In the first three installments of our Great Crate Update series, we tested a wide range of modifications on our GM Performance Parts (GMPP) LS2 crate engine. After installing two different types of roller rockers, a mild Comp cam, and a FAST intake manifold in Part 1 (Nov. '06, p. 72), we staged a no-holds-barred intake shootout in Part 2 (Dec. '06, p. 56). The third part (Feb. '07, p. 62) saw an NOS nitrous kit twist the dyno needle to 633 hp, after which an intercooled Vortech supercharger (sans nitrous) pushed the total to more than 700 hp.
A FAST XFI engine-management system was employed throughout, as well as a crankcase full of Lucas synthetic oil, a set of Hooker long-tube headers, and a Meziere electric water pump. Since the LS2 was equipped with a drive-by-wire throttle body, we also took the liberty of replacing the factory unit with a manually operated 90mm version from FAST.
For this month's story, we set aside the power adders in favor of a hotter cam and a set of CNC-ported cylinder heads from Total Engine Airflow. For the cam side of the equation, we selected an XER281HR grind right out of the Comp catalog. This dual-pattern unit offers a 0.595-/0.598-inch lift split, a 232-/234-degree duration split, and a 112-degree lobe-separation angle. While we expected the extra lift to pay big dividends with the ported heads, we were also curious to see how the new cam would perform when paired with the factory LS2 castings.
Before running the new cam, we reestablished a baseline with the milder XR265HR grind from our first story. Thus equipped, the LS2 motor produced 486 hp-15 horses shy of the 501hp max achieved in Part 1. We made timing sweeps, air/fuel sweeps, and even performed a compression test in an attempt to account for the disparity. Finding nothing out of the ordinary, we chalked the difference up to the fact that our previous test session took place on a different dyno. Since we were more concerned with power gains than absolute numbers, we decided to continue our test.
The cam swap was completed in record time-Gen III swaps are not difficult on the engine dyno-and we were ready to tune. After duplicating the air/fuel and timing curves used with the smaller cam, we were rewarded with a peak reading of 530 hp. The XER281HR cam offered more power from 4,200 rpm up, and it lost only a few lb-ft of torque below that point. Given the extra 44 peak horsepower, that's a worthwhile tradeoff.
Next, we turned our attention to the cylinder heads. Off came the factory LS2 units, and on went the new ported versions from Total Engine Airflow (TEA). The TEAs started life as 243 castings, the same as our factory jobs. Unlike our stockers, these were treated to a full CNC port job, including work on the intake and exhaust ports, as well as the combustion chambers. Thanks to this porting make-over, intake and exhaust flow checked in at 340 cfm and 263 cfm, respectively.
Because the CNC work increases the size of the combustion chamber, it is necessary to mill the TEA heads in order to duplicate the factory compression ratio. Unfortunately, in our haste to install the heads on our test engine, we managed to omit this step. As a result, compression was actually reduced by as much as 0.50 points as compared with our previous tests. We suspect this reduction cost us approximately 8-10 hp through the entire rev range.
With the TEA heads in place, peak output jumped from 530 hp to 575. There was a minimal loss of power down low, but this was likely attributable to the drop in compression. Past 4,500 rpm, the power gains offered by the TEA heads increased with engine speed.
In addition to the huge performance improvement, we liked the fact that the CNC-ported casting bolted in place as a factory head does. There was no need to change pushrod length or install aftermarket rocker arms. Instead, we replaced the factory head gaskets with Fel-Pro units and reused the factory rockers and pushrods.
Given that our mild-mannered LS2 was now producing 575 hp, we couldn't help but wonder how a pair of turbochargers might affect output. Surely 700 hp was possible, but what about 800? Will the stock GMPP LS2 short-block take that kind of stress? Check back with us next time for the answer.
GMPP LS2 Crate Motor, Comp XR265HR vs. Comp XER281HR
We were pleasantly surprised by the broad power band offered by the larger XER281HR cam. Peak output jumped from 486 hp to 530 hp, and there was no significant penalty in low-speed torque production. The larger cam lost a few lb-ft from 3,000 rpm to 4,200 rpm, but these losses were minor compared with the massive gain in horsepower at the top of the rev range.
GMPP LS2 Crate Motor, Stock Heads vs. TEA CNC-ported
After witnessing the power gains offered by the hotter cam, we were curious to see how much additional power we could obtain with a set of CNC-ported heads from Total Engine Airflow. According to TEA, these heads flow a whopping 340/263 cfm (intake/exhaust) at 0.650 lift. This extra airflow proved its worth by boosting peak power from 530 hp to 575 hp. Unfortunately, an installation oversight resulted in a 0.50 point loss of compression as compared with stock. Had we been able to match the factory compression ratio, our peak numbers would have been even more impressive.