Boost Chart

Dyno Chart

By John Hunkins
Photography by the author

Whatever it is they put in the water cooler at Vortech Engineering, it's got the staff cranking out some great new products. Take Vortech's latest salvo, the V-1 T-Trim compressor; a savvy engineering and marketing marvel that's designed to bridge the large performance gap between the super-popular S-Trim street blower and the venerable medium race-size R-Trim.

In marketing terms, the T-Trim fits between the S- and the V- 1 R-Trims, but on paper (and in testing) the T-Trim surpasses the original R-Trim with about 9 percent more airflow capacity. With a theoretical horsepower range of up to 825 hp, the T-Trim is actually midway between the S-Trim and the newer V-3 R-Trim (the smallest blower in the larger Mondo family of compressors).

We predict that the T-Trim will he very popular with streeters and racers alike because it delivers its air package in the shape of a V-1 compressor. The T-Trim installs in the traditional passenger's-side location and uses the brackets and hoses of entry-level Vortech street kits. As a result, those folks with V-1-style blowers (A-, B-, S- and R-Trims) can swap to the T-Trim without having to buy or fabricate special brackets and plumbing, as is the case with the Mondo V-3 and V-4 units. Vortech design engineer Mike Reagan says, "Assuming you already have a cogged-drive Vortech, it's just a matter of swapping the supercharger. If you've got the serpentine drive, then you've got to change the crank pulley and idler pulley, too. You can still use the serpentine belt with the T-Trim if you want; you just won't be able to take full advantage of it's output, which can go as high as 25 psi."

In the bang-for-the-buck department, the T-Trim is an incredible bargain, particularly for those who already have some form of V-1 on their Mustangs. In our back-to-back dyno test, the T-Trim made over l00 hp more than an S-Trim on a race-prepped engine, yet the base price for upgrading a heavy-duty S-Trim to a T-Trim is just $315.95.

Vortech maintains that any S-Trim being upgraded to a T-Trim must have the heavy-duty bearings because of the high load placed on them by cogged-belt systems. Vortech's Reagan says, "For this reason we are allowing T-Trim upgrades only to those S-Trim customers who already have the heavy-duty bearing upgrade. The heavy-duty bearing will sustain a higher speed and handle the forces of accel and decel much better than the standard bearing. This is particularly important when you have a cogged belt system, which obviously won't slip."

The T-Trim compressor may be purchased outright for $2,176.95 (suggested list) if you haven't got an S-Trim to start with, but if you do have an S-Trim, it must first be upgraded with the heavy-duty bearings. Reagan also explained that once a CARB exemption is obtained for the T-Trim, it will be offered in kit form with the serpentine belt drive, but until this happens the T-Trim should be considered a race-only unit.

The secret to the T-Trim's success isn't really a secret at all; it's all about moving air, and at a temperature at which it can still he used. The T-Trim can move up to 1,200 cfm of air at an efficiency approaching 70 percent; that means an unprecedented amount of power can be made (up to 825 hp) without causing a thermonuclear meltdown in your engine.

The movement of copious airflow is made possible by the T-Trim's 3.20-inch inducer diameter (the inlet opening in the center of the compressor) and larger 3.75-inch inlet tube. By comparison, the S-Trim's inducer diameter is 3.0 inches and uses a 3.5-inch inlet tube. It doesn't sound like much, but through the laws of mathematics, that extra .2 inch of inducer diameter yields 13 percent more inlet area over an S-Trim.

Moving this much air can be tricky, especially since engine speed and blower speed play such a big role in how the air is delivered. For example, a street blower like the S-Trim is designed to deliver the knockout punch at lower rpm, whereas a race blower such as the V-3 Mondo delivers the goods at high rpm.

"With the T-Trim we wanted to integrate the advantages of the S-Trim, which is a very good street blower, with the advantages of the R-Trim, which is a very good medium race blower," says Reagan. "With the T-Trim you get the advantage of the S-Trim, which is good low-speed boost, and the strong suit of the R-Trim, which is high flow and high boost. It's hard to do both of these at the same time while maintaining efficiency throughout the whole rpm range, but we lid it, thanks to our blower dyno cell."

The design target was clearly defined, but without use of Vortech's one-of-a-kind blower dyno cell, the job would've been clearly a hit-or-miss proposition. 'We are the only centrifugal blower manufacturer that has the ability to capture all this data," says Reagan. "It helps is to continually improve our blowers in terms of efficiency, and it helps us to compare our products with those of our competitors."

Vortech was instrumental in developing SAE standard J1723, the industry-wide measuring stick for centrifugal supercharger performance. The standard allows for different superchargers to be compared equally on the basis of both airflow and efficiency. Reagan says, "One thing that's kind of neat about the test dyno is that you can speculate on paper how well a blower is going to perform – and that's the way we did it for the first two years – but now we can actually test a blower before it goes into production. Now we know how good a product is beforehand. Also, if a product isn't quite as good as we want, we've got the chance to tweak it without all the guesswork."

Vortech feels that the cost of such a research and engineering venture is out weighed by the test cell's benefit as a design tool, a tool that directly brought about the S-Trim compressor; the Mondo V-3 and V-4 series compressors, and now he T-Trim. Reagan says, "We can generate data from this cell that will allow us to write supercharger compressor maps, something that the turbocharger guys have been doing for a long time. The dyno cell allowed us to adjust the contours of he impeller blades and the volute. The T-Trim, as a result, has a larger inducer than he S-Trim – it's the same size as the R-Trim – but the outside diameter of the impeller is the same as the S-Trim for improved low-speed boost."

The T-Trim is capable of delivering he previously mentioned 1,200 cfm of airflow, but that rate can only be sustained at very high boost levels. With a maximum output of 25 psi, the T-Trim requires a cogged belt drive to prevent belt slippage. With a cogged belt system, however, come other responsibilities, such as providing a high-capacity blow-off valve for decel, and installing the aforementioned heavy-duty bearings for the increased load on the bearing surface.

"We set up the T-Trim as a cogged drive only because it is easily capable of more airflow than a 10-rib serpentine belt can support," says Reagan. "You get to a point where you flow enough air that it takes more power to drive the blower. A serpentine belt drive just isn't capable of supporting that.

"Also, if the customer is running a cogged system, a Vortech race bypass valve is necessary, even if it's only run on the street. The race bypass is needed because the T-Trim is capable of so much more airflow. With the blower at high rpm and the throttle closed, the air needs a high-volume escape path or damage could result."

If you're getting the idea that the T-Trim isn't for just any Mustang, you're right. Although the T-Trim is likely to receive a California Air Resources Board exemption order (it's been designed with good low-speed attributes and to be emissions-compliant), the airflow of the T-Trim has been built with high-horsepower in mind. "We don't recommend the T-Trim for engines that aren't modified" says Reagan. "That's because it won't really be any advantage. The T-Trim is more efficient at higher levels of airflow, and a stock engine just can't take advantage of it. For these engines, an S-Trim is a better choice."

Selecting the right combination of parts for an engine is one of the most important keys to unlocking power. And for many cars, the T-Trim will be a much better "fit" for the combination, particularly the rapidly growing group of serious street-oriented Mustangs and small-tired race cars in the 10- to 9-second range.

To illustrate the effectiveness of the T-Trim in the right application, we found a test platform thanks to Jeff Barkan of Hauppauge, N.Y Jeff was looking to step up the power in his '93 Cobra Mustang, so he turned to the folks at Second Street Speed in Perkasie, Pa. Second Street assembled a 317-cubic-inch short-block for Jeff using an SVO block, 3.125-inch-stroke Moldex forged crank, Oliver 5.400-inch billet-steel rods and JF 9.1:1 forged-aluminum pistons. The block was topped with a ported FFI truck lower, a Hogan's sheetmetal intake, pocket-ported Will-Burt Street Heat aluminum heads with l.94/l.60-inch valves, a Comp Cams mild custom hydraulic roller cam (.530/.590 inch lift), a 75mm BBK throttle body and 55-lb.lhr. injectors. A Motec M48 computer manages the fuel and spark, and 1 ³/4-inch Stahl long-tube headers vent through 2-hamber Flowmaster mufflers.

Jeff was one of the first customers to receive a T-Trim blower, so he was understandably eager to see the difference over the S-Trim that had been in his original Cobra engine. To make the playing field even, Jeff's old S-Trim would be tested back to back with the T-Trim on his new engine, on Second Street's SF901 SuperFlow dyno. But before the swap, the Motec M48 computer was first dialed in with the new T-Trim, which was equipped with an Auto Specialties cogged pulley system (75-tooth crank, 30-tooth compressor pulley).

The Motec M48 computer employs a programmable boost compensation table that modifies fuel delivery as a function of boost. The Motec system easily lends itself to a blower test like this because once the right boost compensation table is programmed, a blower swap will have little bearing on the basic fuel load table. Simply put, once the computer knows the basic breathing capability of the engine, the boost compensation table adds fuel based on manifold pressure, that being strictly a function of the blower.

After the T-Trim was run on the dyno and the Motec was programmed, the pulley was swapped over to the S-Trim, and the S-Trim was installed. In final tune, the T-Trim twisted the dyno needle to 745.9 hp at 5900 rpm, and 664 lbs.-ft. at 5800 rpm. Boost rose steadily and peaked at 22.6 psi, right at the end of the pull (6100 rpm). It should also be noted that the pulley sizes were selected to bring impeller speed to 55,000 rpm (peak impeller efficiency for the T-Trim) at 6100 rpm.

With no change in pulley size, the S-Trim would also see 55,000 rpm at 6100 engine rpm, but this would be well above the 45,000-rpm efficiency peak of the S-Trim (not to mention the S-Trim's absolute maximum rated speed of 50,000 rpm). The results of the dyno test show how the S-Trim runs out of steam at the top end, a testament to the top-end punch of the T-Trim.

By comparison, the S-Trim – no slouch itself – registered 644.3 hp at 5700 rpm and 601.4 lbs.-ft. of torque at 5600 rpm. Boost peaked early at 17.9 psi, checking in 200 rpm sooner than the T-Trim, and then declined as efficiency dropped off. With just the blower swap, there was a net peak drop of 101.6 hp and 62.6 lbs.-ft. of torque. With just as much interest, we noted how the T-Trim's low-end and midrange stayed with, and then outpaced, the S-Trim. Unlike a race blower with typically sluggish low-end performance, the T-Trim held up both ends of the bargain, a sweet deal for a dual-purpose street car like Jeff's.

Jeff's engine is a made-to-order candidate for the T-Trim, so it's understandable that the performance difference between the T-Trim and the S-Trim is so great. A less powerful engine will undoubtedly show less improvement, but more to the point, without the T-Trim, the next step up from the S-Trim would ordinarily be the V-1 R-Trim, a compressor with far less bottom-end than the T-Trim. Of course, beyond this is the Mondo V-3, a definite no-no for the street unless the goal is to get out-torqued at the stoplight by the postman's Jeep.

Simply put, the T-Trim fills a big void in the Vortech blower lineup. This alone guarantees the success of the T-Trim. The fact that advanced research tools have been employed to beef up the bottom-end performance of the T-Trim is just sauce for the goose. And if there's one thing we're sure of, it's that lots of geese will get eaten.