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Custom GM LS7 Engine - Horsepower!

It's crazy Gen IV power with numbers like 730 hp and 571 lb-ft on pump gas!

Photography by Schwartz Extreme Performance

427ci GM LS7 Gen IV - 730 HP And 571 LB-FT On Pump Gas
Jeff Schwartz, Schwartz Extreme Performance, Crystal Lake, IL
We've all heard the buzz about the 427ci 7.0L LS7 engine that first appeared in the '06 Corvette ZO6, which made a solid 505 hp and 475 lb-ft of torque. This engine started life as a factory handbuilt piece massaged with titanium rods, an 11:1 compression ratio, a forged-steel crank, and a factory dry-sump oiling system. Never before had GM built an original-equipment engine with CNC-ported heads until the LS7. But even that wasn't good enough for one of Jeff Schwartz's Extreme Performance customers. The customer wanted more horsepower, so Jeff dialed in a custom roller cam, better pistons, and a set of headers and cranked out 730 hp at 7,400 rpm. Think about that-bolt in a cam, add a set of headers, and pick up 225 hp. This motor's not cheap, but where else are you gonna find 1.7 hp/ci on pump gas?

A. All these 7.0Ls begin life with LS7-specific rectangle-port heads treated to a full CNC-porting exercise and fitted with monstrous 2.20-inch titanium intake and 1.61-inch sodium-filled exhaust valves. The intake ports measure 270 cc, and GM's own literature says they flow 352 cfm at 0.700-inch lift. The stock cam only goes to 0.591-inch lift. Do you think they had a bigger cam in mind when they designed these heads? Oh yeah, these are also 12-degree valve heads. Stock Gen III are 15 degrees. It was only a few years ago that NASCAR heads were at 15 degrees. Now a production engine has that beat.

B. What you can't see from this angle is the nearly stock GM Performance Parts composite LS7 intake manifold sporting stock fuel injectors, a stock 90mm electronic throttle body, and a Schwartz Extreme Performance Power Spacer and 103mm mass airflow (MAF) sensor.

C. The factory hydraulic roller cam measures a mere 211/230 degrees at 0.050-inch tappet lift with 0.591-inch lift on both intake and exhaust, and that's with 1.8:1-ratio rockers. The lobe-separation angle on the stock cam is a stunning 121 degrees (compared with most performance cams at 106 to 114). Jeff wouldn't talk about his custom-ground Comp hydraulic roller camshaft, since he spent so much time developing it, but the lift has to be close to 0.700 with the duration perhaps around 230 degrees or shorter. The engine idles at 10 inches of manifold vacuum at 925 rpm.

D. Think we're not in the middle of the next Golden Age of Horsepower? When the factory builds a 427ci all-aluminum engine that makes 505 hp, what else do you call it? This block is different from other Gen IV blocks with 4.125-inch, siamesed iron-sleeve bores that Jeff honed to 4.130 inches. He also retained the stock forged crank and 6.067-inch-long titanium rods but added a set of 11:1 Mahle forged-aluminum pistons to replace the OE castings. The only other upgrade to the rotating assembly is a set of ARP rod bolts.

E. Those are 1 7/8-inch stainless headers with a very progressive 3-inch collector with wide-band oxygen sensors in both banks. Note that the engine also retains the factory coil packs.

F. That's the factory ECU that controls everything, including the drive-by-wire electronic throttle control (ETC). Don Bailey did the tuning using HP Tuner software, yet the engine retains its stock fuel injectors.

How do you prelube a Gen III/Gen IV engine with the oil pump mounted on the crank? Pressurize a 5-quart container, fill it with oil, hook it to your motor, and turn on the valve. The pressure will push the oil through all the passages and prelube your engine. That's the way GM does it.

Want to see this motor run on the dyno? Click here.

DYNO CHART
RPM TQ HP
3,200 439 267
3,400 449 291
3,600 464 318
3,800 471 347
4,000 502 382
4,200 519 415
4,400 529 443
4,600 535 468
4,800 544 497
5,000 555 528
5,200 563 558
5,400 570 586
5,600 571 610
5,800 568 627
6,000 564 644
6,200 563 664
6,400 560 682
6,600 555 697
6,800 549 711
7,000 543 724
7,200 533 730
7,400 518 730
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