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Redline Update: Supercharged Slant-Six Dyno Struggles
If you’re unfamiliar with Hagerty’s Redline Rebuild Slant-Six, Davin Reckow and the Redline Rebuild crew saved a rare, aluminum-block Slant-Six they pulled from a barn-find wagon. Due to its presumed low mileage, it was cleaned up and given some fresh rings and bearings. Before it was freshened up, the team put it on the dyno for some baseline numbers, and it produced 120 hp and 173 lb-ft of torque. Now, with a new hone on the cylinders on the inside and some beautiful paint on the outside, it was back to Apex Competition Engines to see how things shook out. “Things didn’t go exactly as hoped,” explained Davin, noting that the engine keeps running rich and output is actually down to 108 hp. From where we were sitting, that paint job should have been worth at least 10 hp.

Davin and the Redline Rebuild crew had bigger plans for the little wagon, and the aluminum block was probably not the right foundation, so they sourced an iron block to build a rowdier version that would wake up the long roof. To keep things moving, and finally have some long-awaited results, they hooked up the more powerful engine to the dyno to break it in and sort out the numbers.
The iron-block version is fitted with a TorqStorm centrifugal supercharger along with a four-barrel carb to help keep up with the air and fuel demand. First, the fresh engine was fired up and run for 20 minutes to get the cam and lifters the proper break-in. Aside from some timing issues that had to get sorted out and a small leak in the oil pan, the cam break-in went as expected and the engine was given some time to cool down.
Next up, the guys plumbed the carburetor hat so the supercharger boost could be put to good use. The first try saw the engine going lean once it got past 4,000rpm, so larger main jets—number 75 jets in place of number 70s that they started with—were installed in the metering block. It took lots of tweaking and a full day on the dyno, but the results were worth it.
“You’re always chasing your tail on how to tune something. . . You make a change so it should be going where it’s going and it goes the other direction. . . Well that’s exactly what we’ve been fighting all day,” said Davin.
The Redline Rebuild crew was hoping for about 10 pounds of boost from the TorqStorm supercharger but they were only seeing eight. Despite that modest output—the supercharger could be spun faster for more airflow—the combination of added boost, the hand-ported head, and improved exhaust all added up to more than double the output compared to the factory rating. The leaning tower of power now produces over 340 horses, and that’s at just 5100rpm!
There will be more to come from both engines, as Davin is already scheming up a smaller supercharger pulley to get a couple more pounds of boost out and really give the wagon powerplant a shot in the arm.
My ex put 220k miles on a ’70 Valiant until the iron ants ate the body. She said the car never used oil. Bought brand new for a dollar a pound, sold for scrap 90% less.
One wonders how well the EFI from a 4.0 Jeep would work on that Aluminum motor.
My first car had a 225 slant 6. I loved that car, 67 Barracuda, drive it 110,000 miles after a full rebuild of the engine. Never let me down. First car and first engine rebuild, I barely knew what I was doing but it was unkillable. Good memories.
We had a ’66 Dodge Dart with 225 slant six. Traded it in after 230k miles. No issues ever. Great car.
I did some studying in college on AC fluid flow. Not enough to be an expert, but enough to know it exists. The math is similar to electrical circuits, but it is a lot harder to model realistically. I suspect that unpredictable AC effects hamper a lot of performance builds, and that crazy manifold is bound to be loaded with them