This is going to cause some headaches for the forum dwellers who claim that nothing less than rectangle-port heads and a giant cam will make 500 hp on an LS engine. We made nearly 500 with a little cam, a factory truck intake, a pair of nearly stock cathedral-port heads, and a 150,000-mile iron 6.0L short-block. We're a bit surprised, too—but only slightly. While everybody else says you need to go big, we think being conservative might just be an asset, after all.

In parts I and II of the Iron Maiden saga, we began with a baseline dyno test of the stock engine and ended by testing a set of CNC-ported 5.3L heads from West Coast Racing Cylinder Heads (WCRCH), a stock LS6 camshaft, shorty headers, and a factory LS6 intake manifold that made 457 hp and 455 lb-ft of torque. Those are stout numbers, but now we're gonna really step on the throttle! Our Test 1 baseline for this installment is the results of the final test from last month.

Jumping right into it, we removed the LS6 camshaft and replaced it with a Comp 269 LR roller with 15 degrees more intake duration, 9 degrees more exhaust, 0.050-inch more valve lift, and a tighter lobe-separation angle. All of these things added up to a cam that would add some power, but perhaps more importantly, not sacrifice the low-speed throttle response we're trying to preserve. To that end, despite this cam's more aggressive specs, it's still really mild and idled on the dyno at 14 inches Hg of manifold vacuum.

Following the scientific method of controlling variables, we only changed one thing for this test, but it was enough to make a huge difference in the power curve. Normally, we would expect that adding a longer-duration cam would hurt the torque at the bottom in favor of making horsepower at the top, but with the cam still conservative at only 219 degrees at 0.050, Test 2 revealed that at 2,600 rpm we gained 15 lb-ft and added as much as 26 lb-ft at 3,800 rpm, while peak torque improved from 455 to 472, a gain of 17 lb-ft. Of course, the horsepower increased as well, with a peak gain of 18 hp to 475 hp at a mild 5,800 rpm.

We were now making a solid 475 hp, but there were still minor gains to be made. We dropped the shorty headers in favor of 1 3/4-inch long-tube headers, still running with mufflers. That change saw an amazing 27 lb-ft of torque improvement at 3,000 rpm, while average torque jumped a solid 10 lb-ft. Peak horsepower gained 9 hp, which is certainly nothing to scoff at. The longer primary tubes are the main reason for the improvements.

The next test was the one we had been waiting to perform: returning that simple yet amazing TrailBlazer SS intake back on the Iron Maiden, now with the bigger cam and ported 5.3L heads. Up until now, we'd been using the factory LS6 intake. This may seem like a step backward, with a combination that is little more than a stack of near-OE parts—a 150,000-mile 6.0L truck short-block, tweaked 5.3L heads, a stone-stock truck intake, and a very conservative Comp cam. Yet the power this combination makes is astonishing.

We'll admit, we tried hard to make that 500 hp level. But after a few attempts, we wanted to keep it real and claim what we made: 496 hp at a loafing 5,600 rpm, with an equally impressive peak torque of 496 lb-ft at 4,800 rpm. What's more, the engine never made less than 420 lb-ft of torque from 2,600 rpm all the way through 6,000. Now, let's look at the average torque numbers. Test 1 started with an average of 417 lb-ft, which is not bad. But with the addition of just the cam, the long-tube headers and the TrailBlazer intake, the average torque jumped by nearly 45 lb-ft. The peak torque from Test 1 to Test 4 rumbled from 455 to 495 lb-ft.

Let's put these numbers into perspective. A stock Chevrolet Performance 454 HO crate engine is rated at 500 lb-ft of torque at 3,500 and 438 hp at 5,300. To be fair, Chevy uses a more conservative testing procedure and correction factor that reduces the power numbers. Plus, the cam in this Rat crate engine is even smaller than the one in the Iron Maiden. But the Rat is packin' 454 ci. Our Iron Maiden is a junkyard refugee at 364 inches, and in its current configuration makes almost the same torque, but 60 hp more. And the Maiden is dramatically lighter. So, what we really have here is mild big-block potency in a very small package—a big bang in a small box.

There was also one last test we wanted to run in this session. Until now, we'd been focused on EFI for our fuel-mixing duties but realized that some car crafters may want to run with a more traditional carburetor instead of messing with the electronics.

We'll admit that we're definitely carb-friendly. We like carburetors because they're simple, so we decided to compare a dual-plane intake setup since our goal is building torque for the street. We realized it wasn't fair to compare the Edelbrock Performer RPM dual-plane and 750-cfm carburetor with the TrailBlazer intake, since the taller truck intake doesn't fit under many hood lines. Instead, we chose to compare it with the LS6 intake.

Even with its short height, the LS6 intake still enjoys a longer runner than the dual-plane carb intake. The LS6 (Test 3) managed 480 lb-ft against the 463 lb-ft of the carbureted/ dual-plane intake. Power levels were a little closer, with the old-school carburetor able to pump the horsepower to 475, while the EFI pushed the peak to 484 hp.

The only place where the carburetor might have an advantage is in cost. Including the price of a new Edelbrock Performer RPM, a new Holley 750 mechanical secondary carburetor, and an MSD ignition box, this setup comes in at just less than $1,250. If you already had a carburetor, the price falls to just more than $650—quite a bit less expensive than an EFI package.

Since performance is what we're really all about, we simulated the peak power combination with both the TrailBlazer SS intake and the carbureted version. If you recall from Part II, the Quarter Pro simulation program estimated that our Orange Peel Chevelle with 3.50:1 gears, 26-inch-tall tires, and good traction at a 3,500-pound race weight would run 12-teens at 113 mph. This current combination with the ported heads, Comp cam, long-tube headers, and the TrailBlazer SS intake would push the Chevelle to 11.60s at 117 mph. The carbureted version would be slightly slower at 11.90s at 115 mph. These are estimates based on a very minimal tire spin. Traction plays a big part in running these times, as we're dealing with big-block torque levels.

As impressive as these numbers are, we're pretty sure there is still more power hiding in the induction system. Looking at the relatively low peak horsepower rpm point, it's clear that, while formidable, the TrailBlazer SS intake is holding this effort back from even bigger numbers. We plan to try a few different intake manifolds in an upcoming session to see if we can perhaps bump up the power a little more and perhaps gain another small bump in cam timing.

The Iron Maiden is living up to her name, with strong performance so far. It's clear that from here on the gains will become smaller and harder to achieve, but we think this Maiden is still hiding power in between those iron walls!

See all 12 photos

See all 12 photos We completed Iron Maiden Part II with the CNC-ported, 5.3L heads, an LS6 intake, and the shorty headers that made 457 hp and 344 lb-ft of torque. This is the baseline for all our power comparisons for this installment.

See all 12 photos The next step (Test 2) was to replace the stock LS6 cam with a much stronger yet still mild Comp LSR cam with 219 degrees at 0.050 duration and a touch more than 0.600-inch lift.

See all 12 photos All the tests in Part III used the ported 5.3 heads tuned up by West Coast Racing Cylinder Heads. With respectable flow numbers and good velocity, combined with a bump in compression, these heads really work—at half the cost of a set of aftermarket LS heads.

See all 12 photos For Test 3, we removed the shorty headers and replaced them with a set of long-tube, 1 3/4-inch headers that were also fitted with mufflers.

See all 12 photos Kevin Crocie, son of our good friend, Ken Crocie, stopped by during our dyno session, so of course we immediately put him to work. He's just buttoning up the install of the TrailBlazer SS intake manifold and checking the header bolts to make sure they're tight.

See all 12 photos

See all 12 photos This is the Iron Maiden in its 496hp configuration with the WCRCH-ported heads, TrailBlazer SS intake, larger 102mm throttle-body, electric water pump, long-tube headers, and 219 Comp camshaft. This package idles at 875 rpm with 14 inches of manifold vacuum.

See all 12 photos We also wanted to test a carbureted configuration and chose the Edelbrock Performer RPM dual-plane, since torque is what we're after. Although a single-plane would have made more peak power, it would have sacrificed too much torque for our liking.

See all 12 photos Topping off the Edelbrock intake was a Holley 750 HP carburetor. This configuration is certainly simpler to install and uses the MSD ignition controller to generate the spark. This package was down slightly against both the TrailBlazer SS and LS6 intakes but still made 475 hp.

See all 12 photos This graph tells the whole, torque-filled story. At 3,000 rpm, there is a difference of nearly 60 lb-ft of torque between Test 1 and Test 4. That would feel like a mild nitrous hit in a back-to-back comparison. Plus, the Test 4 curve never drops below 400 lb-ft of torque over the entire rpm range. Those are mild big-block numbers.

See all 12 photos We chose to compare the carbureted intake test with the LS6 EFI intake since they are both low-profile manifolds that will work in tight engine compartments. The shape of both curves is very similar, with the EFI manifold making just a little bit more power everywhere compared with the carbureted curve.

Cam Specs

Camshaft Duration Valve Lift Lobe-Separation Angle (LSA) at 0.050 LQ4 -'01-'04 - Int. 196 0.457 114 LQ4 - Exh 207 0.457 LS6 - '02-'04 - Int. 204 0.555 117.5 LS6 - Exh 218 0.551 Comp 269 Lr - Int. 219 0.607 112 Exh. 227 0.61 Show All

Test 1 - Best from Part II CNC-ported heads, LS6 cam, LS6 intake, shorty headers

Test 2 Add 219 COMP cam retained CNC heads, LS6 intake, and shorty headers

Test 3 Add 1 34-inch primary long-tube headers

Test 4 Add Trailblazer intake

RPM TQ1 HP1 TQ2 HP2 TQ3 HP3 TQ4 HP4 2600 366 181 381 189 389 192 410 203 2800 371 198 390 208 409 218 424 226 3000 384 220 404 230 431 246 443 253 3200 392 239 416 253 440 268 450 274 3400 397 257 420 272 441 286 454 294 3600 408 280 430 295 444 304 462 316 3800 421 305 447 323 453 327 473 342 4000 432 329 455 347 460 351 479 365 4200 441 353 462 369 464 371 481 384 4400 450 377 466 390 470 394 487 408 4600 452 396 469 411 477 417 493 432 4800 455 415 472 432 480 439 495 452 5000 454 432 469 447 478 455 494 470 5200 449 445 465 460 472 468 487 483 5400 441 453 455 468 464 477 477 490 5600 428 457 443 473 452 482 465 496 5800 413 456 430 475 438 484 447 494 6000 396 453 414 473 420 480 430 491 6200 381 450 400 472 405 478 415 490 AVG 417.5 348.7 436.2 364 446.7 371.9 461.5 383.8 PEAK 455 457 472 475 480 484 495 496 Show All

CARB vs. EFI Test

RPM Carb Carb EFI EFI TQ HP TQ HP 2600 378 187 389 192 2800 396 211 409 218 3000 412 235 431 246 3200 426 260 440 268 3400 436 282 441 286 3600 443 304 444 304 3800 447 324 453 327 4000 451 344 460 351 4200 456 365 464 371 4400 459 384 470 394 4600 460 403 477 417 4800 462 423 480 439 5000 463 441 478 455 5200 454 450 472 468 5400 446 459 464 477 5600 437 466 452 482 5800 424 469 438 484 6000 414 473 420 480 6200 402 475 405 478 AVG. 435.1 362.1 446.7 371.9 PEAK 463 475 480 484 Show All

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 four- to three-bolt throttle-body adapter 551511 Summit Racing $20.69 AC Delco LS6 intake, used w/TB 88894339 eBay Motors $400.00 Comp LS1 269Lr cam 54-456-11 Summit Racing $388.97 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 valvespring kit 26918CS-KIT Summit Racing $339.97 Edelbrock Performer RPM LS intake 71187 Summit Racing $316.84 Holley HP 750-cfm carburetor 0-80528-1 Summit Racing $590.36 MSD LS6 ignition controller for 24x 6014 Summit Racing $337.46 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