IROC-Z vs Z28: What Actually Separated Them

The full run of the car, launch to last year, is covered in the IROC-Z story, and there is more on that here. This one is narrower. What did the extra money buy, and how do you tell the two apart on a driveway today?

IROC-Z vs Z28: one car, one option box

Start with the code. The IROC-Z package was RPO B4Z, offered on the Z28 from the 1985 model year and named after the International Race of Champions. It was not a separate model from 1985 to 1987. The package price in 1985 was $659. One later source puts it at $696, so if you see that number on a forum, that is where it came from.

Buyers took it in a big way. In 1985 the IROC-Z was about 31 percent of Z28 sales, 21,177 cars. In 1986 it was 49,585 cars, about 56 percent. By 1987 it was 38,889 of 52,863 Z28s. Do the math and that is roughly three out of four. The option had become the car.

Here is the part that trips people up when they shop. The VIN does not tell you which one you have. From 1987 the series letter is P for every Camaro, and Z28 and IROC-Z are option codes (Z28 and B4Z), not VIN codes. The engine digit in the VIN helps. It will not prove the package.

What the B4Z money bought

The IROC-Z was a handling package first, and the parts list reads like one. Over a 1985 Z28, the B4Z added:

The Z28's own wheel and tire size and the exact anti-roll bar diameters for both cars are not settled in the records I trust, so I am not going to quote them. What is settled is the direction. The IROC-Z sat lower, rode on wider rubber, had better rear shocks and a brace tying the front structure together. It cornered harder and rode rougher. Anyone who has driven one on a broken road will confirm the second part for free.

"Half an inch lower, bigger bars, Bilsteins and fat tires. That is the IROC-Z. The rest is stickers. Pay for the parts, not the door decal."

Mike Sullivan

Where the engines split

For most buyers the engine choice was the same on both cars. In 1985 the LG4 four-barrel 305 and the LB9 Tuned Port 305 were on both the Z28 and the IROC-Z. The LB9 was rated at 215 hp that year. The exception was the L69 305 H.O., which was offered only on the IROC-Z, only with the five-speed, for $680. Chevrolet built 2,497 L69 IROC-Zs for 1985, about 12 percent of that year's IROC-Z run. If someone sells you an L69 plain Z28 from 1985, ask questions.

The bigger split came for 1987. That year the L98 350 with Tuned Port Injection arrived, ordered as RPO B2L for $1,045. It was rated at 225 hp and 330 lb-ft, and it was IROC-Z coupe only, automatic only. A 1987 Z28 without the B4Z package could not have the 350 from the factory. So a 1987 "Z28 350" with no IROC equipment is either a swap or a story.

1988 to 1990: when there was no Z28 to compare

For 1988 Chevrolet dropped the Z28 as a model. The IROC-Z content became the top car's content, and the lineup was the Sport Coupe and the IROC-Z, coupe and convertible. The fair way to say it is that the IROC-Z replaced the Z28 for 1988 to 1990. Chevrolet built 24,050 IROC-Z coupes and 3,761 IROC-Z convertibles for 1988. The details of that shuffle are in our piece on the 1988 lineup change.

One wrinkle from that year matters if you are judging a car by its wheels. For 1988 the IROC-Z came on 15 in wheels as standard, and the 16x8 wheel became an option, N96, at $468. So a 1988 IROC-Z on 15s is not automatically a car that lost its original wheels. A 1985 IROC-Z on 15s is a different conversation.

The IROC-Z ended with the 1990 model year, when Chevrolet did not renew its deal with the race series and Dodge took over. For 1991 the Z28 came back as the range-topper and the IROC name was gone. That makes the comparison a 1985 to 1987 question. After that it is IROC-Z or nothing, and then Z28 again.

Telling them apart today

Decals are cheap. Wheels are easy to swap. Fog lamps and rocker extensions are parts you can buy. None of that proves anything. What proves a car is paperwork showing the B4Z code, and hardware that matches it underneath.

Asking prices will tell you the market cares about the letters. Fine. Pay the premium when the paper backs it, and treat a Z28 dressed as an IROC-Z like what it is: a Z28 with nicer stickers. A real IROC-Z from 1985 to 1987 is a better-handling Z28. That is the whole difference, and it is enough.

Sources and notes

• Chevrolet Camaro (third generation), Wikipedia: IROC-Z chassis content, L69 count and 1988 wheels
• Eighties Cars: the 1985 Chevrolet Camaro IROC-Z, B4Z content, engine split and share of Z28 sales
• Hagerty: IROC-Z, when the Camaro got its mojo back
• Muscle Car Facts: 1987 Camaro, L98 and IROC-Z production
• Camarotech: 1987 Camaro VIN and RPO codes, including B4Z and B2L
• Conceptcarz: 1988 Camaro lineup and production by model