Under Pressure: Installing a Roush Supercharger on a 4.6L
One of the fastest methods of adding horsepower and torque is to introduce boost to the engine. This can be accomplished in two ways- Supercharging and Turbocharging. While both are technically supercharged, there are differences in how they work and each has its own benefits and drawbacks. Both operate by forcing air into the engine, creating boosted levels of pressure inside the intake. This puts more air and fuel into the engine, causing it to make more power. How they do this is the difference. A turbocharger derives its power from the exhaust gasses, spinning a turbine which is coupled to a compressor that runs to the intake system. Turbos typically have some amount of lag because of this. The turbine takes a little more time to spool up. You can get the idea by spraying a water hose onto the pedal on a bicycle, it takes a second to get spinning, but once it’s going, it is easy to maintain. A supercharger is different. There are two main types of superchargers- roots (also screw-style, but they are similar) and centrifugal. Both are directly driven from the engine’s drive belts, so they are always spinning with the engine. This means no lag and almost instantaneous response. Roots style blowers are mounted to the intake itself, so there is little adjustment for installation, where turbos and centrifugal blowers can be mounted in different configurations to fit the chassis.
For ease of installation, durability and turn-key simplicity, there is nothing quite like a roots-style blower. The install is straight-forward; replace the stock intake with the new one, sit the supercharger on it, and re-tune the computer. They make it sound so easy, but is it really that simple? We plotted a course to find out. With a bone-stock ’05 4.6L Mustang GT in the shop and three large boxes full of boost, the task was at hand.
There are many options when it comes to choosing the right blower for your car. Just about everybody makes a Mustang supercharger, picking the one you want comes down to three things- brand preference, performance, and price. Brand preference and price are subjective; you have to make that choice yourself, but the one area that is objective is the performance. The stock 4.6 block is capable of handling 500 hp, but that is about it, any more power and you start having durability issues. That is not saying that 525 hp is going to destroy it the second you start it, but it won’t last as long as it would under the 500 hp mark. Considering all of these factors, we opted for the Roush RS2300 TVS blower. The TVS supercharger is made by Eaton, the TVS design uses two high-helix (the twist rate of the lobes) rotors with 4 lobes per rotor, which makes them very efficient. This design builds power much faster than other blower types, which means you get more enjoyment at regular speeds, not just in the higher-rpm ranges. In other words, stoplight to stoplight action will be better, not just on the top end. The phase 1 R2300 kit is calibrated for 8-9 psi of boost, and should increase flywheel power to 475 hp with 435 ft lbs of torque, which with an average 13% parasitic loss through the drivetrain, should net about 405 hp and 370 ft lbs. Compared to other roots-style blower kits for the 3-valve 4.6, the power per dollar is great, this kit will hit your wallet for around $6K, where the other kits we have seen are pushing $7K for the same power levels.
Roush’s website indicates that this is an 8-hour, advanced mechanic job that requires basic tools. The only part that is advanced is reading the manual. This sucker is 72 pages long, with about 2 steps per page. While most of it is straightforward, some of the illustrations are hard to decipher, and the wiring modifications are confusing. As a matter of fact, the wiring slowed us down, pushing the install into the second day. Don’t let that scare you off though, once you figure out what the instructions are trying to convey, it is a simple task. We completed the install during working hours at the shop across two days, it took us approximately 10 hours start to finish.
The results were impressive. Supercharged power is different from naturally aspirated power. From a dead start, the power will not seem much different, but as the engine revs up, the boost kicks in and the relief valve (which bleeds off the boost at idle) closes, and you will feel an increase in power. Unlike nitrous, where you feel an immediate jump in power, supercharged power increases gradually and throughout the entire RPM range. Due to editorial time constraints and the SEMA show, we were not able to get the car on the dyno, but judging by the seat of our pants, it’s all in.
Stock 2005 4.6L 3 valve Mustang GT performance numbers (from Ford)
300 hp 320 ft lbs at the flywheel (adjusted to 261 hp, 278 ft lbs with a 13% loss through the drivetrain)
The Roush supercharger increases flywheel power to 475 hp, 435 ft lbs, which means you will see a realistic 410-415 hp, 375-380 ft lbs at the rear wheels, all while running premium pump gas. In stock trim, this Mustang was knocking down 13.70s in the quarter mile. With the blower, we should be in the high 11-second range. That is a huge increase in speed and power. All in a days work.
1. Before a wrench is turned, the fuel system needs to be drained. This is done by pulling the fuel pump fuse and cranking the motor for about 10 seconds. If it starts, let it idle until it dies, then crank and additional 10 seconds. Otherwise you’ll get fuel spraying on you at 60 psi.
2. We pulled the hood for access, but it is not required. Removing the front bumper cover, however, is necessary.
3. We pulled all of the sensor plugs from all of the pertinent sensors. Several of them have a tab like the one shown here- the red tab slides out about 1/8”, then you can depress the black tab in the center to release the plug. Make sure you note what each plug goes to.
4. Next, the airbox and connecting tunnel were removed along with the throttle body. This system reuses the stock throttle body, so don’t toss it.
5. Before moving any further, the stock computer (ECM) has to come out. The Roush package requires the stock ECM be sent to Roush via the provided Fedex next-day shipping. We sent ours off on a Tuesday and had it back Thursday morning. Keep this in mind if you are doing this to your daily driver. Most other kits come with a tuner, but that adds about $500 to the price. If you already have a tuner, a quick call to Roush may help alleviate the wait.
6. Several vacuum lines have these tricky connectors. Simply depress the white ring and then pull the connector off. Don’t try to pry the ring out with a pick, that will ruin it.
7. The high-pressure fuel line requires a special removal tool. These come in a kit from the local parts store for about $10-15. You need it.
8. With all of the lines removed, the intake was unbolted and removed. Save the stud bolt from the driver side rear, you will need it later.
9. The alternator and stock water bridge were removed. You are going to get water into the engine valley, don’t stress that, it drains to the ground. You don’t want to get a bunch of water in the heads though, so stuff the front ports with rags. We changed the oil before we fired it up just in case anyway.
10. The alternator must be modified to fit. These ears (one of each side) were removed with a recip saw and cleaned up with a die grinder. You also have to separate the lower water return hardlines (which run under the manifold and modify another bracket.
11. The wiring is the most confusing part, and its mostly because the instructions are ambiguous as to where you need to route them. These two wires from the MAF sensor plug had to be cut and rerouted to the middle of the harness at the back of the engine. You are going to need a lot of tape for a clean install.
12. The instructions call for a crimp-on union, then soldering it. The crimps are not very user friendly (and we have good tools) and simply not necessary. Place the two wires together (forming an X), then twist them across the opposing wire (creating a smooth joint, not a pigtail!), and solder.
13. The intake includes an air-to-liquid intercooler. This takes up a lot of the room underneath the intake. The kit comes with some new piping to get all the right connections. Make sure the rubber hoses are routed correctly before mounting the intake. We learned that the hard way.
14. There are several pieces you must reuse, like the radiator fill plug in the water neck. This plug allows you to fill the cooling system to capacity without trapping air.
15. The intercooler radiator mounts behind the factory bumper brackets, it’s orientation is not very clear in the instructions, but it only fits one way.
16. Using the included drill guide, the front subframe was drilled to fit the intercooler water pump. This location is a tad low; you might have to adjust it if your Mustang is significantly lowered.
17. Next, the intake was placed on the motor and the supercharger after that. The intake must be aligned with the front alternator bracket before the supercharger goes on.
18. The kit comes with new fuel injectors for the new fuel rails. The rubber O-rings must be lubed up with assembly lube before installing them. Be careful not to get ANY oil or lube inside the injector.
19. The alternator bracket and alternator were installed next. This places the alternator quite high in the engine bay, but it still clears the stock hood.
20. Routing the new serpentine belt required two sets of hands and the manual diagram, but it went on easy enough. The kit comes with new stickers to give you a permanent reference.
21. The outlet of the supercharger is on the back of the blower. To put the throttle body in the appropriate location, the kit comes with an aluminum elbow. This may be easier to install before the blower is bolted to the intake, but this is how the instructions read. Don’t forget the gasket.
22. The stock throttle body is reused. For apples to apples, we stuck with it, but you can up the output by going with a bigger throttle body.
23. Midway during the install, we found a spring-clamp ring installer in the tool box. This is basically a necessity for this install. All of the supplied hose clamps are spring-clamps, as opposed to worm-gear clamps. There are some really tight spaces on this engine, and this tool was a life saver. We also needed a few ratcheting wrenches from Gearwrench to get the job done.
24. The car already had a 97mm air cleaner tube, so we reused it. The Roush air tunnel has a mount for the MAF sensor, but it also comes with a plug, which we installed.
25. The back of the intake elbow has all the required vacuum ports. There is one spare port as well. There is a port on the back of intake for a boost gauge, but we have not hooked that up yet.
26. The intercooler is air-to-liquid, so it requires coolant. We used some Purple Ice additive which breaks down the surface tension of the water/antifreeze mix, allowing the coolant to transfer heat better, which reduces the overall temperature. Only about an ounce is needed for the intercooler’s small capacity, so we added the rest to the engine coolant.
27. The finished installation. All we had left at this point was to install the recalibrated computer, drop the hood and fire it up.
28. This is what happens when you install a supercharger. The whine coming off of this blower is incredible, it just screams “I am awesome”, and that is a good thing.
Sources:
GearWrench
Roush
http://www.roushperformance.com/
Royal Purple
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