LPE actually offers four significantly different cylinder head CNC porting options for the Gen III engine plus options. There is a design for the 4.8 and 5.3L engines, another for the LS1, one for LS6 heads, and yet a fourth for the larger 6.0L engines. The stock 5.3L aluminum heads come with 1.89/1.55-inch valves along with a 62cc chamber. LPE's CNC porting generally uses 2.00-inch or larger intake valves for most combinations, but given the 5.3L's small bore size of 3.779, Haines opted for stock 2.00-inch LS1 intakes. LPE did mill the heads from the stock 62cc chamber down to 57 cc's to bump the compression from 9.45:1 to 10:1.
As you can see from the dyno power results of Test 5, the heads not only increased airflow throughout the valve lift curve, but more importantly were worth increased power throughout the entire engine test from 2,000 rpm through 6,800. As you can see from the test data, even at 2,800 rpm (for example), the ported heads are worth a solid 10 lb-ft of torque. But it's the combination of these ported cylinder heads and the larger camshaft at engine speeds above 4,400 where the combination really shines. Looking at the peak horsepower point, the LPE-ported heads were worth an amazing 33 hp over the stock heads at 5,800. Even at the peak, the heads produced a solid 24 hp, making an amazing 437 hp. Remember, we're talking about a 5.3L, 325ci truck engine here, not some big-inch thumper. This is still on pump gas and with a completely stock bottom end. This computes to a impressive 1.34 hp per cubic inch (hp/ci).
We also wanted to see what a shorter runner intake like the Comp Cams FAST LSX composite would do on our smaller 5.3L engine. In order to do this, we had to also change the front accessory drive on the engine since the truck accessory drive is very tall in the front and will not clear the lower LS1/LS6/FAST LSX-style intake throttle-body. This meant changing the entire front dress on the engine since the truck balancer/pulley arrangement is deeper than either the Camaro or Corvette style accessory drives.
With the accessory drive and intake bolted on, we chose to retain the stock 75mm throttle-body. As you can see from the comparison of Test 5 and 6, the shorter length runner manifold (along with the accessory drive) surprisingly didn't hurt the torque in the low-rpm range. Generally, a shorter runner length manifold like the LSX intake will trade off some torque for top-end horsepower gains. Some of this torque improvement is certainly attributable to the average of 6 hp gained from the change to the F-car accessory drive.
The major improvement in power occurred from 5,600 rpm and up where the LSX manifold really shined, boosting power as much as 22 hp at 6,200 compared to Test 5 (14 hp if you account for the accessory drive change). Overall, the power was impressive with this little 5.3L engine spinning up a peak of 458 hp at 6,600 and a torque peak of 392 at 5,800 rpm.
5.3l To GoIt's no secret the Gen III small-block is a stout engine that responds to virtually any breathing or camshaft modification. It turns out that the 5.3L is as responsive as its larger 5.7L LS1 brother. Do the math on this spinner and you quickly discover that this equates to 1.4 hp/ci. Granted, this combination cannot be deemed inexpensive since a complete pair of CNC-ported LPE heads will cost $1,595 (add $600 without a core) and the LSX intake is almost $800. We used these components to illustrate this small engine's potential to make outstanding pump gas power without the need for a supercharger or nitrous. If you think of this engine as a late-model 327, cranking out 450-plus horsepower from this little of an engine is plenty impressive.