LS7/LS9 Hybrid - Jekyll-and-Hyde 7.0L - Chevy S10 - LS Engine Build

It's the ultimate LS-engine "what if" scenario: Could the blower from the Corvette ZR1's LS9 engine be dropped on the larger-displacement LS7 found in the Z06? That would create the ultimate "factory" combination—especially because it would drop into any GM truck that came with an LS engine, dating back to '99.

Enthusiasts started dreaming up this ultimate power combination the second the LS9 was revealed to displace 6.2 liters, rather than the LS7's 7.0L size. That's a significant 13-percent difference in volume, but GM said it went with the smaller bores to ensure a safe, long-lasting powertrain—one that would be subjected to considerable boost pressure over its lifetime.

"On the OE side, all the considerations for 100,000 miles worth of durability must be considered," says an anonymous GM drivetrain engineer we spoke with. "The power goals for the LS9 were reached with the smaller displacement, which offers thicker cylinder walls for greater safety margin, so there was no need to step up to the 7.0L displacement."

That's a great textbook answer and we certainly wouldn't cast aspersions on the LS9's 638 hp output, but when there's a larger-cube version of the same engine family, you just know the performance world wouldn't let the combination go untried. That would be like Dr. Frankenstein having both a spare brain and access to a graveyard, but passing on the opportunity.

1. The standard cylinder block for the 7.0L LS7 is the foundation for Thomson's LS7/LS9 hybrid engine and is available through GM Performance Parts under part number 19213580. It's aluminum with pressed-in steel bore liners and forged-steel main bearing caps; the bores measure 4.125 inches in diameter.
1. The standard cylinder block for the 7.0L LS7 is the foundation for Thomson's LS7/LS9 hy
2. Machine work prior to assembly includes deck-plate honing of the cylinders and line-boring of the crankshafts mains. They're common high-performance engine-building procedures, with the line boring supporting the addition of ARP main studs.
2. Machine work prior to assembly includes deck-plate honing of the cylinders and line-bor
3. To reduce piston temperatures (especially under boost), Thomson Automotive machined the cylinder block to accept oil squirters, similar to what's standard in the production LS9 engine. It is a precise, multi-step process that taps into one of the block's primary oil passages. The squirters themselves are carburetor air bleeds.
3. To reduce piston temperatures (especially under boost), Thomson Automotive machined the

Brian Thomson isn't Dr. Frankenstein, but he's created more than his share of LS-based monster engines at his shop, Thomson Automotive near Detroit. In fact, he's had great success melding the LS7 with the LS9 blower, developing basically a crate engine package (including a pre-programmed E67 controller) that delivers around 770 hp and 840 lb-ft of torque on pump gas. The torque comes on soon, too, making more than 800 lb-ft by only 3000 rpm, which really helps launch today's heavy GM trucks.

"It's a sweetheart of a street engine," says Thomson. "It starts, idles, and has the low-speed drivability of a stock engine, but when you tap into it, it's amazing. With more than 800 lb-ft and the instant power delivery of the blower, it's an engine with two distinct personalities."

OK, so maybe it's not Frankenstein's monster, but more of a Jekyll and Hyde engine. Regardless, we recently took note of the assembly and dyno-testing of one of these engines, which was destined for the Chevy S-10 project vehicle of New Yorker Joe Jones. It officially made 769 hp and 844 lb-ft, with a safe air/fuel ratio of about 11.4:1 under full boost.

4. The camshaft is one of the key components in making the hybrid LS7/LS9 engine deliver big power with surprising street civility. We were sworn to secrecy on it, so we can't reveal its specs. It works well at giving the engine a docile idle and excellent low-speed tractability.
4. The camshaft is one of the key components in making the hybrid LS7/LS9 engine deliver b
5. A Callies forged steel crankshaft is used, delivering a 4.000-inch stroke that combines with the 4.125-inch bores to give the engine its 427ci of displacement. It's used with an LSA oil pump, which is a high-volume unit for a conventional wet-sump oiling system, but doesn't require the longer-snout crankshaft of the dry-sump LS9 or LS7.
5. A Callies forged steel crankshaft is used, delivering a 4.000-inch stroke that combines
6. The LS7 crank has a more common six-bolt flange, rather than the LS9's nine-bolt flange. Although the nine-bolt design delivers theoretically greater clamping strength, the six-bolt flange is more compatible with a variety of flywheels.
6. The LS7 crank has a more common six-bolt flange, rather than the LS9's nine-bolt flange

7. Stock LS engines (except LS9 and LSA) have press-fit dampers and consequently no keyway on the crankshaft. To prevent slippage at the boost and power levels this engine will be capable of, Thomson insists the crank is fitted with one.
7. Stock LS engines (except LS9 and LSA) have press-fit dampers and consequently no keyway
8. Forged I-beam rods (in the stock, 6.067-inch length) from Oliver are used in place of the LS7's titanium rods. The lightweight titanium rods simply aren't designed for the load and power levels of this engine. The effect of greater mass on the rotating assembly with heavier I-beams will be quickly offset with the rise in boost pressure under load.
8. Forged I-beam rods (in the stock, 6.067-inch length) from Oliver are used in place of t
9. The LS7's cast-aluminum pistons were replaced to enhance strength under high cylinder pressure and reduce compression. Forged aluminum, coated pistons from Diamond were used. They are dished to lower the compression ratio to a detonation-avoiding 9.0:1. The blower-specific pistons also have a thick crown and reinforced pin bosses.
9. The LS7's cast-aluminum pistons were replaced to enhance strength under high cylinder p

10.The pistons' gold-colored top coating is a ceramic material from that reduces heat absorbed by the pistons —a notable concern with a high-horsepower, supercharged engine. Also, the skirts of the pistons are Teflon-coated to reduce friction.
10.The pistons' gold-colored top coating is a ceramic material from that reduces heat abso
11. The rod/piston assemblies are fastened to the crankshaft with ARP bolts via the stretch method, which is a more accurate way of ensuring the proper pre-load and clamping force on them. Essentially, the bolts are stretched until they are within the sweet spot of elasticity. That's usually between 0.005-inch and 0.006-inch, which is right where the bolt shown here registered on the gauge.
11. The rod/piston assemblies are fastened to the crankshaft with ARP bolts via the stretc
12. Interestingly, the larger-capacity LS7 cylinder heads weren't used, but only because their intake ports didn't match those of the supercharger manifold. That made the factory LS9 heads the only real choice, which is fine, because they're based on the high-flow L92 head and manufactured with a stronger alloy that helps them withstand the extra heat that comes with forced induction.
12. Interestingly, the larger-capacity LS7 cylinder heads weren't used, but only because t

13. Stock 2.16-inch titanium intake valves and aftermarket (but stock-size) 1.59-inch Inconel exhaust valves are used. The thermal properties of the Inconel valves better suit the higher combustion temperatures of a force-inducted engine.
13. Stock 2.16-inch titanium intake valves and aftermarket (but stock-size) 1.59-inch Inco
14. Valvetrain details read essentially like those for a stock LS9, including the stamped, non-roller 1.7-ratio rocker arms. The valve springs are matched to the Thomson's proprietary camshaft specs.
14. Valvetrain details read essentially like those for a stock LS9, including the stamped,
15. To align with the LS9 supercharger pulley, Thomson uses a complete LS9 front dress assembly, including the water pump, brackets, accessories (alternator, power steering) and 10-rib pulleys. Even the LS9 valve covers must be used, because the alternator and power steering pumps won't fit otherwise.
15. To align with the LS9 supercharger pulley, Thomson uses a complete LS9 front dress ass