Slow Car Fast
January 14, 2009 - I picked up a spare speedometer on eBay.
The plan is to stuff electronic guts inside the stock gauge, and I figured having an extra would make me more comfortable taking it apart. I'd rather not go to a $300 adapter or use Autometer gauges, I like the old Smiths look. Besides, it was cheap!
entry 138 - tags: interior, gauges
February 16, 2010 - My plan has been to somehow stuff an electric speedometer inside the classic Smiths case.
The Camaro's T56 uses an electronic sender and the MG has a completely mechanical version.
Of course, I'm a long way from needing a speedo. But I'm not feeling completely healthy and poking around wires is more attractive right now than cutting and welding. Thus the electric emphasis of the last few days.
Well, it's not going to be easy. Looks like quite a challenge, actually. Enough of one that I started looking for alternatives. I already know of one, which is basically a small electronic motor in a box that takes an electronic signal in and spins a cable at the appropriate speed. It's a decent option, although a bit more of a kluge than I'd prefer. If you're converting a Miata with molded plastic gauges, you don't have a lot of other options. But the MG uses individual gauges, of course.
Poking around, I discovered that there actually exists an electronic Smiths speedo. It's not a perfect match to what I have, but it's awfully close. Close enough to work. And as a bonus, it's actually significantly less expensive than the little "gerbil box" motorized adapter. Excellent.
What about the tach? It's expecting a four-cylinder, so it'll read twice as fast with 4 pulses per crank revolution instead of 2. Some poking around pulled up an article on the British V8 site that explains how to add a potentiometer to easily make the tach adjustable. But wait, it gets better. 1972 was the only year to be fitted with a potentiometer from the factory. At the time the article was written, it wasn't known if this gave enough range to make it work with a V8, but I'm very willing to find out. If not, I'll just solder in a different one. Perfect.
entry 289 - tags: gauges, wiring
February 1, 2011 - I've been working on gauges recently.
The parts just arrived to mate my mechanical oil pressure gauge to the engine. The biggest problem was how to deal with the usual oddball British flare fittings. After doing some measuring, I was able to sidestep the problem by cutting the flare off and using a 1/8" compression fitting. It's a perfect fit. That goes to an AN -3 flare, then it's all just off-the-shelf race stuff. I still have to get behind the dash to make sure the connection to the gauge is tight, then we'll see how it works!
The coolant gauge has been more of a hassle. The one for the engine computer works fine so I can monitor things that way, but the dash gauge reads really low. At 180F, it's just come off the C peg. After some putzing around with the gauge and checking wiring, it looks as if the culprit is the temperature sender in the head. The GM part measures 3800 ohms at 63F and about 150 ohms at 185F. A parts-store piece I also have on hand is the same at 63 and 200 at 185F.
The MG sender apparently measures about 800 ohms at 68F and 33 at 190F. So I need to find one that's somewhere in that ballpark. It doesn't have to be perfect, just close enough that the gauge stays near the middle at normal operating temperature. I'll stop by NAPA tonight and see what I can find.
entry 547 - tags: gauges
February 3, 2011 - I swapped in the 6178 sender today, and it does sit just above C when cold.
That's fine, it shows the gauge is alive! I wasn't able to run the engine to see how it behaves at 180F or so, but I already have a pretty good idea. So that's good.
I couldn't run the engine because I'd mis-measured the length of the AN -3 line I needed. Either that or the length included a fairly large radius 90 degree section that was on one end. Anyhow, the end result was a high-pressure oil system that isn't sealed up. Of course, as can be expected with AN fittings, there are none to be found in town anywhere. So I've had to order another one in from Summit Racing. Argh.
I've taken on a new project, as you can see here. It's being documented on the Flyin' Miata site even though it's one of my own. Why? Because some of the FM fans might enjoy it, and it is a Miata. It's not going to be a long one, but it is going to involve a bit of bodywork and a repaint for a friend. It'll be my practice run for the MG.
entry 549 - tags: other cars, gauges
February 13, 2011 - We have a full complement of gauges!
It took a few tries to get the correct length of line for the oil pressure gauge, but it's in. I haven't run it up to full temperature yet but there were no leaks upon initial startup.
The car's been kept in the garage for the last couple of weeks due to cold weather, snow and race tires. The temperature's supposed to be nice this week, so it might come out for some extra exercise.
The Miata is coming along. I'm into the bodywork now. I cannot wait to shoot paint, it's so much more rewarding!
entry 555 - tags: gauges
February 15, 2011 - The Big List keeps getting shorter!
Unfortunately, the coolant gauge has to go back on it. It reads way to high, settling right on the H at normal operating temperature. I'll try the other one, and if that doesn't work I'll add a parallel resistor to the GM sensor. Easy enough to sort out.
I had the car out today in some unseasonably warm temperatures. Man, this is a fun little critter.
entry 556 - tags: gauges
February 20, 2011 - The other coolant sender is better, but not right.
It reads right between N and H during normal operating temperatures. I'll deal with that soon. Right now, I'm spending most of my time doing the body prep on the Miata. It'll get painted next week, then I'll start on the bodywork for the MG.
entry 557 - tags: body, gauges