In the Dec. '10 and Feb. '11 issues we took a vacation from our senses and performed a good old-fashioned cylinder-head shootout. Part one compared all the cathedral-port (LS1/LS2) heads on the market, and part two tested the available rectangular-port (LS3/L92) heads to see which flowed best and made the most power. The cathedral-port heads were run on a 408ci stroker, while we stepped things up to an even more powerful 468 stroker to properly test the LS3 heads. Now we've gone even crazier to evaluate the almighty LS7 heads. Though the LS7 castings share the rectangular ports of the LS3 heads, they up the flow ante with raised ports, altered valve angle and locations, and even larger titanium valves. Not long ago these factory LS7 castings would have been considered full race heads.
The cubes combined with flat-top pistons and 70cc chambers to produce a static compression ratio of 13.5:1. Sealing the beast was a set of Cometic MLS head gaskets secured by ARP head studs. Additional components include a Moroso pan, pickup, and windage tray; a custom timing chain from Comp Cams designed specifically for the tall-deck block (one extra link per side); and the largest off-the-shelf hydraulic roller cam available in the Comp Cams catalog. The 309LRR HR15 offered 259/275 degrees of duration at 0.050 tappet lift and a 115-degree lobe-separation angle. This cam has 0.624-inch lift with the 1.7:1 rockers used on most LS applications, but we ran 1.8:1 rockers for 0.660 lift. Comp Cams also supplied a set of link-bar hydraulic roller lifters and hardened pushrods. The bill for the short-block was $12,159. All the heads were run with a Mast Motorsports high-rise, single-plane intake with a Holley 1050 Ultra Dominator carb.
Jetting and timing were performed to optimize power production, though every head made best power with 30 degrees total ignition lead using 100-octane Rockett Brand racing fuel. Note that the tall-deck RHS block required intake spacers.
We first ran the stroker with a set of as-cast, stock LS7 heads and found peak numbers of 742 hp and 684 lb-ft of torque and average numbers of 635 hp and 647 lb-ft. Every one of the aftermarket heads bested those numbers. See the results in the chart, where we reveal the peak power numbers as well as the average horsepower and torque from 3,600 to 6,700 rpm, the torque reading at 4,000 rpm, and the flow numbers at the standard 28 inches of water.
There wasn't a dog in this bunch. There is a sizable gap in price between the most expensive and least expensive heads, but they all made big power. There was greater variance than what we saw in our LS3 test (where every head tested made virtually the same power), but in reviewing the numbers, we had to ask ourselves what the real difference in e.t. or seat-of-the-pants feel would be between the 13.5 average horsepower and 12.9 average torque numbers that separate the lowest-priced heads and the biggest-power heads we tested.
We were also interested to note that, in general, the heads with the better flow numbers produced better power, as you’d expect. But the flow bench does not tell the whole story; looking at flow alone, you might not select the SDPC heads, yet they outpowered some of the heads with similar or slightly higher flow numbers. There’s still some magic in port and chamber shapes.
Bottom Line: Every LS7-based head is amazing. The Procomp heads clearly win the low-price contest, using import castings and domestic porting to make more power at a lower price than even the stock LS7 heads. Judging by the average power numbers, the Texas Speed PRC heads seem to offer the best value, and the Mast Black Label heads crank out the highest power.
