When it was introduced in the waning days of the ’80s, the Quad 4 represented a massive step forward for GM. Oldsmobile (along with Batten Engineering and Feuling Engineering) developed the 2.3-liter iron-block, four-valve DOHC aluminum-head powerhouse for the smaller end of its rapidly expanding FWD lineup. Concurrently, a 750hp twin-turbo 2.0 L version made big news in the longtail Aerotech (HRM, Mar. ’87), a full-bodied aerodynamic wonder on a March Indycar chassis that A.J. Foyt piloted to 266-plus mph and the American closed-course speed record at Fort Stockton, Texas.
Production Quad 4s debuted in the ’88 model year. In a day when Oldsmobile’s 307ci V-8 made 180 hp in H.O. trim, a Four with half the displacement and the same horsepower at the flywheel propped everyone’s eyes open with toothpicks. (Base Quad 4s produced 30 hp less.) Why, Ford needed a turbo to get the same power output out of its 2.3L Four. Later, W41-package Olds Calais and Achievas made 190 hp.
Olds went racing with the Quad 4, primarily in IMSA Firehawk and SCCA Showroom Stock, racking up multiple class victories, manufacturers’ class championships in ’89 and from ’91-’93, and promoted its victories aggressively. The IMSA-prepped cars featured non-A/C serpentine belts and other aftermarket tricks, some of which may still be available through the GM Performance Parts catalog and may be adaptable to newer cars; thanks to optimization and a lack of emissions equipment, these engines made roughly 220-230 hp.
Though a success in terms of units built and race victories (and no one ever complained about the power), the 2.3L Quad 4 was bashed by the motoring press for its rough and tumble attitude. As a result, virtually every change made to the Quad 4 has been in the name of improved emissions and greater noise, vibration, and harshness (NVH) suppression. A 1995 redesign decreased bore and increased stroke, bumping displacement to 2.4L; balance shafts smoothed things out, and it had improved lubrication and cooling, plus power output that has stayed at 150 hp despite near-yearly tweaks. The Quad 4 name was dropped when the 2.4L was introduced, and is now referred to as the 2.4L Twin Cam, but for this story we will refer to all engines of this type as Quad 4 and use displacement to differentiate between the two. All inspection was done at Katech Engineering, which worked with Quad 4s in its racing heyday.
Since the Quad 4 has been around for a dozen years, there should be an ample supply in local boneyards. We got together with GM Racing’s Mark McPhail, a strong proponent of front-drive performance, tore a 2.3L and a 2.4L apart, measured the changes, saw what improvements the factory made over time, and figured out what pieces from one engine could work on another. McPhail notes that there were many running changes throughout the engine’s life, and that just because your car is set up a certain way, it doesn’t mean that that parts car you’re pirating from in the yard will have exactly the same ones. “Assume nothing,” he warns.
You can mix and match any number of components (with varying degrees of difficulty), but McPhail feels that the strongest Quad 4 setup would mate a 2.3L head to a 2.4 block, thereby combining the strongest block and the best-flowing head and cams; he would also ditch the balance shafts. He warns that the ’95 engine was a “transitional” engine—a 2.3L with balance shafts—and to avoid it for serious performance upgrades. Also, a single-cam version of the Quad 4 was available in some models; it only lasted a couple of years and should be avoided.
Since it’s not always possible to swap a newer block into an older car (or vice versa, for physical or emissions reasons), we’ve tried to pick out each engine’s strong points so you can choose modifications for your own Quad 4 powered monster. All we need now is an aftermarket to step up and cater to the millions of Quad 4s out there… the GM Performance Parts catalog offers some pieces, but sadly it’s only a fraction of what’s available for popular V-8 applications. Check your GM Performance Parts dealer for availability. Other long-discontinued pieces were once available through the Rocketparts catalog (we saw one dated 1993); these pieces exist somewhere, but you may have to do some digging. Our plan is to get a 2.4L and start playing on the dyno.
