In last month’s issue we outlined the series of events that resulted in a complete rebuild of the 455 H.O. in our ‘72 Trans Am. What started out as a simple frost plug repair quickly escalated to a full blown rebuild, as we found several additional issues at the time of disassembly that could have certainly ended much worse. There are no two ways about it—we dodged a major bullet.

With only 1,286 Trans Ams built during the ’72 model year, and the fact that ours retains its numbers-matching drivetrain, we were set on reusing as many original components as possible during the 455 H.O. rebuild. Looking to improve reliability, we made a few concessions that would remain undetectable from any external view. This would also give us a chance to inject some modern technology, which could boost performance slightly, too.

Knowing a new crankshaft and pistons were required, it made sense to purchase a complete rotating assembly that would include everything needed to assemble the short-block. We opted for a forged 4340-steel crankshaft as it offered increased durability for only a few hundred over the cost of a cast replacement. It also made the jump to a stroker assembly a sensible choice—it didn’t add to the cost, would increase total displacement by a few more cubic inches, and could possibly add a few extra lb-ft of torque.

Flat-tappet camshafts remain an excellent performance value, but roller technology provides several advantages. When compared to a similar flat-tappet, a roller-grind can open the valves quicker, which allows for more seat time. The result is improved idle quality with no degradation to full-throttle performance. The friction loss associated with the roller lifter may also free up a few more horsepower, too, and because hardened components are used, they’re unaffected by modern spec oil and aren’t susceptible to lobe and/or lifter failure like flat-tappet cams.

A quick call to Butler Performance netted most everything we needed for our rebuild, including a high-quality rotating assembly. It and the other pieces we ordered were delivered to our doorstep in a matter of days.


A quick call to Butler Performance netted most everything we needed for our rebuild, including a high-quality rotating assembly


We searched through Comp Cams catalog and considered a few of its off-the-shelf hydraulic roller grinds. We couldn’t find the exact specs we wanted so we simply ordered a custom-ground unit, which arrived along with everything else we needed for the valvetrain in little more than a week.

Willard Auto Machine (WAM) in Omaha, Nebraska, was enlisted to machine the 455 H.O.’s existing components to accept the kit we’d purchased, perform the complete engine assembly, and then measure the freshly rebuilt 455 H.O.’s performance on its in-house engine dyno. Follow along as the rebuild progresses and the 455 H.O. proves its worth as a formidable street engine, generating impressive numbers from a relatively simple combination. And to think we were satisfied with its performance before the rebuild!


HPP Engine Buildup Worksheet

  • Engine Displacement: 468.8 ci
  • Horsepower: 433
  • Torque: 517 lb-ft
  • Bore/Stroke: 4.195/4.25 inches
  • Engine Built By: Willard Auto Machine

Block

  • Block Description: ’72 code-YE 455 H.O.
  • Preparation: Clean and inspect, soda-blast, bore and hone cylinders to 4.195, align-bore
  • Deck Height: 10.220-inch
  • Crank: Eagle forged 4340-steel, 3.25-inch main journals, 2.2-inch rod journals, 4.25-inch stroke
  • Preparation: ESP Armor finish
  • Balancer: Powerbond stock replacement
  • Connecting Rods: Eagle forged 4340-steel, H-beam, 6.8-inch length
  • Bearings: Sealed Power on mains and rods, Dura-bond for camshaft
  • Pistons: Ross, custom design for Butler Performance spec, 4.191-inch, 8.5cc valve relief volume
  • Wristpin: 0.990 in, full floating
  • Piston Rings: Total Seal
  • Deck Height: Zero
  • Rotating Assembly Balanced: Yes

Oiling System

  • Windage Tray: Tomahawk Replacement
  • Oil Pump: Pro-Series from Butler Performance, approximately 70 psi
  • Oil Pan: Canton stock replacement

Heads

  • Casting: ’72 No. 1972 455 H.O. Round-Port
  • Preparation: Clean, install new valveguides, machine
  • Valves: Ferrea stainless-steel, 2.11/1.77-inches
  • Valve Seat Angles: Multi-angle with 30-deg intake and 45-deg exhaust seats
  • Valvesprings: Comp Cams 987-16
  • Valvespring Install Height: 1.8 inches
  • Valvespring Pressure: 125-psi seat, 325-psi open
  • Valve Retainers: Comp Cams 740-16
  • Valve Locks: Comp Cams 614-16
  • Rocker Studs: ARP 7⁄16-inch
  • Rocker Arms: . . Comp Cams cast-alloy roller, 1.5:1 ratio
  • Combustion Chamber Volume: 100 cc
  • Compression Ratio: 9.2:1
  • Intake Port Volume: 170 cc
  • Air Flow Numbers at 28 Inches:

Before Rebuild

*Lift Int/Exh

  • 0.050 0.41/0.24-inch
  • 0.100 0.74/0.51-inch
  • 0.200 0.139/0.97-inch
  • 0.300 0.190/0.133-inch
  • 0.400 0.209/0.149-inch
  • 0.500 0.212/0.160-inch
  • 0.550 0.213/0.165-inch

After Rebuild

*Lift Int/Exh

  • 0.050 0.43/0.27-inch
  • 0.100 0.81/0.57-inch
  • 0.200 0.153/0.123-inch
  • 0.300 0.200/0.155-inch
  • 0.400 0.214/0.168-inch
  • 0.500 0.222/0.175-inch
  • 0.550 0.223/0.177-inch

Camshaft

  • Brand: Comp Cams custom hydraulic roller
  • Duration at 0.050: 224/236-deg
  • Duration Advertised: 275/287-deg
  • Lift with Specified Rocker Arms: 0.502/0.520-inch
  • Lobe Separation Angle: 113-deg
  • Intake Centerline: 109-deg
  • Lifters: Comp Cams hydraulic roller
  • Pushrods: Smith Brothers 8.65-inch length
  • Timing Chain: Federal Mogul CTS-3112R

Induction System

  • Carburetor: ’71 455 H.O. Quadrajet, #7041268, 828-cfm
  • Primary Jets/Rods: 74/43
  • Secondary Rods: CV 0.0527-in
  • Secondary Rod Hanger: Stamped “R”
  • Fuel Pump: Carter M6405
  • Intake Manifold: ’72 455 H.O., No. 488945 cast-aluminum

Ignition

  • Distributor: Pontiac points-type No. 1112126
  • Points: NAPA CS-89
  • Distributor Gear: BOP Engineering composite
  • Coil: Stock ACDelco
  • Wires: Stock-replacement ACDelco
  • Spark Plugs: ACDelco No. R45TS
  • Total Timing: 34-deg
  • RPM Total Timing Is Reached: 3,200

Exhaust

  • Exhaust Manifolds: Reproduction round-port by Ram Air Restorations with 2.5-inch outlets
  • Exhaust Pipes: 2.5-inch
  • Muffler: Reproduction crossflow-type from Waldron Exhaust

Gaskets

  • Brand: Fel-Pro



Dyno Results
On WAM’s in-house dyno, the freshly rebuilt 455 H.O. peaked at 433 hp at 4,800 rpm and 517 lb-ft at 3,500 rpm. If the figures calculated from our initial chassis dyno session before the rebuild are correct, we increased output by at least 100 units each! Reviewing performance at each point reveals how well suited this combination will be for the street.
RPM HP TQ
2,600 249 487
2,700 261 492
2,800 273 496
2,900 282 498
3,000 297 506
3,100 307 506
3,200 320 512
3,300 329 513
3,400 340 514
3,500 354 517
3,600 361 517
3,700 367 516
3,800 380 512
3,900 388 515
4,000 392 511
4,100 395 496
4,200 402 494
4,300 407 486
4,400 410 483
4,500 416 478
4,600 426 477
4,700 429 477
4,800 433 467
4,900 433 463
5,000 429 448
5,100 420 432
5,200 424 423
5,300 425 415
5,400 422 408
5,500 422 401
Avg. 373 482


SOURCE
Comp Cams
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
Butler Performance Group
2336 Highway 43 S, Dept. HPP
Leoma
TN  38468
Eagle Specialty Products, Inc.
8530 Aaron Lane
Southaven
MS  38671
662-796-7373
www.eaglerod.com
D&R Auto Paint and Supply
8710 J St.
Omaha
NE  68127
Canton Racing Products
232 Branford Road
North Branford
CT  06471
203-481-9460
http://www.cantonracingproducts.
com
Willard Auto Machine
7620 N 96th St
Omaha
NE  68122
402-573-8984
http://www.wampowered.com/
Federal-Mogul
26555 Northwestern Hwy.
Southfield
MI  48034
248-354-7700
www.federal-mogul.com