When we left our intrepid Iron Maiden in Part 1, we shook the all-stock parts tree to make enough power to get your attention. No one expects an old iron head 6.0L to make 430 horsepower with nearly the same amount of torque. Imagine how much work you'd have to do to a 355ci small-block Chevy to make that number it would difficult without porting the stock heads and adding a big cam. And we're just getting the limbered up.

To review, we ended Part I with a mild Maiden makeover using a stock LS6 camshaft, an equally stock LS6 intake and throttle body, and shorty headers. That doesn't sound like much, but it paid off with 430 hp and 435 lb-ft of torque.

This month we'll push a little harder to see how much power we can make while emphasizing useable torque and horsepower rather than chasing peak numbers. For those in the know, the LQ4 is the pedestrian version of the 6.0L truck family with only 9.5:1 static compression. It's also common knowledge that compression adds power everywhere so we thought that a set of production aluminum heads with a smaller chamber would help.

Frankly, this could have been a much more rewarding step if we'd not screwed up. In the Iron Maiden shop, we have an ever-growing pile of LS parts. So of course, we grabbed the wrong set of heads when packing to go to Westech. What we had planned to test was a set of stock 4.8L/5.3L heads (casting numbers 706, 852, or 895) that offer a tiny 61 cc chamber. Our Compression Lessons chart illustrates how the compression would change with various heads. Unfortunately, we mistakenly installed a set of stock LS1 853 castings. These heads helped the power slightly, but not like we would have seen with a set of much tighter chamber 4.8L/5.3L heads.

Our fellow tech writer and dyno flogger Richard Holdener reports roughly a 15 hp gain with stock 5.3L heads on a 6.0L. Our 5.7L head test bumped the average power by 9 hp but lost a small amount of torque in the process. This is really budget stuff we're doing since 4.8L/5.3L heads are very easy to access. The 4.8L/5.3L results make sense since an increase of 1 full point in compression is worth roughly 4 percent power and at 430 hp a 4 percent gain is 17 hp. On the Power Curve chart, see Test 2 which peaked at 433 lb-ft of torque and 432 hp.

The next plan was to evaluate how much that vaunted Trailblazer SS intake was worth over the LQ4 truck manifold. We've read some of Holdener's testing on this intake and we were impressed enough to see the results for ourselves. The book on the Trailblazer SS intake is that it makes more torque than the LQ4 intake and more horsepower than the low profile LS6.

The best part of this plan is that you can buy this new ACDelco intake from RockAuto for a mere $140. Granted, it's a bare manifold so we configured it with our stock 8.1L 30-lb/hr injectors and a very affordable Holley aluminum LS1 fuel rail assembly. This will require a separate aftermarket fuel pressure regulator. This intake also needs a 4-bolt throttle body. The only one available at the time of our test was a FAST 102mm version that we borrowed. Some may claim this larger version offers a slight power advantage, but at 430 hp, any advantage would be minimal. As an alternative, you could adapt a three-bolt throttle body using an adapter made by ICT Billet that uses a 75mm through hole. We've included a part number in our parts list.

The Trailblazer SS intake lived up to its hype offering a major bump in the torque curve with an average torque gain across the entire rpm spread of 7 lb-ft over the truck intake along with an 11 hp peak horsepower increase. The negatives are that this intake is just as tall and slightly wider than the LQ4 version, and it's hardly a thing of beauty. But if this manifold will fit under the hood, it is a star player in the power-per-dollar game.

Next we wanted to see how the LS6 intake would fare with this combination. This is a popular intake because it will fit under any hood line. We tested the LS6 intake with a stock 78mm throttle body, and as you can see, the combination did lose some low-speed torque compared to both the truck manifolds but picked up the horsepower against the LQ4 intake, so that the averages were very close. However, the Trailblazer SS intake was better than both the LQ4 truck and LS6 intakes.

Our next step was where we anticipated we could pump up the power across the entire rpm curve. Previously we mentioned how adding the 5.3L heads would bump the compression and power. We decided to take that one step further. In previous stories, we've had great luck with a set of 5.3L heads that were treated to CNC porting by Richard Reyman and his crew at West Coast Racing Cylinder Heads (WCRCH).

The package starts by increasing the intake valve size from 1.89 to 2.00-inches and some CNC pocket porting which improves the flow slightly. But the real gains are on the exhaust side. The accompanying flow graphs reveal how much the intake and exhaust ports improve with his help. We also had WCRCH mill the already small chambers to 58 cc, which bumped the compression up to 10.8:1. Combined with the fact that LS engines don't need a lot of ignition timing anyway and this compression is still conservative enough to run on 91-octane fuel.

As you can see from Test 5 in the Power Chart and graph, the addition of these WCRCH-ported heads was worth some serious power across nearly the entire curve and especially above 4,000 rpm. We averaged the torque gain from 4,000 to 6,200 and came up with an average increase of 20 lb-ft. Any time you can bump the torque that much across a 2,000 rpm band, that's an outstanding way to help street performance. We can guarantee you will instantly feel that in the seat of your pants.

Peak number improvements were just as good with the WCRCH ported 5.3L heads. Peak torque jumped from 435 to 455 lb-ft and from 431 to 457 horsepower a push of a solid 26 hp. Often, gains like these in peak power come at a loss of low-speed torque and drivability but not here. These little heads that everyone else ignores also bumped the torque even at the lowest rpm we tested. Win-win might be a clich, but it applies when you really do win everywhere.

Remember that this final test is based on our 150,000-mile short block, LS6 intake and equally stock LS6 camshaft. These are parts that other people discard yet we're now making 457 hp. This also means we've left a bunch more power on the table. The sharp ones among you are already banging on your keyboards "Shove a cam in it, bolt that Trailblazer intake back on it and spin it up!".

We've already done that. But like any good Hollywood serial script writer, we intend to leave you hanging. We can tease you a little with a hint that we're going to stick in that bigger but still-mild cam, a set of long-tube headers, and that Trailblazer SS intake and bump the average torque by over 40 lb-ft with similar numbers for average horsepower. If that doesn't get your attention, you might want to check your pulse. Stay tuned it's about to really get fun!

See all 17 photos

See all 17 photos For our first head swap, we thought adding compression might help power throughout the rpm curve, so we chose a set of stock aluminum LS1 heads with about a 5 cc smaller chamber and slightly better flow numbers. These were completely stock heads right down to the valve springs.

See all 17 photos The stock aluminum 5.7L 853 castings use the same 2.00/1.55 valve sizes as the 6.0L versions but have a smaller 67cc chamber vs. the stock 6.0L 71cc chambers. Adding the 5.7L heads pushed the compression from 9.5:1 to 9.85:1.

See all 17 photos Swapping heads also meant adding new Fel-Pro MLS head gaskets to ensure that we had optimal cylinder pressure sealing clamped with ARP head studs. We could have used head bolts, but the studs make life easier on the threads in the block. The dished pistons reveal that this is an LQ4 truck engine.

See all 17 photos It's worth noting that we continued to use the electric water pump on these tests which was worth 9hp at peak over a stock truck accessory drive.

See all 17 photos When we swapped in the aluminum heads, we also added a set of Comp 0.080-inch wall thickness pushrods along with a set of upgraded stock rockers with Comp's high performance trunnions. Both are really intended as durability improvements so we don't worry any more about bent factory pushrods.

See all 17 photos The real key to the power gain with the West Coast Racing-ported heads is the combination of more compression and better-performing exhaust ports.

See all 17 photos Test 1 and Test 2 retained the stock truck intake manifold with the remaining tests employing this stock LS6 intake and 78mm throttle body.

See all 17 photos The final test was the combination of the ported heads with the LS6 intake, stock throttle body, and the shorty headers. Dyno guru Steve Brule' pulled the handle and our iron lady pushed the torque up to 455 lb-ft and horsepower to 457.

See all 17 photos If we plugged this 457hp Iron Maiden combo into our Orange Peel Chevelle with a TH350, mild converter, 3.55:1 rear gears at around 3,500 pounds, the car could potentially run 12-teens at 113 mph. Not bad for an engine with a near-stock idle!

See all 17 photos Since the number came out so good, we decided to do a leak-down test and were pleasantly surprised at the roughly 12 percent number on cylinder 2. The other cylinders were similar. We never touched the rings or the cylinder walls except to clean them.

Washer Tech

We ran into an issue when bolting on the heads that deserves attention. When torquing the head studs, it felt like something was giving way like a bolt was stripped yet it wasn't. It seems that it's very easy for either a head bolt or stud washer to turn as opposed to remaining stationary under the bolt head. If the washer begins to turn as torque is applied, this essentially converts the washer into a bearing. Here's the issue. Almost 50 percent of the torque applied to any bolt is used to overcome the friction between the underside of the bolt and the washer. If the washer spins, it reduces this friction and that additional torque is applied to the fastener. This is usually more than enough additional torque to either permanently elongate the bolt or pull threads out of the block.

The problem stems from the really smooth surface of the head bolt spot face on Coyote, LS, Ford EcoBoost, and even Chrysler Hemi engines. The combination of this smooth machining and the ARP washer can cause the washer to spin under load. This is especially prevalent if there is lube between the washer and the head.

The fix is easy. ARP recommends sanding the head side of the washer with 60-grit sand paper for three or four strokes. That will help the washer grip the head. We tried this and it works very well and we were able to torque right up to the recommended 70 ft-lbs with no problem.

See all 17 photos Sanding the head side of the washer with 60-grit prevents the washer from spinning. This sounds unreal, but if that washer spins and you keep pulling on the torque wrench, you will either destroy the bolt or worse- pull the threads right out of the block.

Compression Lessons

Cylinder Chamber Compression Head Size Ratio for LQ4 LQ4 6.0L 71cc 9.5:1 LS1 5.7L 67cc 9.8:1 LM7 5.3L 61cc 10.4:1 WCRCH 5.3L 58cc 10.8:1 Show All

Flow Test

See all 17 photos

See all 17 photos These graphs illustrate the flow increases from the WCRCH porting work on the 5.3L castings. As you can see, the major improvements occur on the exhaust side.

Stock Iron 6.0L vs. WCRCH Ported 5.3L Heads

Valve Lift 6.0L 2.00" Intake Ported 5.3L Int. 2.00" 6.0L 1.55" Exh. Ported 5.3L Exh. 0.1 66 69 57 56 0.2 140 135 110 100 0.3 198 194 148 143 0.4 235 238 166 177 0.5 250 264 175 197 0.6 255 250 184 207 Show All

These flow numbers are from WCRCH and were generated on a 3.78-inch bore. On a larger 4.00-inch bore engine, the flow numbers will improve slightly especially at higher valve lifts.

1.89 / 1.55 Valve sizes for stock 5.3 heads

2.00 / 1.55 Valve sizes for stock LS1 and 6.0L LQ4 heads

Power Chart



Test 1 Best Power Baseline from Part I (LS6 cam test)

Test 2 Add 5.7L LS1 aluminum heads w/ truck intake, shorty headers, LS6 cam

Test 3 Add Trailblazer SS intake manifold w/ 102 mm throttle body

Test 4 Add LS6 intake manifold w/ 90 mm throttle body

Test 5 Added CNC ported 5.3L heads retained LS6 intake and cam

RPM TQ1 HP1 TQ2 HP2 TQ3 HP3 TQ4 HP4 TQ5 HP5 2600 352 174 355 175 359 178 353 175 366 181 2800 360 192 368 196 366 195 362 193 371 198 3000 376 215 380 217 381 217 378 216 384 220 3200 382 233 388 237 389 237 386 235 392 239 3400 389 251 395 256 396 256 391 253 397 257 3600 400 274 406 278 408 279 402 275 408 280 3800 412 298 416 301 420 304 412 298 421 305 4000 419 319 420 320 428 326 419 319 432 329 4,200 426 340 423 338 433 346 423 338 441 353 4,400 430 360 429 359 438 367 429 360 450 377 4,600 432 378 430 376 439 385 433 379 452 396 4,800 435 397 433 396 442 404 435 397 455 415 5,000 435 414 432 412 442 421 434 413 454 432 5,200 426 422 425 420 436 431 427 423 449 445 5,400 416 428 415 426 426 438 416 428 441 453 5,600 403 430 402 429 414 441 404 431 428 457 5,800 388 428 389 430 400 441 389 429 413 456 6,000 --- --- 378 432 388 443 378 432 396 453 6,200 --- --- 364 429 373 441 364 430 381 450 Avg. 403.6 325.7 402.4 334.9 409.3 341.4 402 334.8 417.5 348.7 Peak 435 430 433 432 442 443 435 431 455 457 Show All

Note: The baseline test used here as Test 1 is Test 3 from Part I because it offered the best power numbers. The Test 4 results from Part I suffered from bent pushrods.

Parts List

Description PN Source Price Used LQ4 iron 6.0L N.A. Swap meet $550.00 Holley HP ECU 558-500 Summit Racing $1,120.95 Holley EFI harness for LS 24x/1x 558-102 Summit Racing $382.96 Holley harness for LS truck injectors 558-214 Summit Racing $153.95 Sniper fuel rail LS1 850005 Summit Racing $114.95 Summit shorty LS headers SUM-9021 Summit Racing $199.97 Stock LS6 camshaft Used Friend $50.00 AC Delco Trailblazer SS intake manifold 12580420 RockAuto $137.79 ICT Billet 4 to 3-bolt throttle body adapter 551511 Summit Racing $20.69 AC Delco LS6 intake, used w/TB 88894339 eBay Motors $400.00 Comp LS rocker trunion upgrade kit 13702-KIT Summit Racing $141.97 Comp stock length Hi-Tech pushrods 7955-16 Summit Racing $131.97 Comp beehive valve spring kit 26918CS-KIT Summit Racing $339.97 Fel-Pro head gasket, MLS - Left 26472L-053 Summit Racing $74.97 Fel-Pro head gasket, MLS - Right 26472R-053 Summit Racing $78.97 ARP head stud kit 234-4110 Summit Racing $359.16 West Coast Racing 5.3L head CNC 5.3L Stage 2 WCRCH $1,062.00 Hooker long-tube, 1.75-inch dia. headers 2289HKR Summit Racing $597.95 Holley Sniper LS1 fuel rail assembly 850005 Summit Racing $114.95 Show All