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1985 Chevrolet Camaro IROC-Z28 - A Big Impression

James Hoffman’s blown LS1-powered IROC proves inspiration starts early and runs deep

Barry Kluczyk Dec 17, 2013
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Like so many of us, James Hoffman's affinity for a specific car was forged at an early age. For him, it was the iconic Camaro IROC-Z when he was only 16. Rather than a gleaming example seen under the lights at an auto show or watching an older neighbor's pristine example cruise down the street, Hoffman's infatuation was instigated by a trashed car.

 Chevrolet Camaro Iroc Z28 2/8

"It was a black-and-gold IROC-Z that a local dealership had sitting on the lot," he says. "It was actually a theft recovery, and it was in rough shape. The glass was broken out of it, the locks were punched in, and the dealership was repairing it. I drooled over the car for days. From that, I always knew I'd have an IROC someday, but couldn't afford one at the time."

Not surprisingly, finances – more specifically, the lack thereof – prevented young James from purchasing the IROC of his dreams, so he made due with a 1982 Z28 Indy pace car replica that was in admittedly sad shape.

"I spent a lot of time and energy fixing that car up," says Hoffman, an engineer, who lives in the western Michigan town of Lowell. "I developed the ‘bug' for working on my own cars during that project and things have never been the same. I sold that car a couple years later and have regretted it ever since."

A couple years later, he stumbled on a white 1985 IROC-Z in the local classified ads and bought it. He took the car to a car show and met Doug Warren, president of the Western Michigan Camaro Club, who chased him down to discuss Hoffman's IROC. Warren passed away in 2010.

"Doug laid the foundation for me to become a Camaro nut to the core," says Hoffman. "He was a walking encyclopedia of Camaro knowledge and also owned a white 1985 IROC-Z. He explained to me how rare they were, because it was a mid-year color introduction."

1985 Chevrolet Camaro Iroc Z28 Side 3/8

Rare or not, it wasn't long before Hoffman cracked into the virgin, 65,000-mile Camaro's powertrain. The original 305 engine and 700R4 trans were tinkered with at first, giving way to a 400 small block that, because of an incompetent machine shop, was not long for this world. Discouraged by the failure of the 400, Hoffman eventually doubled down with a healthy 350 Tuned Port setup. He also swapped the 700R4 for an LT1-based T56 six-speed manual.

The warmed-over TPI motor served the IROC well for several years, while Hoffman concentrated on other aspects of the car, such as switching out the original blue-gray interior to all-black, along with a nice set of fourth-gen Trans Am leather seats, which bolted right on the stock mounting points. He also upgraded the inadequate third-gen brakes to a set of LS1 binders, using conversion brackets he made himself, and bolted on a set of two-piece billet wheels.

 Chevrolet Camaro Iroc Z28 4/8

As time passed, the 350 engine's performance remained strong, but its high-compression configuration, and other factors, made it a compromise for daily driving.

"The engine always ran warm and was not enjoyable in traffic – and even with the six-speed, it was only good for about 12 mpg," says Hoffman. "I didn't feel comfortable driving the car back and forth to work, or taking it on road trips, and my goal was to put together a fast, very streetable car that could hang with most, if not all, of the late model cars coming out of the factory. The 350 was good, but it just but left me wanting more refined performance, and definitely better fuel mileage."

As fate would have it, the 350 consumed itself on the drive home from a cruise event, prompting Hoffman to immediately confront his next powertrain decision: Enter the LS1.

1985 Chevrolet Camaro Iroc Z28 5/8

"I kicked around the idea of swapping in an LS1, but at the time it wasn't a common project. A friend of a friend caught wind that I might be in the market for an LS1, and told me about a great deal I could get on a new LS1 crate engine sitting in another guy's garage," he says. "Luckily, I had another friend who was a dealer for TREMEC, and he was able to score me a new LS1-style T56 at cost. After gathering up all the other necessary parts, the fun began."

The engine was installed in stock condition, and the 350-horsepower LS1 immediately transformed all aspects of the car's performance, from acceleration to the handling dynamics, that came with removing about 100 pounds off the nose of the car with the all-aluminum engine.

"I had never driven an LS1-powered car until the first time I took my car on its maiden voyage," Hoffman says. "It is immediately clear that I'd made the right choice with the swap, but I was not prepared for the high-rpm power and actually hit the LS1's rev limiter so quickly, I thought I broke the motor."

The Camaro's original 10-bolt wasn't up to the performance dynamics of the newly LS-ized IROC, and it retired with a vengeance at the drag strip. Hoffman unceremoniously swapped it for a Moser-based 9-inch setup. It was fitted with 4.11 gears, which the high-revving LS1 enjoyed, returning neck-straining acceleration and up to 30 miles per gallon on the freeway.

 Chevrolet Camaro Iroc Z28 6/8

Of course, great performance becomes only adequate after you get used to it, so it was only natural that Hoffman began to explore enhancement options for the LS1. The heads-and-cam seemed the logical route, but he also started looking at forced induction.

"I wanted more power, while retaining reliability, drivability and the good gas mileage I was used to," he says. "After looking at centrifugal blowers, I decided to follow GM's lead and went with a positive-displacement supercharger. I wasn't chasing peak horsepower numbers, but instead wanted to bolt something on and never touch it again. Also, the instant torque at any rpm level was appealing for a street car."

Because there isn't a blower kit for LS1s in third-gen F-cars, Hoffman adapted Magnuson's Eaton rotors-based kit for the LS1 GTO. He ordered the kit with 1:1 rear pulleys, so he could run a larger pulley up front and avoid belt slippage. He also upgraded to a 92mm billet throttle body, with a remote idle air control circuit (IAC), which allowed the setup to fit under the hood without clearance issues.

When the blower was installed, the car was delivered to Baker Engineering, in Nunica, Mich. ( for dyno tuning. It put down 450 horsepower and 440 lb-ft. of torque to the rear wheels.

"The performance is terrific," says Hoffman. "The car still manages to pull down 28-29 mpg on the highway, as long as I stay out of the boost. It also idles and runs like stock, never runs hot, and starts every time. Basically, you'd never know the blower is on the car until you hit the gas and the bypass slams closed."

If there was a downside to the supercharged engine's broad torque curve, it was the inadequacy of the 295-series rear tires to maintain their grip on the pavement. Unfortunately, that's about as wide as you can go on a third-gen F-car.

 Chevrolet Camaro Iroc Z28 7/8

"I had seen some guys use a fourth-gen mini-tub kit in these cars, but didn't like the idea of losing the rear seats and cutting up the interior panels," he says. "My wife, Carrie, and I also had a baby on the way and knew I would need the rear seat and seat belts. So, after some careful measuring and calculations, I decided to fabricate my own mini tubs."

The homebuilt tubs added about 2.5 inches of much-needed clearance inside the rear fenders, enabling 335-series rubber to tuck with factory-perfect clearance. In fact, you really have to look twice at the width of the rear tires before you suspect there have been internal tweaks to the sheet metal. Hoffman paired the wider rubber with a set of forged, three-piece 18-inch wheels that have a deep concave profile, emulating the design of the original IROC wheel design, but in a more contemporary form. The fronts measure 18x9 inches and rears are 18x12. No, they weren't cheap, but the appearance is priceless. The car looks great with them.

The wheels complement a reserved exterior that retains the factory profile of the original IROC, save for some shaved moldings and stripes. It also uses a stock fourth-gen cat-back exhaust, for a factory appearance, and a sedate exhaust note. And because no project is truly complete, Hoffman plans on upgrading the brakes again, with 14-inch rotors and six-piston calipers. And we'd be surprised if, after a little more time with the blower motor, he doesn't sneak in even more engine mods.

All this from the impression left by a trashed Camaro more than 20 years ago. It's a good thing he didn't stumble on a beat-up LeCar back then, because LS1 swap or not, there's no such thing as "Renault High-Tech Performance" magazine.

1985 Chevrolet Camaro Iroc Z28 Rear 8/8

Data File

Car: 1985 IROC-Z28 Camaro

Owner: James Hoffman
Block: GM crate LS1 (346 cid / 5.7 liters)
Compression ratio: 10.1:1
Heads: Stock LS1
Cam: Stock LS1
Pushrods: Stock
Rocker arms: Stock
Pistons: Stock
Rings: Stock
Crankshaft: Stock
Rods: Stock
Throttle body: 92mm custom billet with remote IAC
Fuel injectors: 42 lbs/hr
Fuel pump: Walbro 255 lph
Ignition: Stock
Engine management: Stock LS1 PCM Tuned by Baker Engineering
Power adder: Magnuson MP112
Boost: 6.5 psi
Intercooler: Stock Magnuson heat exchanger/intercooler
Exhaust system: Stainless Works 1-3/4-inch Long tube with 3-inch Y-pipe and fourth-gen F-body cat-back outlet
Transmission: TREMEC T56
Clutch: GM LS7
Driveshaft: 3-inch chrome-moly
Front suspension: Koni Red adjustable struts; cut IROC springs
Rear suspension: Koni Red adjustable shocks; QA1 150-lb. mini-coil spring, adjustable perches, custom-fabricated mini tubs
Rear end: Moser 9-inch with 4:11 gears and Trac-lock Posi
Brakes: LS1 Camaro front and rear, with drilled/slotted rotors
Wheels: Custom one-off deep-concave profile, 3-piece forged aluminum with hidden hardware
Front tires: Toyo R888 P265/35R/18
Rear tires: Toyo R888 P335/30R/18
Fuel: 92-octane
Race weight: N/A
Best ET/mph: N/A
Best 60-ft. time: N/A
Current mileage: 95,000
Miles driven weekly: 15



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