7 Oct 2013

“The Fasted Road in the West” – for some people.

The Willow Springs trackday event was this weekend, but unfortunately my fuel pump failed (probably) after four laps. Finding a spare Walbro 255 lpm unit turned out to be impossible; no car parts store, offroad outlet, or Honda go-fast shop had it, so my weekend ended early. Obviously the pump must be used in <em>some</em> cars, I just don’t know which ones. In hindsight I have no one to blame but myself for not bringing a spare pump; I thought that parts stores stocked them, nope. I’m lucky that it was a clean failure instead a slow decrease in pressure, as that’s seriously bad news for a turbo engine. The pump still ran but sounded odd, and there was zero fuel pressure, so it seemed to be the pump. That aside, I learned that:

1. The car is fast as hell, 132 mph down the front straight (GPS speed, so it’s accurate), and that was just getting started. I can almost hear Walter White saying, “*I* am the one who passes!”
2. Never did find the braking or cornering limit. The hotter the brakes and tires got the better it worked.
3. The small amount of tire wear was very even.
4. Probably the best news is that drop-throttle testing showed no oversteer, the biggest concern of the suspension design and rear weight bias. Of course, since the car never reached the limit of adhesion, it’s hard to know how much margin I had.

A Bosch “044” pump is on order. A reader said that he suspects that the Walbro died due to sucking air. I can’t completely discount that theory because I don’t know for sure what happened, but why was it able to last 1000 miles of street driving but only four laps on-track? The tank has a built in accumulator to which fuel is returned from the fuel rail. The tank was nearly full, about a 10″ head on the pump. The tank has a lot of baffling along with one-way mouse doors all leading to the accumulator. So while I don’t know for sure what killed fuel flow, it’s hard to blame air.

The Web rumors about the Walbro pump not being reliable “seemed” true and the initial thought was, “once asked to provide real flow it just couldn’t.” However, after thinking it through it seems unlikely. I think that the pump <em>always</em> provides full flow and the fuel pressure regulator decides how much to choke off the return line in order to provide a given pressure. Curious about how the pump failed, it was disassembled and to be honest I was impressed with its quality. Everything looked fine other than some discoloration on one set of commutators, though resistance of the motor was constant regardless of position. The rotor wiring was not broken or burnt, the gear pump components looked fine, and the one-way valve on the outlet was functional as well. This has me a bit worried; maybe the problem is somewhere else, but where? A failed fuel pressure regulator? It read zero psi with the pump on and the engine obviously wasn’t getting fuel, so maybe it was passing 100% of the fuel back to the tank, which might result in no indicated pressure? Or, could there be a huge blob of aviation fuel tank sealant used during construction that broke free and plugged up either the outlet port or the inlet fuel filter? Of course, playing devil’s advocate, maybe that blob of tank sealant just floated away from the outlet port and will return on a future date. It could also be that one of the one-way fuel doors broke off and ended up against the fuel exit port, though that seems less likely. The engine quit under braking going into Turn 3, so if the door broke loose I’d expect it to slide forward, away from the pickup.

Oh well, what’s done is done and a Bosch 044 pump (which is claimed to be far more¬†reliable) has been ordered. While replacing it, the inlet fuel filter will be examined for massive clogging (though it’s hard to believe that it could instantly plug up like that). The Bosch will be plumbed in and we’ll see if fuel pressure returns, and if so, great.¬† It should be in and running next weekend and we’ll see what’s what.

As for the cars that showed up, there were Miatas, Porsches, Corvettes, a few Alphas, BMWs, five original Mustang GT350s, and a supposedly authentic aluminum-bodied Cobra. The Mustangs sounded like they were going about 180 mph, getting about a 1:35 lap time. The Cobra was slightly faster with a 1:33, but the big surprised was the 10-yr old BMW M3 and its 1:32! Very impressive. I didn’t bother timing myself (thinking there was plenty of time for that later) and didn’t even start the GoPro, figuring I’d recorder the later faster laps. Uh huh.

Lastly, on Saturday night we were up late taking time exposure shots of the car (more on that later) and a desert fox came walking by—no kidding. It looked like a small dog with a huge bushy tail. I suspect he lived somewhere near the track and survived off leftovers he found in the trash cans. Anyway, he came to within 10-15 feet of us and just sat down! I started to reach for the camera and he ran off. That would have made a cool picture. Anyway, there’s another track event in about a month at California Speedway. That’s about the latest possible timeframe for getting observations into the book. The only downside, if you can call it that, is that the track is very fast, not really what I wanted for an initial handling checkout. Of course, no one says that I have to go 150 mph through the fast bits.