L92 Cylinder Heads Install - It’s All In Your Heads

Putting Modified L92 Cylinder Heads on a 4.160-inch Bore Block

Ro McGonegal May 24, 2011 0 Comment(s)
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I was advised to leave the engine combination as it was built, because each piece had been selected for

1107chp 02 O  L92 Cylinder Head Install 2/20

its specific contribution to the whole. That was years ago, ancient really, in 2003. Arguably, this engine built by Katech at the behest of then-Chevrolet Special Projects engineer Mark McPhail, was the largest of its type (4.160x4.160) at the time, 452.3 ci to be exact. Today, LS engine technology is a quantum leap from 2003. Through the use of deck spacers and/or tall-deck aftermarket blocks, 500 ci or more is stone reality at a considerably cheaper rate.

View this engine, based on the hideously expensive C5R aluminum race block (currently tagged at $6,400 to $9,250, depending on aftermarket vendor), as one built from a 9.260-inch low-deck GMPP LSX Bow Tie block that can be had for as little as $2,000. Since it is iron, it has been designed to withstand tons more power and torque than the optimum, aluminum C5R—which was originally envisioned as a road race entity that likely would not exceed 427 ci or 700 hp.

But a 427 wasn’t big enough, McPhail reasoned, so what we really needed was a 454. The crankshaft in this engine is a prohibitively expensive billet piece as crafted by the legendary Hank the Crank Bechtloff (now retired). Today it would fetch on the far side of $4,000. By comparison, a GMPP LSX or Lunati long-stroke forging can be had for thousands less. The connecting rods are Carrillo H-beams; the pistons are CP forgings, again built especially for this project.

On the Katech dyno this engine produced 554 hp at 5,600 rpm and 577 lb-ft of torque at 4,400 rpm, providing more than enough power to propel a 4,000-pound vehicle to an untuned, tire-spinning 12.20 at 115 mph. On the street, however, the B-body was uncannily able to dodder around in Fifth or even top gear without so much as a whimper or a shudder, smooth and linear.

But greed hooked us. We surely wanted to see at least 500 hp at the wheels. Enter LS engine builder/tuner Mike Norris, a Corvette doctor and fabricator who welcomed the accommodation and expanse of the ’66 Biscayne that this engine is in. We’d read about the affordable but highly productive qualities lurking in the L92 truck cylinder heads, ones that were posed on a 4.00-inch bore. We’d read about gains of 40 hp or more, but how would these castings enable an engine with a larger bore size and how much of an improvement would they make compared to the early 64cc combustion chamber GMPP CNC LS6 heads?

1107chp 19 O  L92 Cylinder Head Install 3/20

As it turned out, not enough to justify the time and expense but happily better than the flywheel claims we’d read about. Under throttle, the engine responds better than it did before in a smoother, more linear exhibition. By the seat of our shorts, the sled doesn’t feel demonstratively quicker. We’d seen a bit more than 19 mpg on an 800-mile scoot from Memphis to Tampa (0.62:1 Sixth gear, 3.89:1 axle gear, 2.41:1 final drive) keeping the revs at 1,900 rpm or approximately 70 mph. Though torque peak has been raised a few hundred rpm, throttle response at low revs in higher gears hasn’t diminished one iota.

At the rear wheels, the changes produced a gain of 31 hp and 15 lb-ft of torque. We thought that the Scoggin cam would pick up even more, but it did not. The upshot? Even though they’ve been extant for at least eight years, the “obsolete” CNC LS6 cylinder heads (commonly $400 more per set than CNC L92s) and matching intake manifold are extremely capable devices. If you’ve already got the stuff, keep it. If you’re building from scratch, you should definitely investigate the CNC L92s.

Stuff

FAST XIM controller and harness
Jesel shaft rocker arm system, 1.8:1 ratio
II Much Fabrication rocker cover breather and catch can, alternator spacer, remove FAST eDIST, and install FAST XIM and new harness
Moroso sheetmetal rocker covers, 8mm primary wires
Mike Norris Motorsports labor, dyno testing/tuning, billet fuel rails, LS3 injectors: 39 lb/hr (at 60 psi)
Red Line 10W30 synthetic oil
Scoggin-Dickey Performance Center SD 8801 CNC L92 cylinder heads, 65cc combustion chambers, Manley Race-Flo series stainless steel valves: 2.165-inch intake; 1.590-inch exhaust, S-D/Patriot double springs: 1.80-inch installed height; closed pressure: 135 pounds; 1.15-inch compressed height, open pressure: 375 pounds; titanium valvespring retainers, SD 0121 hydraulic camshaft, 92mm throttle body, L76 intake manifold, and Cometic MLS head gaskets.
Trend 7.5-inch pushrods

Cam Specs

GM ASA Cam SD-0121 Cam
Duration at 0.050: Intake 226 degrees Duration at 0.050: Intake 226.2 degrees
Lift: Intake 0.525 inch Lift: Intake 0.610 inch
L/S (degree): 110 L/S (degree): 114
Exhaust: 236 degrees Exhaust: 234.3 degrees
Exhaust: 0.525 inch Exhaust: 0.626 inch

Help From John Parsons

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The engine had a small but persistent oil leak at the rear of the block. The head/intake manifold swap story revealed the origin: Both of the rear intake manifold bolts were missing. John Parsons is an engineer/hot rodder/upscale car builder who surmised that there may also be an internal pressure problem so he machined a rocker cover breather system and fabricated the corresponding overflow canister. The catch can end goes into the intake manifold, the breather side (that uses the original breather opening) on the tightly sealed Moroso sheetmetal rocker cover issues into K&N air intake tract. Primary ignition wires are solid-core 8mm Moroso. Parsons also fabbed a 1-inch spacer to move the alternator outward so that it would clear the end of the taller Moroso rocker cover).

Regarding a persistent engine misfire at proximately 4,500 rpm, he removed the early (and sometimes problematic) FAST eDIST module and installed a more modern FAST XIM box (thank you David Page) in its place. Then, all power and ground circuits were rewired. Parsons: “The actual problem with the original stuff was a badly frayed crank signal wire.” All of this conspired to make the engine cranking sequence way too long and the engine difficult (farting, backfiring, and the like) to start when cold. The new XIM module was the cure.

“The insulation was cracked and missing altogether in some spots. Worse, it was wound around the ground wire for the signal—a real mess. I redid the power and ground circuits so they come directly off the battery as recommended by FAST. Problem solved.”

Base 454 Runs

RPM Power Torque
2,600 201.1 406
2,700 214.5 417.2
2,800 226.1 424.1
2,900 239 432.9
3,000 253.7 444.2
3,100 270.1 457.5
3,200 282.6 463.8
3,300 298.7 475.4
3,400 314.1 485.2
3,500 328.7 493.3
3,600 341.7 498.5
3,700 356.8 506.4
3,800 368.6 509.4
3,900 378.7 510
4,000 386.2 507
4,100 394.3 505.1
4,200 402.6 503.4
4,300 412.2 503.5
4,400 423.3 505.3
4,500 433.6 506.1
4,600 441.2 503.8
4,700 449.5 502.3
4,800 457.9 501.1
4,900 462 495.2
5,000 466.4 489.9
5,100 469.1 483.1
5,200 473.3 473.3
5,300 472.9 468.6
5,400 474.8 461.8
5,500 471 449.7
5,600 473.3 443.9
5,700 466.5 429.9
5,800 464.9 421
5,900 462.2 411.5
6,000 460.9 403.4
6,100 453 390.1
6,200 450.5 381.6

Base 454 Runs

RPM Power Torque
2,600 201.1 406
2,700 214.5 417.2
2,800 226.1 424.1
2,900 239 432.9
3,000 253.7 444.2
3,100 270.1 457.5
3,200 282.6 463.8
3,300 298.7 475.4
3,400 314.1 485.2
3,500 328.7 493.3
3,600 341.7 498.5
3,700 356.8 506.4
3,800 368.6 509.4
3,900 378.7 510
4,000 386.2 507
4,100 394.3 505.1
4,200 402.6 503.4
4,300 412.2 503.5
4,400 423.3 505.3
4,500 433.6 506.1
4,600 441.2 503.8
4,700 449.5 502.3
4,800 457.9 501.1
4,900 462 495.2
5,000 466.4 489.9
5,100 469.1 483.1
5,200 473.3 473.3
5,300 472.9 468.6
5,400 474.8 461.8
5,500 471 449.7
5,600 473.3 443.9
5,700 466.5 429.9
5,800 464.9 421
5,900 462.2 411.5
6,000 460.9 403.4
6,100 453 390.1
6,200 450.5 381.6

With SD Heads

RPM Power Torque
2,600 210 424.3
2,700 221.2 430.3
2,800 235.3 441.4
2,900 250.4 453.5
3,000 265.5 464.9
3,100 281 476.1
3,200 296.8 487.2
3,300 313 498.2
3,400 327.2 505.4
3,500 339.8 509.9
3,600 351.8 513.3
3,700 361.4 513
3,800 372.3 514.6
3,900 383.5 516.4
4,000 396.8 521
4,100 408.5 523.4
4,200 419.9 525.1
4,300 429.8 524.9
4,400 439.2 524.3
4,500 446.6 521.3
4,600 455 519.5
4,700 462 516.2
4,800 469.9 514.1
4,900 477.9 512.3
5,000 483.7 508.1
5,100 488.4 502.9
5,200 493.4 498.4
5,300 496.4 491.9
5,400 487.8 484.2
5,500 501 478.4
5,600 500.2 469.1
5,700 499.8 460.6
5,800 499.2 452.1
5,900 495.2 440.8
6,000 491.5 430.2
6,100 487.8 420
6,200 482.9 409.1

With heads & cam

RPM Power Torque
2,600 215.3 434.9
2,700 226.2 440
2,800 238 446.4
2,900 249.6 452.1
3,000 263.1 460.5
3,100 276.6 468.6
3,200 291.4 478.3
3,300 305.9 486.9
3,400 320.4 495
3,500 333.8 500.9
3,600 345.7 504.4
3,700 357.9 508
3,800 366.9 507
3,900 377.5 508.4
4,000 390.3 512.4
4,100 403.2 516.5
4,200 414.3 518.1
4,300 427.3 521.9
4,400 437.6 522.3
4,500 446.9 521.6
4,600 455.4 520
4,700 463.2 517.6
4,800 472.5 517
4,900 480.6 515.1
5,000 485.9 510.4
5,100 492.1 506.8
5,200 497.2 502.2
5,300 500.7 496.2
5,400 502.6 488.8
5,500 505.4 482.6
5,600 505.9 474.5
5,700 503.5 463.9
5,800 502.4 454.9
5,900 499.4 444.5
6,000 499.1 436.9
6,100 492.6 424.1
6,200 489.2 414.4

Flow comparison

Stock L92
Lift Intake CFM Exhaust CFM
0.200 153 126
0.300 225 162
0.400 277 192
0.500 313 206
0.600 336 218
0.650 327 221
SD8801
Lift Intake CFM Exhaust CFM
0.200 154 117
0.300 223 179
0.400 282 202
0.500 323 219
0.600 349 232
0.650 356 237
GMPP CNC LS6
Lift Intake CFM Exhaust CFM
0.200 147 111
0.300 215 155
0.400 262 198
0.500 290 210
0.600 307 218

Sources

Scoggin-Dickey Parts Center
Lubbock, TX 79424
800-456-0211
http://www.sdparts.com
Red Line Synthetic Oil
Benicia, CA 94510
707-745-6100
http://www.redlineoil.com
Norris Motorsports, LLC
Winter Garden, FL 34787
407-616-2518
http://www.mikenorrismotorsports.com
Jesel
Lakewood, NJ 08701
732-901-1800
www.jesel.com
II Much Fabrication
Germantown, MD
www.iimuchfabrication.com
Trend
800-326-8368
www.TrendPerform.com
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