RHS Head Swap - LQ=HP

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