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.
Picked up some 1/8″ plate for fabricating brackets (for just about everywhere.) The OEM drivetrain-side mounts are bolted on and will guide how the chassis-side mounts fasten to them. The mounts need to be fairly strong since they have to handle vertical loads of maybe 5x for hitting worst-case potholes (about 2000lbs total.) Then there’s engine torque which can be 600 lb-ft or so, depending upon traction and gearing. In fact, the worst combination is to be at full throttle – at the edge of adhesion – and hitting a bad pothole; the shock loads through the engine mounts are quite large. And, if builders bolt on a supercharger and wide racing slicks and go drag-racing there’ll be even more force. That’s why they’ll all be triangulated; though it adds tubing, it’s better to be a few pounds heavy instead of having the drivetrain drop out half way down the track…
Speaking of brackets, someone asked how complete the chassis is. I asked if I should include the time to make brackets in my answer. That is, the chassis is probably 70% done if brackets aren’t included, but probably 30% if they are. Brackets take a ton of time, probably as much as doing the tubing; it’s just how it goes. Oh, and once again the rule-of-thumb is proving correct, that each end of a tube takes about 30 minutes to fully fabricate. Have six tubes to make and weld? Figure six hours to do it. Hmmm, doing some quick math, there’s roughly 100 tubes in the car so that means roughly 100 hours to build the chassis, then probably that much time again for all the brackets. Actually, these numbers are high because that’s how long it’s taking <em>me</em> – and the first car always takes the longest. Once it’s documented, future car’s should go much faster, especially when it comes to the brackets.
Along with the correct fuel filler from Aircraft Spruce came their latest catalog – great bathroom reading! Go to their site and order one; it has a lot more stuff in it than the website.
And finally, several people asked how I like using the Makita LC1230 saw – it’s a beast. The blade turns a lot faster than expected and I learned a lesson early on. In hindsight it’s perfectly clear what happened and why, but it was pretty exciting. I wanted to cut a round tube at an angle, so set the vice and tightened it down. The blade just barely touched the tube – and it shot out of the saw at about Mach 7 across the garage. (The wife coming out and asking what the noise was, “uh,… nothing.”) The problem was two-fold, clamping round tubing in a vice with flat sides, and cutting it at an angle. The projectile tube had an impressive spiral pattern of teeth marks all down its side. Lesson learned, I now only cut round tubing at 90 degrees since I haven’t made an adaptor to properly hold it. For square tubing it’s fine, with the cut end is absolutely clean, with not even a tiny burr on it.
One thing nice about Aircraft Spruce is how fast they take care of problems; the correct part’s already on the way.
Saw this posted in a car-building forum: “… have been reading Kimini posts for months. as a matter of fact, he’s the reason I’m in this mess. love his car build and listened to him and now am convinced that rear-engine is by far the best path to follow.” I hope I guided him down a path where he’ll be happy!
Been reviewing the rear suspension and changed the type of spherical bearing to a stronger part. Since the forces on this bearing are three-dimensional it means one of the forces is applied axially, a spherical bearing’s “weak direction.” The only way to solve it is to use a larger bearing, which works out well since the OEM bolt that runs through it is too small anyway so it’ll go up a size for the larger bore.
My best friend in the world, Cooper, our dog, is getting old. He’s starting to have rear leg problems that long-time readers may recall was caused by a slipped disc years ago. Some days he’s fine and other days his rear legs are somewhat uncoordinated, making it hard for him to walk very far on our outings which he loves. He looks to me for everything, and the last thing I have to do for him is going to be very, very hard. What’s strange is how I get more emotional about him than I do at people’s funerals. Someone once told me, “treat your friends and animals as though each day is the last day you’ll see them.” I try, but it doesn’t make it any easier.
Almost but not quite. I ordered an identical gas filler (even used the same part number as last time) from Aircraft Spruce. Their website is a bit, um, 1990’s, lacking pictures so you really never know what you’re ordering. They don’t even list brand names so you can’t confirm the item on the actual manufacturer’s website what you’re ordering and, surprise, it’s the wrong part. Anyhow, while the front (shown) is the same, this version is intended to bolt directly to a gas tank. Unfortunately I need the panel-mount unit that connects to a hose that runs to the tank. Not cheap (and a lot more expensive than last time I ordered one) but so good-looking I can’t resist, again.
It was pointed out that perhaps I shouldn’t be building an engine at the same time I’m building everything else. It’s a very valid point, potentially having to sort both suspension issues and engine problems can be very non-productive. I absolutely agree but can’t help myself, it’s a mental thing. When the car is “done” I really want it to be done, not with a potentially tired-out engine of questionable health that may or may not be reliable. Yes, it could get a leak-down check and just call it good but I just want to do the whole job up front. There are other issues, too, that regardless if the engine’s built or not it still has to be tuned since it has an aftermarket computer. I’m going to have it professionally tuned so in one afternoon it’ll be ready to go. Also, for the first track event I’ll probably crank the boost down in order to concentrate on handling issues (like there’d be any of those, phffft.)
Cooper-Dog at my feet, a drink on the table, Stranglers and The Stray Cats on the headphones, working on the manuscript, life is good.
Rear main chassis tubes are in. The main diagonal and rear cross tube will wait since it makes accessing the drivetrain difficult. The chassis could be lifted off the table, leaving the drivetrain in place if I had more overhead room, oh well. I should probably tack-weld in a temporary cross-tube and diagonal just to keep things square until the real deal happens.
Received two key parts for the gas tank, a vent and filler neck, both containing one-way valves to prevent fuel spillage if inverted. The connecting rods have been ordered and sometime this week the pistons will also be ordered. Need to order the uber-cool flush mount filler cap, too. If I get tired of working on only the chassis I might build the gas tank.
Weeknights are filled with keeping the manuscript ahead of the build, creating detail drawings, writing accompanying text, and constantly reviewing and rewriting existing chapters. This is the best way to write a book like this, in parallel with the build so important notes aren’t left out. In fact, you can see a sheet of paper at the bottom of the third picture; it’s a page from the manuscript being used as directions on tube placement. This way the book you get is already tested and proven, and of course, Jim, my “beta tester” is hard at work on his chassis, too.