Boston Clam Bake

The back ordered clamshell couplers and ferrules arrived and Abe was able to get most of them welded, but I’m still waiting on the XRP PROPlus hose and crimp collars.

The swirl pot is finished. The two -12 inlets on the top left connect to flex hose, the -24 outlet on the bottom right connects directly to the 1-1/2” stainless steel tube that runs down the side pod and the two threaded bungs on the middle left attach to a chassis bracket.

The radiator inlet and outlet are connected to the 1-1/2” stainless steel tubes via -24 hose and clamshell connectors.

Right side, the radiator weld ferrule is just tacked

Left Side

1-1/2” stainless steel tube, weld ferrule, clamshell coupler and hose end

The next step is to finish the welding the tubes in the engine compartment and fabricate the flex lines once the parts arrive.

C7 180-Degree Crossover

I’ve been doing some additional research on 180-crossover exhausts, specifically on LS engines. While the C7 video in the last post has an LT and I have a LS7 my engine is a custom build and supercharged like the LT, so it hopefully provides some insight into what mine might sound like. In any event, that car has a build thread and I was able to determine how it was fabricated. As I previously mentioned, the optimal approach for scavenging and sound is a round collector with the tubes firing in a sequential clockwise or counterclockwise manner. As can be seen in the picture below the fabrication is top notch and flat collectors were used for fitment reasons.

I was curious if the fabricator was able to optimally sequence both collectors. As can be seen below, the top collector is as good as you can get with a flat shape, but scavenging/sound won’t be optimal between B and C. The bottom collector has two discontinuities; B-C and D-A. Does it matter? Probably very little, but a round optimally-sequenced collector would likely sound a little more refined.

Here’s another video of that car. The first 30 seconds has an x pipe and the following 30 seconds has no merging after the collectors. The owner preferred the version without the x pipe so that part of the exhaust went in the recycle bin. Interestingly, Abe fabricated and installed an x pipe in a Ferrari 812 Superfast last week and everyone preferred that sound.

The following picture shows the version with the x -pipe.

Here are a couple of other video/sound clips. All of the cars are white and I’m fairly sure they’re all the same car. I don’t think the first video has an x-pipe and the last two definitely don’t have one. In any event, they provide some inspiration.

180-Degree Crossover Exhaust

There’s nothing wrong with the grumble of an American V8. I have a cobra with a 427 side-oiler, Webber carbs and side pipes. It sounds bad ass and I love it, but I want to do something a little different for the SL-C. I considered doing a 180-degree crossover exhaust, but there is no room to do it unless I cut through the top of the body which I don’t want to do. So, I was planning on a simple exhaust using the OEM exhaust manifolds because, according to my engine builder, custom headers may look cool, but they won’t generate any more power and will only lead to heat, fitment and leaking issues.

However, I keep looking at the 2-3/8” between the Daily dry sump and the bottom of the car. I considered lowering the engine to lower the center of gravity, but the supercharger snout and induction tube would hit the 2” x 6” chassis tube. If this were a pure race car, I’d notch the chassis and lower the engine, but for my use case that doesn’t make sense. It occurred to me that the space under the oil pan could be used for a 180-degree crossover exhaust.

So, what’s a 180-degree crossover exhaust? To understand that you need to first understand the high-level differences between a cross-plane and flat-plane engine. A cross-plane crank has journals separated by 90 degrees and a flat-plane crank has journals separated by 180 degrees. When viewed along the axis of rotation a cross-plane crank looks like a cross (i.e., “+”) and a flat-plane crank appears flat (see image below). If you think about it, if two lines are 180-degrees apart they are parallel and will appear flat when the plane that intersects them is viewed on its edge.

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The following table summarizes the high-level pros and cons of each approach.

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With the exception of the recent Mustang Shelby GT350, all American V8s have a cross-plane crank and many “exotic” cars (e.g., F1, Ferrari, Lamborghini, McLaren, etc.) have flat-plane cranks. There has recently been a lot of hype that cross-plane engines are exotic. This is a pile of bull you know what.

Firstly, a cross-plane crank can only be used on an engine with a number of cylinders divisible by eight, which for cars means 8 or 16 cylinders. Secondly, flat-plane cranks are used in everything from Honda Civics to mail trucks. This article does a great job discussing the nuances between cross and flat-plane engines and the origin of the recent hype.

OK, back to the exhaust… Flat-plane cranks optimize the intake and exhaust processes by alternating pulses between the the left and right sides of the engine — L-R-L-R-L-R… These even pulses, when combined with a high-revving valve train, are what gives Ferrari’s and Lamborghini’s their “exotic” sound.

A cross-plane crank doesn’t alternate pulses between the left and right sides. It has a R-R and L-L in the middle of the firing sequence which is what creates the “American” rumble. This also creates a crowded condition in the collector because two exhaust pulses, separated by only 90 crank degrees, are flowing through the collector. This requires a larger collector and reduces scavenging, both of which have a negative effect on power.

Enter the 180-degree crossover exhaust. Rather than plumbing all the tubes from each side into the same 4-1 collector, two of the tubes from each side are crossed to the other collector to create evenly spaced exhaust pulses — just like a flat-plane engine. This produces a broad power band (i.e., smaller collector), increases scavenging and results in a sound with less rumble, at least at mid to high RPMs.

The original GT40s, including the ones that won Le Mans in the 60’s, had 180-degree crossover exhausts. The picture below is of an original GT40. You can see why the exhaust is commonly referred to as a “bundle of snakes.” Most headers are made by sectioning fixed-radius, mandrel-bent U’s and welding them together. If you look at the graceful curves on the headers below, it’s clear that they weren’t made that way. I’m not sure how they did it, but it took some serious skills.

Yeah, I realize that a crossover exhaust will be a lot of work, create potential leaks and create heat issues, but if it were easy everyone would do it. While the original bundle of snakes increased power my fitment constraints may cost me some power (e.g., longer and skinnier primaries, increased number of bends, etc.), but I have excessive power so that’s not a concern. So why am I going to try and do it? For the sound. The sound of the Vette in the following video is bliss… please ignore the irresponsible driving.

That car has an LS7 with equal-length 36” long primaries. For fitment reasons the primaries are 1-3/4” and the collectors are flat. Round collectors, particularly when the primaries are sequenced to fire in a circular pattern (clockwise or counterclockwise), offer superior performance due to improved scavenging.

I conceptually understood that two of the primaries from each side had to be crossed over, but how a double pulse on each side occurred and how the tubes were routed wasn’t intuitive to me. To get my brain wrapped around things I put together the following diagram which illustrates the exhaust pulses down the left and right cylinder banks for eleven compression strokes:

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Note that the stock exhaust creates a double pulse in each cylinder bank; the right during compression strokes 4 and 5 and the left during compression strokes 8 and 9. The 180-degree crossover exhaust crosses these primaries to the opposite side which creates a symmetrical pulse down the left and right cylinder banks.

What do you buy for an 8-year old when a pandemic is looming? LEGOs of course. What do you buy a 50ish-year-old boy? Big-boy LEGOs. Specifically, a plastic LS7 engine block and an 1-7/8” icengineworks set to mock headers.

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The plastic blocks are attached to the exhaust flange using a block starter / tube adapter which are composed of pieces of rubber sandwiched between stainless steel disks. When the screw is tightened the rubber is compressed causing it to bulge. The large piece of rubber grips the inside of the exhaust tube and the small piece of rubber grips the plastic block.

I didn’t have short starter tubes tacked to the exhaust flange as suggested by the instructions so I tried to insert the block starters directly into the exhaust manifold. That didn’t work because the exhaust ports are D shaped and the starter blocks are round. A little grinding was all that was required to get everything to fit. From left to right; front of starter block, rear of starter block, and disassembled starter block with modified front and rubber disks.

I had to drill a relief hole in the middle of exhaust port to accommodate the nutsert and screw on the backside of the tube starter. I subsequently realized that I had the flanges mounted upside down ;-)

I’m not sure if I’ll be able get it to work out the way that I want, but it gives me something to do during the pandemic!

We Don't Need No Stinking C7 Hubs

In response to my last post I was asked the following on the GT40's forum:

I would have thought they would have gone directly to the C7 hub and 33 spline stub axle. Cheaper hub ($90) but still a X Tracker and with the larger/stronger 33 spline strength.

I don’t know what drove Superlite’s decision, but the dynamics of their procurement process is obviously different than ours and you would also need to take into account the pricing and availability of the larger-spline-count stub axle.

I’ve been talking with Hill McCarty at Agile Automotive about a new transaxle and during that process we discussed hubs. Long ago they had made modifications to support the latest version of the C6 ZR1 wheel bearings. Although they have never had any play in the bearings they age them out every two years. So that’s about 10 events per year, several of which are 24+ hours with the car pulling 2 lateral g’s. That’s a lot more abuse than my car will ever see — well, other than some launches :-)

Hill did point out that heat needs to be properly manged. While the aluminum upright does a pretty good job of wicking away heat so long as there is air flow, you need proper brake ducting if you’re pushing the car that hard.

With top-end C6 hubs the weak link is probably the CV joints. This is particularly true if you have a Graziano because the 4WD design, which is useless for a SL-C (at least so far), has asymmetric axles with the right axle being a good bit shorter. This puts more strain on the right-side CV joints.

Rear Upright and Hub Upgrade

Some of the SL-C builders who are tracking their cars were blowing out their rear bearings. The stock C4 bearings and 27-spline stub axles are OK for street use, but they are not suitable for a SL-C on racing slicks (forum discussion here). While Superlite offers a racing upgrade for the suspension it’s not suitable for the street. In mid 2019 Superlite began shipping cars with new uprights, C5/C6 bearings and 30-spline stub axles. In addition to being more robust, the new hubs have integral reluctors which are an improvement over the reluctor rings that I had previously installed on the CV joints. Specifically, everything is enclosed and there is no need to fabricate custom sensor brackets which might get knocked out of alignment.

Fortunately, Superlite offers an upgrade path for existing cars like mine. The upgrade comes with the following; two uprights, two spacers, six stainless steel dowel pins and two stub axles. Unlike the previous generation uprights which were handed, the new uprights and spacers are symmetrical and can be used on either side. I wasn’t sure what the two 7/16”-14 holes where at the top of the uprights so I called Superlite. Apparently the new upright is the same as the one used on the GT-R which uses cross bolts for the top billet piece. So what might have been four different upright parts, is one. In addition, the use of a spacer allows a thinner piece of aluminum to be used for the upright which reduces material costs and machining time. This was a smart change.

The pictures below compare the older right rear upright (on left, part# SLC-RR-UR-01R) to the new upright (on right, part# SL-RR-UR-02RL).

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Right rear uprights as viewed from inside the chassis; old on left, new on right. The front of the car is to the left.

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Right rear uprights as viewed from the wheel; old on left, new on right. The front of the car is to the right. Note that the new upright has the spacer mounted using dowels in the three smaller holes.

Right rear uprights as viewed from the front edge; old on left, new on right. The 1/2” thick spacer is mounted to the new upright which makes the new assemble ~0.2 thicker than the old version. I had drilled and tapped holes for the parking brake bracket when this picture was taken.

Superlite forgot to send me the dowels, so I ordered some from McMaster (part# 90145A541). The first step is to insert the dowels into the uprights (light taps are all that’s needed). As mentioned above, the uprights are symmetrical so you need to insert the dowels into the side that faces the hub/tire. Once that’s done, the uprights are handed. The spacer can then be placed over the dowels and lightly tapped until it’s flush with the upright.

Another benefit to the new version is that it’s easier to drill and tap holes for the parking brake brackets. As can be seen in the pictures above, there is significantly less pocketing in that area than the old version and the middle web is ~0.91” (~23 mm) thick which easily accommodates M10 screws. I used the DRO on the mill to drill the holes, but I used layout dye and a micrometer to prevent another D’oh. Measure five times, drill and tap once. Following the 2x thread diameter rule of thumb for aluminum I drilled the holes 25 mm deep and used a M10-1.5 bottoming tap.

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I bought SKF Corvette Racing Hubs from TPS Motorsports with pre-installed ARP studs. According to their website:

The SKF Corvette Racing Hub unit is designed to provide high stiffness during cornering, thereby reducing piston knock-back and the need to tap the brakes (confidence tap). It has <10 micron run-out and is designed for durability and to maintain preload at sustained loads of 1.2g!

Six M12 - 1.75 mm thread x 75 mm Socket Head Cap Screws and six M12 washers are needed to mount the hubs to the uprights. I’m not sure what comes in the new kits, but McMaster only had that length in iron oxide so I spent a bunch of time looking for zinc-plated ones. The smallest quantity I found was a box of 80, so if anyone wants some PM me and I’ll ship six to you at cost.

I drilled the socket head cap screws so that I can add safety wires when the car is finished. The hub can be clocked in any of three orientations and I positioned it so that the wires would be as close as possible to the parking brake. This keeps them away from the primary brake caliper and enables me to run those wires with the electric parking brake wires. The reluctor wires are very close to the stub axle and there is no provision to keep them in place. I’ll figure out how to affix them once the parking brake brackets are machined.

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I wasn’t able to mount the upgraded Brembo GT two-piece rotors to the hubs because the holes machined in the rotor hat by Superlite have a very tight tolerance (a good thing). I assumed that the longer studs were slightly askew so I opened the holes a little. I found that that a 31/64” bit fit the holes perfectly, so I used one to locate each hole on a drill press. After clamping the rotor to the table, I used a 1/2” bit to open the hole and then a counter sink to chamfer the edge. While not a complicated process, I also chamfered the other side so in total that’s 20 hole locating and clamping operations, and 50 bit changes! I was able to get the rotor to fit by tapping it with my hand which caused the threads to create a few shavings. My bit set only goes to 1/2” so I’m going leave things tight for now.

I’m waiting for some parts to be plated (e.g., the ball joint plate, lower shock pins, etc.), so I haven’t mounted the hubs to the car yet, but I’m not expecting any issues.

Note that I didn’t upgrade the front uprights and hubs because, as discussed in a previous post, I had already upgraded the front hubs to re-buildable race hubs which are much nicer than the SKF racing hubs. Unfortunately they are no longer available.

Holes on a Tangent

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I was asked how I cut the clean holes on the tangent of the swirl pot. While I do have access to Abe’s tube notcher, this was simple because the holes were drilled at 90 degrees. I used a bi-metal hole saw that I purchased at Home Depot (sharp tools make clean cuts). I dropped a scrap piece of tube into a vice on the mill so that when I dropped the quill it would just miss the end of the tube. This allowed me to see where the saw would plunge and to move the Y-axis until it looked like I had everything lined up perfectly (i.e. the outer edge of the cut was just inside of the ID of the tube at the middle point). I then slid the tube under the hole saw, put some oil on it and cut away… nope, I was off a little so I tweaked the Y-axis and did another test cut…. bingo, it was spot on. 

In went the real piece, I aligned the x-axis so that the middle of the saw was aligned with the sharpie mark (see on first hole above) and the hole came out perfect. I moved the X-axis and drilled the second hole. The inside was cleaned up with a deburring tool similar to the one shown below and the outside was cleaned up with the tube finisher discussed in a previous post.

This could have been done almost as easily using a drill press and a drill press vice. I would orient the vice so that the fixed jaw was closest to column, clamp a piece of scrap and eyeball alignment the same way as described above. Since you can’t tweak the X-axis on a drill press, I’d cheat the fixed jaw a little closer to the column so that shims could be used to tweak the position. I keep scraps of every thickness in a box to use as shims when mocking or machining parts. If you don’t have a cache, just order a bunch of small pieces of various thicknesses from McMaster. I’d then clamp the vice to the table, do a test cut, and shim as needed. The only trick would be to not rotate the tube when drilling the second hole.

Coolant Swirl Pot

I’ve been through a bunch of iterations on the cooling system. At this point, I not using any of the heating or cooling parts supplied by Superlite nor the LS7 mechanical pump. During the process the following diagram has been through multiple iterations and hopefully this is the final, final, final version — LOL.

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As I’ve previously mentioned, the single best resource that I’ve found on automotive cooling systems is this article on 4x4 Pirates. While it doesn’t mention remote electric pumps or mid-engine cars, its content is directly applicable.

My current plan is to not run a thermostat, but I have ensured that there is space to add one if needed. The LS7’s mechanical pump places the thermostat on the inlet side of the engine for reasons covered in the aforementioned article. While placing it on either side would work, fitment works better for me on the inlet side.

The one feature that I’m going add that isn’t covered in the article is a coolant swirl pot. Apparently these are very common in race cars to separate air bubbles. The Raver SL-C has one and the following excerpt is from Engineer to Win:

I still consider the water system de-aerating swirl pot (as described in PREPARE TO WIN) to an absolute necessity on any racing car... I strongly prefer to make the header tank non-circulating as shown in FIGURE [184']. In this case I run a good sized hose (say, dash 10 or dash 12) to the inlet of the pump simply to facilitate the filling of the system. If, for whatever reason, the header tank is part of the coolant circulating system then the size of this line must be severely restricted (say 1/4" ID) in order to prevent any sizable portion of the coolant from following the path of least resistance from the header tank to the water pump, bypassing the radiator(s) entirely.

—Carroll Smith

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Do I need one? No, but I needed to merge the two -12 lines from the engine into the the 1-1/2” tube that runs sown the left side pod and the swirl pot serves that purpose. In addition, continual de-aeration can only help things considering that 2% air in the system results in 8% less heat transfer, but 4% air results in 38% less!

The swirl pot is made from 2-3/4” aluminum tube and I decided to dome the top to promote air bubbles escaping… plus it looks cool;-) I purchased a 4” half sphere and while I was pondering how in hell I was going to clamp it so that I could cut the tip off, Abe tack welded it to a scrap 4” tube which made it easy to cut on a horizontal band saw. Once the cut was cleaned up, I needed to mark the exact center. To accomplish this, I put some layout dye on the middle, stood it on end against a vertical surface, measured the OD on a digital height gauge, divided that number by two, reset the gauge to that number, and rotated the cap while marking it with the foot. Given that all of the lines intersected, I knew that I had the center — or as close as possible given that the OD wasn’t perfect.

I used a hole saw to cut the bottom and the arbor created a hole in the middle. Rather than fill the hole, I decided to enlarge it and add a bung for a drain. I ground the back side of the weld bungs until they were flush with the inside surface. I’m still waiting for a couple of parts, but it’s almost ready for Abe to weld together.

Self Quarantine + Garage = Quality Time

My son is interested in cars, but for the most part he’s memorized the specs on all of the exotics. He’s somewhat interested in the SL-C project, but I’ve been careful to not push it on him. One of the good things to come out of sheltering at home is that we’ve had an opportunity to spend some quality time in the garage — what’s better than that?

The battery in my 1993 BMW 850 CSi was dead and my charger couldn’t revive it, so I figured I’d teach my son how to swap the battery. In the end, I learned that the car has two huge batteries in the trunk. To get to the second one, we had to remove the CD changer (the black box above the wrenches). It was the first CAN Bus car and it had two ECUs, one for each cylinder bank — apparently one wasn’t powerful enough to manage 12 cylinders. I guess to power all of the new-fangled electronics it needed two batteries. It’s kinda cool because the car is passing through three generations — James Richard bought it, James Scott is enjoying it and James Connor is being groomed for it LOL

Last week we also went over thread pitches, tapping and drill press basics. He then drilled some holes in scrap, used clecos to keep everything aligned and then riveted them together. Connor thought the clecos and rivet gun were cool. Next week we’re going over milling machine basics — fixturing, edge finding, facing, making slots, using the DRO, etc.

So being stuck at the house isn’t all bad!

A-Pillars

ALL PICTURES AND ACTIVITIES SHOWN AND DISCUSSED IN THIS POST THAT TRANSPIRED OUTSIDE THE BOUNDS OF MY HOUSE OCCURRED BEFORE I SELF QUARANTINED. Well “self” is a euphemism for my my wife and mother demanding that, given my underlying health conditions, I not leave the house. I’m going stir crazy, but the last thing that I need is those two opening a can of whoop ass because they thought I sneaked to Abe’s shop to have some welding done!

The front hoop is constructed from a single piece of 1.5” DOM with a flat top and constant radius bends on the sides. While this is easy to manufacture, it doesn’t closely follow the body which has a non-constant radius. If the interior isn’t finished, the hoop is noticeable, but not overpowering. However, when the interior is finished and the hoop is covered, the A-pillars overpower the interior. They’re not in keeping with the organic dash, tub, roof liner or door cards. In addition, the optional A-pillar covers don’t cover the hoop and require an extra 1/4” or so of fiberglass to be added.

Nice interiors are expensive and there’s a price point where it makes sense to modify the front hoop to reduce the size of the A-pillars. I’m not sure what that number is, but I’m aware of one SL-C with a $45k interior with massive A-pillars. That car should have had a modified front hoop.

The picture below shows how large the gap is between is between the front hoop and the body.

There’s two ways to shrink the A-pillars; (1) cut the front hoop off of the cage and fabricate a new one or (2) stretch the existing hoop. Note that it’s my understanding that Superlite has changed the way they manufacture the front hoop which makes it narrower. This would increase the need for the mod as well make the stretching approach infeasible.

In any event, I decided to stretch the hoop with a hydraulic jack. We started about one third of the way from the top of the hoop and worked our way down. Non-marring vice grips were clamped to the hoop to prevent the jack from slipping off. As the bottom of hoop expands the mounting plates lift off of the chassis and the outer edges pitch upward. At some point the outer edges of the mounting plates began to collide with the body. So I removed the body and trimmed the mounting plates with a cutoff wheel. I didn’t cut them off because they were useful to keep the jack from slipping off. The body was replaced, and additional stretching was done.

Once the right amount of stretch was achieved, the body was removed and the mounting plates were cut off with a portable band saw as close as possible above the weld. The bottom of the cut tubes were then trued up and made parallel to the chassis with a sanding wheel.

A new bottom plate was fabricated from 1/4” steel. There are two ways to fill the gap between the bottom of the hoop and the mounting plate: (1) machine a slug with a shoulder that slides into the hoop or (2) fabricate a pedestal for the hoop to sit on. Apparently it’s a common practice when fabricating cages inside of a car (i.e., one in which the roof can‘t be removed) to construct the cage shorter than needed so that the top joints can be welded in the car and the entire structure subsequently raised on pedestals. The pedestals seemed the easiest option, so that was the direction I took.

I fabricated two rectangular pedestals from 3/16” steel. No matter how I oriented the pedestals, the rear outer bolt holes on both sides were covered by the pedestal. Most builders could just relocate those holes, but I have removable side-impact bars which have tubes in the foot box that are welded to backing plates for the hoop, floor plates and the upper suspension mounting points. So, relocating those holes was a non-starter. The issue was solved by welding nuts, which will be located inside of the pedestals, to the top of the mounting plates.

Ratchet straps were used to tweak the location of the hoop and then everything was tack welded. With all of the changes to nose structure and suspension mounting points, I want to realign the suspension and body again before doing the final weld. The hoop isn’t as tight as I want, but it’s a huge improvement.

I had cut the dash to fit the old hoop and the white arrow in the pictures below illustrates how much the bottom of the hoop moved. Previously the fit to the dash was tight and now I have a lot of filling to do.

#MeToo-Endorsed Cooling Pump Inlet and Outlet

I didn’t want to use the cooling pump’s barbed inlet or outlet. Fortunately, the cap is removable and made of aluminum so I cut the barbs off. A Y-shaped outlet was made from a 1-1/4” and two 3/4” tubes. The junction of the Y was slot shaped and a mandrel mounted in a hydraulic press was used to bend it round so that it would match the larger tube.

Two -12 ORB weld bungs were shortened on a lathe and a shoulder was machined to keep everything concentric during welding. In the picture below, the top bung is stock and the two at the bottom have been modified.

The Y was welded directly to the pump’s cap to keep packaging compact and to reduce the number of connections that might leak. The cap was replaced and the pump was mounted to check the outlet and to mock the inlet. When we tried to remove the cap to weld the inlet we couldn’t get it off.

Do’h #^#%#$! I had it on and off at least five times, but no matter what we tried we couldn’t remove it. It was late and with removal attempts quickly escalating, I decided that for the cap’s safety we should resign our efforts for the day. Abe was able to remove it in the morning. We’re not sure what the issue was, so we put some grease on the o-ring and compressed the split ring a couple of times.

The inlet uses a 1-1/2” tube for the radiator return and a 1” tube for the heater return. The heater line uses a standard AN fitting and the remaining three lines use clamshell couplers.

All of the weld bungs are female because if the cap were dropped the threads on a male bung might get damaged and wreck the entire part. This allows damaged male threads to be tossed and easily replaced. This “disposable male genitalia” approach is endorsed by the #MeToo Movement. External plumbing does have disadvantages!

A lot of effort went into the cap. If I need to replace the pump, I can simply swap the caps — assuming I can remove it LOL.

Cooling Pump Bracket

The cooling pump bracket was made from 3/16” aluminum plate and 1/8” right-angle aluminum. Two of the pump’s mounting flanges are offset, so aluminum spacers were machined on a lathe. I had Abe weld them to the bracket because that reduces the number of things that I can lose by two;-) The bottom two holes are mounted through the 2” x 2” chassis tube with long M8 screws. The top screw is an M8 into a rivnut located in the top of the chassis tube.

As can be seen below the pump is slammed to the bottom of the car. This provides the inlet with the maximum amount of gravity feed from the radiator, keeps it’s center of gravity as low as possible and it allows the outlet to clear the cold air box.

The next step is to fabricate the inlet and outlet

Cooling Pump

I decided to use a remote electric water pump for the cooling system. I chose Pierburg, the same company that makes my intercooler pump. I initially purchased a CWA200 from Agile Automotive. They spec it on all of their SL-C and Aero builds and they’ve proven it at the 24-hour Thunderhill race and other endurance races. It allowed them to move the engine forward an inch or so and to relocate the pump’s weight to the nose box. Apparently the CWA200 has also been used by several GT2 teams. While the race credentials are nice to have, it’s been proven in many BMW and other OEM applications which is more applicable to my use case.

My engine builder expressed concerns about using an electric water pump. Seven or eight years ago he was retained by GM to test electric water pumps and he burned up a bunch of engines trying to find one that worked when a forced-induction, high-HP engine was pushed hard. Interestingly, the issue wasn’t flow rate. Rather the pumps didn’t create enough pressure to force steam pockets out of the rear of the block. This caused hot spots around the two rear cylinders (i.e., 7 and 8) which scorched their rings.

This need to have enough pressure to force steam pockets from the rear cylinders is why he advised me to leave the rear steam vent ports plugged. He strongly disagrees with the aftermarket steam vent kits that up-size the vent hose because they reduce pressure where you need it the most in an LS motor. Given that he’s been retained by GM for multiple R&D projects and he built the engines for the SL-C national champion after the team had a spate of blown engines from their prior marquee engine builder, it’s worth listening to him. That said, the tests were done a while ago.

To ensure that I would have enough pressure in the block, I upgraded the CWA200 to a CWA400 because its differential pressure rating is 1.9x higher (its flow is also ~40% higher). As can be seen in the comparison table, the CWA400 is marginally (i.e., ~1%) larger and while its max current rating is 2.2x it has an integral motor controller which is driven by a PWM signal. So, I gain ~2x increase in performance for a ~1% increase in size and a ~2x increase in power consumption (but only if I need it). In the end, the upgrade was a no-brainier.

In the pictures below, the CWA200 is on the left and the CWA400 is on the right. The primary physical difference is that the mounting tabs are on opposites sides of the outlet (i.e., they are 180 degrees apart).

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The cap on the CWA200 can be easily removed via four Torx screws, but it can’t be clocked. It took me a while to figure out how to remove the cap on the CWA400. It’s held in place by a split ring. To remove it, I used a large flat screwdriver to compress the ring between a bump on the body and a notch in the lid while twisting the screwdriver between the bump and the edge of the lid. It takes a couple of tries because an o-ring makes everything tight. When putting it back together you want to ensure that the split in the ring is 180 degrees (i.e., opposite) to the notch.

There’s a notch that’s machined in the edge of the lid which fits around the aforementioned bump. The sole purpose of the notch is to prevent the top from rotating and putting strain on the inlet and outlet hoses. The top can be easily clocked to any position by machining or filing a new notch.

Fortunately, the CWA400’s outlet orientation is perfect for my application and I didn’t need to make any modifications. The CWA200, whose cap can’t be clocked and is 180 degrees different, would have been a real pain in the ass to mount in my configuration. This was one of the other reasons why the upgrade made sense.

The next step is to mount the pump.

Pushrod Suspension

The rear suspension uses pushrods and bellcranks (aka rockers) rather than the conventional configuration in which the shock absorbers are mounted directly to the lower control arms. This is an exotic architecture found on Indy Cars, formula cars, prototypes and other pure race cars. While a few exotics have pushrod suspensions most production-based racers such as the Porsche GT3 Cup, a Spec Miata, or a Spec E30 have a conventional configuration.

Pushrod suspensions have the following advantages:

• Packaging: pretty much all open wheel race cars have pushrod suspensions because they allow aerodynamics to be optimized. Specifically, the shock can be placed inside the body (i.e., out of the air stream) and the width and height of the body can be drastically reduced because there is a high degree of freedom with respect to shock placement. If you look at the picture above, it’s clear why packaging is critical for open-wheeled cars.

• Unsprung weight is reduced because the shocks, springs and reservoirs are supported by the chassis rather than the lower control arm.

• Ride height can be adjusted by changing the length of the pushrod without changing the pre-load on the springs.

• Corner balancing can be done via adjustment of the pushrods.

• Body roll is reduced by relocating some weight towards the center of the car.

• Wheel rate can be easily changed by modifying the bellcrank’s motion-spring ratio (i.e., changing the length of one of the bellcrank’s arms). Wheel Rate = Spring Rate * (Motion Ratio ^ 2) * Spring Angle Correction. Since the notion-spring ratio is squared, small changes have a big impact. That said, the SL-C’s bellcrank has a 1:1 ratio.

The SL-C is basically a race car, so it’s not surprising that it has a pushrod rear suspension. The bellcrank is mounted via a large shoulder bolt which is retained by a billet aluminum bushing welded into a 1/8” x 2” x 2” chassis tube. The bushing takes high loads and the bellcrank is in single shear. It would be a nightmare if the bushing deformed because the only way to fix it would be to cut the entire tube out and replace everything. The chassis was welded in a jig at the factory and doing it properly on a finished car would be a challenge. Like some of the other builders, I decided to add a support arm to put the bellcrank in double shear.

Agile Automotive went through several iterations on their endurance SL-Cs and they offer 4130 chromoly parts for their latest iteration:

• 2x barrel welded to a cone (aka misalignment) washer

• 2x tube nut

• 2x bent and notched tube

There is a fair amount of variation from chassis to chassis and even from left-to-right on the same chassis, so they shipped me the parts with only the cone washer and barrel welded. The picture below shows the parts with the ones on the left having the tube’s mill scale and the barrel‘s weld discoloration re.

I’ve found that when loaded in a Dremel the AUSTOR abrasive wheels shown below do a great job preparing irregular metal surfaces (a tube polisher is obviously the best tool for round tube). The kit below costs less than $15 and contains 60 wheels in multiple grits (e.g., 120, 180, 320, and 400).

As intended, the tube needed to be trimmed and each side was on/off the car several times to get fitment right. I placed a grade-8 washer between the tube nut and the billet upright.

Once everything was installed the open barrel didn’t look finished and it would collect water and dirt which might make its way into the bellcrank’s bearing. I designed and 3D printed a cap. The first version had a mundane flat top so I gave it a profile similar to the dimple dies elsewhere.

I also plan on welding a gusset between the 2” x 2” tube and the vertical billet member.

Right Side Pod

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The lines in right side pod are finished. The approach is the same as the left side pod described here. There’s a lot less going on this side! The lines from top to bottom are:

• Air Jack (manifold to front jack, -6, aluminum)

• Heater Supply (engine outlet to heater, -10, aluminum)

• Heater Return (heater to pump inlet, -10, aluminum)

• Clutch (master cylinder to throwout bearing, 3/16”, stainless steel)

• Rear Brakes (residual pressure valve to brakes, 3/16”, stainless steel)

• Cooling Return (radiator to pump inlet, 1-1/2”, stainless steel)

The air jack line won’t be insulated because it doesn’t carry any heat.

While most of the clamps were 3D-printed, I used NotcHead Line Clamps in several locations. The hard line version requires a solid push on the line which results in a reassuring click.

Intercooler Pump Outlet

In a previous post I mounted the intercooler pump with a 3D-printed bracket. I thought about converting the barbed outlet to an AN fitting, but the cap is plastic and I couldn’t come up with a reliable solution. Mega-priced supercars use silicon hose and hose clamps so I guess that it would be OK to use them in this one place LOL.

The intercooler pump outlet’s OD is 20 mm and the stainless steel tube running to the front of the is -10 (i.e., 5/8” or 15.9 mm). To resolve the mismatch a barbed adapter was machined on a lathe from a solid stainless steel rod. This adapter will be welded to the stainless steel hard line once the line is ceramic coated and the insulation sleeve is slid on.

The angle between the pump outlet and the stainless steel tube that runs down the side pod is 112 degrees. After lots of research the closest elbow I could find was a 19 mm ID, 120-degree silicon elbow.

Induction Tube

The space between the body and the chassis is tight and the prior induction tube put a small crack in the fiberglass. It’s difficult to figure out how much space you have with the body in place. However, when the body is removed the tail section sits too low. To solve this, I cut two temporary tubes to support the tail at the correct height which makes it easy to check clearance when the body is off. The vertical sharpie line spanning the temporary support and the chassis makes it easy to align the support and the rubber on top protects the fiberglass.

I was concerned that I’d need to scallop the 2” x 2” chassis tube or use an oval induction tube, but a 45-degree bend was all that it took… well, that’s only the case because we previously positioned the throttle body in the right place and used a tight-90-degree elbow on the cold air box lid.

I used a -64 AN (i.e., 4”) AdelWiggens tube connector to connect the elbow to the induction tube. These clamshell-style connectors have been used in aerospace for over 30 years. They can be opened and closed with a single hand and require no tools. They have some impressive specs, all overkill for an induction tube, but that’s how I roll LOL

• Operating Pressure: 125 psig

• Proof Pressure: 250 psig

• Burst Pressure: 375 psig

• Axial Displacement: 0.250"

• Angular Misalignment: +/- 3.5 Degrees

I had to look up what psig was. It’s pounds per square inch gauge which is the pressure relative to atmospheric pressure as opposed to pounds per square inch absolute (psia) which is pressure relative to a vacuum. I guess if you manufacture parts that can be used terrestrially or in space you need to spec things that take atmospheric pressure or the absence of it into account.

The ferrules are typically butt welded, but I counterbored their IDs on a lathe to allow the them to fit over the tube. This ensured that they were perfectly concentric to the induction tube. Things were a bit sticky out-of the-box so I cleaned the grease off of the o-rings, ferrule grooves and sleeve and applied a thin layer of lithium grease.

Apparently the standard aerospace color for these types of clamps is purple, similar to the red/blue standard for AN fittings. I want to be 100% clear here. It’s purple and not any shade of pink!

The induction system is done other than the cold air box and the duct, neither of which are needed to start the engine.

Cold Air Box - Frame and Top

I started fabricating the cold air box. The top frame is made of 1/8” flat and right-angle aluminum and it’s bolted through the 2” x 2” chassis tube with three 1/4” screws. It’s designed to: (1) allow the body to be removed with it in place which is important during the build and go-kart phase and (2) allow the air box to be removed with the body in place which is important once the car is finished (the wheel and wheel well liner must be removed first).

Underside of frame with Dzus springs installed

My plan is to fabricate aluminum closeout panels to dress up the engine compartment. With that in mind the lid for the cold air box is larger than it needed to be to cover the 2” x 2” chassis rail and to close the gap between cold air box and the wheel well liner. I used four Dzus fasteners to fasten the top to the frame.

Here’s how I got everything to line up perfectly. The placement of springs under the frame was tight so I flipped the frame upside down on the bench, located the springs and drilled a 1/8” hole at the center point of each spring. I then installed the frame on the chassis and clamped the lid in three places. Using the hole in the frame as a guide, I drilled upwards through the lid with a 1/8” bit and inserted a cleco to further clamp the lid to the frame. I repeated this for the remaining three holes. Now that the center hole for the Dzus connector was located, the left and right holes for the rivets needed to be drilled. To accomplish this, I fabricated a simple drill jig — three 1/8” holes, 1/2” apart in a straight line on a piece of scrap. I affixed the center hole of the jig to each hole in the frame with a cleco. After rotating the jig to the desired orientation (i.e. what would fit) I drilled the left hole with an 1/8” bit, inserted a cleco into that hole and drilled the right hole with the same bit. At this point, I had three perfectly spaced 1/8” holes, 1/2” apart in a straight line. The center hole was then enlarged with a 5/8” carbide hole cutter which had a 1/8” pilot so it was easy to get that part right. 1/8” flush rivets were used to affix the springs.

Left, center and right holes for Dzus connector

I repeated the process for the lid with four exceptions; (1) I used 4-40 screws rather than rivets because I didn’t want to drill clearance holes in the frame for the back of the rivets. The screws worked because the lid was 1/8” thick to prevent warping when welding, (2) the left and right holes were were drilled with a #43 bit and tapped, (3) the center hole was chamfered to get the Dzus connector to sit flat and (4) since there were no clearance issues the orientation was determined by what looked best rather than what would fit.

So that’s a total of 36 drilling operations. Screws or nutserts would have been a lot easier, but the convenience of the quarter-turn fasteners was worth the effort.

A bellmouth-style velocity stack was welded to the underside of the lid to reduce air turbulence. It also significantly stiffened the lid which kept it from warping when the 90-degree elbow was welded to the topside. The filter mounts directly to the velocity stack with a stainless steel clamp.

Velocity stack welded, upper elbow not welded yet and Dzus fasteners not installed yet

With the lid fastened via the Dzus connectors, a tight 90-degree elbow was positioned and tacked into place. The seam between the velocity stack and the elbow was welded on the inside and it was carefully ported. I defy you to find the seam in the picture below;-)

Velocity stack and elbow are ported; note that the screws for the Dzus connectors are flush

While not necessary, I had Abe weld the seam between the elbow and top because I didn’t want dirt getting stuck in seam. The picture below shows the finished lid with the Dezus fasteners tightened.

I’m not going to fabricate the actual box or the duct the connects the body to the air box at this point because I don’t need it for the first engine start. With both the source (filter) and the destination (throttle body) in place, it’s time to fabricate the induction tube and connect the two.

Throttle Body Tube

In a previous post I designed weld flanges for the throttle body and supercharger snout and 3D printed them to check fitment. Since then I had them CNC machined from 6061 aluminum and they came out great. Due to minimum volumes I have a few extras so let let me know if you’re interested in a weld flange for ab LS7 or an LT5.

The prior version of the supercharger-to-throttle-body tube was in the passenger’s ear. The new version is much better. The passenger could put a pad on it and use it as a head rest LOL. The good news is that it fits behind the carbon fiber panel so it won’t be seen, but it sure as hell is going to be heard! The improvement was achieved by using tight-radius, mandrel-bent, made-in-the-USA tube from Performance Tube Bending.

One of the neat things that I learned from Abe is how to surface finish tube like a pro. Apparently there’s a specific tool for sanding and polishing tubes. It’s basically a belt sander with two fixed rollers and a third roller on a spring-loaded arm. When pressure is applied the belt conforms to the tube’s OD. Once I had removed the big grooves, scratches and dings, I found it useful to mark the remaining blemishes with a black sharpie. Similar to using a guide coat during body work, you sand the area until the black is gone. The video below shows a surface-prep belt (similar to a scotch pad) on a 4” aluminum tube. In this case the tool is clamped in a vice and the tube pushed into the belt. When I used the tool to remove the mill scale on the 1” OD chromoly, I switched things around and clamped the tube in the vice.

The tubes had some relatively deep grooves from the bending process. In addition there are some minor ripples on the inner radius of the bend. Even with the right tool it took me over an hour to get the surface to a perfect condition. Well, it actually took 45 minutes longer than that because when Abe went to tack weld the pieces on the car it didn’t fit…

WTF? D’oh! I accidentally used the cut end! Next time I’m going to use a sharpie to put some big “X’s” on the cut end.

Things would have gone faster if I had a belt with more aggressive grit for the first pass and a narrower belt when working on the inner radius. In any event, I’m happy with the results.

The next step is to fabricate the cold air box.

Intercooler Pump and Bracket 1.1

I previously posted about a bracket that I designed and 3D printed for the intercooler pump. It was a nice bracket, but when I went to install it I realized that there was a better location which required the pump to be as tight as possible to the bottom of the car and the chassis tube. So, into the bin went the bracket.

When designing the new bracket I held the pump in place and rotated it until I found the best angle for the outlet. I then removed the cap and clocked the body all four positions, each 90 degrees apart. Since the inlet is on the radial axis the electrical connector drove that choice.

One of the nice things about 3D printing is that it’s easy to incorporate features. For example, the picture below shows the back of bracket. The recesses around the mounting holes accommodate the flange on the NutSerts (i.e., gold piece with ridges) which allows the bracket to sit flush with the chassis.

In the picture below, the pump is mounted to the 2” x 2” chassis rail in front of the fuel surge tank. The top stainless steel hard line supplies the heat exchangers in nose and the bottom one returns the coolant to the intercoolers. The pump outlet is clocked two degrees too high so I’m going to tweak and reprint it. Once that’s done I’ll cut the lines, add beads and connect them with silicone hose.

Steering Rack 1.2

I finished installing the steering rack by using the stock top hole to clamp the rack in place while I located and drilled the bottom hole. The rack was removed, both of the stock holes were welded/closed, the top hole was drilled and 1/8” steel backer plates were fabricated.

Agile sent me taller pillow blocks which allowed me to ditch the spacer. Rack-to-steering-arm alignment looks good so I‘m not expecting any bump steer issues. Agile also sent me beefy tie rods with Auora heim joints which are higher quality than the ones provided in the kit. In addition, they have a misalignment mono ball which removes the need to use misalignment washers — two less things to lose!

I also noticed that the uprights were binding on the sway bar drop link brackets about 8 degrees before full lock. I had previously fabricated 1/4” spacers to allow the brackets to clear the top of the shock pins. This extra height was exacerbating the binding. It then occurred to me that I could clip the corner of the shock pin. This resolved the binding so I tossed the spacers. This also enables me to remove the shocks without removing the brackets. Duh, I wish I had done that sooner!