How a Hot-Rodder Home-Built a Twin-Turbo V12 From Two Toyota 1JZs
https://youtu.be/19LVlU6AEnUThat's exciting in itself, but it becomes far more enticing when you learn a little more about it. See, this V12 engine was made by melding two Toyota 1JZ 2.5-liter turbocharged inline-sixes together at the crank. And it was almost entirely home-built by a long-time hot-rodder with unconventional tastes and amazing fabrication skills.
"Pure, blind, dumb luck," Don Groff tells me over the phone. The 71-year-old retired designer of manufacturing equipment is explaining how, and why, he turned two straight-six motors into one 5.0-liter V12. "I didn't want a huge cubic-inch motor," he told me, "and I realized those motors breathe really well—guys can turbo them and get a lot of power out of them."
So without doing much in the way of investigation or measurement, Groff picked up twin 1JZ engines yanked from early-'90s Toyota Supras, cut the blocks just above the oil pan gasket surface, and scratch-built a new crankcase out of TIG-welded 3/4-inch steel. "Where I got lucky is the head bolt pattern is symmetrical," Groff tells me. "You can flip the head end-for-end. There are 13 oil drain-back holes in the block. Those are what I used to bolt the cylinders to the crankcase.
"I didn't know any of that when I bought the motors. I just got lucky."
Groff wanted even firing pulses and inside-the-vee exhaust routing—the latter to let folks know immediately that this wasn't a factory production V12. These design considerations meant angling the cylinder banks 120 degrees apart. He mounted the right-side cylinder head backwards, modifying it so the cam gears stayed at the front of the engine. Groff laid out a new crankshaft, each rod journal now carrying two connecting rods instead of one, with oiling details and machining handled by Scat.
"If I had it to do all over again, I might have made it a 90-degree vee, odd-fire motor," Groff says. "I didn't know until I committed to what I did, that Ferrari V12s are a 75-degree vee and odd-fire. That might be why they sound so good."
Most folks start an engine project with a clear idea of the vehicle it's going into. Groff went about it the other way. "The motor came first," he told me, explaining that his original plan called for an offset drivetrain sitting side-by-side with the cockpit. While working on chassis design, he determined the engine was far too wide for an offset layout. What resulted was the mid-engine open-wheel single-seater you see here, the engine attached to a Corvette six-speed manual transaxle. Aside from some precision machining of the engine blocks and heads, and a custom wiring harness and initial ECU programming by Nth Moto, every piece of the project was done by Groff himself.
"This is kind of seat-of-the-pants engineering," Groff says.
The target is 800 horsepower. Each 1JZ made around 300 hp stock; roughly 18 lbs of boost from the twin Garrett GTX turbos and an E85 tune should meet the power goal, no problem. "It'd be nice to brag about 1000 horsepower, but there's no reason to do that other than talk," Groff says. "You can't hook it up and you can't drive it anywhere near safe. Eight hundred was just an arbitrary target that I thought would run good and let the parts live."
As for how he plans to use the open-wheel V12 dream machine? "I'm basically gonna chug around the neigborhood and around town," Groff tells me. "I didn't build it to any track or race organization's spec, so I question if they'd ever let me go around a track at any kind of speed."
It's a project that's been eight years in the making so far. That doesn't surprise Groff: "I figured it'd be 10 years total, and I'm not gonna be far off that," he told me.
"I just love to build stuff. The whole project makes no sense, except it's what I wanted to do. It makes me happy. Bottom line, that's all that counts. I didn't think the world needed another '32 Roadster."