Got a shakedown in at Streets of Willow, working out some kinks and relearning the car. Even over weight with the Laguna Seca exhaust and a passenger I was thinking the car felt quick, drag racing with an Audio R10 down the straight, and then in a later session I switched over to a secondary page on the dash display and saw I was only making about half the boost I should’ve been.
Worked out several other details while there, and towed home with a new top priority: find my boost!
Made some DIY caps for the intake piping so that I could pressurize the system and started the hunt. The primary issue was immediately obvious; there was a significant leak in the intercooler core itself. I couldn’t put air in fast enough with the shop air to even build up any pressure.
Pulled the intercooler off the car and tested it alone, and found there were a dozen or so points in the core where pressure was leaking out between the bars significantly. So I had put a chunk of hours into building this custom intercooler, not knowing that the core was defective from the start. We suspect it was leaking less initially which is why it made pressure on the dyno, and then worsened after being bounced around and stressed. Not the news I wanted, but I was glad to have something in my hands that I knew was the cause (the worst part of an issue is
I dove into making intercooler #2, and because we had seen super happy IATs with the first intercooler I decided to take this opportunity to use a smaller core for #2 to try to cut a few pounds. This time I used an off-the-shelf intercooler that already had endtanks to try to cut down on fabrication time a bit… but the inlet and outlet still had to be modified so it really didn’t save much.
Intercooler #2 held pressure perfectly:
With the new intercooler in place I was able to pressure test the full system and pinpointed a few more smaller leaks. The seal between each coupler and pipe can be quite finicky. I’m using a combination of Murray clamps on the thin wall aluminum tubing and T bolts clamps on a couple of the thicker wall connections, like the outlet of the supercharger. The T-bolts actually deform the thin wall aluminum tubing, which I saw first hand on one of my pipes, so the Murray clamps are better in those locations, but they aren’t without their finicky nature either. The one connection that never had any issues was the Vibrant HD clamp in the cold side piping. I also found a small leak in the blowoff valve fitting.
A quick side note, this highlights one of those inherent differences between turbos and superchargers that you don’t really think about until you’re dealing with it. A supercharger is far more sensitive to boost leaks than a turbo; up to a point, a turbo will compensate for leaks in the system by just spinning more until the wastegate sees the target boost achieved. A supercharger has no way to compensate, it spins exactly the same as it did without leaks, and any pressure lost to a leak is just lost. All in all, this was a good learning experience about how sensitive things can be to leaking, and I’m making pressure testing a routine step in the future any time anything in the charge pipe system is disassembled and reassembled.
Switching to fuel, at the track datalogs showed fuel was struggling a bit more than before. Then a few days later while idling in the shop the pump quit completely. Rather than swap in another Deatschwerks DW300, to be sure the low pressure side of the fuel system could supply anything we asked of it I decided to switch from a DW300 pump to a DW400. The DW400 is a big pump that doesn’t really fit the Miata, but I modified the pump fixture and brackets to make it work. Then I redid the high current pump circuit with heavier gauge tefzel wire, larger fuse, etc. so that we can run the pump properly, even at the 20+ amps it draws at high pressure if needed.
Booked a local dyno to verify everything was sorted. Numbers didn’t matter, just wanted the data logs from a few pulls. Everything is back in the green, but seeing 1.0-1.5 psi less now than in our first round of tuning at UMS, with a small but definite delay in the ramp up in boost when plotted by RPM.
Leading theory at the moment is that the smaller intercooler is causing a more significant pressure drop. To test this I’m going to add a second boost sensor in the hot side charge pipe so we can see the delta pre and post intercooler, and depending on what we find I might have a third intercooler build in my near future. We’ll see.
But for now, it’s running well and making decent power so it’s buttoned up and going in the trailer tomorrow for Miata Reunion at Laguna Seca.
