In order to compare the new...
In order to compare the new Vortech Si blower against the obsolete S-trim, we needed a suitable candidate. Curt Burrell's '96 Cobra fit the bill, with a built engine and a V-1 S-trim supercharger.
The Vortech Superchargers' S-trim centrifugal supercharger has to be one of the most popular superchargers for late-model Mustangs-and for good reason. They make great power, are relatively easy to install, and have an excellent reliability record. In recent years, advancements have been made to the internal gearing to make them whisper quiet, for the more discerning enthusiast, and they have also begun to offer self-contained supercharger head units for those that prefer the easier install.
Not one to rest on its laurels, Vortech just redesigned the S-trim, and the new impeller design has led to improvements in efficiency, and subsequently, power output. To put the new Si-series blower to the test, we looked to Rick Anderson at Anderson Ford Motorsport in Clinton, Illinois. Anderson just happened to have a great candidate for the test, and was very interested to see what the new supercharger design could do.
Said test subject came in the form of Curt Burrell's '96 Cobra, which features a D.S.S. Racing-built 283ci short-block with forged internals, unported stock heads and intake manifold, stock cams, and Bassani mid-length headers with an X-midpipe without cats. Other modifications include an Accufab single-blade oval throttle body, AFM PMS and Power Pipe, a PRO-M 80mm mass air meter, 60-lb/hr fuel injectors, an overdriven damper, an AFM clutch and aluminum flywheel, as well as a T-45 built by ProMotion and 4.30 rear gears. It also sports the venerable Vortech V-1 S-trim supercharger.
The SI bolts right on in place...
The SI bolts right on in place of the S-trim head unit. To begin the swap, remove the coolant reservoir tank and the supercharger inlet elbow.
For the lowdown on the new Si blower, we called up Vortech's Motorsport/Media Relations Manager, Ricky Best. "We wanted to make the current design more efficient, create more horsepower at the same boost level, and lower the charge temps," said Best. "The Si impeller design is a lot more efficient. It also flows more air than an S-trim-almost as much as a T-trim."
According to Vortech, the Si-trim unit is capable of operating at a peak efficiency of 78 percent, which is a 6 percent improvement over the S-trim. In addition to producing a cooler air charge, the more efficient design reduces the load on the engine, which results in greater net horsepower and torque gains.
Another key objective in developing the Si-trim was to extend the useful performance range of the supercharger. Due to its increased efficiency and flow at higher performance levels, the Si-trim can support applications that demand more airflow and pressure than what was considered practical with the S-trim. Where the S-trim could support 625 hp, the Si, with its improved efficiency, can support up to 775.
With the tank and inlet elbow...
With the tank and inlet elbow out of the way, disconnect the drain and feed lines, and then unbolt the bracket.
Here's the breakdown on the S-model superchargers from Vortech. The "V" designation refers to the case and the gearing inside the blower. V-1s feature the straight cut transmission gears, which offers superior strength over noise reductions. The V-2 features the SQ line of helical cut transmission gears, which greatly reduces the whirring, whistling gear noise. Finally, the V-3 blowers feature an all-new transmission gear design that incorporates helical cut transmission gears for noise reduction in a self-contained supercharger head unit.
The S-trim (and SC-trim) impeller design as we know it has been retired and replaced with the superior Si impeller across the product line. The Si impeller design can be used with any of the V-series head units. For those who have an existing S-trim blower, the new Si bolts right up to the same brackets.
"To upgrade to an Si from an S, the blower has to come to us," says Best. "We offer an impeller upgrade for S-trims that are in good shape for $329, which includes the new volute and Si impeller. For older S-trims, or ones that have been run hard, we'll replace the bearings and seals if needed for an additional $325.95.
With a component, that simply...
With a component, that simply bolts in place of another, there aren't many changes to the outside. The volute on the Si (right) is new, but the main difference is the impeller inside the blower.
The side of the blower case...
The side of the blower case that bolts to the bracket is slightly different, but it still bolts right up to existing S-trim brackets without any issue.
Our car's owner, Curt Burrell,...
Our car's owner, Curt Burrell, swapped the oil line over to the new Si head unit, followed by the 3.00 pulley.
The superchargeR bracket is...
The superchargeR bracket is bolted on next, and the Si is ready to be installed onto the 4.6L.
On the dyno, the Si is an impressive performer, as it produced more boost from 3,000 all the way to 6,500 rpm using the same 3.00 blower pulley. Our '96 Cobra test subject produced baseline numbers of 587 rwhp and 497 lb-ft of rear-wheel torque at an average boost level of 16 psi. With the Si-trim head unit pressurizing the top side of the engine, power production rose to 615 rwhp and 550 lb-ft of torque at the wheels with an average of 19 psi of boost.
"Vortech did an excellent job because it improved power all the way through the powerband. It's easy to make improvements at the top end," says Anderson Ford Motorsports' Rick Anderson. "The way it picks up at the low-end-a street guy is going to feel that big time. It's really neat that they went back to a non-current blower and made it better." We agree with Anderson.
For a model update, the Si is super impressive, and the improved performance should keep your Mustang ahead of the competition.
The Business of Boost
Rick Anderson took the liberty of recording the boost level on each run before and after the Si swap. You can easily see that the Si is making more boost earlier, and continues leading all the way to redline.
| | | | | Average | | | | Average |
| Boost | Boost | Boost | Boost | Boost | Boost | Boost | Boost | Boost |
| RPM | S-trim | S-trim | S-trim | S-trim | S-Trim | Si-Trim | Si-Trim | Si-Trim | Si-Trim |
| 3,000 | 3.2 | 3.2 | 3.2 | 3.0 | 3.1 | 4.2 | 4.2 | 4.2 | 4.2 |
| 3,500 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 5.8 | 5.7 | 5.3 | 5.6 |
| 4,000 | 5.8 | 5.7 | 5.3 | 5.5 | 5.6 | 7.3 | 7.8 | 7.6 | 7.6 |
| 4,500 | 7.8 | 7.6 | 7.1 | 7.3 | 7.5 | 10.5 | 10.5 | 9.6 | 10.2 |
| 5,000 | 9.4 | 9.4 | 8.9 | 8.9 | 9.2 | 12.4 | 13.0 | 13.1 | 12.8 |
| 5,500 | 12.1 | 11.9 | 11.7 | 11.4 | 11.8 | 15.3 | 15.5 | 15.1 | 15.3 |
| 6,000 | 14.2 | 14.6 | 14.4 | 14.0 | 14.3 | 17.9 | 17.8 | 17.4 | 17.7 |
| 6,500 | 16.0 | 16.0 | | 16.5 | 16.2 | 19.7 | 18.7 | 18.7 | 19.0 |
The oil supply line is connected...
The oil supply line is connected to the head unit. The Si is available in V-2 oil-fed or V-3 self-contained configurations.
The serpentine belt is hooked...
The serpentine belt is hooked up next.
The AFM Power Pipe and inlet...
The AFM Power Pipe and inlet tube are next.
Our subject vehicle doesn't...
Our subject vehicle doesn't employ a charge cooler, so the more efficient Si should help with the intake charge air temperatures.
Tuning is accomplished with...
Tuning is accomplished with the Anderson Ford Motorsport PMS.
The 28 hp and 53 lb-ft of...
The 28 hp and 53 lb-ft of torque is a welcomed improvement, but more impressive is the fact that gains were seen across the entire powerband.