us the best shot at all my hard work translating into positive results. So I towed the car 300+ miles through 110° F Arizona summer to get Hyper in the right hands. With swamp coolers, temps in the shop were a humid ~90° F which is about worst case scenario for what we’d see on track.
Hyper was on the dyno all day. Like, 9:30 AM to 9 PM. Lots of time spent on details, playing with cam timing, swapping things back and forth to see what worked best, different pulley sizes, etc.
Now I know EVERYONE wants numbers, but that is going to remain confidential. I’m very happy with the results so far. I’m considering where we’re at now ‘stage 1’, with two pulley sizes available dubbed “extra conservative” and “conservative”. We’re up against a fuel flow limitation on the current hardware with E85, so cannot run any more boost until we sort that further. Once we do, we can throw a tad more boost at it for a ‘stage 2’.
@ 8.5 psi of boost the fuel juuust begins to fall behind. Commanded rail pressure is 20 mpa (2900 psi) and that tapers to 15 mpa in the last 1,000 rpms. Doesn’t appear to be a shortage on the low pressure side because pressure there is 120 psi tapering to ~95 psi. When we checked that low side pressure we were really surprised to see it that high. The Corvette fuel filter is supposed to be pulling that down to ~60 psi, so it seems my filter is bad. That’s getting replaced this week. But at any rate we weren’t wanting for fuel on the low side. We have some curiosity about whether the LF4 HPFP might be under-driven by the LFX cam, but with the difficulty of swapping them, it wasn’t something I could do while we were there. But, the fact that the LFX HPFP operates at 15 mpa, which is what we were tapering to, up top, makes me doubt that we’d see any better results on the LFX pump. I could be wrong about that, not sure yet.
I’ve ordered a LF4 exhaust cam (on national backorder) to check it against an LFX cam whenever it finally arrives. I’ve also ordered one LF4 fuel injector so see if it fits the LFX. We’ll figure things out, just need to work through the variables. At this time I wouldn’t suggest the LF4 HPFP to anyone until we know more.
I will say that I had been expecting a rather peaky setup with the Rotrex, going by what I am familiar with on BPs, but the setup has exceeded my expectations there – it retains a very flat torque curve similar to naturally aspirated, just with much more torque than before. Horsepower grows linearly with rpms with the largest gains up top, just like expected with the Rotrex. This is exactly what I was aiming for: all the good stuff about the engine package we have, just turned up a notch or two.
To avoid the pitchforks and riots I’ll give this away: we’re currently putting better power and more torque to the wheels than a Ferrari F430 on similar dyno.
Since we have Miata Reunion @ Laguna Seca coming up where I’ll need to run the big muffler, I have the alternate down-the-center rear exhaust on the car. One of the few times I get to hear it sounding more like a traditional V6:
Can’t wait to get in the driver’s seat and start shaking it down. First up is a local autocross this coming weekend where I can make sure nothing major is falling off the car and things are operating as expected, then I’ll be scheduling some track testing time in the next few weeks.