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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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

1107chp 09 O  L92 Cylinder Head Install 2/20

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

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