By Richard Holdener/Photos by Author
We will skip right past the notion of whether you really need 1,000 hp, and jump right into how to get 1,000 hp. The reality is that most race cars have trouble putting four-digit power levels to the ground, let alone street cars, but since 1,000 hp seems to be the new 500 hp, let’s dive right in.
Not long ago, 1,000 hp was the holy grail of power, but today, 1,000-hp street cars have become common place. The reason for this massive escalation of power is both technology and turbocharging.
Turbos have not only greatly simplified power production, but have also combined with modern fuel injection to allow such levels to be safely run on street cars. By combining boost from efficient turbos with modern fuel injection and electronic boost control, a street car can drive around like every other mild-mannered Clark Kent, and then, just as easily, transform into a boosted man of steel. But, like any super hero, there is a back story to the successful transformation!
Our story began with the purchase of a well-used, 5.3L LM7 from a local junkyard. The 2003, 5.3L truck motor was shipped from a wrecking yard in the Ohio area. Though we kept the short block primarily stock on our LM7, the motor was disassembled and given some love before subjecting it to the power-producing modifications.
You see, fellow enthusiasts,, the best way to maximize power production of a turbo motor, is to make as much power as possible before adding boost. This way, you simply multiply the existing power. The greater the starting power output, the lower the boost level required to reach any given power level.
Since we were looking for nothing less than 1,000 hp, we decided to take the necessary steps to improve the power of the naturally aspirated 5.3L before adding a pair of boost makers. Before making the power modifications, we disassembled and cleaned the LM7, honed the cylinders and decked the block.
We completed modifications to the stock short block by increasing the factory ring gap from .019-.032. Increased ring gap is the key to keeping the stock (cast) pistons alive at elevated power levels.
With our high-mileage, stock 5.3L short block now factory fresh (sort of), we set in on increasing the power output. By now, you should be aware that the power output of any boosted (turbocharged) motor is a function of the power output of the normally aspirated motor multiplied by the boost pressure (pressure ratio).
What many enthusiasts don’t realize is that your normally aspirated motor is already running under atmospheric pressure of 14.7 psi. If we were to double this atmospheric pressure (with boost from a turbo or blower), it is possible to double the power output of that motor. Lucky for us, this power/boost formula works regardless of the starting power output. If we apply the formula to a stock 5.3L, which makes 355 hp under our test conditions, we would get 710 hp at 14.7 psi.
On the other hand, if we increase the power output of our motor to 500 hp with ported heads, the right cam and a powerful intake, adding the same 14.7 psi of boost would put us near 1,000 hp! Put another way, adding 14.7 psi to a 355-hp 5.3L will yield a tad over 24 hp per pound of boost. The same 14.7 psi applied to a 500-hp (NA) motor will yield 34 hp per pound of boost. Which would you rather have, 24 hp/psi or 34 hp/psi?
To increase the power output of our 5.3L, we added the proverbial 1,000-hp camshaft. In truth, there is no magic 1,000-hp cam, but rather a combination of components that work in conjunction with a powerful cam grind. The wimpy 5.3L truck cam was first replaced by a healthy 281LR HR13 cam from Comp Cams. The LSR cathedral-port grind offered a .617/.624 lift split, a 231/239-degree duration split and a boost-friendly 113-degree LSA.
Plenty powerful for a 5.3L, the Comp cam was teamed with a set of GenX 215 heads from Trick Flow Specialties. The Gen X 215 heads featured full CNC porting, 215-cc intake ports and a 2.04/1.575 stainless steel valve package. The combination allowed the head flow to exceed 320 cfm, or more than enough for our little LM7. The head/cam combo was combined with a powerful Fast LSXRT intake and matching 102-mm (Big-Mouth) throttle body. Fast also supplied a set of billet fuel rails to provide sufficient fuel flow for our 160-pound injectors. The thick-deck, TFS heads were secured using Fel Pro MLS head gaskets (.053 thick and 3.950 bore) and ARP head studs. The larger (64-cc) chambers employed on the GenX 215 heads dropped the static compression of our modified LM7 by nearly .5 points.
The combination obviously paid off, as the modified 5.3L was run on the dyno with a Fast XFI/XIM management system. Run with 1 ¾-inch, long-tube headers and tuned to perfection, the naturally aspirated 5.3L produced peak numbers of 503 hp at 6,600 rpm and 443 lb-ft of torque at 5,600 rpm. The impressive power output was put to good use after we installed a pair of 76-mm turbos from CXRacing.
The turbos were run with a dual-core, air-to-water intercooler and a pair of TurboSmart waste gates. The DIY turbo system featured shorty truck heads and custom 90-degree bends that included T4 turbo flanges and waste gate flanges. Run first at a peak boost pressure of 5.5 psi, the twin-turbo 5.3L produced 696 hp and 606 lb-ft of torque. Imagine that, nearly 700 hp at just 5.5 psi.
That power level represented 35 horsepower per pound of boost! As impressed as we were with the low-boost power, we came to see 1,000 hp and that is exactly what we saw after cranking up the boost to 15.4 psi. Run at this elevated boost level, the twin-turbo 5.3L produced 1,013 hp and 872 lb-ft of torque.
The efficiency dropped slightly to just over 33 hp per psi of boost, but this was likely due to the reduced ignition timing and hotter charge temps. Ice water in the cooler would certainly improve things, as would replacing the race fuel with E85, but it’s pretty hard to be unhappy with over 1,000 hp at just 15.4 psi on a 5.3L!