You may or may not know about the Polaris RZR Pro R and its status as the most powerful factory side-by-side out there. It makes 225 horsepower at the crank from a naturally aspirated, 2.0-liter four-cylinder, which is crazy for a stock rig that weighs less than a ton. It's still not enough for some folks, which is why LaRue Performance decided to boost one with compound turbos, E85, and plenty more. Now it makes 643 hp at the wheels, with the potential for way more.
That's a bunch, especially when you learn that's with the stock block, head studs, and a single turbo. Owner Matt LaRue tells me they've cranked the boost up to 35 pounds with no issue, logging roughly 20 dyno pulls at 600+ whp. It uses Brian Crower rods, pistons, camshafts, valve springs, and retainers, while LaRue handles the ECU tuning in-house. They haven't broken the 643 whp figure with the compound setup quite yet, mainly because the intercooler is maxed out in terms of flow.
LaRue wouldn't reveal the exact turbo setup, but he mentions the larger of the two measures 80 millimeters. The compounds apparently cost $6,000 on their own, and while he plans to sell a similar kit in the future, it won't be cheap. LaRue Performance's entry-level RZR Pro R turbo package starts at $8,000 for reference, and it makes 340 whp on 110-octane race gas. This is a clear step up.
"It'd be awesome if we had a motor dyno so we can see what it's really doing at the crankshaft because it loses a lot at the tire," LaRue explains. "We see a 30-35% loss if, from the factory, they make 225 hp. We haven't had a car here make over 165 whp stock."
LaRue notes that they're able to extract a bit more by aligning the rear tires. It almost doesn't matter what goes on with the front tires because they seem to rarely touch the ground. Whether it's on asphalt or sand, the UTV tilts skyward with the throttle pegged. Clips of the Pro R at the dunes show it ripping huge wheelies, and LaRue says it was turned all the way down there with about 100 fewer hp.
It doesn't stop here, either. LaRue is working on eclipsing 700 whp next and then moving on to power levels that rival the world of highly built street cars.
"We're targeting Honda [K20] power numbers. That's definitely bigger [than what we have now]," LaRue admits. "I don't know, as far as motor construction, how a K20 is built compared to a Polaris motor but it's doing pretty good if we're at like 640 whp and we're still on the stock head bolts. I don't know if that's tune related because we've blown up a lot of RZR motors in the past, so we have a pretty good idea of what's going on there."
No matter where this build ends up for power, it's already extremely impressive. It's one thing to swap in a more powerful engine from another make and model, but modifying the factory Polaris unit to this point makes the build even more special if you ask me. These guys are finding the limits of the stock platform, which I'd wager are way higher than most people thought in the first place.
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