18 June 2018

Had a brief dream of backing Midlana off a trailer and realized there’s a problem, in real life as well – that unless the angle is very mild, there’s a fair chance the diffuser will drag. Have to take some measurements before that happens.

On a related note, I found an unintended airflow experiment has been going on. Back when I replaced the turbocharger studs (more on that in a moment), the turbo oil feed line and feed adaptor had to be removed. It leaked a little and dripped onto the diffuser near its front center. Because of the way the diffusers attaches, some of that oil ran to the forward edge and got caught up by the air flowing under the car. The cool part – which looks better than the picture – is that the air flow remains well attached as it flows aft. What’s hard to see is that near the front edge, the air flows in and sort of “funnels” into the center channel of the tunnel, showing that the strakes are working as well. Also, along the top edge of the picture, you can see how the air flowed up onto the frame/Gurney flap, which would be expected if it was doing its thing. Good.

Regarding the turbo studs, after doing some more reading and getting some helpful hints on the Midlana Builders’ Forum, it was decided that they’re being replaced again, with the only type of stud that won’t stretch under high heat – Inconel. Actually ordering them though was a bit of a drama. For whatever reason, they’re fairly common in the aftermarket – in Australia – but not so much here. Testing the waters, I found they wanted about $50 shipping for their $50 parts, so no go there. In short, they were found domestically in a somewhat-surprising-but-shouldn’t-have-been source, Mazda. Seems the factory had such serious problems keeping their turbos attached to the second(?) gen RX-7, that they use Inconel studs. Thanks somewhat to mass production, they’re “only” $12 each, but hopefully once they’re in, that’ll be the end of that.

As an aside, a vendor in the US advertises “Inconel” studs, but reading the fine print, it turns out they’re actually “Incoloy”, which research shows isn’t the same thing. The vendor tried convincing me they were and that Inconel is just a brand name of Incoloy, yet research seems to indicate that Inconel has more nickel in it and is quite a bit more expensive (less profit). We use the material at work for really high temperature applications and use Inconel and nothing else, so there.

Lastly, if someone tries selling you fasteners and claims they’re Inconel, a simple test is that they will look like ordinary steel (not stainless) but are non-magnetic.

9 June 2018

I know how much you guys just love it when I post non-car related stuff. This year a couple of hawks had babies in a nearby tree and have been visiting the yard, looking for mice, lizards, and gophers. Usually I don’t have the good camera handy and by the time I do, the moment’s gone. This time I got a couple really good shots; I like the first one because of the glint in his/her eye, and the second one, I’ve definitely been spotted!

 

8 June 2018

The aluminum strakes were swapped in; notice how the aluminum end plates are now tucked under the body panel instead of on top. Because it’s cantilevered out behind rear axle centerline, it means that its vertical motion is mechanically amplified. I knew this and plan to trim back the strakes if necessary, and it didn’t take long to learn it might be. Backing out the car with the diffuser for the first time, when it rolled from our slopped driveway onto the level street, the rear suspension compressed just a little and I heard a brief scrap. I couldn’t help but laugh that the new diffuser had lasted all but 15 feet before being scarred. If this happens more frequently, it’ll be trimmed.

After finishing the diffuser, I happened to glance at the engine – never a good idea when in a good mood – and spotted that a stud holding the turbocharger had backed out. If that had been it, I wouldn’t be telling you, but it turned out that two were loose, with the second one being a pain because the turbocharger compressor has to be removed to get at it – you may remember the big Circlip pliers bought just for this. Sigh, when one thing gets fixed, it always seems like something else pops up.

New locking studs and nuts were installed and we’ll see how they last. Drilled-head bolts were not used for two reasons. One is the tight clearance, it wasn’t certain whether they could even be maneuvered into position to drop into the turbine housing mounting holes. The other reason is, being bolts, there’s a fair chance that the threads will get frozen in the stainless exhaust manifold, possibly breaking during removal. For now I want to stick to studs and see how they hold up. If they loosen again, safety wire will probably be involved one way or another. Stainless fasteners were not used because they thread into a stainless manifold. I learned the hard way – several times – that screwing together stainless parts is a recipe for disaster. Even spinning them together by hand often results in the metal galling and basically welding itself together. That said, there is a new stainless alloy that would be great in this application: Nitronic 60. The problem is that it’s so new, bolts made of it are really hard to find. Most vendors who handle it just advertise, “we can make whatever fasteners you want out of this material”; yes, I’m sure they can.

Let’s see, what else… wings. Based upon the references regarding diffuser design, placing the rear wing above the diffuser outlet makes a large improvement in downforce, so that’s the plan, but there are consequences though. Much like how the diffuser’s proximity to the ground is mechanically amplified by being behind axle centerline, so too is the downforce provided by the wing. Given how fast the car is, there is some concern that with a rear cantilevered wing, cresting a rise at high speed could allow enough air under an already-lighted front end to lift. For that reason, I think it’s wise to build both front and rear wings and install them at the same time. Hopefully the front wing will produce enough downforce to keep the nose planted.

In other news, one quirk of this WordPress blog template is how it arranges posts. First, they’re always in descending order, meaning that in order to read a multi-entry chronology, you have to read from the bottom up. That’s not a big deal, but it’s got another quirk of how past some number of posts, it places these additional entries on a second page. If you don’t notice the page selection buttons at the bottom of the blog and just start reading from there, you may miss entries hiding on the second page. I just changed the maximum number of displayed blog entries from “10” to “20”, so hopefully hidden entries are no longer an issue.