It didn’t take long for gearheads to figure out that GM’s Gen III truck engines are a great bang-for-your-buck buy for transplantation into a classic muscle car. There are differences, of course, but these powerplants are essentially iron Corvette motors, waiting for a few well-chosen upgrades to turn them into slick street machine motivators. That’s pretty much what we did here—found a truck motor that’s destined to reside in the engine bay of a ’66 Chevelle, and outfitted it with a new COMP Cams camshaft and a set of RHS’ new Pro Action cylinder heads with Clean Cast Technology, which is designed to create “as cast” ports that flow like those in ported heads. The results were impressive—and impressively inexpensive, to the tune of a measly $1,470 clams for a fully assembled pair of lungs. Yes, you read that correctly. Now read on.

The foundation for this project was a 6.0L LQ9 powerplant. This variation of the Gen III family was found in ’02-06 Cadillac Escalades, ’03-07 Chevrolet Silverado SS models, ’04-05 Silverado and GMC Sierra “Vortec HO Editions”, and ’06-07 Silverado and Sierra Vortec Max optioned vehicles. The LQ9 achieves its factory-listed 345 hp and 380 lb-ft of torque by incorporating flat-top pistons to create a 10:1 compression ratio, compared to the 9.4:1-compression LQ4’s 300-325 hp and 360-370 lb-ft of torque. Most importantly, these things can be had cheap. We found one on eBay, complete with harnesses, computers, and a warranty for $2,500. Locally, we’ve found them for half that. You can start a muscle car project with a complete, running engine for as little as $1,200, which is hard to beat.

Our first modification was to scrap the factory intake manifold and fuel-injection system for a simpler and proven carbureted setup, featuring an Edelbrock LS1 Performer RPM intake manifold, MSD 6LS timing module, and a Holley Ultra Street Avenger 770-cfm vacuum secondary carburetor. This is a quick install that we’ve covered before; it works and it’s where we started our day’s testing at Westech Performance. The initial results were what you’d expect from a factory truck motor: lots of torque (400-plus lb-ft all the way to 5,400 rpm), not much in the horsepower department (416 peak ponies at 5,700 rpm, where the stocker is done revving). It’s made to haul loads of whatever at uninspired speeds, not for street/strip warrior duty.

The second modification is certainly the most important: a cam swap, which gave this engine a total personality transplant. “The Gen X engines seem to respond to cam changes so favorably that even the smallest cam can make a big difference,” Westech’s Steve Brulé says. “The heads are so efficient; they’re just waiting for a cam change.” Our testing certainly proved that point, but we were still surprised when we found the stock cam specs on LS1Tech.com; can you say broomstick cam? A switch was in order, though restraint was needed. The LQ9 has flat-top pistons, so attention must be paid to lift and duration when choosing a cam so proper piston-to-valve clearance is maintained. That being said, the cam of choice turned out to be a COMP XR281HR, a piece from the company’s XFI RPM Hi-Lift line. Though COMP does make bigger cams that will fit this application, these ’sticks are still aggressive for an LS application. Which in this case is a good thing. The transformed truck motor recorded a sharp increase in horsepower, as you’d probably expect. It also makes its 495 hp up at 6,300 hp—right around the place a Corvette engine touches its best. Perhaps less expected, however, is the much fatter torque curve, which peaks at a lower rpm (460 lb-ft at 5,100 rpm), and spreads its grunt over a much broader range. It’s a testament to how critical cam choice is, and also to how good the factory heads are. We could have quit here and had a very powerful and cool street/strip powerplant. On the other hand, there was no way we were leaving any ponies on the table.

For our final test, we bolted on a set of RHS’ new Pro Action cathedral-port heads for LS applications. These new lungs, which use Clean Cast Technology to maintain more precise tolerances than are normally found in an “as cast head”, bumped our engine’s compression ratio up to 11.41:1 (due to its 62cc combustion chamber) and added a 225cc intake runner. The extra air and bump in compression allowed our transformed truck engine to really take off, recording 521 hp at 6,300 rpm, along with 476 lb-ft of torque at 5,000 rpm. If the engine is turned on, it’s making more than 400 lb-ft. That’s a total increase of 105 hp more than the carbureted stock long-block version, along with an extra 37 lb-ft of torque at the peak of a much fatter torque band. It’s also a 16 lb-ft and 26hp improvement over the stock lungs. This rejuvenated truck lump makes lots of useful torque throughout the powerband, and it now has a great top end. It should make for one snappy, fun-to-drive Chevelle. We’ll let you know.

LQ9 Shopping List

PN Description Price
ARP 134-3609 High Performance Series cylinder head bolts $170
134-2001 carburetor studs 18
130-2001 intake manifold bolts 31
COMP Cams 26918-16 valvesprings 188
7795-16 Hi-Tech pushrods, 7.375 inches 136
54-428-11 XR281HR camshaft 370
Edelbrock 41183 coil covers 215
71187 LS1 Performer RPM 266
Fel-Pro 1161L/1161R MLS head gaskets 192
1312-3 intake manifold gaskets 26
Holley 0-86770BK Ultra Street Avenger Carburetor 500
302-1 LS Retro-Fit oil pan 400
MSD Ignition 6010 LS6 Timing Control Module 320
RHS 54302-05TS Pro Action 225cc cathedral port heads (assembled) 1,470
TCI 399753 LS1 168-tooth flywheel 215
TOTAL $4,517

Baseline

Holley 770-cfm Ultra Street Avenger
Jets: 73/81 primary/secondary
Headers: 13/4 Kooks long tubes with 18-inch extensions
Fuel: 91-octane unleaded
Advance: 33 degrees
RPM LB-FT HP
3,100 421 248
3,200 419 256
3,300 422 265
3,400 426 276
3,500 429 286
3,600 431 295
3,700 433 305
3,800 435 314
3,900 436 324
4,000 438 334
4,100 439 343
4,200 438 351
4,300 437 358
4,400 437 366
4,500 436 374
4,600 434 380
4,700 431 386
4,800 429 392
4,900 425 397
5,000 422 402
5,100 418 406
5,200 413 409
5,300 408 412
5,400 402 414
5,500 396 414
5,600 390 416
5,700 384 416
5,800 377 416
5,900 370 416
6,000 363 415
Average Torque 418
Average Power 360

Stuff to make it fit

Looking ahead, we had many of the pieces that we’ll need when this mill takes up its new residence under the hood of a ’66 Chevelle. One of these is Holley’s new LS Retro-Fit oil pan. According to Holley, this slick casting provides maximum chassis clearance for GM rear-wheel-drive applications, small-block or big-block, as long as it came with a rear sump oil pan. It also comes with a sump baffle, pickup tube, sump plug, oil filter stud, and an oil passage cover.

What’s it Flow?

(cfm at 28 inches H2O)
RHS Pro Action 225cc Cylinder Heads
0.200 0.300 0.400 0.500 0.550 0.600
2.055 intake 144 202 254 290 301 313
1.600 exhaust 109 154 187 205 210 214

More stuff to make it fit

When it comes time to drop this newly possessed powerplant into its new home, we’ll also need a way to connect the modern Gen III engine to the old-school Turbo 400 trans our Chevelle will be running. For this, we sourced TCI for one of its 168-tooth internal balance flexplates. This stout piece is 0.035-inch thicker than stock, and the starter ring is welded to the plate on both sides for increased strength.

Cam Shaft

Manufacturer: COMP Cams
PN: 54-428-11
Grind Number: XR281HR
Type: hydraulic roller
Valve lift: 0.571/0.573-inch intake/exhaust
Duration at 0.050: 228/230 degrees intake/exhaust
Lobe separation: 112 degrees
RPM LB-FT HP
3,000 419 239
3,100 415 245
3,200 415 253
3,300 419 263
3,400 426 276
3,500 432 288
3,600 437 300
3,700 441 311
3,800 445 322
3,900 448 333
4,000 453 345
4,100 455 355
4,200 455 364
4,300 456 373
4,400 458 384
4,500 459 393
4,600 458 401
4,700 457 409
4,800 457 418
4,900 459 428
5,000 460 438
5,100 460 446
5,200 458 454
5,300 456 460
5,400 453 466
5,500 450 471
5,600 445 475
5,700 441 479
5,800 437 483
5,900 433 487
6,000 429 491
6,100 425 493
6,200 419 495
6,300 413 495
6,400 405 493
6,500 397 491
Average Torque 453
Average Power 409

RHS Pro Action cylinder heads

Advance: 32 degrees
rpm lb-ft hp
3,000 431 246
3,100 427 252
3,200 425 259
3,300 428 269
3,400 436 282
3,500 442 295
3,600 447 306
3,700 450 317
3,800 454 329
3,900 460 341
4,000 465 354
4,100 467 365
4,200 468 374
4,300 469 384
4,400 470 394
4,500 470 403
4,600 470 412
4,700 471 421
4,800 472 432
4,900 474 443
5,000 476 453
5,100 476 462
5,200 475 470
5,300 472 477
5,400 470 483
5,500 466 489
5,600 463 494
5,700 460 499
5,800 458 505
5,900 455 511
6,000 451 516
6,100 446 518
6,200 441 520
6,300 435 521
6,400 428 521
6,500 421 521
Average Torque 468
Average Power 424

SOURCE
Edelbrock (Carbs)
800-416-8628
http://www.edelbrock.com
Westech Performance
11098 Venture Drive
Unit C
Mira Loma
CA  91752
951-685-4767
www.westechperformance.com
Automotive Racing Products
1863 Eastman Avenue
Ventura
CA  93003
800-826-3045
http://www.arp-bolts.com
TCI
151 Industrial Drive
Ashland
MS  38603
888-776-9824
www.tciauto.com
K&N Filters
1455 Citrus Street
Riverside
CA  92507
800-858-3333
www.knfilters.com
MSD Ignition (Autotronic Controls)
1490 Henry Brennan Drive
El Paso
TX  79936
915-857-5200
www.msdignition.com
AMSOIL
925 Tower Ave.
Superior
WI  54880
800-777-8491
www.amsoil.com
Fel-Pro
26555 Northwestern Highway
Southfield
MI  48033
248-354-7700
www.federal-mogul.com
Comp Cams
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
Holley
1801 Russellville Road
Bowling Green
KY  42101
270-781-9741
www.holley.com
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