In our last issue, we started our look inside Borowski Race Engines’ 2.9 liter Whipple supercharged LS power plant. If you point your browser back to that page, you’ll find the engine foundation is based upon a Dart LS block, a Callies crank and rod package and custom Diamond pistons – all of which are stout and engineered to support the pressure-fed small block.
Up top, the standard heads are CNC-ported GM LS3 castings that have been treated to PAC valve springs. The seats and guides are prepped using an ultra-modern Newen machine. Essentially, this single-point, CNC valve seat cutter is one of the most capable seat-cutting machines available on the market today. Single-point seat cutting is the only way to ensure you get the perfect fit and perfect seal each and every time. With an accuracy of less than 0.00012-inch (3 microns), this machine can offer a 100% customizable seat profile. That means it can do everything from single angle, 3-angle, and 5-angle to a contour-radius seat. And it repeats exactly the same from valve to valve.
Rocker arms are GM examples, but they have been fitted with a Comp Cams roller trunion kit. Pushrods are custom Smith Brothers examples. All fasteners are from ARP. For big power applications, McCaul and crew upgrade the block to accept honking ½-inch cylinder head studs.
Before we get to the actual blower, we should note that the Borowski engine package can be upgraded with LS7-style heads from both Brodix and All-Pro. In either case, the heads are CNC ported in-house and given the same CNC valve job on the Newen machine. Other top end options include a set of Crower stainless steel rockers, Crower Enduramax needleless roller lifters and upgraded PAC valve springs, Manley valve locks and Manley retainers.
At the very top of the engine, it’s easy to see the complete Whipple 2.9 liter twin-screw blower arrangement. These Whipple supercharges include an intercooler, and they’re fitted with a 170-mm single blade throttle body and 65-lb fuel injectors. McCaul notes that in many applications, this blower will fit under a stock hood.
Why use a twin-screw, positive-displacement supercharger for street? According to Ken McCaul: “OEMs use positive displacement superchargers on small blocks to get the throttle response and drive-ability of big blocks. The screw compressor is by far the best supercharger available today; it’s the only supercharger to provide a positive displacement design for maximum low-end torque as well as high efficiency for maximum top-end horsepower. The vacuum bypass valve provides naturally aspirated gas mileage and driveability under cruise or light load conditions with virtually instantaneous boost once you put your foot into it. Centrifugals and turbos suffer lag during shift points, on-off throttle and off the line boost. Roots-type superchargers are inherently inefficient, especially at higher boost levels.”
Ken adds: “The 2.9 liter supercharger fits under most hoods without modifications. Their high efficiency reduces heat generated, compressing the inlet air. The integral inter-cooler is very effective at maintaining a low manifold air temperature, which allows higher compression ratios and more timing for higher horsepower.”
The drive assembly is a custom serpentine setup. The serpentine kit includes: power steering pump, air conditioning compressor, 225 amp alternator, water pump and an ATI Super Dampener. Everything is polished, and Borowski adds a set of polished billet valve covers along with a custom ignition wiring system (coils are typically from MSD).
The engines are supplied with a complete Holley Dominator EFI fuel injection setup along with a full complement of Holley sensors and wiring harnesses. If you’ve studied these pages in the past, you’ll find that the Holley Dominator is one of the most powerful EFI systems available today, and to make it even better, it’s also very user-friendly.
Fair enough, but how does the blown 427 perform? On the dyno, with pump gas in the fuel cell, the Borowski bad boy cranks out 975 horsepower and 768 foot pounds of torque – all on only 12 pounds of boost. With a load of high octane C16 in the tank, boost can be increased to 19 pounds. The result? Try 1155 HP! Yikes. Even better, here’s a video of the engine on the dyno (note that it’s sufficiently mild to operate a custom A/C pump):
This is one bad-to-the-bone small block, and it’s streetable too! Next issue we’ll step it up with a look at Borowski’s take-no-prisoners 4.0-liter LS. You ain’t seen nothin’ yet!