LeMon Porsche
The continuing saga of a 24 Hours of LeMons Porsche 924 endurance race car.
2 years ago
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Finishing Touches

Crankcase Breather — with all smog equipment stripped off, the crankcase vents to the atmosphere instead of back into the airbox. Eschewing a $30 aftermarket filter, we constructed one from a beer can, a hose clamp, a sock, and some rivets. Price: less than 50 cents, not including the beer.

Fuel Pump — the stock fuel pump puts out in the neighborhood of 90 psi. When constricted by the fuel pressure regulator before going to the carbs, it ballooned and then completely blew out a fitting, dumping gallons of fuel onto the floor and sending the team scrambling for the kill switch and fire extinguishers. Here we have a diminutive $40 low pressure fuel pump that puts out 6 psi. Made a nice little mounting plate in the right rear wheel well. Jim plumbed and wired it.

Throttle Cable — Reused the brake cable from a bicycle. Snipped and crimped it around an eye to fit onto the accelerator pedal. Now we can actually drive! Price: $8.00.

Choke Plate — This little mod lets us choke the engine for cold starts inside the car. The old one that came with the carbs was made of soft aluminum and broke at the mounting holes. We put some scrap stainless into the notcher, a scary machine that would like nothing more than to eat your fingers, smoothed it out with the grinder and dremel, then threw it on the drill press. Done and done. Price: free! Fingers lost: none!


2 years ago
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Jon instructs how to properly manhandle the motor to get it to align with the clutch bellhousing. This technique saves you endless frustration and skinned knuckles trying to thread the bellhousing bolts.

2 years ago
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The full racing potential of the 924 NA. Only 16 built. One is for sale in NY for $15K.
http://bringatrailer.com/2011/05/19/bat-exclusive-1980-porsche-933-scca-factory-racer/

The full racing potential of the 924 NA. Only 16 built. One is for sale in NY for $15K.

http://bringatrailer.com/2011/05/19/bat-exclusive-1980-porsche-933-scca-factory-racer/

3 years ago
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Front caliper install

The Passat front calipers bolt up quite nicely to the stock 924 steering knuckle. Hooked up to the upgraded stainless steel brake hose, they make it look like we finally have a serious braking system.

A couple surprises came up during the installation. The left and right calipers are basically mirror images of each other, and they have unique part numbers to avoid confusion between them. They are designed so that the bleed screw sits on the bottom of the cylinder in the installed position so when the brakes are bled, sludge and other debris can be cleared and all old fluid eliminated. On the Passat caliper, the hose fitting also sits on the bottom of the caliper adjacent to the bleed screw.

Upon completing the driver side caliper, it became obvious the brake hose fitting was going to interfere with the control arm in a left turn. At full droop with the car in the air, the wheel can barely turn, scraping the hose against the control arm as the rear of the knuckle turns in. Installed this way, we would probably eventually lose steering or the brake. So, the obvious solution is to swap the driver and passenger side calipers so that the hose connection (and bleeder) sit at the top of the caliper. This is one of those details too rarely documented (remembered?) on mods like this one. So here it is – you need to install 1990 Passat calipers upside down and backwards on the Porsche 924.

the other little surprise was discovered after torquing down the two mounting bolts on the steering knuckle. The hub wouldn’t spin. Closer examination reveals that the caliper dust cover, a thin metal disc attached to the steering knuckle on the inboard side of the brake rotor, doesn’t quite clear the slightly larger calipers. There is a section cut out of the dust cover to accommodate the stock Porsche calipers. But with the Passat calipers, when you bolt them down they squeeze the corners of the cutout into the rotor, interfering with the brake mechanism and effectively seizing the caliper. One solution is to remove the dust cover entirely – it isn’t really a necessary component. However, removing it requires first removing the rotor, which on the Porsche 924 is also the wheel bearing. It’s not a big deal, but it’s a pain unless you have bearing work to do or an extra hour on your hands. Another solution is to grab some pliers and bend back the offending corners.

3 years ago
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Master Cylinder Rebuild


Upon disassembly and inspection, we deemed the master  cylinder in good enough condition to rebuild rather than replace. Before rebuild, it was blowing brake fluid past the seals and into the brake booster. It might have ruined the booster, we can’t be sure. You need to have a running car to effectively test the booster’s operation. We may get away with an nonoperational booster — it’s only purpose is to ease operation of the brake pedal, and it doesn’t affect the actual integrity of the braking system. We’ll test it on the street, and if we’re not happy with the feel, we’ll change it out for a new one.


The rebuild kit is basically a set of replacement rubber seals and a few thin metal washers. You disassemble the parts, clean them, and throw on the new seals. Even though the old components showed little signs of age or wear, the difference in action of the master cylinder after rebuild is incredible. The tolerances are apparently quite small, and the performance of the rebuilt component will surely be noticeable.

3 years ago
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New Rollcage Downbars


Last race we got away with bends in our rollcage rear downbars, but were given a stern warning to fix them. Now that the fuel tank is out and there is no fire hazard, we can move them forward and weld over where the tank normally sits. Jed has done a great job fabricating reinforced spreaders from 1/8” steel per the new LeMons rule requiring 24” square for all spreader.

3 years ago
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Suspension Mods


Our car arrived from Germany without the optional front and rear anti-sway bars (ASB).  ASB are critical to preventing body roll in turns. We’ve begun the job of stripping the front and rear sway bars from our ‘78 parts car and installing them in our ‘77 track car.

The modification to the front is basically a bolt-on upgrade. The chassis came pre-drilled for the ASB mounting brackets. However, the control arms do not have mounts for the sway bar ends, so we need to remove them from the ‘78 and install them on the ‘77. We’ve discovered that the ball joints in the ‘78 control arms are larger than in the ‘77, so we’ll need to purchase these replacements to complete the installation.

Modifying the rear requires some fabrication and modification. The torsion bar carrier in the ‘77 that came without the rear ASB option does not have mounting brackets. These need to be fabricated from steel and welded to the torsion bar carrier. Some 924 owners take a shortcut and clamp the bar to the carrier tube, but this moves the ASB about an inch backwards, which is not the optimal geometry.

We made a cardboard pattern from the ‘78 mounts, and Frank Lally, the owner of the fabrication facility Simtek and generous lender of workspace (and father of NASCAR Rookie of the Year Andy Lally!), used his laser cutter to craft them from sheet steel. Next, they’ll be bent in the press and welded into place on the carrier tube.

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Front Brakes

The brake line couplings are frozen. Managed to get one out, but the rest of them are rounding out in the wrench. Gonna need some professional help to cut and re-flare the lines. Just ordered some stainless steel braided hose to replace the weak rubber ones.

We got beefy new calipers for the front. We’re going with a mild modification we learned from the folks at 924board.org. It turns out that stock 1990 Passat calipers are a bolt upgrade for the 924. We gain about 6mm of cylinder diameter, meaning more volume, meaning more clamping power. Bonus: they are practically the same price.

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Carb Conversion Underway

The first step of the conversion is a total teardown of the intake and fueling system. The fuel regulator, injector lines, air intake, intake manifold, miles of vacuum and smog lines, and various other extraneous parts are unbolted and removed. The whole system is surprisingly massive, taking up a huge portion of the space under the hood. Removing this complexity is a huge additional benefit of doing the carb conversion.


We went on a parts run to secure vacuum fittings and tubing, along with fuel lines and fittings to complete the plumbing under the hood. The intake manifold appears to be warped slightly, very likely from its original fabrication. The thick plate that mounts against the cylinder head will act like a heat sink when welded. When it absorbed the heat during fabrication, it did so unevenly, resulting in the warp. It seems to flatten though when bolted to the cylinder head. Fingers crossed. Hopefully we’ll test fire this coming weekend.


3 years ago
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Carb Disassembly and Cleaning

Having no idea the condition of the carbs we bought — nor much documentation on hand regarding our particular model of Makuni bike carbs — we tore them down for a look inside. The guts look servicable, some minor corrosion here and there, but nothing serious. There was some gunk in one of the main jets, but that was probably the worst of it. Surprisingly, there is only a single e-clip groove on the jet needle, which limits some of the mixture adjustments we can make. The needle regulates fuel flow from 1/4 to 3/4 throttle, so it’s crucial it’s operating optimally. We may need to swap these out for new ones when we get some data back from our test drives.

Back to available documentation — the closest we’ve come are a set of manuals for other models of Makuni carbs. These appear to be BST40ss carbs, originally fitted as OEM equipment to a Suzuki GSXR bike made sometime between the late 80’s and late 90’s. It’s possible we’ll find some documentation from Suzuki. At least we know we can bring them to a bike shop that services GSX bikes.

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