May 29, 2014 at 1:00 am

A lap of Belle Isle. . . with an IndyCar star

0 to 60 with IndyCar driver Ryan Briscoe
0 to 60 with IndyCar driver Ryan Briscoe: Auto critic Henry Payne joins Briscoe for a lap around the Belle Isle track.

Belle Isle’s State Police speed patrol is taking the week off.

Once a year, the Chevrolet Detroit Belle Isle Grand Prix converts the island’s sleepy, 20 mph speed limited web of roads into an IndyCar racetrack, where speeds reach 170 mpg. Concrete highway barriers topped by fences line either side of the roadways, converting 2.36 miles of uneven asphalt into a makeshift road course.

Common two- and three-lane park roads become a high-speed tunnel of concrete that would make a Cedar Point roller-coaster veteran smile.

Courtesy of a Chevy track preview day for media, I strapped into the passenger seat of a 426-hp, 6.2-liter, 2014 Camaro SS with IndyCar star Ryan Briscoe for a hot lap through the 14-turn tunnel.

Jinking through the fast, Turn 1-2 complex, the 4,100-pound muscle car flirted with lateral 1.0 g-forces before vaulting onto the main straight at 110 mpg, then braking hard for Turn 3, a 90-degree right-hander.

This weekend, Briscoe’s average lap time around Belle Isle will be 105 mph.

He will navigate the same turns in a Chevy V8-powered, 650 horsepower Dallara chassis, pulling a neck-bending 3.5 g-loads (forces equivalent of 3.5 times his body weight) through the first two turns before pegging the speedometer at 170 mph down the Turn 2-to-3 straight. On the binders into Turn 3, he will experience 4 g of horizontal braking, his eyeballs straining to pop out of his head.

Like a bowling ball hurtling down the local lanes, the brutish Camaro squalled and yawed from corner to corner on the constantly turning course. Belle Isle affords little breathing room as only the 2-to-3 straight is actually straight. The high-speed back and front straights are sustained curves that test car balance and driver courage as competitors try and time passes through very small braking windows.

Flogging the SS, Briscoe kept up a steady chatter with me as he explained the track and its perils. His favorite part of the circuit?

“The last two corners are quite tricky,” explains the 32-year-old Aussie. “It’s quite shaded there so it’s (got) lower grip. But they are quite fast, especially Turn 14 onto the front stretch. It’s always so slick it’s easy to tag the wall.”

Not to worry in the Camaro. Because he’s less familiar with the SS equipment, open-wheel driver Briscoe drove conservatively around the Belle Isle course. “I don’t’ want you to vomit in the car,” he told a fellow scribe. “But by the time I get back, I’d like to see you fall out of the seat.”

Andy Pilgrim was a different story.

The veteran sedan racer drives a Cadillac CTS-V in the Pirelli World Challenge Series (an IndyCar support race this weekend). He was intimately familiar with his media-day steed, a 6.2-liter Caddy, and he held nothing back. An F18 fighter pilot pal once told me his goal on media days was to make the accompanying journalists lose their lunch.

As a 25-year racing veteran, I found Pilgrim’s hot laps a blast. But I can’t help but think a few of my colleagues might have been green around the gills afterward.

As entertaining as the sedan laps were, however, it’s barely a simulation of the brutal, 70-lap, two-hour, twin marathons Briscoe and his comrades will endure this Saturday and Sunday.

The Belle Isle GP is a sponsorship sellout this year with ticket sales running 7 percent ahead of last year for good reason: The racing has gotten better. Adding the Turn 2-to-3 straight has brought a needed passing zone, and the dual Saturday-Sunday race format doubles the action for spectators. It also doubles the stress on drivers.

“We lose weight (in the races),” says Briscoe. “I’m a little guy, but I probably lose 5-6 pounds.”

The twin bill tests these fit car jockeys just a week after their marquee oval race, the grueling 500 miles of Indianapolis.

“You come here and there’s not one thing in Detroit that is like the Indy 500. They are so different,” says Briscoe. “Indy ... is extremely mentally draining. It’s a long race — three hours at 220 mph and you’re that close to disaster corner after corner. You finish the Indy 500 and you are destroyed. Around here, it’s more the physical aspect that is going to drain you. And having the double header complicates that.”

With increased horsepower this year over last, Briscoe expects faster lap times even as the Dallara chassis hasn’t changed. Hmmm. I hear the Indy Racing Experience offers rides in two-seater IndyCars at Indy. Maybe they’ll bring one for Belle Isle media day next year?

I always wanted to know what 3.5 g felt like.

Henry Payne is auto critic for The Detroit News. Find him at hpayne@detroitnews.com or Twitter @HenryEPayne.

IndyCar driver Ryan Briscoe, prepping for this weekend's Chevrolet Detroit Belle Isle Grand Prix, will average 105 mph in the race. / Steve Perez / The Detroit News