TURNING A 1991 MUSTANG INTO A PERIOD-CORRECT SUPERCHARGED STREET/STRIP FIGHTER

Back in the spring of 2022, we set out to launch a new project car build that would be the subject of a video series. We wanted to focus on a vehicle that was widely attainable, which at the time meant that it probably couldn’t be something from the original muscle era, especially since we wanted to start with a running, driving example.

However, we knew we could find a subject from the ’80s or ’90s, a time when factory performance was back and on the rise; this is also a period that collectors are starting to embrace. Naturally, we thought of the Fox-platform Mustang, but our $10,000 budget soon proved to be a challenge - good 5.0 cars were climbing right past that point.

Meanwhile, there were still lots of third-generation Camaros and Firebirds to choose from, and while interest was also building for Reagan-era F-bodies, we were able to land one of the more desirable models well within out budget: a relatively clean 1987 IROC-Z with the factory Tuned-Port Injection 350 and most factory options.

From there, “IROC Rehab” was born as a video series, and our two-week-long shooting and wrenching session yielded six episodes that are now live on both the Hemmings YouTube channel and our website, plus we covered the build for Hemmings Muscle Machines.

Attempting to complete projects involving significant upgrades within two weeks’ time while recording video was an ambitious undertaking, yet we managed to pull it off with the IROC, and the payoff was a strong response to the video series, which made clear that nostalgia for a whole new generation of performance cars was mounting.

Finding A Fox

When it came time for a follow up project, we had to reconsider the Fox-era Mustangs. To adhere to a similar budget, we thought we might be able to find a GT hatchback with an automatic, since five-speed LX models are the ones that seem most valued right now. We also knew that automatic cars were more likely to have avoided being heavily modified and thrashed during the 30 years that have passed since they were new.

At the same time, we find that automatic five-ohs also seem to be the ones that didn’t get beat up by speed-crazed youths; Mustangs purchases by people just looking for a fun cruiser were often ordered with the automatic and tended to live easier lives.

After a lengthy pursuit, we wound up with an LX after all, though it was indeed an automatic. It was nearly bone stock, and in very nice condition, but we were not able to squeeze this one into our $10,000 cap and had to dig a little deeper. It was worth it to find a car with no real rust or evidence of previous crash damage, and we really didn’t want something that had already been modified.

Our new-to-us 1991 LX 5.0 had a set of BBK “shorty” headers already installed, which carried an E.O. (exemption order) number, meaning they are considered emissions legal. They are designed to connect to the factory catalytic converter H-pipe, though our car had also been fitted by a previous owner with an “off-road” pipe devoid of cats; we installed a new cat pipe during the project to make it legal again.

Apart from that, the Mustang was as Ford built it, nearly untouched down to the original air cleaner noise baffle. It did have a set of aftermarket lowering springs, though the factory struts and shocks appeared to have been left in place. The car had a nice stance, but the ride quality was terrible. We made a note of it and added that to the list of things to address later.

What To Do?

With a subject vehicle finally in our possession and feeling sufficiently confident that it was a good, sound example with no real maladies, we started to plan our upgrades. We wanted our Mustang to make more power, but we also wanted to relive the days of the Fox Mustang craze back in the ’90s. The decision was made to create a street/strip car incorporating cues from that time, but with the capability to run respectable quarter-mile times while remaining reliable enough for commuting—just like many of these cars had to do back when they were nearly new.

One catch is that, for our “Rehab” projects, time is of the essence. As video-based efforts, these must be completed while the video crew is on hand, and that has meant we’ve had two weeks to get everything done while capturing all the shots needed to produce a six-episode series.

We managed to pull that off with the IROC, but there were still concerns among the team. The consensus was that we should avoid digging into the small-block on this one, as cracking the seal” on a 30-year-old engine for the sake of swapping the cam and cylinder heads seemed like asking for trouble given the tight timeline.

There were other considerations that arose as well. One that surprised us was the availability of some once-common Mustang hop-up bits. We expected that on the IROC, but not the ever-popular Fox. Yet when we tried to get certain items - an upgraded intake manifold for example - the shelves were bare, with no shipping dates even being offered.

So, if we didn’t want to go inside the engine, and we couldn’t get our hands on some of the more effective “bolt-on” upgrades, how could we make more power? The simple answer was forced induction.

Centrifugal superchargers were not a new concept in the ’80s, the advent of the fuel-injected 5.0 Ford gave rise to a renewed interest in this form of power adder. ProCharger was actually late to the game when it launched in the mid ’90s, but that didn’t seem to matter. The company included a twist in its kits, merging a high-efficiency supercharger with the then-uncommon accompaniment of intercooling. While air-to-air intercoolers were frequently being used with turbochargers, they had not yet been a normal addition for belt-driven superchargers. ProCharger’s kit for the 5.0 was highly regarded back in those days, and, though the company has continued to develop and evolve its offerings ever since, that same Fox 5.0 kit remains in the catalog, and it’s even got an E.O. number for smog legality.

That kit seemed the perfect solution to help us gain a significant boost in power without messing with the engine. In fact, this kit is intended to be used on a stone-stock 5.0, and it does not require any custom tuning to the factory engine management. It also doesn’t require any major alterations to the car itself - a few holes drilled to mount an auxiliary fuel pump in the rear, some trimming to accommodate the intercooler, and not much else.

Diving In

We decided to dive into the supercharger installation as the first part of the project, since it was likely to be the most complex procedure. We had taken the Mustang to Twisted Synergy Motorsports in Rensselaer, New York where proprietor Kevin Martin put the car on his chassis dyno to establish a baseline of 186 hp at the wheels.

We then returned to the shop at the Hemmings Garage to delve into the installation, which turned out to be fairly straightforward, as the accompanying steps illustrate. We returned to the Twisted Synergy dyno once the Mustang was back together, before moving on with the Rehab project, and were pleasantly surprised at the results: 306 hp to the wheels with 9 psi of boost (this kit can be further adjusted and turned for up to 14 psi). This was right in line with what ProCharger says can be expected; their low-end gain estimate is 60-percent of the un-boosted horsepower output, and we were seeing 65 percent.

We’ll follow up with a more detailed story on the supercharger installation story in a future issue, but for now, take a look at the steps involved in the first leg of our Fox Rehab project, and then check out hmn.com/foxrehab or visit the Hemmings YouTube channel to view the six-episode video series. Our next update on our Fox Rehab project will cover the rest of the build project, including upgrades to the AOD transmission and to the rear axle.

Fox Rehab, Part 1: ProCharger Installation

Sources

Classic Industries: 800-854-1280, classicindustries.com
POR-15: 800-457-6715, por15.com
ProCharger Superchargers: 913-338-2886, procharger.com
Summit Racing Equipment: 800-230-3030, summitracing.com
Twisted Synergy Motorsports: 518-466-0662, twistedsynergymotorsports.com
U.S. Radiator: 323-826-0965, usradiator.com

2024-04-03T17:16:33Z dg43tfdfdgfd