Words And Photos: Richard Holdener

GM may have offered a couple of more powerful factory LS motors, but the LSA and LS9 each required a hefty dose of forced induction to top the magnificent 7.0L LS7.

Sporting more than just 427c.i., the LS7 offered an impressive combination of cubes, compression, and cam timing, to say nothing of the highest flowing cylinder heads in the LS line up. Even diehard big block enthusiasts have to give it up to the modern LS7, as this all-aluminum monster was more than up to the task of carrying the torch for its legendary namesake. Never mind the 427s of yesteryear, the modern version offered not only more power than the previous 7.0 liter motors, but arguably more than its 454 predecessor. Not only is the current LS7 more powerful, but it also offers considerably less weight, better fuel economy, and reduced emissions. Try running one of those muscle-car big blocks in your Corvette, and see what kind of fuel mileage you get!

Yes, the modern LS7 is head and shoulders better than the original, but that doesn’t mean we can’t make one even more powerful.

As good as the modern LS7 is, the GM engineers never designed the motor with maximum power in mind. Like the rest of the LS family, the 7.0L 427 takes very well to modifications like enhanced cam profiles, ported heads and (in our case) a revised intake manifold. While a FAST intake will certainly improve the power output of a stock LS7, it is even more beneficial on a modified version. As luck would have it, the guys at Cool Machine Performance (CMP) were heading to the dyno to test some LS7 cam profiles, and we talked them into allowing us to run a quick intake swap.

The only way to demonstrate the gains offered by upgrading the factory LS7 intake was to perform a back-to-back test. Naturally the test would include optimizing each combination, but as it turned out, both intakes made best power at 13.0:1 air fuel and with 31 degrees of total timing.

Though sporting over 427c.i. and wearing CMP LS7 heads, the all-aluminum test motor began life as an LS3. To achieve the desired bore size of 4.130 inches, the LS3 block was sleeved and bored to receive a 4.0-inch, Manley stroker assembly. The forged reciprocating combo included 4.130-bore, forged flat-top pistons, matching H-beam rods and the Platinum-series stroker crank. The forged slugs relied on a Total Seal ring package to maximize sealing and power production. The custom CMP LS7 cam was teamed with an adjustable cam sprocket and Aviad dry-sump oiling system. Topping this modified LS7 was a set of CMP Brodix SI LS7 heads. These CNC-ported heads featured (smaller-than-stock) 258-cc intake ports, 108-cc exhaust ports and (small) 62.5-cc combustion chambers. For the cfm crowd, peak intake flow checked in at a hair over 395 cfm. The exhaust flow was equally impressive with 259 cfm. The numbers suggest these LS7 heads were capable of supporting more than 800 hp on a more serious application.

In preparation for our intake test, the LS7 was first equipped with Kook’s long-tube headers, a FAST XFI/XIM management system and filled with Lucas 5W-30 synthetic oil. Other fancy bits on the test motor included an ATI Super Damper, Meziere electric water pump, and FAST 102-mm throttle body.

Run as described with the stock LS7 intake, the stroker produced peak numbers of 641 hp at 6,800 rpm and 553 lb-ft of torque at 5,400 rpm. The combination was dead repeatable, so off came the factory intake and on went the FAST LSXR.

Equipped with the FAST intake, the peak numbers jumped to 663 hp at the same 6,800 rpm, but the peak torque of 569 lb-ft occurred slightly higher at 5,600 rpm. The FAST intake not only gave us an additional 20+hp, it improved the power curve from 4,400 rpm to 7,000 rpm, with no loss of power below that point.

Power gains are always welcome, but they are that much better when that extra 20 hp comes with no trade off in low-seed torque. If you’ve got an LS7 and are looking for an extra 20 hp, drop on the FAST LSXR!

The power curves show the stock GM intake was far from ideal on this modified LS7 stroker. Equipped with the stock intake, the CMP LS7 produced 641 hp at 6,800 rpm and 553 lb-ft of torque at 5,400 rpm. Replacing the stock intake with the FAST LSXR resulted in a gain of more than 20 hp, with peaks of 663 hp at the same 6,800 rpm, but 569 lb-ft of torque at a slightly higher 5,600 rpm. The FAST intake improved the power output starting at 4,400 rpm, and those gains increased with engine speed.

Sources

Brodix
brodix.com

CMP
coolmachineperformance.net

COMP Cams
compcams.com

FAST
fuelairspark.com

Lucas Oil
lucasoil.com