By Sam Haymart
We often hear people ask, “I just got this Roush Stage3, what can I do to get more power out of it?”, “How much power will a supercharged Roush really put out?”, and “What mods can I do?”.
The following is our best answer. This archive is based on factual and anecdotal information gathered over time from various blogs, reported experiences from a wide variety of Roush supercharged Mustang owners, and bit of wisdom we have gleaned from sources within the engineering brain trust that created these cars. Because of this, the following information should be considered to be somewhere between opinion and fact, but closer to the latter. We suggest that your results may vary and we invite you to keep us up to date on what has worked for you and to what degree it has not.
The 2001 to 2004 Roush supercharger system that was installed in Roush Mustangs including the Stage 3, 360R,380R AND 440A is one of the most engineered and comprehensive supercharger packages for modern cars that has ever been created. The system was a factory installation for the aforementioned Roush Mustangs but has also been made available in the aftermarket as a kit for 2001-2004 Mustangs. There simply is no other package available today that has been subjected to a higher level of OEM level testing, proving, engineering, and manufacturing. There is now a ROUSHCharger kit for the 2005+ Mustangs, but this system is quite different and warrants it’s own “101” write up.
The heart of the supercharger system is a custom specification M90 blower that was optimized by Roush. The M90 used has some proprietary differences that Roush specified for their units that give it superior efficiency and flow compared to the “off the shelf” blower from Magnussen/Eaton. Further, the intake manifold and intercooler assembly has a level of flow and low restriction elements that is unmatched by anyone, giving the entire system an above average performance advantage compared to other systems with the same boost of 6 psi.
One of the most common misconceptions about the Roush supercharger system is that it is overpriced. That is easy to assume if you are not fully aware of the vast array of parts and components that comprise the system as well as the “total engineered package” that it represents from an OEM quality, drivability, and reliability standpoint. With over 140 items, components, or assemblies the package literally fills the bed of a full size pickup truck and is often considered to be a “sex change” for the car. (See 2001-2004 Roush Supercharger Parts List & Installation Manual-PDF 13mb)
One of the second most misconceived notions about the system is that it is easily modified just as any other car or system is. With any other car modders have spoken the language of custom tunes, larger throttle bodies and mass air sensors, fuel system mods, and other bolt on approaches. In the case of the Roush supercharger system these are not always successful or prudent options.
Tuning:
The package includes a completely different fuel system and ECU that utilizes proprietary software. This software has evolved in different versions from 2001 to 2004, but all variations share the common outcome of OEM programming that taps the maximum safe performance from the stock 4.6 2V engine. The Roush ECU is a special “learning” unit. It actually moves the various map tables instead of moving within the map tables like a standard Ford ECU. The Roush ECU reads the O2 sensor outputs and adjusts the tables and where in them to read the data. This for instance, is one reason NOT to use MIL eliminators with a Roush supercharged car or an off-road pipe as doing so cripples the Roush ECU’s ability to read and adjust to important data. (see Exhaust section)
The ECU is not “chip-able” as the port has been removed or blocked. It cant be overwritten without permanently damaging the long tested and engineered Roush tune. If your car or supercharger is under warranty, this would void it. The stock tune takes the air/fuel (AF) ratio right up to the edge of safety. When people start replacing different parts that the Roush ECU is tuned for, there are varying results.
Intake Tract:
The Roush Supercharger package uses a larger 75 mm throttle body (TB) sourced from BBK or Visteon, and 85mm* mass airflow sensor (MAF) sourced from the Ford Lighting pickup. The stock Mustang GT air box and filter however have been retained. One of the most common and popular mods that many Stage 3 owners have utilized is a larger tube Cold Air Intake system. One of the biggest don’ts is using the Roush CAI on the Roush SC system. Even though it looks like a marriage made in heaven, the end at the TB….does not match in size and causes the air to tumble and actually cost you horsepower! Use the correct size CAI for the best gain. Systems from BBK and Tunable Induction have been popular with owners.
With a good fitting unit, in most all cases the power gains from this mod have been noticeable and measurable with varied results that range from 10-20 hp on average depending on the system. We have yet to hear of many cases where this modification has caused any engine damage or AF ratios to be off enough that the ECU could not manage.
Going beyond the CAI to changing a MAF has been done by a few people with yet to be measured long term or short term results. In almost any case when you replace a MAF you need to calibrate the MAF to match the ECU. The few owners that have done this have posted hp dyno numbers that may show a slight hp gain, but this has yet to be proved out. Be sure to check your AF ratio after installation.
Fuel System:
The Roush system uses 38lb injectors, The part numbers are actually 36lbs. But Roush bench flowed all injectors to 38lbs. The system uses special Roush fuel pumps and pickups within a proprietary Roush fuel tank. This tank was later modified by Roush to be used as a factory tank for the ‘03/’04 Mustang Cobra. The fuel pumps are the same as the ‘03/’04 Cobra pumps except that they have a special pick-up assembly with slosh cups to retain fuel in high G turns. This system holds gas in place in order not to lean out the engine. The Mustang Cobras don’t have this! The Roush ECU again is programmed for this hardware. Information that we have obtained from sources over the years tell us that this fuel system is good up to about 425-435 hp at the flywheel before it will start to run out of capacity. This means that with all the modding in the world, you will have trouble exceeding this barrier without adding more hardware fuel flow. Couple this with the fact that the stock Ford 4.6 2V engine is really only structurally able to produce up to 425-435 hp before the specter of engine failure or premature wear come into your horizon. This is the reasoning for the fuel hardware induced hp limit Roush intended to keep engines from blowing apart.
Exhaust:
Stage 3 owners have successfully added various combinations of headers, X-pipes, and mufflers for additional horsepower. The Roush factory spec cars all came with Magnaflow side or rear exit exhaust systems which is a pretty good upgrade from the Ford stock exhaust. The side exhaust mufflers will flow only slightly less than a comparable Magnaflow rear exit system. The Roush Megaflops are a packed muffler not a baffled muffler, hence the great gas flow. Engineers attest that there are no side exhaust mufflers that will give you more hp vs. the stock Magnaflows except changing to a rear Magmata system (additional 5 hp). A few owners who have changed the stock U-Turn side-exhaust mufflers however with straight through mufflers like Flowmaster’s racing series which are installed on a 45 degree angle straight to the side-pipe outlets have claimed additional gains of 5-7 rwhp
Owners have reported mild gains on average of 5-8rwhp with catted X-pipes. Also note in all Roush performance testing the Magnaflow catted X pipe delivered more hp gain than any other brand. Note again, that using MIL eliminators and/or and off road X pipe severely cripples the Roush ECU’s ability to adjust and compensate, setting the table for less performance and unsafe AF ratios.
Supercharger Pulley:
There have been smaller supercharger pulleys marketed for the Roush supercharger system that ups boost by about 1-2 lbs. This pulley has even become a part of the Roush spec 440A model. The Roush 440A combined the Magnaflow Catted X-pipe with the pulley to get the 400 hp in the 440A. Many Stage 3 owners have bolted on the smaller pulley and we have yet to hear of anyone with detrimental results. Owners have reported a stronger pull and rwhp gains of 9-15 hp on average have been reported. Of course, adding a pulley increases boost and theoretically leans out the AF ratio. The ECU can mitigate this to a degree but if you live in areas with high altitude like Colorado or hot temperatures like Arizona, you probably want to make sure your AF ratios are safe once installing the pulley.
Under-drive Accessory Pulleys and FEAD:
On a supercharged car, under drive accessory pulleys are not a mod. This is because in most cases under drive pulleys actually slow the supercharger and lessen the boost. Secondly, on a 1999-2004 Roush supercharged car, there is the FEAD accessory drive that provides a second serpentine belt that drives the supercharger. It is driven off a second floating crankshaft pulley separate from the standard accessory drive. It is carried on the front by a fixed bracket that effectively takes the leveraged end loading off the crankshaft, leaving it only to take the rotational loads of the supercharger. Because of this, the stock accessory drive and locations of the components are not stock and are difficult to modify anyway.
Intercooler:
Some dedicated gear heads have tried using freon type sprays, extra fans and other cooling measures on the heat exchanger of the water-to-air intercooler in hopes of cooling the air charge and thus gain power. This does work in principle, but this approach has not yielded a mainstream following. There is a larger heat exchanger that is manufactured in the aftermarket that has a significantly larger capacity that some owners have tried. We have yet to see any significant proven results at this point in the way of dyno tests to tell how much if any gains come from this.
Heads, increased displacement, and cams:
At this point we don’t have any data from real world owners or cars who have utilized larger displacement versions of the 4.6 engine or have had custom head or camshaft installations. There have been a few owners reported to be working on such modifications and we will revise this archive when we get data from them.
Nitrous:
Don’t do it unless you have a new motor sitting in a crate ready to be next for game.
So how much power can I get?
Most stock 2001-2004 Stage 3/360R/380R supercharged Mustangs have reported rwhp numbers that range from 335 to 360. That is pretty good considering they are factory specified at 360 and 380 at the flywheel. Cars that have added a CAI and/or exhaust modifications have been reporting a range of 350 to 390 rwhp depending on the level and type of modifications and region where the testing occurred. The highest numbers we have seen to date reported by dyno sheet are right at about 400 rwhp give or take.
* The Roush Parts List calls for an 80mm MAF. At the time of this writing this anomaly has not been explained.
