“We squared the case and we bored the spigot to 92.710 mm,” says Lee. “A stock spigot would be 90.259 mm, but by boring we were able to make the cylinders very thick (for better cooling characteristics).” LN Engineering made cylinders to Lee’s specifications, maintaining a strict tolerance of .0015 mm for cylindricity, circularity, and concentricity.
“That’s a very high tolerance within the world of racing,” says Lee. “By going with a thick-wall cylinder, we also had to bore the cylinder head register to 95.250 mm to fit the cylinder into the head.”
New titanium alloy valve-spring retainers were machined, with Lee claiming the alloy is “approximately 300 percent stronger than stock.” The valves were custom-made in-house using Inconel. Says Lee: “Because it is such a strong material at operating temperature, we were able to make the valve stem a lot smaller than a stock 10-mm stem.” Due to the high operating temperatures of an air-cooled engine, Lee says he also focused on valve-guide materials.
“The old-style valve guide material gets fairly soft at temperature, so the factory valve guide is very long to keep the valve from flexing,” he says. “Using my material, I was able to design a valve guide that doesn’t protrude into the intake runner and the exhaust exit to block flow.” Lee says the challenge lies in selecting a valve guide material with both good stiffness and good lubricity.
HMR also co-developed the connecting rods, partnering with U.K.-based Arrow Precision. Emphasis was placed on precision balancing the connecting rods, as well as the pistons, crankshaft, flywheel, and pulleys. “The stock flywheel and crankshaft can normally be five to nine grams off,” explains Lee, who required component balance within .05 gram. Speaking of mass, he boasts that, between the connecting rods, pistons, and pins, he “shed in the neighborhood of 300 grams per cylinder. That’s a lot of load savings from the main bearings.”
The result of this attention to detail is a smooth-running powerplant that, with a mild compression ratio of 9.8:1, produced 93 hp at 5240 rpm and 113 lb-ft of torque at 4080 rpm on the dyno while running on pump gas. Al wanted to stick with the stock Zenith carburetors, but Lee believes a Weber conversion might yield another 20–30 horses.
A twist of the ignition key in the middle of the dash brings the 1.8-liter mill to life. At first, nothing in the jangling patter muted by the stock-spec Dansk muffler is beyond the ordinary. Even under load, it’s difficult to detect a slightly deeper growl. On the other hand, the 45+percent improvements in power and torque make for a real kick in the seat as the engine pulls solidly throughout the rev range. Through a sweeper, this Porsche feels eminently sure-footed on its Boge shock absorbers, which provide nice damping and smooth lateral transitions.
As the miles pass, you notice the silky smooth nature of the 1.8. Gone is the familiar flat-four massage in the small of your back. Redline is set at 6300, but this foot isn’t about to prod the revs beyond 5250 during a short stint behind the wheel. After the drive, Lee is quick to ask, “Did you take it past six grand?” He’s visibly deflated by the answer, but perks up when the smooth-as-glass powerplant is mentioned. “The more balanced the components are, the smoother the engine is,” he enthuses. “When something is a few grams off at one gravity, it is completely different than when it’s a few grams off and rotating at 5000 rpm.”
As for the Citros, it’s clear that they’re pleased with the results of the near three-year project to resurrect a car that has seen them through their life together. Certainly, digging deeply into some Porsches reveals far more than merely interesting mechanical bits.