In highly competitive racing classes that place strict limitations on engine modification, scratching and clawing for that last percentile of hp separates the apex predators from the bottom-feeding rodents. In this upper echelon of professional engine building, the cumulative effect of a bunch of little tricks—like minimizing ring drag, stabilizing the valvetrain, maximizing cylinder wall integrity, and experimenting with countless valve jobs—pumps up factory horsepower ratings to ridiculous levels. That’s precisely what the School of Automotive Machinists & Technology (SAM Tech) did to fortify its COPO LS7 for NHRA Stock Eliminator competition.
The resulting numbers are absolutely astonishing: 825 horsepower and 8,300 rpm with a hydraulic roller camshaft, factory GM cylinder head castings, and a production LS7 aluminum block. That’s nearly two horsepower per cubic inch—and 320 hp more than stock—despite utilizing basic hardware that’s not much different from what’s found in a stock C6 Z06. Like, how is this even possible? As SAM Tech Director of Education Judson Massingill so eloquently explains, “Getting the first 90 percent of an engine’s hp potential is easy, the next five percent is hard, and the last five percent is a real SOB.”
Although no Pro Stock or Sprint Cup team in their right mind would ever reveal trade secrets of this caliber, as an educational institution, SAM Tech was more than happy to divulge what it takes to build a race-winning Stock Eliminator LS7. Cutting-edge projects like these serve as the perfect testbed for students and instructors to apply lessons learned in the classroom to real-world race engines. Make no mistake; this isn’t a weenie bracket motor or some street/strip sissy. Unless you have a buddy who works for Warren Johnson or Hendrick Motorsports—and doesn’t care about keeping his job—SAM Tech’s LS7 utilizes some of the most innovative, creative, and interesting horsepower secrets you’ll ever see.
From Stock to COPO
Straight from GM, the COPO LS7 is no ordinary LS7. Although GM’s official horsepower rating of 425 is supposed to make people feel all nostalgic, the figure is completely bogus. “The 427 big-block in the original 1969 COPO Camaro was rated at 425 horsepower. That rating was legit, and after blueprinting the motor and bumping up the compression ratio, they made 575-600 hp,” Judson explains. “Today it’s different. GM just dreams these hp numbers up. The COPO LS7 is rated at the same 425 hp as the original ’69 COPO Camaro, but it actually makes 730-740 horsepower straight from GM.”
Even after accounting for the differences in SAE and STP (standard temperature and pressure) correction factors, the horsepower gap between the COPO LS7 and a stock LS7 is immense. The COPO’s long-tube headers and Holley Hi-Ram intake manifold are obvious upgrades from stock, but diving beneath the valve covers and oil pan reveal more significant changes. Although the COPO engine shares the same block, bore diameter, and stroke dimensions as a production LS7, its rotating assembly is completely different. It features a Callies Compstar steel crankshaft and forged 6.100-inch rods matched with Mahle 13.0:1 pistons. In addition to increasing the compression ratio more than two full points over stock, the pistons boast a Grafal anti-friction coating and low-tension rings.
The COPO’s camshaft is a completely different animal as well, with 233/276 degrees of duration at 0.050 and 0.630/0.630-inch lift. This is quite a bit larger than the 211/230-at-0.050, 0.591/0.591-inch lift cam found in the stock LS7. The 43-degree duration split on the COPO may seem radical, but when matched with CTS-VR hydraulic lifters, PSI beehive valvesprings, titanium intake valves, and a COPO-specific CNC program that squeezes a smidgen more airflow out of the LS7 cylinder heads, the combination turns 8,000 rpm out of the box. Consequently, the challenge of building a competitive Stock Eliminator LS7 isn’t merely improving upon a stock 505hp LS7. The daunting mission at hand is improving upon a highly optimized COPO LS7 that’s already producing 200-plus hp more than stock.
Porting cylinder heads is difficult enough as it is, but throwing a rulebook into the mix is like trying to design a set of ports with one arm handcuffed to a workbench. Fortunately, sanctioning bodies are sometimes forced to revise rules that are difficult to police. “Racers have figured out how to hide port work, so the NHRA has given up on trying to enforce that rule. Instead, they’ve come up with a maximum allowable volume for the ports and a minimum volume for the combustion chambers,” explains Judson.
Given these restrictions, improving airflow is much more difficult, but not impossible. “There’s a lot of airflow potential in the valve job. We can’t run larger valves, so we move the seat out to the far edges of the valve, which effectively makes the valve perform as if it’s bigger,” says Judson. “From there, we try different cuts on the seat where it transitions from the edge of the valve into the combustion chamber. Then we try different back-cuts on the valves to see what works best. We ruin quite a few valve seats to get the angles and cuts just right, and what we end up with is very different than what comes from GM.”
Straight from the factory, the COPO LS7 head castings flow an impressive 375 cfm. Despite having to work within an NHRA-specified maximum port volume, SAM Tech somehow increased airflow to 390 cfm. “The maximum intake port volume we’re allowed is 275 cc, so we milled down the intake flange surface to shorten up the length of the port just slightly. This gives us some extra room to touch up the short-turn radius, bowl and valve job area and increase the cross-section a bit without exceeding the cc limit,” Judson reveals.
To wring some more rpm out of the COPO LS7, SAM Tech spec’d out a custom camshaft to take advantage of their improved cylinder head design, and also focused on stabilizing the valvetrain. After testing several different grinds, SAM Tech opted for a custom Comp 258/276-at-0.050 cam. The additional 25 degrees of intake duration helps build cylinder pressure higher in the rpm range, and the wide 116-degree lobe separation angle further extends the powerband at high rpm. Since the NHRA limits maximum valve lift to 0.641 inch, as no surprise, the cam picks the valves up exactly 0.641 inch.
Although the excellent factory GM valvetrain is a tough act to follow, SAM Tech recognized some areas for improvement. “The CTS-VR lifters that GM uses in the COPO LS7 are some of the most incredible lifters I have ever seen, but GM sets the plunger travel in the middle like a street car. For our COPO build, we took a set of factory LS7 lifters and shimmed them up so they only have 0.012-inch of plunger travel,” explains Judson. “That enables them to function more like a solid roller lifter. They probably don’t make too much of a difference at 7,800 rpm, but they’re definitely an improvement above 8,000 rpm.”
According to Judson, reducing mass on the “valve side” of the valvetrain is far more important than reducing mass on the “pushrod side” of the valvetrain. “We installed a set of PAC springs and upgraded to titanium retainers and locks. Every gram of weight you can save on the retainers and locks makes a big difference in valvetrain control and durability,” he asserts.
If increasing cylinder pressure is the key maximizing torque, then converting that torque into as much hp as possible involves preventing cylinder pressure from falling off at high rpm. With the countless hours and dollars that go into optimizing the induction package and valve events to achieve those key objectives, preserving cylinder pressure is just as important as creating it. “You can’t have any blow-by going into the crankcase,” Judson explains. “Any cylinder pressure that’s getting past the rings is pressure that isn’t pushing down on the pistons. Ring seal is critical, and the cylinders must stay round.”
With a 4.400-inch bore spacing and 4.125-inch diameter bores, cylinder wall thickness is already at a premium in a stock LS7. Since NHRA rules allow for up to a 0.070-inch overbore, racers are bound to push the limit even further to pick up some additional displacement and give the valves some extra breathing room. To reduce cylinder distortion while also enjoying the benefits of a larger 4.185-inch bore, SAM Tech shipped the block off to ERL Performance to replace the factory gray iron liners for a set of Darton dry sleeves.
As engine rpm and piston speed increase, parasitic power loss skyrockets. Even in stock trim, the LS7’s relatively long 4.000-inch stroke yields a brisk piston speed of 4,666 feet per minute at 7,000 rpm. Simply raising peak rpm to 8,300 rpm increases piston speed to 5,533 feet per minute. That means that each piston in SAM Tech’s COPO LS7 is dragging its rings up and down the bore an additional 14.45 feet per second compared to stock, which equates to a whole lot of friction. The obvious solution is applying a deep plateau hone to the cylinder walls to strike an optimal balance between oil retention and a slick surface finish. “On a high-end racing engine, the right cylinder hone and ring package can make a 25-35 horsepower difference,” Judson asserts.
While a slick cylinder wall finish is rather ordinary by race engine standards, the other friction-reducing tricks SAM Tech’s LS7 has up its sleeves are anything but. The NHRA rulebook strictly regulates piston design by prohibiting gas ports and specifying a minimum ring groove width. As a clever workaround, SAM Tech replaced the COPO LS7’s standard 0.043-inch top and second rings with thinner 0.027-inch Total Seal units. The reduced surface area offered by the thinner rings cuts down on friction and provides superior conformability to improve cylinder seal.
Nevertheless, thinner rings are more prone to flutter, which would usually be a bad thing if it weren’t for Total Seal’s ingenious solution. By matching the thin rings up with gas-slotted ring spacers, the result is additional ring support and further enhanced ring seal. “The horizontal slots in the spacers work like gas ports. They route cylinder pressure behind the rings to force the ring face into the cylinder wall,” Judson explains. “This means you can run lower-tension rings, reduce friction, and still have great ring seal. As cylinder pressure decreases in the later stages of the power stroke, the slots allow the pressure behind the rings to bleed off quickly, reducing ring drag.”
Since pistons aren’t the only components in the rotating assembly subject to frictional power loss, SAM Tech devoted equal attention to the crank and rods as well. The spec crankshafts and rods mandated by the NHRA effectively ban the use of smaller-diameter Honda rod journals as a means of reducing bearing friction. SAM Tech had to get more creative by narrowing the Number 1 and 5 main bearings 0.055 inch and the rod bearing 0.062 inch. “Due to crank flex, the bearing load on the Number 2 and 4 main bearings are much higher than on the Numbers 1, 3, and 5. A crankshaft with center counterweights can help even out the loads, but the spec crank we have to run doesn’t have them so we stuck with standard-width bearings on the Number 2 and 4 mains,” Judson explains.
When the task at hand involves accelerating the crankshaft with as much ferocity as possible, anything that enables the crankshaft to rotate more freely can potentially reduce parasitic power loss. Although the LS7 block’s deep-skirt design provides excellent support of the main caps, the downside is that it isolates the crankcase into four separate sections. Consequently, crankcase pressure can create resistance against the piston as it travels down the bore. A vacuum pump offers an easy solution, but they’re banned by the NHRA on the COPO LS7.
Recognizing this problem, GM enlarged the breathing windows on the LS7 main caps to improve bay-to-bay ventilation. SAM Tech took things a few steps further by radiusing the breathing windows and polishing out the crankcase to a smooth finish by removing casting flash. As Judson explains, “The enlarged breathing windows allows air that gets pushed down by the pistons to escape, preventing it from getting trapped in one compartment. Polishing the crankcase reduces the risk of stress cracks, and it also helps the oil drain back into the pan more easily.”
01. With a stream of Renegade 116-octane fuel running through the rails, the COPO LS7 performs best on 31 degrees of timing. SAM Tech varies the air/fuel ratio between 12.7:1 and 13.2:1 depending on the level of competition on a given race weekend. A Holley Dominator EFI system is tasked with engine management duties.
02. Beyond 700 hp, the factory LS7 block is notorious for cracking, particularly in forced-induction applications. Replacing the factory gray iron liners with Darton ductile iron sleeves virtually eliminates the possibility of cylinder wall distortion and cracking.
03. When honing a race engine, the goal is to have just enough surface area on the wall finish to seal the rings, since too much surface area can compromise oil retention. As such, SAM Tech hones the COPO LS7 to an RA value of 10-12, and a RZ value of 100-120.
04. The Gen III/IV small-block’s deep-skirt architecture separates the crankcase into four distinct “compartments.” GM casts recesses between each bay of cylinders, beneath the pan rails, to improve crankcase breathing.
05. SAM Tech radiused the breathing notches in the block and the main caps to further improve bay-to-bay crankcase ventilation. Removing casting flash from the crankcase eliminates stress risers and the potential for cracks to develop.
06. Main bearings Number 1 and 5 have been narrowed from 0.805 to 0.750 inch to reduce friction. Since the Number 2 and 4 main bearings endure the most abuse, and the Number 3 bearing serves as the thrust bearing, SAM Tech left them at the stock width.
07. To account for forging variations, the NHRA allows for an additional 0.015-inch of stroke length. Not surprisingly, many racers now offset grind the Compstar LS7 cranks to 4.013 to 4.015 inches to gain an additional 1.3 to 1.5 cubic inches of displacement, depending on bore diameter. With a 4.185 bore and a 4.015-inch stroke, the SAM Tech COPO LS7 checks in at 441 cubic inches.
08. The NHRA limits maximum valve lift to 0.641 inches, but duration specs are unrestricted. Limiting the travel of the lifter plungers allows for more aggressive ramp opening rates. On the dyno, the COPO engine ran best with two degrees of cam timing advance.
09. The bushed lifters bores reduce the size of the oil hole to 0.045. Since the factory LS7 block does not benefit from priority main oiling, limiting the flow of oil to the lifters and the heads offers more consistent oil pressure and prevents oil from dripping back down onto the crank.
10. The NHRA mandates a spec Compstar 6.100-inch steel rod as well as a spec piston. The SAM Tech combo utilizes Compstar rods, but several manufacturers—including Eagle and Carrillo—offer NHRA-approved components as well. Tight regulation keeps rotating assembly bobweight at a reasonable 1,750 grams.
11. After narrowing the rod bearings from 0.792 to 0.730 inch, SAM Tech chamfered the edge of the bearings as well. Compared to the stock bearings (left), the Clevite units (right) feature an anti-friction coating.
12. SAM Tech opted for Wiseco pistons with a 12cc dome, but CP, Ross, and Diamond offer NHRA-approved pistons as well. According to Judson, there is a negligible difference in piston weight, ringland thickness, and overall quality between each brand, but he prefers the consistent quality offered by Wiseco.
13. At 0.027 inch, the Total Seal rings (right) aren’t just super thin, they also utilize a proprietary coating to reduce friction. The 0.016-inch spacers offer similar benefits to gas ports by incorporating 15 horizontal gas slots around their perimeter.
14. By tying all five main caps together, the DM Performance stainless steel girdle reinforces the mains and adds rigidity to the bottom of the block. Its design can potentially decrease oil windage as well.
15. Since the factory cast LS oil pans serve as a structural component of the block, the Stef’s pan features beefy 1/2-inch-thick billet rails. The pan’s 7-quart capacity and deep sump allow oil to drain as far away from the crank as possible to reduce windage. Judson estimates that the pan is good for 10-12 hp.
16. The GM oil pump is yet another surprisingly capable factory component. SAM Tech enlarged and radiused the inlet and outlet, but otherwise the pump is stock. To eliminate any flow restriction on the suction side of the pump, it’s fed by a larger-diameter Stef’s pickup tube that increases oil flow and prevents cavitation at high rpm.
17. Instead of a fixed compression ratio limit, the NHRA specifies a maximum piston dome volume of 12 cc, a minimum combustion chamber volume of 66 cc, and a minimum quench clearance of 0.041 inch. SAM Tech opted for 0.055-inch Cometic MLS head gaskets and set the deck clearance at 0.008 out of the hole. By increasing the bore and stroke to 4.185 and 4.015, respectively, SAM Tech bumped up the compression ratio from 13.5:1 to 14.8:1.
18. Both the length and cross-section of a port determine its total volume. By milling the intake flange surface 0.050, SAM Tech was able to increase the port cross-section at the short-turn radius and bowls without exceeding the NHRA-mandated limit of 275 cc.
19. The word on the street is that the COPO LS7 cylinder heads are worth 12-15 hp over a factory LS7 head due to differences in CNC programs. SAM Tech’s port work increased flow from 375 to 390 cfm.
20. The stock Del West titanium intake valve and sodium-filled exhaust valves are so light and durable that SAM Tech saw no reason to replace them. They check in at 2.025/1.615 inches, which is the max allowed by NHRA rules.
21. Thanks to the lightweight valves, excessive spring pressure isn’t necessary. The PAC valvesprings feature 235 pounds of seat pressure and 520 pounds of open pressure. Titanium retainers and valve locks reduce mass compared to the steel factory GM hardware.
22. The stock 3/8-inch LS7 pushrods are quality pieces, but higher valvespring pressure increases deflection. As such, SAM Tech upgraded to Smith Brothers 7/16-inch chrome-moly pushrods, which required enlarging the pushrod holes in the cylinder heads just a tad.
23. Limiting the plunger travel of the lifters meant that the non-adjustable factory LS7 rockers were no longer viable. SAM Tech replaced them with a set of steel T&D 1.8:1 rockers. The NHRA checks the actual valve lift at the rocker arms, which works out to 0.641 inch on SAM Tech’s LS7.
24. Essentially a tunnel-ram with a forward-facing throttle body, the spec COPO Holley Hi-Ram intake manifold represents a monumental improvement over the stock manifold at high rpm. SAM Tech enlarged the bolt holes just in case it needed to be shifted slightly for better port alignment, but otherwise the intake is stock.
25. In stock trim, the SAM Tech COPO Camaro ran a best of 9.51 at 141 mph. With a hopped up LS7 between the framerails, the car has run a best of 9.14 at 145.58 mph. Students and instructors work tirelessly at the shop and at the track to squeeze maximum performance out of the COPO package.
26. Any competitive engine combination conceived by skillfully interpreting the rulebook is bound to generate some controversy. However, SAM Tech’s COPO LS7 passed a full NHRA teardown with flying colors at the 2015 Chevrolet Performance U.S. Nationals. NHRA technicians gave the engine their seal of approval after closely inspecting the intake ports, exhaust ports, combustion chambers, valve heads, valve stems, cam lift, cylinder bore, stroke length, deck clearance, gasket thickness, intake manifold, throttle body, and lifter plunger travel.
|On The Dyno|