27 Jan 2018

As I was putting the new tires on I saw something that made me think “that’s strike 2 for Discount Tire.” The first time was when they bent all four of my lightweight racing wheels and then denied it. This time, a lazy employee mounted one of the tires with a label on or very near the tire bead. What you see is after I tried tearing it off, hoping that it just looked like it went across the bead. Apparently it does and it remains to be seen if it’s going to leak.

Went for a test drive and being new and very sticky, the tires throw all kinds of grit into the air; I wouldn’t want to be driving behind me on a less-than-clean road! Noticed pretty quick that the ride was really firm and realized they were inflated to support a 3500-lb car. Sure enough, they were all 35 psi and were backed down to 25, but they’ll likely need to drop to 20 psi, if not 18. One of the big perks of a light car is the low cost of consumables like tires and brake pads. Hellcat, Corvette, Mustang, and Camaro drivers have substantial tire budgets.

In other news, there’s how to mount the wings. The 1-meter wing sections are designed to accept a 1″ tube through the center of pressure. Because of the width and where the support points will be, the overall assembly will consist of a 36″- 1 meter inner piece with the support points at each end. To the same supports will be additional 18″ outboard sections attached to the same mounting points, making the entire assembly as wide as the outside of the tires. It would be nice if the assembly breaks to for storage, as it’s going to spend most of its time up in the rafters. I don’t want a huge and clunky 3D assembly, so some sketching is in order.

26 Jan 2018

I know it’s been quiet but plenty has been going on:

During initial cold-start, the car always stalls during the first attempt, but after that it’s fine. Though not a big deal, I feel the car needs to demonstrate that it has a tune better than just “okay”. To fix that means backing up a bit to explain.

The ECU provides many adjustable tables and tuners use different methods and personal preference to achieve a desired tune. Point being, some tables have a choice of several variables to use to achieve the same objective. For example, the idle valve calibration table can be dependent upon engine speed OR coolant temperature. It had been set to engine speed but at some point, some bonehead (cough) switched it to coolant temperature, probably wondering “I wonder what this does.” What I – I mean, he – didn’t realize was that the ECU just shrugs and says “okay”, without altering the table other than the units. This resulted in the rather humorous realization that what had been 700-1500 rpm was now 700-1500 degree C! The only reason it worked at all is a testament of the ECU’s closed-loop idle function – it just made it work. It ran surprisingly well, too, which is one reason why it took weeks to catch the error. It’s also a stern reminder that tuners have to be very careful about ignorantly changing things – setting something wrong can destroy the engine in seconds. I got away lucky, though I do know better than to idly mess with more critical parameters. No pressure at all, this tuning thing…

Anyway, now the car starts first try and idles properly even during initial cold-start in the morning, with “cold-start” being defined (in Southern California) as coolant being less than 20 C.

Another ECU change was to reduce boost in 5th and 6th gear – disappointing but necessary to keep from destroying the OEM gears. With 400+ ft-lbs of torque, the gears, used to seeing ~160 ft-lbs, just won’t last. Unfortunately it makes Midlana uncompetitive at Autoclub Speedway where top speed is 150-170 mph. That said, there’s another change, below, that may make that a moot point, maybe.

The next issue was the persistent engine oil leak. I thought I had fixed it by applying sealant to what seemed to be the leaking fitting – nope. Now it looks like it’s a different fitting that’s leaking – one with another Stat-O Seal – not very impressed with them but it may be due to the machining on the pan. Anyway, the fitting was backed off enough to apply sealant and screwed back in. While in there, sealant was also applied along one edge of the front cover where it’s been weeping since new. The engine was started and warmed up, hopefully drawing sealant into the leak and adding heat to cure it. Now we wait and see, sort of like playing Whack-A-Mole.

Next topic: wings! I’ve gone round and round with putting them on, waffling between thinking they’d be awesome, to being afraid of them for what they allow, letting drivers run much further out onto thin ice and counting on something invisible to save them. For example, a driver gets used to a wing’s benefits of holding the back of the car down and preventing a spin at high speed. Meanwhile, the wing stops working for some reason, like, oh, falling off, and great excitement ensues, like this guy – https://www.youtube.com/watch?v=_LnmD7kxHUw

Another concern is that the benefit depends upon things that the driver has little or no control over: wind speed and direction, and disruptive airflow from other cars. My brother countered that wings aren’t all that different than brakes; if either fail it’s going to be a wild ride and it’s on the designer/builder/maintainer to keep an eye on them. I don’t completely agree with for the above reasons, but curiosity made me decide to give them a go.

Because of my dislike of composite work (read: not having a proper workshop to do things right), I  went with extruded aluminum wind generator blades from  http://www.thebackshed.com/windmill/Trade/AlBladeOrders.asp. With a chord of only 6″ they’re not optimum, but a duel-element assembly should be enough to prove out the idea. As said before, we just do trackday events; there are no points, no championships, and no chance at F1-stardom. Being aluminum extrusions means fabrication will be about 100 times easier and faster than a foam-core layup.  The visual change isn’t going to be subtle – the rear wing and endplates will take up the entire width of the car, 72″ (1.83 meter) wide. The only time they’ll be mounted is for track use; on the street they’re not only pointless, but pretentious and attract all the wrong kinds of attention.

Lastly – tires. They’re ready to be replaced because time has flown by – they’re now 7.5 years old (read: hard)! The rears are really worn as well, bad for a cop to notice. The good news is that they’re fairly evenly worn, meaning the camber gain curve is just right. Nitpicking, the center is slightly more worn, indicating that tire pressure could stand to be a bit lower. The thing is, with such a light car, going with lower pressure makes them more “squirmy” and they currently run around only 18 psi. That said, in general, for track use, more pressure means better traction, at least to a point.

I chose to go with Nitto NT-01s this time. The sizes are the same*, with 205-40/17 in the front and 275-40/17 in the rear, but a different brand. My brother uses the same brand and is very happy with them because they remain sticky a really long time, so I thought I’d give them a go as well. It also removes one more variable of difference between our cars.

Sort of tire related, Miata front hubs are one-piece units that aren’t intended to have the bearings removed (maybe they are but I’m not bothering).  People who race Miatas complain about short bearing life, but since Midlana has about half the weight riding on them, I think they’ll be fine. That said, some play has developed in the front tires that at first I though was due to rod-end play, nope, it’s the bearings. Given that they’re used parts of unknown lineage, they may well just be worn out, so to “reset the clock”, they’re being replaced. This will better serve to see how long they’ll last on Midlana from new.

Oh, one more thing. Because the rear tires were so worn and about to be replaced anyway, I intended to record a burnout for people who enjoy that sort of thing. When the moment came though, several things happened. One was that the location wasn’t quite as deserted as I would like, so there was some concern about undue attention. Another was that I discovered that I have a lot of sympathy for mechanical things and don’t enjoy subjecting the car to such antics. That said, I did do two, only they didn’t turn out as expected. Flooring it in first did indeed spin the tires, but the car sped up fast enough such that the tires never got hot enough to smoke or leave big shameless marks on the street. I’d also tried it in second, thinking that maybe I needed to increase how fast the tires were spinning, but again, the car just shot forward, a likely consequence of a lot of weight on the driven tires and being so light – a good thing. Yeah, I know F1 cars can smoke their tires on demand, so maybe I just suck at abusing the car 😛

*When magazines do tire tests, they typically pick some common size and do back-to-back track tests, then post the times. Whatever tire has the lowest time is deemed best, at least until the next tire comparison. There’s one thing many of the magazines leave out though, how a given tire “size” is more of a suggestion than fact. That is, a “255-40/17” tire from factory X is indeed 255 mm wide. Factory Y decides to one-up their competition, coming out with their own “255-40/17” tire which has a tread width of 265 mm. Factory Z, not to be outdone, released yet another “255-40/17”, this one with 270 mm tread width. Guess which one will most likely win? Tire comparisons based on a given size won’t necessarily find the best tire, exactly, yet the irony is that it doesn’t seem to matter. Class rules usually go by what’s printed on the side of the tire, not by what they really are. Anyway, these new “275mm” tires are about 6mm wider than my old “275mm” tires, making them 281 mm. Okay.