28 June 2013

Well that wasn’t much fun…

Drove the car to work this morning, and driving in was uneventful. Driving home however was much more stimulating due to very heavy traffic (apparently everyone’s leaving town for the upcoming short week.) That meant driving along at 5-20 miles per hour for more than an hour. Just to keep things interesting, in first gear, engine speed was a little high, and in second, a little too low. And finally, it was about 100 deg and promises to be hotter this weekend. Stuck in the situation, it was a chance see how coolant and oil temperatures reacted to the heat:

1. The radiator fan apparently moves plenty of air, because once engine rpm rose a bit, coolant temperature dropped about 6-10 deg immediately.

2. However, while stationary or at low engine rpm, the coolant temperature would not drop.

3. Oil temperature got as high as 110 deg C, too high in my opinion, especially considering how lightly-loaded the engine was. This was not surprising since without a cooling medium, no oil cooler can work well. On the other hand, the engine was loafing and wouldn’t be expected to be dumping much energy into the oil… apparently the engine thought otherwise. It’s very likely that I’ve vastly underestimated the amount of heat that a turbocharger adds into the system…

The above points mean that though the fan was doing its job, coolant flow is insufficient at low rpm. It was recently recommended that I have an electric water pump and yes, it would keep coolant moving regardless of engine rpm. That should keep the coolant temperature from not dropping while at low speed. Obviously for track use this isn’t a big deal, but moving the coolant faster will help cooling regardless of speed. And since the car will spend a lot more time on public streets than on-track, it seems like a good idea (though I wonder how I would know if it quit… high coolant temp I guess!)

Preface the following with: transmission gears 1-4 are dog-engagement, and this turns into a long-winded thing…

Playing with the clutch in traffic and having plenty of time to think about it, I realized that I’ve been using the clutch wrong. Using the clutch or even double-clutching wasn’t working as well as expected, and I think I now know why.

There are three different rpms to juggle: engine/clutch, the transmission input-side gear cluster, and the output-side gear cluster (with the latter always being some proportion of road speed.) Unless all three are matched, grinding will result when shifting. Say the car’s speeding up and it’s time to shift. Immediately after moving from one gear to neutral, the engine/clutch, input and output-side gear clusters are all initially spinning at the same speed, then start diverging at different rates. The engine and input-side gear clusters start coasting down, while the output cluster will spin at a fixed percentage of road speed. Because the clutch is pushed in, the engine is now disconnected from the transmission, engine speed and the input gear cluster speed will also begin diverging.

I understand that the secret to shifting a dog-box is to double-clutch, where when passing through neutral, the clutch is briefly let out to match engine speed to the input cluster speed. Next, the clutch is pressed again, the shifter moved into the next gear and the clutch let out… and this is where my doubt starts. That is, even though the above is done, all it accomplishes is to make the engine and input cluster spin at the same speed, while the output cluster continues to spin at some proportion of road speed, but doesn’t have anything to do with input shaft speed. Unless all three speeds perfectly match, the gears will grind. I think that when shifting from first to second gear, there’s no way around waiting for the engine to spin down until it matches the output cluster speed. You just have to wait, and nothing can speed up the process.

Yes, a dog-box can be forced into gear at any time depending how rude you’re willing to be, but consider what’s happening. In an instant, the engine is  forced to change speed and match the output gear cluster. Lets say that instead of waiting for the engine to spin down from 6000 rpm to 4000 rpm so that second gear can be smoothly engaged, the driver just “makes it happen.” In about 0.01 seconds, the engine speed is forced to drop 2000 rpm, which briefly has the effect like throwing a wrench onto the spinning front pulley bolt. It’s going to go “BANG”, and if nothing breaks, the tires will likely chirp. After seeing people do it on-line I tried it exactly once and won’t ever do it again. Yeah I’m sure it saves X seconds per lap, but it’s my car and I’m the one who has to pay for fixing things… Also,  breaking the rear tires loose has got to be a bad idea during a race. So, I can’t see any way to smoothly shift from 1->2, 2->3, or 3->4 without just waiting it out. That said, the longest wait will always be the 1->2 shift because the gear ratios have the largest percentage difference. The other shifts take less and less time the closer together the ratios are. After realizing that I had to wait just the right about of time, I could shift with no ugly noises at all, even without using double-clutching.

Now on the other hand, I can see how double-clutching works when going from 2nd to 1st. In this case, engine speed must be increased to match the gear speed and blipping the throttle can quickly match them up. However, when going from 2nd to 3rd, we just have to wait, or at least, I will be.

24 June 2013

Change of plans. After doing a lot of thinking and reading, the decision was made to change to an oil-to-coolant heat exchanger and electric water pump. I was beating around the bush, not confronting the reality that a turbocharged engine has special needs. Adding the oil cooler was good but didn’t have enough airflow, always a problem when mounted aft. I almost bought a small radiator fan for it but it seemed like a band-aid on top of a band-aid. It turns out that Lotus Elise owners (a similar drivetrain arrangement) also have high oil temperature, especially when running the supercharged model in warm areas of the country. Somewhat surprisingly, the stock Lotus has front-mounted oil coolers and the engine has to push oil through about 12 feet of hose, something I don’t want to do.

The owners swap in an oil-to-coolant heat exchanger near the engine which transfers oil heat into the coolant, putting more stress on the radiator. To deal with that they install the biggest radiator that fits. The reason for me also adding the electric water pump came from a racing buddy who swears that Honda water pumps don’t work well pushing water all the way to the front of the car and back again. I asked how he knew that, since he only worked on FWD cars. I also asked that if that’s a problem on FWD drivetrains mounted at the rear, why don’t they all have electric water pumps… never really heard an answer. I’m also reminded of how, without a thermostat, my engine ran at 150 degrees F on the freeway, which indicates to me that I have plenty of coolant flow. (To be fair though, that was at an ambient temperature of about 60 deg F, so figure running at 100 deg in the desert is 40 deg higher, which would increase that to 190 deg, before adding the heat-exchanger.) It may be overkill but at the same time I’d hate to tow the car 100s of miles to a trackday event (never mind the entry fee, gas, motel, and food expenses) and have it overheat. Assuming this works well, there’s not much else from preventing running a trackday event, other than it unfortunately heading into the hottest part of the year around here – the car might be fine, not so sure about me!

Oh, and a good thing happened during a test drive yesterday… the realization that I’m much more comfortable with the car; the extreme trepidation about things falling off or breaking seems to be lifting. Speaking of pushing the car, I’m curious whether it can leave the line in second gear… probably, though the clutch might not be too happy. Doing so of course means no shifting all the way to 60 mph, and we all know how important that is 🙂 Once the issue with oil temperature is cleared up there’ll be more interesting videos 🙂

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.

9 June 2013

With the car running well I took part in the San Diego British Car Club run into the local mountains; the first real outing for Midlana. Cars and Coffee – 120 miles of freeway driving – didn’t involve twisty roads, bicyclists, trees, motorcyclists, boulders, rocks, and very steep cliffs…

It went well, but no video of triple-digit speeds, smoky burnouts, or drifting, just… <a href=”http://youtu.be/-DHajQTBLnE”>driving</a>. As with Kimini, no trip was complete without stopping by the Palomar Observatory, barely visible through the trees in the distance.

Coming down the south face of the mountain would have been fun, except that a group of motorcyclists deciding to coast down, at 20-30 mph. That’s fine… except that they wouldn’t pull over for the long line of cars behind them.

On the way back, stopped at a grower’s stand and bought 25 avocados for $5… farmer-direct prices are always good.

Put about 150 miles on the car with no problems… mostly. The engine was reporting high oil temperature, as high as 125 C, which I’m not convinced is real. The sensor was calibrated with water and an accurate thermometer, so I don’t know why it would be off but it’ll be checked again. Also, oil pressure seemed low. This I can believe since I used the inaccurate gauge on the air compressor to calibrate it. I was reminded that I do in fact have an accurate pressure gauge… a tire pressure gauge! I’ll have to make an adapter so compressed air can be used to calibrate it again. Oil pressure and temperature are too important to have wishy-washy readings.

The wind around the windscreen is really annoying. Even with earplugs, the low frequency “thumpings” goes right through them. In the video you can see me moving my hand around to find the wind’s path. Even with the baseball hat adjusted as tight as possible, any speed over about 70 mph threatens to tear it right off my head. Cobra-style wind-wings will work, or possibly bowed Lexan side curtains that snap into place between the side of the windscreen and the shoulder-height side tube. There will need to be a solution.

7 June 2013

After much correspondence with the very helpful people at Competition Clutch, the following (with the advantage of hindsight) is now clear:

1. There was nothing wrong with the clutch. However, pulling it out did allow confirming that the pilot bushing was present (there was some question at to whether there was one.) Also, upgrading to the lighter diaphragm spring greatly lightened pedal effort.

2. Once they learned how how light my car was, they said that a better choice would have been one of their mid-range single-disc units. The weight of the car is the important factor when considering a clutch, and 1600 lbs doesn’t warrant a twin-disc clutch. The clutch will simply never see a huge amount of torque – the tires will spin first. They said that it should basically last forever – good!

3. Twin-disc clutches engages near the top of pedal travel (requiring only about 1″ of travel to do so.) However, to <em>completely</em> disengage the clutch requires several additional inches of pedal travel due to air-drag between the spinning and non-spinning components. And, a dog box is more likely to exhibit grinding gears due to no synchronizers masking a slowly spinning input shaft.

3. My clutch master cylinder was too small. While it resulted in very light pedal effort, it wasn’t moving the clutch enough to fully disengage it. Moving to a proper size master cylinder resulted in an “OMG Gezzus Christ” level of pedal pressure, heavy enough that when I’d push it in, I’d raise up out of the seat, probably around 150 lbs of pedal pressure… not acceptable, even if correct. So I backed off to a 13/16″ cylinder  which seems perfect. Not too heavy, and even after heat-soaking, there’s no grinding. I’m just going to have to get used to the fact that when leaving a stop, nothing happens until the pedal is very nearly completely released. As it is now, after the light goes green I sit there like a goof because I’m not used to releasing the clutch pedal so far before it bites. Give me time.

I’ve began tentatively experimenting with heel-and-toe shifting, and the transmission works great… when done right of course. I worry that there may be some embarrassing grinding episodes on upcoming videos… and NOW I understand why I sometimes hear 18-wheel drivers struggling to shift. Anyway, this should be the last post regarding the transmission issue.

Regarding the search for a generic hood scoop, the first inquiry went about as expected. A Chinese-made part that looked like it might fit was found, but since the sides are curved, it seemed wise to confirm with the mfg whether it would cover the rectangular hole in my engine cover. I sent a question saying that I had a custom car and wanted to know if it would cover a hole of size X. The “answer” was, “our scoops fit practically all cars. If it doesn’t fit, contact us, and we may ask for pictures, and we’ll remove your car off our list if it doesn’t and you get to keep it.” Sigh… So I sent back a slightly testy response, saying that it was a custom car so it’s not on any mfg’s “list”. Can’t they just answer the question?” The reply came back, “it won’t fit.” Wonder if it’s true or whether I worried them…

2 June 2013

Took the car out again to fully heat-soak it, and… the grinding issue is still there but not nearly as bad, and it can now be put into reverse without much fuss. A big difference between the old and new clutch is where it engages. The old one engaged near the floor, while the new one catches way up high. I’m going to call and ask if that’s normal, or whether I set the stop wrong…

The next issues, though smaller, are actually fairly annoying. With the air cleaner right behind my head, when I get on the gas it’s like being near an industrial-size sand blaster… effing loud. The search is on for a small generic hood scoop to cover the air filter element, to point the intake (and  noise) toward the rear of the car. Preliminary searching has found that generic Interweb air scoops are sorely lacking for dimensional data, making it hard to find one of known size.

After that, wind-wings will be attached to the sides of the windscreen to stave off the wind whipping around and pummeling me in the left ear. The job will be fairly easy thanks to having roll cage tubing surrounding the windscreen.

1 June 2013

The engine is back in and the car’s running again, finally! It’s very promising; no grinding going into reverse, though the car needs to be driven more to better let it heat-soak. The icing on the cake is that Competition Clutch also changed the diaphragm springs to lighten the clutch pressure, and it’s much nicer.  No longer is it a constant reminder of driving a “race car”, now it’s not like a regular OEM clutch. Very impressive for a clutch that’s rated at “only” 500 ft-lbs!

Regarding the higher-pressure wastegate springs, either Tial makes inaccurate springs, I design awesome headers, or the MAP sensor is reading a bit low. The new 0.6 bar springs produced an indicated 0.54 Bar, which is okay, but that’s not the main curiosity. It’s that there doesn’t appear to be any boost-creep – except that’s just not possible. Think of boost as a water pressure gauge attached halfway along a length of garden hose. With the hose pressurized but the spray valve closed, the pressure gauge will read the pressure fed to the hose. However, open the spray valve and the pressure reading will drop to read the back-pressure caused by the open spray valve, plus the fluid drag along the walls of the hose. No matter how high-flowing the spray valve is, there will always be some back-pressure, and the higher the flow, the more there’ll be. And yet, a third-gear pull showed boost maintaining 0.53 Bar within a few counts from 3000-7000 rpm.

For those wondering why I’m using Bar units for boost measurement and not PSI, it’s due to how the flat dash handles data. The Honda ECU measures MAP in Bar, so initially – being American – I  converted it to psi. That worked fine – but only for positive boost. The dash is apparently unable to digest negative MAP values, wrapping negative values around to 65XXX – a sure sign that their software can only handle unsigned (non-negative) inputs. Not a big deal, and after using it for a while it’s become quite natural but took a bit of getting used to. 1.0 Bar = 14.5 psi (atmospheric pressure at sea level.) Most of the time the dash displays about 0.4-0.6 Bar, meaning that the intake manifold is pulling a vacuum (anything below 1.0 Bar.) If it reads 1.0 Bar it means boost is balanced against manifold vacuum, and 1.6 Bar means it’s 0.6 Bar above ambient pressure, or 8.7 lbs, though my setup isn’t quite reaching that for some reason.

There’ll be more driving tomorrow but I can’t go too far from home; I’m on-call this weekend. Would have been tempting to do a run up Palomar Mountain… but oh well. Probably just as well since things need to be checked out several time since it was so heavily torn apart.