Who says GM isn’t racing? If the Z-28 isn’t a bona fide racing car— in street clothing for this test—then we’ve never seen one. Chapter IV, Touring Cars, Group 2, Appendix J, FIA International Sporting Code requires that 1000 of the Group 2 sedans (more popularly known in this country as Trans-Am sedans) be series produced and that’s the reason for the Z-28’s being. No question that the Z-28 is doing its stuff either: two of them followed two Porsche Group 6 prototypes home at Sebring to finish third and fourth overall and win the Trans-Am category of Sebring’s 12 hours.
Z-28 is a typical Chevrolet code designation for a performance package which adds $400.25 to the basic Camaro 6-cyl coupe price of $2694 and includes a 5-liter (302-cu-in.) V-8, slightly modified spring rates, quicker steering and identification trim. To that $400 is added $100.10 for power-assisted disc front brakes and $184.35 for 4-speed manual transmission. Our test car was equipped with still-quicker (17:1 overall) steering at $15.80, limited-slip differential ($42.15), power steering ($84.30) and a host of such items as interior trim packages, custom steering wheel, deluxe seat belts (!) and a tack-on fiberglass “spoiler” for a total price of $4435. To the basic Z-28 package can be added a whole range of racing parts, available from Chevrolet dealers.
This story originally appeared in the June 1968 issue of Road & Track.
The chrome-trimmed 302 engine is a combination of the 327 block (4.00-in. bore) and the 283 crankshaft design (3.00-in. stroke)— but with a stronger, forged steel crank instead of the cast nodular iron one of the 283 and other “mild” Chevrolet engines. The 302 comes in a rather wild state of tune: its standard camshaft gives 346° duration for both intake and exhaust valves— 118° of overlap. Mechanical lifters and 1.50:1 rockers give a valve lift of 0.485 in; an optional cam provides equivalent overlap with greater lift, but our test car had the standard one. Compression ratio is 11.0:1 and carburetion is by a single Holley 4-barrel rated at 800 cu ft/min. Our test car also had, as its only item from the “dealer” list, a set of tuned headers (installed by Bill Thomas Race Cars, as these are never installed at the factory anyway) which add another $200.The engine makes no bones about its character. It idles lumpily at 900 rpm and has very little torque below 4000rpm, considering the car’s great weight (3355 lb). It does start easily from cold, however, the automatic choke putting idle speed up to something like 1500 rpm; very little mechanical noise is heard from under the hood though the headers give it a nice tingly sound. Getting off the line in acceleration tests the car slews smoothly to the right but, even with the clutch dropped at 4500-rpm, it gets off to a relatively leisurely start until the engine can get up over the 4000 hump. Then, hold on! From there it revs so freely that it seems it could go on forever. We found 7500 to be a good shift point as far as the engine was concerned, but above 7000 (63, 85 and 113 mph in 1st, 2nd, 3rd resp.) the diaphragm-spring clutch became reluctant to re-engage after our rather unmerciful shifts—so we were forced to use 7000. Chevrolet rates this engine at 290 bhp @ 5800 rpm, which may be true as far as it goes, but we think the curve keeps climbing to something more like 350 bhp @ 6200. We even think the torque rating of 290 lb-ft @ 4200 is conservative.
The Z-28 can be had with a range of final-drive ratios from 3.55 to 4.88:1. The standard 3.73:1 would seem best for road use, if anyone seriously contemplates using the car for such; our car had a 4.10:1, probably good for road racing but getting the engine into much noise and vibration at freeway speeds. Fuel economy? Who cares?— but 11-mpg average, if you must know.
The 4-speed gearbox is the familiar and beloved Muncie unit with the not-so-beloved Muncie shift linkage. This example wasn’t as bad as some we’ve tried, but the linkage is stiff and notchy, characteristics aggravated by Chevrolet’s dumb sliding-plate shift lever seal. Fortunately the latter comes only with the optional console, a conventional rubber boot doing the job when no console is ordered. Our test car had the optional close-ratio (2.20:1 1st) box, appropriate for the high numerical final drive. An 11.0-in. clutch with 2450-2750-lb spring pressure (larger and stronger than that supplied with the 396 engine) is still sufficiently light for the average male to operate easily, though as mentioned earlier it does have some trouble at high engine revs.
Though the FIA regulations allow the use of any springs and shocks in racing, the road Z-28 sticks surprisingly close to stock Camaro suspension. The front coil springs (112 lb/in. at the wheel) and 11/16-in. anti-roll bar are left unchanged from everyday Camaro 327s. At the rear spring rates are considerably stiffened: 25% more than for the 396 model, or 131 lb/in. at the wheel. Like the 396, 350 and the 4-speed 327 Camaros (and all Firebirds) the Z-28 uses multi-leaf rear springs instead of the standard Camaro single-leaf ones; this is a necessary move for any engine-transmission combination likely to be delivering great shock loads to the rear axle as the single-leaf jobs don’t do much in the way of controlling axle motion about its own horizontal centerline.
With its E70-15 wide tires the Z-28 is a stable, near-neutral car that has no trouble setting excellent lap times around any reasonably smooth course. The trick with a car like this, with all that torque available in the right gear, is to find that point where you’re using just enough throttle to get it around a turn neutrally rather than plowing or spinning out. Our test car had power steering, which would be a must with all the weight and the 17:1 ratio, but this is so lacking in feel that one has to learn to drive without the help of feedback from the tires . . . and that's not much fun.
Lining material for the Z-28 brakes, otherwise no different from the normal power disc/drum Camaro option, is harder and thus eliminates any trace of fade in our usual fade test as well as putting the pedal efforts up— to the benefit of pedal feel—a bit. Proportioning isn’t good for panic stops in the unladen car: we got only 19 ft/sec/sec or 0.59-g by jamming on the brakes at 80 mph. By controlling them carefully we got up to 24 ft/sec/sec. Again, FIA rules allow changes that will make the brakes more satisfactory, and special parts are on the dealer option list.The stiffer rear springs (which also add frictional harshness over single-leafs) and the tighter shocks that come with the package do give the Z-28 the general sort of ‘'clumpity-clump” ride we've come to expect of Pony cars with handling packages, and the unit body of the Camaro isn’t as resistant to rattles and squeaks as its weight would indicate. But the ride isn't super-stiff either and we found it to be generally acceptable. We can say little about the driving position or comfort that we haven't said over and over about Pony cars; the steering wheel is close, the seats mediocre and not adjustable for back angle, vision to the front excellent (except for a too-high, too-long hood) and to the rear poor; the minor instruments, add-on options, not well placed for reading; excellent heating and ventilation, aided here by air exits in the doorjambs. The separate lap and diagonal seatbelts generally adopted by Detroit this year (including this Camaro) are bothersome to use and messy to not use; we presume this will be taken care of in a year or so when the designers get around to putting a little ingenuity to the problem of passenger restraint.
Surprisingly enough, the usual Chevrolet warranty— 2 years or 24,000 miles on the car in general and 5 years/50,000 on the drivetrain—applies to the Z-28. Servicing is needed only every 6000 miles, and there’s enough room around the compact engine that the enthusiastic owner won't be discouraged from a little tuning on his own. The car is straightforward throughout.
The Z-28 offers a lot of performance for the money; how many 4-seat cars can you name that will do the 1/4 mile in 14.9 sec, hit 142 mph and cost just $4435? On the other hand, it’s not what we'd call "tractable"’ and, despite its stability and performance, it’s pretty clumsy to drive. However, Chevrolet obviously achieved what they set out to do—namely, build a race-winning Trans-Am sedan.