23 June 2013

Though there’s been a lack of updates, it’s not been due to a lack of activity.

Since reinstalling the engine, the gas smell is back. This has been an on-going issue even though every hose and fitting has been checked. It’s likely that the tank itself is “weeping”, a tiny leak that’s not enough to drip and the gas may be evaporating directly into the air. Several people have recommended a “sniffer” device that’s used for locating leaks such as this and maybe we have one at work I can borrow. Of course accessing the tank is necessary, which is a lot of work actually… whoever designed this didn’t plan to be dropping the tank several times a year…

I noticed when removing the fuel cap there’s always a “whoosh” as pressure escapes. That seemed odd since the tank was vented with the OEM Miata vent assembly… though it was installed without knowing exactly what it did, so out it came to reveal its secrets. It contains a small cage and inverted cup. When fuel nears the top of the tank, the trapped air inside the cup causes it to float up, sealing off the vent line to keep liquid fuel from leaving. The puzzling part was that it also had a spring under the cup which kept it seated against the vent. Apparently it was designed to let air into the tank as it emptied, but not let fumes out – that was a problem. It’s likely the Miata tank has another thingie to handle out-flowing fumes, which is probably routed to a charcoal canister. Since I don’t have any emissions gear, the vent was modified by removing the spring so that the cup sits loose, allowing tank fumes to escape out the vent yet still seal if the car goes on its head. Presto, no more “whoosh.”¬† I can still smell gas but it’s not quite as strong, no longer building up pressure in the tank and possibly pushing liquid fuel through a small hole.

Spent much of the week trying to figure out where to mount the oil cooler. The problem was a lack of data, as in what’s the air flow at various locations (I didn’t want to take the time to instrument the car, at least for now.) There’s also accessibility, coupled with trying to keep it relatively close to the oil filters so the hoses aren’t too long. It was finally placed below the license plate, with the idea that the low pressure behind the car would provide decent airflow. A drive in mixed traffic showed that it worked, somewhat, cutting oil temperature rise roughly in half, down to roughly 105 C, still high given that this wasn’t track temperatures. Speaking of that, the displayed oil temperature¬† matched the infrared thermometer, so the readings are valid. Some freeway driving showed that the faster the car went the lower the oil temperature got, which makes sense. I’d imagine that at some speed though, it’ll start going up again as frictional losses becoming higher than improved air flow through the cooler, which brings up the next topic…

I’m considering adding a cooling fan on the intercooler. It would serve multiple functions: improving air flow through the intercooler, pushing more air through the engine compartment, and increasing airflow through the oil cooler. Haven’t thought of a down-side yet, other than the sound of it running all the time, though it probably won’t be very loud compared to everything else.

The air scoop was finally added and went a long way toward quieting down intake noise.

Spent today fabricating one “wind wing” to go on the side of the windscreen frame The conclusion was that it needs to be larger, or more accurately, a slightly different design to really work well. More on that later.

Went to an open-house event at a custom wheel manufacturer, HRE – pictures tomorrow… it’s late.