Big motor, big blower and big air intake: The 1,000hp 7.0L LS powering the RPO Series Cama
If you do a search for the word excess in your online dictionary or through Wikepedia, chances are that you'll find a picture of the new RPO Series Camaro from Mr. Norm's Garage. What (you ask) sets these apart from the multitude of '10-and-newer tuner Camaros currently available? In this case, the excess comes in the form of horsepower. Where the stock motor is rated at just a tick over 400 hp, Mr. Norm's felt this just wasn't adequate. What if a ZO6 Corvette owner pulled up along side with 500 hp? How about a Viper with 600 hp or maybe even a Shelby Super Snake Mustang sporting 750 hp?
This irrational escalation eventually led right past doubling the power output of the stock LS3 into the rarified air of stratospheric four-digit power levels. That's right, current (or potential) Camaro owners, Mr. Norm's plans to offer a street-legal Camaro sporting as much as 1,000 hp. Truth be told, their offerings include more modest power levels as well (as we saw in our test of the 650- and 825-horse RPO cars in the December '10 issue), but it was the big number that caught the attention of our editor and, without a moment's notice, we asked them to put their money where their mouth is (or at least their advertising claims).
Truth be told, we could think of no better way to spend an afternoon than strapping someone else's supercharged 7.0L stroker to the dyno and cranking up the boost. The current generation of small-blocks has never failed to impress with its power output, but imagine taking an already stout LS3, adding displacement, bolt-ons, and boost. Now that's a party!
Obviously the right supercharger goes a long way toward adding the necessary power, but excessive boost is not only worthless, but can also be downright destructive on an otherwise stock engine. It takes much more than a ton of boost to coax 1,000 hp from an LS3. Not surprisingly, the stock internals were never designed to withstand such prodigious power outputs. Proper attention to the remainder of the motor was in order before you can add the boost required to eclipse four-digit power levels.
With the new 3.6L Kenne Bell Liquid Cooled supercharger waiting in the wings, the guys from Mr. Norm's decided to team up with the LS experts from Turnkey Engine Supply (www.turnkeyenginesupply.com). Turnkey Engine Supply whipped up an impressive LS stroker designed specifically for the rigors of forced induction. The task was made all the more difficult by the fact that the LS stroker had to not only produce big power number, but also do so on pump gas and in emissions legal trim. The package is in the process of emissions certification as of this writing, but things look good for a honest-to-goodness, emissions-legal, 1,000hp (pump gas) Camaro mill.
To reach the three-tiered goal (emissions legal, 1,000hp, pump gas), Turnkey took a three-tiered approach by combining a drop in static compression ratio with increased displacement and improved airflow. The hope was that the bigger motor would offer not only more displacement and airflow, but simultaneously reduce the chance of harmful detonation.
The more displacement was achieved by replacing the wimpy cast crank with a more suitable forged steel stroker crank. In addition to the increased strength, the forged crank also increased the stroke from 3.622 inches to 4.10 inches. When combined with a set of forged connecting rods and pistons with a 4.070-inch bore, the result was a bulletproof bottom end and a finished (LS7-matching) displacement of 427 inches (7.0 liters). The dished pistons also combined with the ported LS3 heads (from Dr. J's Performance) to produce a static compression ratio near 8.5:1. Though the drop in compression of roughly two points had a negative effect on power, the low-compression motor was much more pump-gas (premium unleaded) friendly.
1 The boys at Turnkey Engine Supply whipped up an LS3 not only capable of taking the boos
2 The 7.0L short-block received a custom hydraulic roller cam that offered over .600 lift
3 Known for tremendous flow right out of the box, the LS3 heads were given the once over
The extra displacement and drop in compression was combined with extra airflow that came in the form of the ported heads and a revised cam profile. The custom dual-pattern Comp Cams profile featured over .600 lift, a blower-friendly (wide) lobe separation angle and around 240 degrees of duration (at .050). The ported LS3 heads were set up with the appropriate valve spring package to work with the high-lift Comp hydraulic roller cam. Though additional power is available with true rollers, our test motor featured stock LS3 rockers.
Obviously, the highlight of the supercharged 7.0L was the blower itself. Not content to rest on the laurels of its impressive 2.8L, Kenne Bell has recognized the need for even higher power levels and recently introduced the new 3.6L twin-screw supercharger. From a size standpoint alone, the 3.6L was capable of supporting over 25 percent more power compared to the 2.8L. In addition to the increased displacement, the new 3.6L also offered a number of desirable design features including a proprietary rotor configuration, Seal Pressure Equalization, and a revolutionary new Liquid Cooling system. The result of these changes was not only a larger, more powerful supercharger, but one that offered a significant reduction in parasitic losses. All superchargers suffer from the parasitic losses associated with driving the blower. Different superchargers operating at different boost and power levels require different amounts of energy to drive. Increasing the power output of the motor is simply a matter of reducing the amount of power required to drive the supercharger. When a new design (like the 3.6L) combines more power and boost potential with a reduction in parasitic losses, you know you've done something right. Now throw in a drop in charge temperatures and increased component life from the Liquid Cooling (LC) and Seal Pressure Equalization (SPE) and you have one serious supercharger.
What makes the new 3.6L Twin Screw supercharger from Kenne Bell so impressive? From a size (or displacement) standpoint alone, the 3.6L is bigger than the old 2.8L. What this means is that for every revolution, the bigger blower will process more airflow. Spinning the same speed as the smaller blower, the 3.6L will force more air (and therefore boost pressure) into the motor. While this bigger-is-better philosophy seems like a no-brainer, there are limitations, or more accurately, proper applications for the larger blower. The ideal application for the larger 3.6L blower is not a stock 4.8L LS truck motor running 7 psi of boost, but rather a 400-plus inch stroker pumping 15-plus psi of boost. The larger 3.6L Kenne Bell blower was designed for high horsepower and/or high boost applications. Given its ability to support 1,200 or more ponies, it is less than ideal for someone looking to produce just 400 hp. The big blower will obviously do the job at lower boost and power levels, there are better blower choices for more modest power applications.
4 Though additional power can be had with a set of aftermarket roller rockers (like the u
5 Topping off the already stout stroker was nothing less than a 3.6L twin-screw superchar
6 The new 3.6L offered a number of revolutionary new design features including Liquid Coo
Not just bigger, the new 3.6L blower is also better. Better in this case means that with extensive research and development, Kenne Bell has managed to significantly reduce the parasitic loses associated with driving the supercharger. Since the parasitic losses are essentially power absorbed by the motor to drive the blower, the power is not applied to accelerate the vehicle. Reducing these losses effectively increases the amount of power available for acceleration. According to Kenne Bell, the new design has reduced the parasitic losses to the tune of 75 hp. To put this into perspective, the 3.6L will produce the same amount of power as the smaller 2.8L blower at roughly 3 psi less boost. Put another way, the improvement in parasitic loss is equivalent to running an extra 3 psi of boost, but without the associated increase in charge temperature. Some of the drop in parasitic losses can be attributed to the fact that the larger blower simply spins slower to produce the same amount of boost as the smaller 2.8L.
Additional gains come from a revised 4x6 rotor pack, meaning the male and female rotors sport four and six lobes respectively, differing from the less efficient 3x5 combination used by the competition. Changes to the rotor pack were combined with a unique discharge shape to optimize port timing, maximize airflow, and minimize charge temperature.
Additional improvements to the 3.6L included Liquid Cooling (LC) and Seal Pressure Equalization (SPE). One of the obstacles to overcome with a twin-screw supercharger is the temperature differential between the inlet and outlet sides of the blower. Since internal compression takes place inside the twin-screw, the air entering the blower is much cooler than the air exiting the blower. This temperature differential increases with elevated boost levels. Running very high boost levels means that one end of the blower can become much hotter than the other. The problem with this is that the expansion rate of case and rotors is also a function of the temperature. Given the dramatic temperature differential between the two ends of the blower at high boost levels, the growth rate of the case and rotors at each end will be dramatically different. Obviously the clearances must be designed to facilitate this differential, but Kenne Bell has found a way to minimize the temperature differential by cooling the hot end of the blower. This is accomplished by routing the intercooler water through a cooling cavity on the hot side of the supercharger. The result is a reduction in the tendency of the rotors to spread apart causing gear lash and the attending changes in rotor timing.
In addition to the reduction in the expansion rate, the cooling system also increases component longevity and decreases the charge temperature. The increased component life comes from a reduction in oil temperature. The supercharger gears are spun in a sealed oil bath. The elevated temperatures produced by the higher boost levels obviously have a negative effect on oil temperature at the hot side of the blower (the discharge is right next to the oil reservoir). Elevated boost and rpm levels significantly increase the temperature of the gear oil. The revolutionary new cooling system helps reduce the case and rotor temperatures, which in turn help reduce the gear oil temperature. The reduction in gear oil temperature increases the service life of the drive gears, rotors, and associated bearings. The byproduct of the decrease in case, rotor, and oil temperature is a reduction in charge temperature. According to their testing, the Liquid Cooling system reduced the charge air temperature exiting the supercharger (before the intercooler) by over 20 degrees (from 367 degrees to 344 degrees on a motor running 25-plus psi of boost). Lower temperatures equal more oxygen molecules, which in turn equals more power. Let's not forget the associated reduction in the potential for harmful detonation.
7 Running the Kenne Bell supercharger on the engine dyno required use of a number of fact
8 Increasing the boost was a simple matter of changing either the lower crank or upper bl
9 Often overlooked, the inlet system into the supercharger plays a critical role in power
Another trick applied to the new Kenne Bell 3.6L Twin Screw is something called Seal Pressure Equalization (SPE). The twin-screw design featured a front seal to separate the gearbox from the rotor pack. The problem is that this front seal must resist internal pressure supplied by the supercharger. The greater the boost levels, the more pressure applied to the seal. Recognizing the potential of the situation, Kenne Bell designed the SPE system, which effectively equalizes the pressure on both sides of the seal to eliminate the differential. Using a pressure relief system, the pressure is vented from the back of the seal to the inlet tube or air filter.
Relieving the pressure eliminates the chance of seal failure thereby preventing rotor pressure from entering the gearbox. According to Kenne Bell, the standard seal system works very well up to 20 psi of boost. It is in the 21-30 psi range where the SPE system comes into play, though the SPE does offer considerably less seal wear and friction under high-vacuum, cruise conditions. This helps eliminate the tendency to pull oil from the reservoir. The combination of the temperature reductions from the Liquid Cooling and the extended seal from the SPE has practically eliminated seal wear at high boost and vacuum conditions (not to mention adding a few extra horsepower).
The Kenne Bell 3.6L blower applied to the RPO Series 1,000hp Camaro also featured an air-to-water intercooler. A dedicated system (separate from the engine cooling) was employed to reduce inlet charge temperatures. Even efficient twin-screw superchargers increase the charge temperature with boost, but that heated inlet air is cooled by passing it through a heat exchanger housed in the lower intake manifold beneath the supercharger. The free-flowing intake manifold both minimizes flow restrictions and provides ample room to house the intercooler. The intercooler system included a high-flow electric water pump and secondary (front-mounted) heat exchanger used to dissipate the heat to atmosphere. Both the heat rejection and recovery rate are exceptional on this system and are one of the many reasons why such elevated power levels can be run on pump gas. Kenne Bell also supplied the necessary fuel rails and 75-pound injectors for this supercharged 7.0L.
The final element in the equation was airflow to the supercharger. Critical on positive displacement superchargers, the inlet system of the 3.6L supercharger received as much attention as the blower itself. Not wanting to restrict the power output of the big blower with what is essentially a restrictor plate, Kenne Bell design not only a Mammoth intake manifold, but matching single-blade, oval throttle body and 4.5-inch air intake system. Every component (from the air filter to the Mammoth intake) must meet the airflow requirements of the motor or the power will suffer. It stands to reason that a 1,000-hp motor should not be saddled with a 700-hp intake manifold, MAF assembly or air filter. The cast-aluminum Mammoth intake manifold, single-blade throttle body and MAF were designed after extensive testing on both the flow bench and chassis dyno. Ditto for the dedicated cold air intake and even the K&N air filter. The object of the inlet system is to minimize restriction at wide open throttle. Any vacuum present in front of the supercharger equates to a corresponding drop in boost pressure and power output. Less air in equals less power out.
10 Kenne Bell also went big (to the tune of 4.5 inches) on the air intake system and cust
11 Naturally the high-horsepower motor required plenty of fuel. The LS3 supercharger kit
12 All testing was performed using a set of 1 7/8-inch stainless steel headers from Ameri
While the 3.6L Kenne Bell blower and 7.0L Turnkey engine combination sounded like a match made in LS heaven, we came here to see some big numbers. As it turned out, the combination delivered exactly that. Running a pulley combination that delivered a tick under 18 psi of boost, the supercharged 7.0L LS3 pumped out 1,018 hp at 6,500 rpm and 962 lb-ft at 4,300 rpm. As expected from a positive displacement supercharger, this motor pumped out huge torque numbers, even down lower in the rev range. We started our dyno pulls at 3,700 rpm, but this motor demonstrated that it wanted to exceed 950 lb-ft even below that point.
The benefit of big engines with ported heads and efficient cam timing is that these monster pump-gas power numbers came at less than 18 psi of boost. The more efficient the normally aspirated package, the less boost required to achieve a desired power level. Lower boost means less chance of detonation, definitely a plus when the power production comes on pump gas.
Having already run mid 11s at over 125 mph with the 650hp package and low 10s at nearly 135 mph with the 800hp combo, we fully expect the 1,000hp RPO Series Camaro from Mr. Norm's to be an easy 9-second machine. Put the Camaro on a diet, crank up the boost a little, and we believe this thing might dip into the 8s. That, readers, is what Boosted Beyond Belief is all about!
13 The supercharged LS3 stroker was tuned with the FAST XFI/XIM. The FAST engine manageme
14 After treating the new motor to a break-in period and some fresh Lucas Oil, the superc
15 Graph: Kenne Bell/Mr. Norm 1,000-hp 7.0L LS3
The guys at Turnkey Engine Supply know a