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

16. The LS9 supercharger assembly delivered from General Motors includes both the compressor and an integrated liquid-to-air charge cooler mounted on top, along with the fuel rails, injectors and throttle body already installed. The sixth-generation, TVS positive-displacement blower comes from Eaton and is their largest-ever Roots-type compressor, displacing a significant 2.3L per revolution.

It was only a few years ago that even a 500hp street engine was newsworthy. The fact that Thomson is explaining why his engine "only" makes 770 horses on the street demonstrates how far we've come with LS engines and tuning. Of course, we can't discuss a 770hp, 840 lb-ft, LS9-blown engine without bringing up cost—and this one tallies a pretty strong price tag of around $35,000. Thomson doesn't dance around the cost. It is what it is.

"The LS7 and LS9 parts aren't cheap, so it's an expensive engine to build, no doubt about it," he says. "But more than simply a great dyno number, you get an engine with excellent, factory-quality drivability. We put a similar engine in a car last year and did more than 3,000 miles on the Hot Rod Power Tour with the A/C on and didn't have a lick of trouble."

17. On the 6.2L LS9, the blower generates about 10.5 pounds of boost, but only about half that with the 7.0L displacement, so Thomson machined a new, smaller-diameter pulley to spin the blower faster and bring the boost up to about 14 psi.

17. On the 6.2L LS9, the blower generates about 10.5 pounds of boost, but only about half

Installation of the engine may require some mild fabrication to accommodate the unique LS9 accessory drive system and its wider belt, but hood clearance shouldn't be an issue on fullsize GM trucks and SUVs.

Installation details notwithstanding, the engine's dual-purpose performance—dependability with tire-shredding power—reinforces the Jekyll-and-Hyde personality of Thomson's LS7/LS9 hybrid. It's the sort of monster we'd like to have lurking beneath the hood of our favorite Silverado or maybe an Escalade that would shake up the country club setting; Quiet and unassuming one moment, and a terror the next. That's the way to keep the other guy guessing.

Dyno Chart
RPM	LB-FT	HP
3000	807	461
3100	814	480
3200	822	501
3300	826	519
3400	829	537
3500	831	554
3600	833	571
3700	837	590
3800	839	607
3900	842	625
4000	844	643
4100	843	658
4200	841	672
4300	839	687
4400	834	699
4500	826	708
4600	817	716
4700	807	722
4800	796	727
4900	786	733
5000	771	734
5100	759	737
5200	749	742
5300	740	747
5400	731	752
5500	723	757
5600	717	765
5700	707	768
5800	697	769
5900	683	768
6000	672	768
Peak numbers in bold.

18. Another pulley change involves the 10-rib damper, which is sourced from ATI. Thomson machines a custom hub for it to mount on the crankshaft. Look closely and you'll see the pulley is divided; the wider section is connected to the blower and power steering pump, while the narrower section is for a separate belt that drives the alternator and air conditioning system. This engine won't use A/C, so a custom idler pulley will be created.
18. Another pulley change involves the 10-rib damper, which is sourced from ATI. Thomson m
19. Until a suitable, 100mm electronic throttle body can be sourced, Thomson sticks with the 90mm GM unit, although it has proved a restriction on the larger-displacement, force-fed engine. There's probably 20 hp to be realized. The LS9 supercharger assembly comes with 48-lb/hr fuel injectors. Thomson swaps them for higher-capacity, 65 lb/hr injectors.
19. Until a suitable, 100mm electronic throttle body can be sourced, Thomson sticks with t
20. No detail is too small: The use of cold-range spark plugs is necessary to help stave off detonation. For this engine, it was a set of Autolite Racing 5243 plugs.
20. No detail is too small: The use of cold-range spark plugs is necessary to help stave o

21. Here, the supercharger assembly is bolted in place. The factory 2.5-bar MAP sensor (seen at the rear of the intercooler cover) is used to ensure accurate air pressure readings when the blower is making more than 10 pounds of boost. Engine mapping is controlled by a GM E67 controller from GM Performance Parts, part number 19201861.
21. Here, the supercharger assembly is bolted in place. The factory 2.5-bar MAP sensor (se
22. Aesthetical considerations are part of the package, too. The intercooler cover's original "LS9 Supercharged" is modified by removing the "LS9" section and inserting a custom-milled "7.0L" designation. The metal work is fantastic and gives the engine a premium appearance.
22. Aesthetical considerations are part of the package, too. The intercooler cover's origi
23. With the intercooler cover and valve covers painted, the LS7/LS9 hybrid engine is a striking assembly. As shown, it cost the customer about $35,000, but that includes an E67 controller, the tuning to go with it, and the dyno test.
23. With the intercooler cover and valve covers painted, the LS7/LS9 hybrid engine is a st

24. With base timing of 27 degrees and 18 degrees under boost, along with 93-octane pump gas, the engine produced a best of 769 hp and 844 lb-ft of torque, with 13 pounds of boost. Under maximum boost, the air/fuel ratio goes to about 11.4:1 – plenty safe without sacrificing performance.
24. With base timing of 27 degrees and 18 degrees under boost, along with 93-octane pump g
25. On the dyno, the engine was tested with factory LS7 exhaust manifolds. They make more power than headers, but give up a few pound-feet to headers, but with more than 840 of 'em on tap, they're not missed. Unfortunately, the center-style outlet means they only fit the Corvette chassis.
25. On the dyno, the engine was tested with factory LS7 exhaust manifolds. They make more
26. Along with LS-style engine mounts, installation of the engine was made easier by the fact that Jones didn't want air conditioning. That A/C compressor is otherwise mounted low on the engine and can interfere with the chassis crossmember on vehicles not originally equipped with an LS engine.
26. Along with LS-style engine mounts, installation of the engine was made easier by the f