With all the 1,000+ horsepower ratings permeating the pages of magazines and websites, it’s easy to get complacent about achieving those lofty numbers. After all, they’re seemingly so common that anyone with a salvage yard 5.3L, a couple of Chinese turbos, and some cleverly routed tubing is just a few degrees of timing away from the four-digit dyno club.
It ain’t that easy. It’s true that the airflow capability of the LS engine family enables output in street engines that wasn’t even dreamt of for old-school small-block racing-engine builders, but getting there takes careful planning and prep work. We’re talking about the bottom end of the engine, as well as the clamping capability for the cylinder heads, because when the boost level heads toward 20 psi and beyond, containing that cylinder pressure and ensuring the high-rpm durability of the rotating parts ensures repeatability of that stellar dyno result.
It was for those reasons that Australian performance specialists Harrop Engineering turned stateside and to experienced LS builder Brian Thomson to helm the assembly of an engine topped with their latest 2.65-liter supercharger. Like the LT5 engine in the new Corvette ZR1, the supercharger uses the latest and larger Eaton TVS rotors to pump out more boost. Improved adiabatic efficiency, as well as reduced drive power requirements, helps expand the power capabilities from the compressor’s new rotors. On a 427-cubic-inch foundation and pushing about 15 psi of boost, that should make for about 1,000 horses or so on E85.
“There may be a lot of 1,000-horsepower engines out there, but getting there takes as much attention to detail in the assembly as it does in the amount of boost you can cram into it,” said Thomson. “You have to be very diligent about measuring all the clearances throughout the engine, because at the levels of cylinder pressure and temperature that come with 1,000 or more horsepower, there is no room for error or ‘close enough’.”
An all-forged rotating assembly goes without saying in a build like this and we’ve outlined the details in the accompanying photos. When it comes to the block, however, Thomson decided on Concept Performance’s LSR aluminum block. We outlined the block’s attributes in an earlier issue of Chevy High Performance, but this represents the first build for Thomson with the block, as well as our first engine-build story featuring it. Like Chevrolet Performance’s iron LSX block, it offers six bolts per cylinder head clamping, but in an aluminum casting that weighs only 113 pounds.
One thing the LSR block doesn’t offer, however, is provisions for oil-jet piston cooling, giving us the opportunity to try out another new product: Get’M Garage’s Piston Cooling System, which allows the main webbing of the block to be tapped for oil jets.
“At the power level we’re talking about, the cylinder temperatures are extreme and the oil helps keep the pistons from literally melting,” said Thomson. “It’s a must in a supercharged LS engine.”
Additionally, Thomson spends hours deburring the cylinder block, smoothing out and knocking down casting edges and other stress risers to eliminate potential sources of cracks.
In part 2 of the story, we’ll finish off the engine with a set of Chevrolet Performance LSX aluminum cylinder heads and the intercooled Harrop supercharger system then push it into the dyno room to see just how easily and reliably 1,000+ horsepower is achievable on a well-prepped foundation.
1. The LSR block casting is made of 356-T6 heat-treated aluminum and weighs a scant 113 pounds with the main caps. It’s designed to accept all of Chevrolet’s production and LSX cylinder heads and other components.
2. A cross-braced lifter valley is another of the LSR’s rigidity-enhancing features. Each valley section has its own oil drain-back hole. The block casting also features thicker front and rear valley walls than production LS blocks.
3. The valley braces, however, interfere with GM lifter valley plates, which incorporate crankcase ventilation ductwork. On a strictly racing engine, that ductwork could be eliminated, but it should be retained on a street engine, so Thomson trims the tops of the braces for clearance.
4. One of the LSR’s unique features is double cross-bolts for main caps #2, #3 and #4. That makes them eight-bolt caps for greater crankshaft location accuracy and overall strength. The main caps are from Pro-Gram Engineering and are made of sturdy SAE 1045 billet steel. With the double cross-bolt feature on caps 2, 3, and 4, they offer 40 percent more main cap surface area than stock-type caps.
5. Spun ductile iron cylinder liners offer a tensile strength of around 120 ksi versus the approximately 30 ksi tensile strength of the conventional gray cast iron used in most OE engines. Ductile iron is also relatively plastic, meaning it flexes more than comparatively brittle cast iron, which helps prevent cracking of the sleeves.
6. The block was delivered bored and honed with 4.125-inch bores, but Thomson prefers to put his own hone pattern on the cylinders, so he took the liners out to 4.130 inches.
7. The block was then comprehensively deburred to eliminate sharp edges that could lead to cracks under extreme cylinder pressure. Every detail counts when building for 1,000 durable horsepower.
8. A feature that engine builder Brian Thomson likes to include on his engines, but isn’t included with the LSR block is piston-cooling oil jets, which are used to douse the bottom of the pistons with engine oil. It’s a smart way to enhance overall performance and durability. Thomson typically makes his own squirters, but for this project Get’M Garage’s new oil jet kit, which includes the jets, as well as the fixtures, drill bit, and requisite tap to install them.
9. Installing the oil jets starts with securing the Get’M Garage fixture to each main web of the block and drilling down through the oil galleries until the drill bit breaks into the bottom of the cylinders.
10. After running a tap through the holes, the jets are threaded into the block, with just a touch of blue Loctite thread sealer to secure them. Thread down until they’re just below the bearing surface of the main web. And while the jet looks like it’s going straight into the main web, it’s angled several degrees toward the cylinder.
11. Here’s the installed oil jet, which has a 0.020-inch outlet. It will shoot engine oil at the bottom of the piston to keep down its temperature. At the extreme cylinder temps that come with supercharging or turbocharging, the pistons and rings can soften without an aid like this.
12. With the block prepped, attention turns to the rotating parts, starting with a Callies DragonSlayer 4340 forged steel crankshaft delivering a 4.000-inch stroke. Thomson ordered it pre-balanced with a 1,850-gram bob weight, which eliminated the need to machine the crank and add mallory metal later. By the way, the crank is specific for a GM factory-style dry-sump oiling system, with a 1-inch-longer snout to accommodate the oil pump.
13. Thomson tack-welds the steel reluctor wheel to the crankshaft. It’s a holdover habit from building early LS engines that had sheetmetal 24-tooth wheels that tended to slip. Although he hasn’t had any real slippage problems with later-style 58-tooth wheels, it is nonetheless an added measure of insurance. The wheel is TIG-welded using silicon bronze welding alloy.
14. The camshaft comes from Comp Cams, with specs that include 0.629/0.656-inch (with 1.7:1-ratio rockers) and 217/245-degrees of duration at 0.050-inch lift. The intake lobe and exhaust lobe centerlines are each 121 degrees and so is the lobe separation angle (LSA). It’s a comparatively wide LSA that benefits supercharged engines because it reduces valve overlap, which a blower engine doesn’t need. Well, not as much as a naturally aspirated engine.
15. The rod-and-piston combination is a proven one for Thomson and includes 6.125-inch-long forged steel I-beam rods from Oliver—with 2.000-inch big ends and 0.927-inch pins—and Diamond pistons featuring a ceramic coating on the head and a Teflon coating on the skirt.
16. The Teflon coating on the pistons’ skirts reduces friction, while the ceramic coating on the head reflects heat, reducing the pistons’ temperatures, while bolstering its longevity. In fact, the reflective quality of the coating can also distribute heat more evenly through the chamber to enhance combustion.
17. Bolts stretch. Similar to a spring, they stretch beyond their static length in order to deliver clamping power. In most cases, a torque wrench does the trick, but when it comes to the connecting rod bolts, measuring their stretch dimension is a more accurate way of ensuring they’re torqued accurately. Using a bolt stretch gauge, the ideal for this combination is 0.003-inch.
18. A couple of things here: The engine was built with a dry-sump oiling system, driven by a GM LS9 two-stage oil pump (PN 12623097). The crankshaft and camshaft timing gears are also GM items, but the timing chain is a Rollmaster, which is a truly “endless,” or seamless chain (no master link), and has an exceptional surface hardness.
19. When it comes to a windage tray, Thomson uses Chevrolet Performance’s LSX part for 4.125-inch strokes. Yes, the engine only has a 4.000-inch stroke, but the bases of the Oliver rods require a little extra elbowroom. In fact, Thomson still adds 0.010-inch shims (washers) beneath the fasteners to give the rods just that much more clearance.
20. As the short-block assembly nears completion, an LS9 front cover (PN 12598293) was bolted on.
21. An LS7 oil pan was used, but because of the raised position of the windage tray, the inner ribs of the pan required trimming for clearance.
22. Because the engine will be supercharged, the standard 7.43-inch-diameter damper was upgraded to an ATI oversize 8.25-inch damper, which will be matched with appropriately sized supercharger drive pulleys to help increase airflow and boost.
23. With the bottom end of the engine built, we’ll finish off the engine with the cylinder heads and supercharger in our upcoming wrap-up installment—and see whether this strong foundation will support 1,000 horsepower or more. Stay tuned.
Brian Thomson Engines
Photos: Barry Kluczyk