Horse Sense: Most discussions about turbochargers indubitably include some reference to a turbo's size— in millimeters. For those who have always wondered exactly what area of the turbocharger this metric measurement refers to, it's actually the inducer diameter of the unit's compressor wheel. That's the diameter of the point where air actually enters the wheel.
This question is for all of our die-hard Fox fans. How many of you occasionally find yourselves mulling over the idea of parting ways with your beloved '86-'93 GT or LX, simply because the lure of newer models is so strong?
Let's be real about this. While there are all sorts of upgrades that help make them more comfortable as they go on in years, the early cars will never match the tightness and plushness of later Ponies. And, with the Coyote, Roadrunner, and Trinity engines nestled under the hoods of the coveted '11-'14 'Stangs, the choice between keeping your 20-something-year-old friend or opting for a younger thoroughbred can be a bit intimidating.
However, despite the performance-and-aesthetic plusses of the newer rides, at the end of the day, cost is often the critical factor in electing to either step up or stay put. The latest Mustangs deservedly garner a pretty handsome sum. When you factor in the tab for modifying a later-model Pony, you're looking at potentially handing over a lot of bread.
Of course, such investments certainly are worth it in most cases. But, when your budget won't support making such moves, there still are a lot of cool options for making a Fox worth keeping. One option that hit our radar is a twin-turbocharger setup from CXRacing. This SoCal-based company recently starting making moves in the Mustang game after many years of forced-air-inducting sport compacts and intercooling anything on wheels that's fitted with forced induction.
Of course, the concept of adding a pair of turbos to a pushrod-5.0 'Stang's engine is nothing new. However, until now, we haven't seen a complete intercooled turbo system for as low a price as the kit we're working with in this report.
When considering turbos, the bigger-is-better adage doesn't completely apply for the street 5.0s. Even with 331ci and 347ci engines that can support huge 88mm, 94mm, or 101mm turbochargers, bolting those behemoths on daily driven Mustangs doesn't accomplish much. The amount of time it takes for sufficient exhaust pressure to build up in bigger turbos results in turbo lag. Subsequently, boost, rear-wheel horsepower, and torque don't truly come into play until you're going well over any legal speed limit, making the big-single setup much more appealing for 'Stangs that are purpose-built for quarter-mile action.
While a matched pair of smaller turbos (65mm to 76mm) may not produce as much boost as their giant single counterparts, they might sacrifice some top-end power, but they definitely will spool much quicker and still can provide the engine with a sufficient amount of air. This actually makes going with two small hair dryers a much-better option for a street-centered '86-'93 'Stang that no doubt would be a lot of fun to drive when boost and peaking well before 6,000 rpm.
Priced at just a nudge over $2,000, CXRacing's twins set (PN TRB-KIT-MUSTANG-TT-GT35-2-IC; $2,089) is one of the lowest-priced, Fox-specific, bolt-on turbo kits. And in July 2013, CXRacing owner Kevin Xie gave us an exclusive opportunity to evaluate his company's affordable twins, using Greg Montoya's '84 Mustang LX coupe.
Before your Melvin instincts get the best of you, no, the turbo set isn't designed for carbureted 'Stangs. Despite its pre-EFI build date, Greg's sleeper is retrofitted with a 306ci short-block and a complete replica '93 Cobra EFI setup (mass-air, GT-40 heads, Cobra intake, and so on), a big reason why we selected the Pony for this upgrade. The new-tech-for-old-'Stang concept is taken another step further with the removal of the coupe's engine-management and replacement of the EEC-IV hardware with Holley's Dominator EFI system.
Keep reading to see the install performed by CXRacing's Ascension Sanchez and Rene Franco, and learn the details on tuning the turbocharged 306 using Dominator EFI (and the all-important dyno results, of course), all of which can revitalize an old Fox with cool technology for modest cost.
Ascension Sanchez (right) and Rene Franco hang a pair of CXRacing’s turbos on the 306 in Greg Montoya’s ’84 coupe. While installing CX’s Fox-specific twin set may be a bit much for novice ’Stangbangers, the kit’s intuitive design and good fitment will allow mechanically skilled enthusiasts with appropriate workspace and tools to bolt on the system.
This is the eye-catching promotional photo that piqued our interest in working with the CXRacing twin-turbo kit for ’86-’93 ’Stangs (PN TRB-KIT-MUSTANG-TT-GT35-2-IC; $2,089). The system was developed completely in house by Rene using a convertible ’Stang that company-owner Kevin Xie says was purchased specifically for producing the twin set, as well as a big-single turbocharger kit for Foxes. “When we come up with a new turbo idea for a particular vehicle, we go out and buy that exact car before any pieces are made. Having a live model to work with gives Rene the best opportunity to create jigs and templates for our turbo-systems’ tubes that are spot-on accurate, and as such, can be duplicated by our own people—not outsourced—to ensure proper fitment in our customers’ cars.”
The once-carbureted, stock-block 5.0 in Greg’s coupe now displaces 306 cubic inches and benefits from a ’93 Cobra-style induction upgrade (GT-40 heads, Cobra intake, and E303 camshaft).
With a plan to start on the project right away, we turned to our friend Mario Nadel of M&M Towing Service for assistance with transporting the test Pony to CXRacing’s headquarters.
Twin-turbo installation actually starts with the removal of several parts, the most-notable being the ’Stang’s front bumper cover, which must be modified before it is reinstalled.
Headers are also taken out for replacement by CX’s 15⁄8-inch, stainless-steel turbo headers.
If the Mustang still uses a stock K-member, raising the engine slightly to facilitate removing the oil pan is one of the project’s few heavy-lifting requirements.
Engine oil is used to ensure the twin turbochargers are well-lubricated and properly cooled. The oil is sourced directly from the engine (oil filter housing), and is returned to the oil pan afterward via a hose and fitting that must be welded into the pan.
Here’s a comparative look at a basic, upgrade header for Fox Mustangs (top), and CXRacing’s stainless-steel turbo header. Like the bolt-on short-tube, turbo-swap tubes also measure 15⁄8 inches and are designed for standard-port cylinder heads.
Rene bolts the new turbo headers in place using CX’s high-heat exhaust gaskets, which are included with the system.
Both of the kit’s 65mm turbos sit on T-3 housing flanges, which measure 2x2.5 inches. Single-turbo systems typically use turbochargers that require a T-4 flange, like the one that’s shown here (top) for comparison, which is approximately 0.25-inch bigger.
CXRacing uses a pair of oil-cooled T-3/GT35 single-ball-bearing (compressor)/journal-bearing (turbine) turbos that are capable of producing 25 psi of boost. The hair dryers feature 4-inch air-inlet (w/anti-surge venting) and 2.5-inch discharge portals, a 61.3mm (inducer)-by-82mm (exducer) compressor wheel, 62mm (inducer)-by-67.8mm (exducer) turbine wheel, and turbine A/R of 0.82. This tight A/R helps the units spool quickly. The anti-surge shroud on the compressor housing helps prevent the intake manifold from being overloaded under boost by releasing excess pressure from the turbo itself.
Rene handles some of the bench assembly that’s required for each turbocharger (oil fittings, and such) before they’re installed. CXRacing provides all of the hoses, fittings, and miscellaneous hardware that’s necessary for installing the turbo kit.
The position of the driver-side wastegate makes moving the oil filter a requirement. An adapter for the filter housing, as well as the lines and fittings for feeding oil to the turbos, are all standard equipment.
CXRacing designed its Fox twin-turbo system for ’86-’93 ’Stangs, which were equipped with airboxes and thus had natural openings in the passenger-side inner fenders to serve as locations where discharge tubes can be routed from the turbo, and also from the intercooler to the throttle body. With Greg’s coupe being an ’84 that originally had a carburetor, the appropriate cuts were warranted. Determining exactly where to clearance the panel is a trial-and-error process in which Rene mounts, clocks, makes reference marks, and remounts the turbo several times to ensure correct positioning all around.
The CXRacing twin-turbo system includes a pair of 38mm wastegates with 8-psi springs, and dumps that bleed off excess boost.
After a minor amount of cutting and rewelding, Rene created a pipe that clears the pan. Going forward, the transmission type must be specified when ordering a twin-turbo system from CXRacing.
While the system’s downpipes are 2.5 inches, CXRacing offers 3-inch downpipe flanges and V-band clamps as options.
In addition to the ’86-’93 year range, it’s important to also note that the CX turbo kit was developed for Mustangs with five-speed, manual transmissions. With Greg’s Pony sporting a Performance Automatic Super Comp AODE transmission in its trans tunnel, we quickly discovered that the 3-inch exhaust tubing on the driver side does not clear an automatic tranny’s fluid pan.
Ascension bores a passage in the driver-side framerail for that turbo’s discharge pipe, which, like its passenger-side counterpart’s tube, also is plumbed into the intercooler. While CX’s twins system is designed for ’Stangs that still have full accessories (air conditioning, power steering, and so on), a Pony’s battery must be relocated to the trunk or hatch area.
Ascension mock-fits CXRacing’s bolt-in air-to-air intercooler at the front of our test ’Stang. The bar-and-plate ‘cooler features a 3.5-inch core, measures 27x12.5x3.5 inches, and is specifically designed with two 2.5-inch inlets for discharged air from the Fox system’s twin GT35 turbos. All of the aluminum tubing is mandrel-bent, including the large 3-inch discharge pipe from the intercooler to the throttle body. All clamps, silicone hoses, and a blow-off valve also are included with the intercooler.
Wastegates receive boost references from small tubes mounted at the end of the turbos’ discharge outlet.
Once the turbos are mounted, Rene connects 2.5-inch, stainless-steel downpipes to the turbine housings on each unit.
Due to the intercooler’s size, the coupe’s front bumper cover requires a slight amount of trimming for correct clearance. After installing the bumper and marking cut areas, Ascension uses a simple pair of snips to remove material from the cover.
A blow-off (bypass) valve is mounted in the intercooler’s 3-inch discharge tube to release pressurized air when the throttle is closed during shifts (with a manual transmission) and deceleration.
With this system, the mass-air sensor actually is supposed to sit farther down the intercooler discharge tube (inside the inner fender area), before the bypass valve. We elected to swap the sensor’s and valve’s positions for easier access to the mass air, which did require a bit of custom tubing fab by Rene.
Turbochargers emit incredible amounts of heat throughout the engine compartment. CX provides plenty of protective/insulative sheath material for preventing spark plug wires from completely melting.
Here’s a look at the newly twin-turbocharged engine, almost ready to fire. The next stop for Greg’s Pony is the exhaust shop, as a custom mid-pipe (with V-band flanges) must be made for mating the turbo kit’s exhaust to a ’Stang’s tailpipes.
On the Dyno
Nothing beats doubling a Fox ‘Stang's 200 baseline horsepower, especially with a power-adder that looks as sexy as CXRacing's twin-turbo package!
Greg Montoya's EFI'd '84 coupe came to us with a fairly fresh 306 that put out 215 horses in its baseline evaluation on the chassis dyno. After installing CX's twin turbos, peak power climbed to more than 402 horsepower, with just as much torque (in lb-ft) at the rear wheels, with boost limited to only 8 psi.
"This combination can definitely make 30-40 more horsepower with a lock-up torque converter and bigger fuel injectors," said Addiction Motorsports tuner Eddie Rios. "We would see even more if the kit was installed on a Mustang with a manual transmission. So much more, we would have to consider where to limit power because the engine is based on a stock block. I like the way this turbo system is made, its price is perfect, and it definitely makes good boost."
We agree with Eddie's sentiments, especially when the overall price is taken into account. The total for a CXRacing twin-turbo kit and Holley's Dominator EFI is roughly the same price as many other Fox turbo systems—single or twins—by themselves. However, we must note, using Dominator actually is a bit of overkill—Holley's HP EFI is a perfect alternative to the big ECU, as it has many of the same features and capabilities [datalogger, boost controller], yet is priced approximately $750 cheaper because it does not control electronic transmissions and only has one wideband O2 input.
Our friend Eddie Rios of Addiction Motorsports is well-versed in tuning blown and turbocharged Mustangs with stand-alone engine-management systems. In a short time, Eddie has become quite proficient with Holley’s new Dominator EFI. After strapping Greg’s ’84 coupe on the Dynojet chassis dyno, Eddie took a moment to survey CXRacing’s twin-turbo layout.
Greg installed the Dominator ECU (PN 554-114; $1,744), as well as its associated harnesses (main power, universal main MPFI, V-8 injector and Ford TFI ignition), sensors, and such right in his driveway. Using the system’s pre-programmed calibration for a 5.0/turbo combination as a baseline, Greg had the engine fired and running well enough for moderate-throttle and light-boost drives around his neighborhood shortly after wiring the ECU, programming target air/fuel parameters, and allowing Dominator’s self-learning function to do its thing.
Fine-tuning the 306 involved Eddie shutting off the self-learn function, transferring its calibration data to the main fuel table, and then modifying fuel settings in stages, to eventually achieve a safe air/fuel ratio at WOT. The program’s base timing advance is 20 degrees, which actually proved to be a bit too much for our setup. By taking 4 degrees of timing out of the low range and 2 at the top of the rpm window, Eddie was able to achieve air/fuel ratios of 13.5 at idle, 12.0 at 2 psi, and the desired 11.5-11.7 from 4-to-8 psi of boost.
“The Dominator EFI’s self-learning actually does a great job,” Eddie says. “I really like the system’s 3D function, which allows fuel-table changes to be made directly from the grid and on the fly. I didn’t really have to do a lot of building off of the baseline for the WOT tune, but the system is really intuitive and does cover every area associated with tuning a boosted application and making it run well.”
With engine temps anticipated to be higher than normal with the turbos, Greg added a Flex-a-lite 180 Black Magic Xtreme Series electric fan that blows at a rate of 3,300 cfm.
The fan proved to be a perfect upgrade, as the Pony’s coolant remained at a steady 190 degrees throughout the dyno session.
And here is the fully completed turbo project, with the EFI system’s harnesses and sensors installed, and completed with Kevlar covers for the turbochargers’ turbine housings and K&N filters to protect the compressor wheels.
We really like the stealthiness of this setup, which only emits a low murmur when the engine is at idle or low, street-cruising rpm.
The fuel-injector dilemma answered our question as to why we did not see more power from, and a higher rpm plateau for the twin-turbocharged engine. A fix is in the works; exchanging the 42-pounders for 60-lb/hr squirters, which we’re sure will then make being mindful of the stock block a bigger concern.
You can’t beat a dyno graph that looks like this, with rear-wheel horsepower and torque practically mirroring each other throughout the entire run. We attribute the breakup at the top of the run to two things—the coupe’s loose, non-lock-up torque converter, and also the fact that the engine is equipped with only 42-lb/hr fuel injectors. While we don’t have the graph, the 400 horsepower and 403 lb-ft of torque are considerably more than the engine pumped out in its naturally aspirated form (215.6 hp at 5,500/227.9 lb-ft at 4,300).