In Miata terms, we’re making good power. But we’re the underdog by a huge margin against the cars we compete with. No doubt, we make the most with what we have, but with the largest Time Attack event moving to Circuit of the Americas where horsepower reigns supreme, I knew we needed to turn the wick up. We’ll always be down on power compared to the other guys, but that doesn’t mean we can’t give David a bigger rock against Goliath. However, save for some transmission hiccups, reliability has been one of our strengths and I did not want to sacrifice that. I had an idea.
This didn’t happen overnight. I’ve been working on the solution all year in the background.
A year ago, I placed a Rotrex on a box beside my spare motor, and got started:
The first time I took this C38-92 out of the box I realized the challenge I had ahead. I’m used to the C30 units used on Miatas, and had that size in my mind when I was initially looking at the space in the engine bay, placement, etc. The C38 is a behemoth. It would turn out that packaging would be one of the largest challenges at just about every step in this project.
In July I posted a teaser, focusing on the new rolling engine lift. But a few people noticed the blower hanging on the side of the motor…
That was after months of work on the bracket, and the final is actually version 3 after scrapping two prior. That gets expensive when you’re cutting 7000 series aluminum, but it has to be perfect. Clearances are mere millimeters everywhere, and rigidity of the bracket is critical to avoid having belt issues.
The frame rail had to be cut substantially and reshaped, with care taken to add new internal structure to ensure loads from the suspension are still transferred through the frame rail appropriately.
The subframe also had to be cut!
Did the math on pulley sizes and picked a few final candidates to test. We will not be spinning the blower to its redline, no running on the ragged edge here. Then ordered lots of belts and worked out a suitable belt for every pulley:
The packaging challenges continued with the coolers. I needed an intercooler and a cooler for the Rotrex fluid in addition to the engine oil cooler. I also wanted the shortest charge piping possible, made a bit more complicated with the throttle body at center top of the V6 rather than on the side of an I4. Off the shelf intercooler options weren’t going to work, I was going to have to make it. I chose a Vibrant core with the right dimensions for what I had in mind:
To hang everything in place I had to toss the old radiator mounts and make an entirely new frame to hold everything tightly together:
I’ve never made intercooler endtanks before. This project was going to give me a lot of practice on the TIG welder. Drew up and cut pieces to make up the endtank:
The top tank took a while with a tube hand notched mid-bend to merge into the curved tank:
Finished intercooler after quite a bit of welding.
Welding the tanks to the core was a next-level learning experience; you’re welding a butt-joint with the core quadruple the thickness of the endtank, and the core by its nature is trying to suck all the heat out of the weld as you go. Rather proud of how it turned out.
New coolers in new locations meant making all new lines:
On to the intake, and more packaging challenges. I did the math on filter size for expected flow. The filter I had was big for a Miata. The new filter is massive:
The intake tube for the C38-92 is 3.5” and that does not want to fit… anywhere.
More fun welding:
In terms of sensor and component locations, there was some debate about what locations would work best. I made a couple different configurations for charge piping to try the options:
Using a TiAL QRJ blowoff valve, configurable for either recirculating or vent to atmo. Which MAF sensor location we found worked best would determine which config we wanted, so I did both VTA and recirc setups:
The recirculating config uses a hard line that was fun to bend:
The Rotrex points the air inlet straight back, directly at the downpipe. So inevitably, the silicone bend is riiiiight by the exhaust. To give the coupler the best darn shot at nice long life possible, both coupler and downpipe are wrapped, and then separated by a titanium shield with a reflective layer on the hot side:
Crankcase ventilation becomes critical when adding boost. A direct injection engine really benefits from catch cans even naturally aspirated, so it had been on my to-do list for a while. Since this is a race car only I simplified things a bit. Eliminated the PCV, drilled out and tapped both valve covers, and ran lines to a pair of catch cans that vent to atmosphere. With so little space in the engine bay, I ended up placing the cans in the hole that the HVAC system pulls air from on a street car:
The fuel side is tricky. Direct injection can’t be easily upgraded with aftermarket parts the way a traditional fuel injection setup can be. Expecting that we might find we need more fuel than we could flow on the stock system, I preemptively bought a high pressure pump from the Cadillac ATS-V (which runs the twin turbo LF4 engine), to see if the pump would swap in on the LFX:
It is almost identical. The only difference is that the plunger is ~0.100” shorter.
After some measuring we felt pretty sure that the lowest point on the cam lobe that drives the high pressure pump was tall enough to maintain contact with the LF4 pump so we swapped it in on the motor in the car. That is not a fun job. Think coolant reroute but with the engine even closer to the firewall and more stuff in the way.
Colder spark plugs were in order, Brisk Silver RR14S:
t’s all a big paper weight without tuning. That is outside my wheelhouse, and I wanted someone who really knew their field and would give the car the time and attention it needed. For this I teamed up with UMS Tuning. I consulted with Tony through the final stages of the build to ensure everything was configured the way he felt would get us the best run at all things working smoothly. With everything done he made some tweaks to the calibrations of a few sensors on the old tune for startup. It fired first try and idled pretty well.
Pulled it out of the shop, first time sun hit the car since February!
Then loaded up for the 350 miles tow to Arizona to get tuned.
More to come…