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Ruthless Pursuit of Power: The Mystique of the C6 Corvette LS7 Engine - Page 26 of 26





Ruthless Pursuit of Power: Lucky Seven Edition: The Mystique of the 7-Liter, 7000-RPM, LS7 - Page 26 of 26

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by Hib Halverson
© May 2013— Updated:  February 2016
No use without permission, All Rights Reserved

The LS7 introduced a forged steel crankshaft to the Gen 3/4/5 series of Small-Blocks. It was necessary for durability at the LS7's 1.18 specific output and because of its 7100 RPM rev limit. While the new LT1 can't rev to the LS7's lofty limits, it has nearly the same torque curve bellow 4000-RPM and .03 higher specific output. That mandated the same solution used for LS7–a steel crank. While we're on the subject of crankshafts, know that the LT1's main and connecting rod bearings are similar to the increased-eccentricity design pioneered by the LS7.

The new LT1's forged steel crankshaft inspired by that of the LS7.

Image:  GM Powertrain

The new LT1's forged steel crankshaft inspired by that of the LS7.

Through some of that "reaching" discussed above, GM Powertrain learned a lot about cast aluminum pistons for high-performance production applications which previously could only use more expensive, forged pistons. Some of the lessons learned in the program which resulted in a cost-effective, lightweight but, also, durable cast aluminum piston for the LS7, were applied to the Gen V, LT1's cast, eutectic aluminum piston.

The new LT1's cylinder head (left), in some ways vastly different than that of the LS7 (right), did get the 427's valve angle, its valve spring height and the 1.8:1 rocker arm ratio.

Image:  GM Powertrain

The new LT1's cylinder head (left), in some ways vastly different than that of the LS7 (right), did get the 427's valve angle, its valve spring height and the 1.8:1 rocker arm ratio.

While the LT1's direct injection head is mostly a new design, it's 12° valve angle, taller valve springs and 1.8:1 rocker arm ratio come directly from the LS7. Interestingly, serious engine wonks may recognize the new LT1 head's splayed valves as being inspired by the first LS7, a 465-hp, 454-cubic inch, Mark IV Big-Block V8 announced for the 1970 Corvette, but cancelled just before start of production. While no LS7 "rat motor" was put in a car, many were built for over-the-counter sale during the 1970s. All Big-Blocks had splayed (or "canted" or "porcupine" as some old-timers say) valves. With LT1, splayed valves are, as the late Yogi Berra once said, "...deja vu all over again."

The LT1s exhaust manifold inherited much from the LS7 unit but, considering the numbers in which the LT1 will be made, it was more cost effective to make it in cast iron rather than fabricate it from stainless steel.

Image:  GM Powertrain

The LT1s exhaust manifold inherited much from the LS7 unit but, considering the numbers in which the LT1 will be made, it was more cost effective to make it in cast iron rather than fabricate it from stainless steel.

Finally, the LT1's cast iron exhaust manifold is a direct descendant of the LS7's ground-breaking, shorty-header style, stainless unit—right down to the "quad-flow" collector.

And what of the 2015 Z06's LT4? Well, the LS7's influence continues on that engine, too, in that LT4s use a titanium intake valve similar to the parts pioneered by the LS7.

The LT4 uses the same, LS7-derived exhaust manifold as the base C7’s LT1.

With the sixth-generation Corvette out of production, 427 fanatics and C7 owners alike should both be pleased that a little of that LS7 mystique lives on in every LT1 and LT4.

Two More Years

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Thankfully, LS7 had a life after C6 Corvette production ended. Afterall, it seemed like a waste to commit all that cool, racy stuff to the history books so soon, didn't it?

Around Christmas, 2012, the Camaro and LS engine internet was set ablaze when a copy of the 2014 Camaro VIN decoding chart surfaced. It listed an "E" engine code for the 2014 Camaro and, according to that chart, "E" was for "LS7-Engine Gas, 8 Cyl., 7.0L SFI ALUM". At that time, we contacted Chevrolet's spokesperson for all things Corvette and Camaro, Monte Doran, seeking comment on the chart's authenticity. Via email, Mr. Doran replied, "It is our policy to not discuss future products, so I cannot comment on plans for the 2014 Camaro. I can tell you that a very early draft of our 2014 VIN card was leaked online. It was a preliminary version that included both inaccurate and incomplete information."

That started us wondering about the future of LS7 crate motors, so, a day or so later, we asked Chevrolet's Performance Marketing Manager, Dr. Jamie Meyer, to comment. He confirmed the LS7 Crate Engine (PN 17802397) will continue to be available from Chevy Performance.

We got to thinking: Mr. Doran did not actually deny the rumor about LS7 in a Camaro. The Performance Build Center was still building them and at a rate higher than was necessary to meet forecasted needs for Dr. Meyer's crate motors, COPO Camaro race engines and to "bank" enough engines for the last of Z06 and 427 Convertible production. There were still GM Powertrain engineers assigned to the LS7.

Right after New Year's, there was sparse chatter around Camaro Nation hinting that Chevrolet had a secret program underway called "HP" which was a lightweight, LS7 Camaro.

We couldn't confirm any of this, so we decided to sit back and wait...and it wasn't long.

The 2014 Z/28 at it's press introduction at the NY Auto Show. At right are GM NA President, Mark Reuss and GM Global Design chief, Ed Welburn.

Image:  GM Communications

The 2014 Z/28 at it's press introduction at the NY Auto Show. At right are GM NA President, Mark Reuss and GM Global Design chief, Ed Welburn.

At the New York Auto Show on 27 March 2013, Chevrolet showed the rear-drive SS performance sedan, a restyled 2014 Camaro and, in a "just-one-more-thing" moment reminiscent of the late Steve Jobs' legendary product introductions, GM North American President, Mark Reuss, unveiled the new Z/28, a Camaro powered by an LS7. The car was inspired by the 302-powered, Trans-Am road race Camaro of the late-'60s and has a suspension like that of the Camaro SS 1LE, the six-speed manual and the iron-case drive axle out of a ZL1, the carbon brakes off the C6 ZR-1, C6 Z06/Z07 and C7 Z06, a carbon fiber aero kit and a number of light-weighting measures such as: no sound insulation, no trunk carpeting, no power seats, no backseat pass through, no HIDs or foglamps, lightweight battery, lightweight rear window glass, lightweight rear seats, lighter wheels, lightweight single speaker radio (can you imagine? A "mono" radio? How 'bout that for a throw-back?) and A/C as an option. Chevrolet built 515 Z/28s in 2014 and did another 2500 in 2015.

The Camaro LS7 was a slight variant of the Corvette engine, but the differences were not significant from a performance standpoint. The Z/28's 427 uses a different air filter assembly, because the crowded underhood of a Camaro demands it be located off to the side and linked to the throttle body by an intake duct having a 90° bend. Also, for packaging limitations, the Camaro exhaust manifolds, while still of fabricated, stainless steel construction, use a Tri-Y configuration with rear outlets, rather than the Corvette's 4-into-1/center outlet design.

You would think such air filter and exhaust manifold differences might cause a slight performance hit. Turns out the Z/28's SAE J2723 rated horsepower is the same–505.

So...LS7 lived on for a couple more model years in the trackrat's ultimate Camaro. That last part of the LS7 legend will be another chapter in Chevrolet's performance history.

LS7 at a Glance

Displacement:  7008-cc/427.6-cuin.
Bore center distance:  111.76-mm/4.4-in.
Bore x Stroke:  104.775 x 101.6-mm/4.125 x 4-in.
Firing order:  1-8-7-2-6-5-4-3
Compression ratio:  11.0:1
Engine weight:  206-Kg/454-lbs.
Power:  505-hp@6300 rpm SAE net
Torque:  470-lbs/ft@4800 rpm SAE net
Fuel delivery:  sequential port fuel injection
Fuel required:  premium
Emissions controls:  3-way catalytic converters, positive crankcase ventilation
Weight:  455-lbs.

Acknowledgements

Many people were interviewed for this article and many others assisted in its production. Thanks to: At GM: Harlan Charles, Chris Cogan, Mark Damico, Monte Doran, Dennis Gerdemen, Tom Halka, Don Henley, Jim Hicks, Tom Hill, Judy Jin, Tadge Juechter, Jordan Lee, Yoon Lee, Dr. Jamie Meyer, Dave Muscaro, Bill Nichols, Rob Nichols, John Rydzewski, Mike Priest, Shane Smith, and Sam Winegarden. At Katech: Jason Harding, Fritz Kayl, and Kevin Pranger. At Mahle: Aaron Dick. At Del West, Mark Sommer and Shannon Decker. At MPK Photo: Mark Kelly. At Performance Publishing: Dave Emanuel. Corvette Forum Members: Kristoffer Gjevre, Grant Rudnick John Hughes, Dr. Howard Kopel, Rich "Mink" . At: Maritz: Meg Conroy. At DeGroff Head Servce: Mark DeGroff. At Blackstone Labs: Ryan Stark. At Goodson: Dave Monyhan. At Fowler High Precision: Dave Leboeuf. At Bunnin Chevrolet: Chris Williams. At CHE Precision, Inc., Ed Doyle.

Special thanks to Tom Read, Manager of GM Powertrain Communications.

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