We are standing at the control panel of Thomson Automotive's SuperFlow engine dyno as their latest LS creation fires to life and idles at a docile, glass-smooth 650 rpm. No sputs, no sputters, and no hunting. After a few minutes, the oil gets up to temperature and the first serious pull is made. The 7.0-liter (427 cubic inches) twin-turbo engine turns out 1,120 horsepower as if it were just waking up, yawning while stretching its arms.
Brian Thomson, shop founder and LS-engine guru, has been building big-power racing and street engines for more than 30 years, and despite the four-figure dyno numbers, he was surprisingly nonplussed.
"It'll do more," he says, matter-of-factly. He was right. With a few more taps on the laptop, a fuel trim adjustment is made via the Holley Dominator EFI controller and the engine is so ready for another pull. The 7.0-liter pump-gas engine, which is a mix of the very best custom aftermarket parts such as ceramic-coated Diamond pistons and, surprisingly, off-the-shelf GM components (including an LS7 intake manifold and regular-production ACDelco ignition coils), pulls harder than before, nearly "burying" the big, analog torque output dial on the dyno console. In fact, it swings past 900 lb-ft so quickly, it would be easy to assume it was the tachometer.
"That's better," says Thomson. He was right again. The engine zoomed past the 1,200-horsepower threshold, still exhibiting the easy-going attributes you'd expect of a stock engine that makes only a quarter of the power. And while the best numbers of the day—1,225 horsepower and 989 lb-ft of torque—are unquestionably impressive, the engine's performance was more notable for how unimpressive it was while achieving it. As we said, the engine started and idled like your grandma's old Park Avenue, and it pulled its best numbers without even the slightest suggestion of drama. It doesn't seem all that long ago when we would have been crowing about similar refinement on an engine that made half that power.
Incredibly, the Thomson twin-turbo 427 hardly holds the record for peak output from an LS engine, but it's nonetheless a testament to today's threshold of high performance. Twenty-five years ago, computers and fuel injection were feared as the two horsemen of the hot-rodding apocalypse, but the combination of accessible tuning and the tremendous airflow capability of the LS platform transformed the performance industry.
The Good-Old Days Were Never This Good
At its core, the twin-turbo engine's combination is deceptively simple: an LSX block, LSX-LS7 heads, a not-so-radical camshaft grind, and a whole lot of boost via a pair of 72mm Nelson Turbo Engines-supplied turbochargers. Of course, there's more to the assembly than the sum of its parts and tolerances for every component were fastidiously measured with an eye on 1,000-plus horsepower capability. Thomson also installed a custom oil-squirter system for the pistons to ensure the pistons are cooler and well-lubricated under the intense cylinder pressure generated by 12 psi of boost.
Along with six-bolt clamping, the LSX block also offers priority main oiling, which is a key safety factor in an engine like this that generates so much cylinder pressure and heat. As the term implies, it feeds the main bearings first in the oiling circuit, followed by the camshaft, lifters, etc., ensuring those critically important bearings receive adequate lubrication—particularly at high rpm.
The installation destination is a radical Camaro built by HS Customs, in Logan, Utah. The twin-turbo system was a central component of the car's design, whose owner was looking to join the 1,000-horsepower street car club. Prior to assigning Thomson Automotive to build the engine, HS Customs mocked it up in the car, so there wouldn't be any trial-and-error fitment after the engine was assembled. HS Customs then shipped the turbochargers, modified Stainless Works headers, and related plumbing to Thomson's shop.
Believe us, "cheap" or "budget-minded" are terms that will never be associated with the turbo setup, but it is all devastatingly effective. The same goes for the components comprising the rotating assembly, but at least the off-the-shelf Chevrolet Performance iron LSX block and six-bolt LSX-LS7 heads aren't budget-busters. There are a number of other production-based GM parts, including an LS3 oil pan and high-volume LSA oil pump, as well as the LS7 intake manifold and ACDelco coil plugs we mentioned earlier.
Thomson admits the boost and the 1,200-horsepower level are crowding the edge for a coil-on-plug ignition system. "Those coils will handle 1,500 horsepower, but it's the boost you have to be careful about at that level," says Thomson. "When you get to 15 pounds and beyond, the boost can blow out the spark like a candle. We're at a good place right now with the 12 pounds of boost, but if we were taking it much beyond that, we'd have to look at changing over to a distributor."
Holley Dominator Details
Tuning with a factory E67 controller has its limits, too, especially when it comes to very-high-power turbo combinations that rely on a boost controller and other accessories for optimal performance. So, Thomson gave up the mass-air-metered GM control system and went with Holley's self-learning Dominator EFI speed density system. There's a lot to like with the Dominator system and it starts with its relative simplicity. You can pretty much get the engine running as soon as you peck in the basics of the engine's displacement and injector size. There are also a number of basic fuel maps to use as a starting point.
"We've been using it for more than a year now and have had good success with it," says Thomson. "The self-learning capability is very helpful because it will make mapping adjustments automatically in certain situations, which can really save time."
The Dominator ECU will also control up to 24 injectors, multiple stages of nitrous, and the all-important boost controller on Thomson's twin-turbo build. It's also compatible with dual-channel wideband oxygen sensors.
We observed as Thomson's resident tuner took the engine's baseline, get-it-running performance up to its peak power numbers within only a few minutes at the keyboard. Sure, he has logged more hours in fuel tables than Lindsay Lohan in rehab, but it nonetheless proved the system's user-friendliness. It was another aspect of this project that seemed oh-so-easy to achieve.
"It's a good system for novice tuners, too," says Thomson. "There's a lot in there to help someone with little tuning experience to get a more basic engine combination up and running."
To be honest, the pair of 72mm turbos is way more than the engine needs to make 1,200 horsepower, but they leave plenty of room to grow should the car's owner build up a tolerance to the Space Shuttle-like thrust of his Camaro.
"With these turbochargers and the boost they're capable of, 1,600 horsepower is doable—and even more—but this is an engine for a street car, with excellent driveability," says Thomson. "It idles smoothly and runs great on pump gas. We didn't observe any spark knock at the 12 pounds of boost we dialed in and still exceeded the horsepower target by 25 percent."
Cam Miller, the owner of HS Customs, concurs: "It's a great combination that's truly a pump-gas, streetable engine. There are no extra injectors, no water/methanol injection or anything like that – just a straight-up, very powerful engine."
No, this kind of power doesn't come cheap, but we're impressed at how easily it's achieved these days—and how attention to detail can pay big dividends on the dyno.
01. The starting point for the engine is Chevy Performance’s standard-deck LSX block, PN 19260093. Its iron construction makes it strong and affordable. It can also be generously overbored, which is something that can’t be done with production aluminum blocks. More importantly, it has priority oiling and features provisions for six-bolt head clamping, which is essential for high-boost combinations.
02. The LSX block comes with 3.880-inch semi-finished bores and Thomson finished them off to 4.125 inches. Deck plates are used during the procedure to simulate the slight, but important distortion the block sees when the heads are bolted on.
03. Align-honing was also performed on the block to get the main bearing journals sized just right for optimal clearance—and consequently optimal oiling for the bearings.
04. Thomson adds oil squirters to the bottom of the cylinder block bores (arrow), which spray cooling oil at the bottom of the pistons to reduce cylinder temperatures and avoid detonation. Careful machining of the block’s oil galleries is required to accommodate the modification.
05. A forged Callies DragonSlayer crankshaft is anchored in the block, delivering a 4.000-inch stroke, which combines with the 4.125-inch bores to give the engine its 427-cubic-inch displacement. A keyway was machined into the crankshaft nose, because production LS engines don’t have one. It’s a must to prevent slippage on the damper with the high loads and quick engine spin up that will come under boost.
06. Oliver 6.125-inch forged rods are hung on the crankshaft. They’re fastened via the stretch method, which is a more accurate way of ensuring the proper pre-load and clamping force on the ARP bolts. Essentially, the bolt is stretched until it is within its sweet spot of elasticity—usually between 0.005-inch and 0.006-inch.
07. Forged aluminum Diamond dished pistons are used with a heat-resistant ceramic coating on the heads and a friction-reducing Teflon coating on the skirts. The pistons are designed with thicker crowns for greater strength under boost and resistance to the effects of detonation. The dish in the piston is required to keep down the compression ratio to a boost-friendly 9.0:1.
08. The high-volume wet-sump oil pump used on the engine is for the LSA 6.2L supercharged engine and carries part number 12612289. It was selected because it’s a heavy-duty, high-volume pump and, as with Thomson’s engine, it supports a piston oil-squirting system. It’s thicker than a standard LS pump found on, say, an LS3, but it fits behind a stock front cover.
09. One of the attributes that makes the engine a sweetheart on the street is its moderate camshaft. It’s a hydraulic roller from Comp Cams with 0.629/0.656-inch lift and 215/247-degrees duration at 0.050. It also has a wide lobe separation angle of 121 degrees, which reduces overlap for better idle characteristics when the engine isn’t making boost. It also helps reduce the chance for knock, which is much-appreciated when the engine is making boost.
10. Cylinder heads are Chevrolet Performance’s LSX-LS7 six-bolt design. Like the production parts, they have the high-flow, 270cc intake runners, 70cc combustion chambers, and 2.200-inch titanium exhaust valves, but the additional two head bolts per cylinder provides exceptional head clamping strength for forced-induction engines.
11. Valvetrain details include PAC Racing dual-coil valvesprings, titanium retainers, and production LS7 rocker arms, with Comp Cams trunnions. The 580-lb springs (PN 1530) are rated for up to 0.750-inch lift and have a 1.284-inch outer diameter. The seat load is 160 lbs at 2.000-inch installed height. The LS7 rocker arms have a 1.7 ratio. Also in there is a set of Trend 7.900-inch pushrods.
12. Straddling the heads is a GM LS7 intake manifold capped with an LS7 90mm throttle body. It’s also fitted with a set of 85-lb/hr injectors to feed the force-fed 427 all the fuel it can take. It may not look sexy in its black plastic, but it works well with forced induction and fits under the hood of everything.
13. Complementing fuel system components include a Holley Dominator 12-800 inline twin fuel pump, which supports up to 1,800 horsepower. It allows one pump to be used primarily for low-rpm driving and highway cruising, with the second stage kicking when the boost comes up. And by staging the second pump, recirculation and unnecessary heating of extra fuel is eliminated.
14. Perhaps surprisingly, Thomson relies on off-the-shelf ACDelco ignition coils (PN 12611424) that are the same for LS3 engines, LSA engines, and countless others. They perform well up to the limit of what an LS engine can handle with a coil-on-plug ignition.
15. A pair of Nelson Racing Engines 72mm, water-cooled “mirror image” turbochargers feeds a moderate 12 psi of boost into the engine. The mirror-image design means one of the turbos spins counterclockwise, which enables a more symmetrical installation under the hood.
16. Let’s be clear: This is not a bolt-on system. HS Customs scratch-built the plumbing, which includes Stainless Works headers that were sliced, diced, and put back together to mount the turbos in front of the engine. Four-inch-diameter intake tubes funnel the pressurized air charge into the LS7 intake. Because of the header routing, Thomson relocated some of the coil packs and insulated the plug wires to protect them from heat.
17. Complementing turbo system components include a TiAL bypass on the intake tube. There are also a couple of TiAL 42mm wastegates in there somewhere, too.
18. Engine management is controlled by the self-learning, speed-density Holley Dominator EFI system, which has the ability to run up to 24 fuel injectors, progressive nitrous control, and dual-channel wideband oxygen sensor compatibility. It also offers an integrated data acquisition system.
19. Dave Mikels performed all the calibration work, dialing in a tune that easily surpassed the 1,000-horsepower goal, while delivering it on plain-old pump gas. No water/methanol injection, no detonation or spark knock, no nuthin’ – just a clean, safe setup with terrific refinement.
20. There was no dyno drama with the twin-turbo engine. It idled smoothly at 650 rpm and ran easily up to 6,500 rpm, where it made 1,225 horsepower and 989 lb-ft of torque. It crossed the 1,000-horsepower mark at 5,600 rpm and 800 lb-ft at only 4,500 rpm, where the boost really started to come on strong.
|Engine Dyno Testing Results (Stp Correction)|