Worked on the rear suspension pickup points; the bottom frame is tacked up. Once the tubing was in place it became clear that the lower pickups could move forward about an inch. This gives the lower arms more of a straight shot at the uprights which is good structurally. It also frees up more space for the muffler, that’s good, too. It does place the lower triangulation tubes close enough to the transaxle that a (useless) tab sticking out the side of the tranny has to get trimmed, not a problem.
Things were going okay when, within 15 minutes I cut myself, twice, the second time enough that I had to stop to not drop blood everywhere. This is always a sign that I’m not “at one” with the project and if I continue, something worse will happen. So, done for the day, time was spent on the gas tank assembly – in CAD – where’s it’s harder to injure myself.
The gas tank is tentatively done, in CAD at least. By moving one side a little, capacity is now 16 gallons! This is enough for just about any drivetrain builders might want to use and gives the option of cutting it down if not as much capacity is needed. Still waiting for the fuel level sensor, and have to place the various external hose fittings, but it’s getting there.
I had a discussion with a race car designer who feels that the flat diffuser is better. The Katz book (figure 6-39 if you have it) shows that downforce increases with a diffuser angle of up to 12 degrees, while drag actually drops at angles up to about 4 degrees, then increases up to 12, but remains lower than if there was no diffuser. McBeath, in, Competition Car Downforce, discusses curved diffuser design but doesn’t provide data (which is understandable since aero design doesn’t transfer easily between vastly differing cars.) I don’t have a big-ass wing helping to suck air out through the diffuser, though the Katz data does not either which is good for my application. So, since Katz has actual quantifiable data, and because Kimini felt very stable at high speed, I’m going back to the flat design.
I changed the shape of the diffuser. The Katz book only has downforce data for flat diffusers yet all recent cars use smoothly-curving diffusers. That means they probably work better so I’m going that way (who knows if a diffuser on a Sevenesque car will do much anyway but it’s worth a try.) With it curved it also provides slightly more space for the muffler. It does look funny, like skis, but the side panels and fenders will cover them. It will look interesting from the rear though and above the diffuser will be engine compartment vents. The idea is that low pressure air exiting the diffuser will suck hot engine compartment air out through the vents.
Starting on the rear suspension bracketry. I must have measured wrong because my CAD drawing shows I have an inch of clearance under the rear suspension bracket – nope – it’s actually more like zero, which makes the rear mount easier to make. Another good thing is that since it’s so low there’s plenty of room to get the engine out even after it’s in place.
Once the fuel sender gets here I may take a break from the chassis and build the tank. It needs to be in place to make it clear where the control cables and coolant lines need to run. (If you haven’t noticed I like to use the actual parts during construction. It’s the only way to make really, really sure it’ll all fit together.) Speaking of control cables, it doesn’t look like the stock e-brake cable will reach, oh well. I’m investigating what it takes to get the gas tank parts cut via CNC. That would save a ton of time but as always it’s a time-versus-cost issue.
Check out the size of those huge rear fenders. I haven’t measured to see if the full width will be needed but I suspect they will be. They’ll look pretty menacing.
The forum’s starting to get more active which is good. The idea is to have it reach critical mass (meaning, a decent number of posts per day) before the car’s done and the book’s finished. Oh and it’s looking like another beta-tester will be coming on-line. In case anyone’s wondering, two “beta-builders” are enough, any more and it becomes too much to deal with.
The front drivetrain mount is done, though one overlooked aspect was the consequence of swapping pans. I bought a baffled aluminum pan which bolts to an RSX engine. While my transmission is from an RSX, the engine is from a CRV. The CRV stamped steel pan is one size while the aluminum pan is another and it (the aluminum pan) bolts to the face of the transaxle unlike the steel part. However it appears I lucked out because the aluminum pan is actually slighty smaller in the most critical areas so it should still work.
Someone asked why the tubes on each side of the engine don’t meet the floor in the corner of the main bulkhead, instead being welded higher up. That’s because the trailing link pivots go there and the tubes would be in the way. The suspension brackets will double as gussets to strengthen the area though.
Next will be extending the tubes back to complete the floor; that shouldn’t take too long. That’s safe to do because it doesn’t box in the engine, but it is getting near time to take the engine out and start on the rear-most chassis tubes.
As Miata parts were collected there was the question of whether to use Miata calipers or go with aftermarket Wilwoods. Rebuilt OEM calipers are roughly $100 while Wilwood units are around $140 – and half the weight. What’s really driving this is my bad experience with what I think were flexing OEM calipers (granted, not Miata) but I’ll probably just go with the Wilwoods and be done with it. This stuff’s way down the road but making decisions now makes it easier when the time comes.
Ordered the last of the parts for the gas tank. Capacitive-type fuel level sensors (no moving parts and compact) come in two lengths, 12″ and 24″. Since the 24″ unit is more expensive, and because the tank was already about 10″ tall, it was made taller to allow using the 12″ sensor without being cut down. This brings total tank volume to 14.4 gallons which is pretty nice. I think the tank will be a cool side project.
There are a couple different rear body treatments being discussed on the forum but you’ll need to register to see it. As long-time readers know, there was such differing opinion about what looked best that builders are encouraged to do their own. It’ll be a nice way to differentiate and personalize each car so they aren’t simply clones.
Finished the right-side mount and removed the wood stand, letting the weight of the drivetrain down on the left and right-side mounts. Now, I knew better than to think the OEM mounts don’t deflect so I had jacked up the drivetrain an extra 1/8″ to allow for them to get squished – not enough. The oil pan now sits on the table… it’s supposed to be suspended slightly above the table. It’s not terrible, the engine mount is vertically-oriented so washers can be used to raise it. Also, there’s two more mounts to add and once they take on their share of the weight hopefully the pan will be raised a bit without resorting to washers.
Also added the rear transverse tube behind the drivetrain and engine bay diagonals, all of which define the floor under the drivetrain. The front mount will be done next since it needed the floor tubes in place. After that I’m not sure. Doing the rear mount means starting to built the rear suspension structure, which boxes in the drivetrain and can prevent it from being removed due to the low garage roof interfering with the engine hoist. However, the rear mount does need to be in place before the engine’s pulled, and probably won’t be going back in until it’s built, probably after the chassis is off the table. I might make a wood mockup that mimics exactly where the rear mount is so the drivetrain doesn’t need to be in place.
The Midlana forum is pretty quiet though that’s understandable at this point. There’s a fairly extensive FAQ on there now, and some people have been discussing drivetrain choices. Beta-tester Jim is making faster progress than me due to working on his chassis more; you can see some of his pictures in the build diary. There’s a possibility of another beta-tester coming on-line in March.
Got the left-side (transmission) drivetrain mount done and tomorrow the right side will be dealt with. These seem to take forever but it’s probably the mental shift from the big fun stuff to the first of the less-fun little things. The idea is to support the drivetrain off these two mounts so the wood stand can be removed from below it. With that out of the way the lateral tube behind the drivetrain can be fit-up, along with the bracing on the floor bay, then add the remaining two mounts.
Received the nice spherical bearings for the rear suspension. Finding a place that sells bearing cups was a challange but necessary so builders don’t need a lathe. Received some nice Lenox cutting tools. The big blade is for the Makita cold saw to give it more teeth for thinner material. They also make some cool carbide-tipped holesaws that work really well, actually cutting the material rather than tearing it.
Oh and the last picture is going in the book with the caption, “I’ll just add the brackets now and weld the chassis tubes later, it’ll be fine.” This is a great illustration of why it’s so important to attach important brackets last. As I drone on about, heat warpage is a really big deal, as evidenced by the near-1/4″ shift of the bracket during welding of the tubes!
It’s frustrating coming home and thinking I’ll get something done on the manuscript; so many times things dictate otherwise. Today it’s the RAID 10 hard drives… one of them went offline. Backed up all the important stuff, powered down the PC, wriggled the connectors and presto, everything’s now fine. Yeah, sure it is. I hope to make good progress over the next week due to having next Monday and Friday off, depending what pops up, of course.
Worked on the engine mounts Sunday… or should I say, engine mount. It took all day to more-or-less finish one that consists of four tubes and three brackets which, like magic, works out to a not-so coincidental 5-6 hours, just like the rule of thumb says. I’m not complaining; it’s just a reminder that the little stuff takes just as long as the big stuff, much like golf where 7″ putts are just as important as long drives.
This brings back memories of Kimini – though the difference is feeling the pressure to “hurry up already” from people who want the book. I have to be careful not to let that rush me – which surfaced Sunday. I was going to push things and weld on the mount without first welding on the drilled tabs first. Why? Because something’s being welded it gives a sense of “progress”, but a false one since it’s then much harder to attach the brackets later. So I forced myself to put down the welder and quit for the day.
Ordered a bunch of bits for the engine, mostly hardware since some of it’s missing off the donor, clutch slave cylinder, flywheel bolts, engine-to-transaxle bolts, etc, etc.
Cooper’s been feeling much better, running around like a lunatic and wanting to play tug-of-war. It’s great to see him happy, my little hairy kid. I think it’s rather telling how my mood tends to mirror how he’s feeling.