LS2 Crate Engines - The Great Crate Update, Part 4

Our LS2 Gets Super...Naturally

Richard Holdener Aug 23, 2007 0 Comment(s)
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Swapping the heads on an LS2 is worth some impressive power gains, especially when accompanied by the correct cam profile.

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.

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Our first modification involved replacing the Comp XR265HR cam used previously with a larger XER281HR grind. The XER281HR offered a 0.595/0.598 lift split, a 232/234 duration split, and a 112-degree lobe-separation angle. This compares with 0.522/0.529 lift, 212/218 duration, and a 114-degree LSA for the XR265HR.

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.

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The cam swap required removing the stock valve covers, rockers, and pushrods.

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.

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We used a new assembly lube from Lucas Oil to lubricate the new cam before installation.

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.

Vemp_0703_05_z LS2_crate_engine Octane_booster 6/17

Since we expected big power numbers from the cam and heads, we added a can of octane booster to our 91-octane pump gas as a hedge against detonation.

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.




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