Check out Part 1 of our engine build!

Finding 100 horses in a Tri-Power 421

Last month HPP introduced to the readers a ’64 421 H.O. Tri-Power engine buildup being performed by Jim Taylor. The goal of the project is to try and find 100 additional horsepower in a cast-iron cylinder head (casting #716), iron intake manifold, and small intake-valve (1.92 inches) Pontiac. A lofty goal when one considers the small throat area of the #716 cylinder head. To further complicate the task, Jim insists the engine employs Pontiac induction parts from the carburetor air horn to the intake port of the cylinder head, albeit maybe not all from ’64. He had some levers to pull to accomplish his self-imposed goal, so a brief review would be in order.

Recognizing that there are many factors involved to convert chemical to mechanical energy with an internal combustion engine, Jim’s approach was multi-faceted. Every engine suffers from three areas of loss. A loss in engineering parlance is described as something that does not allow the full chemical energy potential from the fuel to be transferred to the crankshaft. These areas are identified as pumping, thermal, and frictional losses.

A pumping loss is the amount of work the engine must perform to fill the cylinders with a charge and then exhaust the spent gasses. Traditional modifications to the intake and exhaust path, such as better flowing components and headers are an example of minimizing pumping losses. The 421 build addressed this with flow bench testing of the cylinder head and Tri-Power manifold with the three Rochester carburetors attached.

Thermal losses can be addressed in many ways with the most effective being an increase in the static compression ratio of the engine. The compression ratio is a result of the change in volume of the bore with the piston at bottom dead center and then at top dead center. In any engine an increase in compression ratio will provide a lock-step improvement in thermal efficiency. Thermal losses are the energy that goes into the coolant and out the exhaust pipe instead of working against the piston.

Jim looked to keep thermal loss at bay and still maintain the engine’s street nature. He accomplished this by pushing the envelope for compression ratio to 10.6:1 and tricking the combustion event to bleed off some of the cylinder pressure at light load with modified cam timing. This would make the Pontiac less octane sensitive.

The dyno test will be run using VP C-9 that is rated with the following specifications:

  • Specific Gravity at 60 degrees F: 0.718
  • Motor Octane Number: 92
  • Research Octane Number: 100
  • R + M/2 = 96 octane
  • Unleaded with no oxygenate added

Frictional losses are the energy consumed by the actual mechanical operation of the engine. These are the turning of the crankshaft and camshaft, the movement of the valves, and the operation of the oil and water pumps. When an engine operates, friction is produced and any efforts taken to minimize it will show up on the dyno needle. Thus, the 421 employed light-weight pistons and rods along with a mechanical advantage created by the valvetrain geometry and modifications to the oiling system to limit oil whip during running.

As an aside to this, in ’63 Pontiac issued a service bulletin to all dealers requiring a new dipstick to be installed in the 421 H.O. engines. What was discovered is that under hard braking as would be experienced after a run at a dragstrip the oil would move forward and away from the pick-up, temporarily starving the lubrication system. The new dipstick was marked so that when it read full, the pan would now have six quarts of oil instead of the normal five quarts. This simple change cured the issue that would not be seen during normal driving.

Now keep in mind that Jim’s self-imposed restriction of employing mostly factory parts made the task of eradicating the three areas of loss much more difficult. For example, the major stumbling block would be the small intake valve size that must be used with the #716 cylinder heads. This is due to the combustion chamber design.

Also, wanting this exercise to mimic what Pontiac could have potentially done when this stellar engine was in actual production, Jim insisted on still using the Delco breaker-point distributor with no electronic conversion.

In many ways, he tied his own hands, but for the dream to be fulfilled, the clock needed to be turned back to the mid-’60s and stay there. The 421 would be era-correct even though it is now 2013.

So get comfortable and follow along as we bring you to that faithful day when the 421 challenged the water brake at Bitner Automotive in Trenton, New Jersey. Let us see if Jim meets his goal and makes his dream come true.

Nowadays only 2 in 10 outer carbs I get in for rebuilding still have the diffusers in them

HPP Engine Buildup Worksheet

  • Engine Displacement: 432 ci
  • Horsepower: 473 at 6,000 rpm
  • Torque: 493 at 4,300 rpm
  • Bore/Stroke: 4.150/4.00-in
  • Block/Crank combo: ’64 421 block, ’64 OE 4.00-in stroke four-bolt main
  • Bore/Stroke ratio: 1.04:1
  • Rod/Stroke ratio: 1.65:1

Bottom End

  • Block description: ’64 421ci #157
  • Preparation: Cook, bead blast, magnaflux, bore, true decks, align bore
  • Deck Height: 10.215-in
  • Crank: Original ’64 421
  • Preparation: Magnaflux, check for equal stroke and index, grind 0.010-in, polish
  • Balancer: Original PMD rebuilt by Damper Doctor
  • Rods: Howard’s billet 4340 certified steel, stock 6.625-in, floating pins
  • Preparation: Weigh, soap and water wash
  • Bearings: Sealed-Power mains and rods, cam Dura-Bond
  • Preparation: Visual, install in rod, torque, measure I.D.
  • Pistons: Icon PN IC892, application 428 +0.030-in with 10cc dish
  • Preparation: Wash after balance for assembly
  • Piston-to-deck height: 0.009-in
  • Piston pins: Icon, SAE 1016 to 1022
  • Method used to retain pins in pistons: Spiral clip
  • Rings: LPC (Liberty Performance Components) premium moly, standard tension
  • Preparation: File-fit for end gap if needed, wash
  • Rod bolts or studs/head bolts or studs: ARP cap screw supplied in Howard’s rods, PMD

Oiling System

  • Windage tray: Original PMD ’70 455, fabricate fit, no bosses at cap #2
  • Oil pan: Milodon 8-quart with extended pick-up, fabricated retention clamp
  • Oil pump: Melling PN M54D with 60-psi spring, made 70 psi at 6,000 rpm with 30W oil
  • Preparation: Disassemble, check ball seat for width, spring tension, plate clearance

Heads

  • Casting number: 97770716, ’64 date
  • Chamber: Closed, special to PMD, 70 cc
  • Head mods: Port, cook, magnaflux, glass bead, convert to screw-in studs
  • Maximum flow at 28 inches of water
  • Intake: 218 cfm at 0.500-in Exhaust: 180 cfm at 0.500-in
  • Compression Ratio: 10.6:1 effective
  • Valves: Competition Products stainless steel, 1.92 /1.66-in
  • Angles used in valve job: 30-deg intake, 45-deg exhaust seat, width 0.040-in intake, 0.060-in exhaust
  • Mods: Intake port match, valve bowl blend, improved short turn radius
  • Retainers: Crower steel
  • Keepers: Comp Cams race locks
  • Valve guides: K-Line, liners
  • Valve seals: U.S. Seal
  • Rocker studs: ARP special 3⁄4-inch bottom
  • Rocker arms: Crower roller, 1.6:1
  • Pushrods: LPC chrome moly
  • Diameter: 5⁄16-in
  • Length: 8.750-in

Cam

  • Brand: Crower PN 60311, solid
  • Duration at 0.050: 247/252-deg
  • Lift: 0.515/0.525 with 1.6:1 rockers
  • Centerline: 110-deg
  • Lobe separation angle: 112-deg
  • Installed position: 110-deg
  • Lifters: Crower solid with EDM oil hole (0.024 inch)
  • Valvesprings: Crower, dual no damper
  • Seat pressure: 110 pounds at 1.600-in
  • Open pressure: 282 pounds at 1.100-in
  • Timing chain: LPC double-roller

Induction

  • Carb: (3) Rochester two-barrels PMD
  • Size cfm: Total flow, 1,050 cfm
  • Mods: Built to factory specifications/ adapt ’64 choke to ’66 center carburetor
  • Jets: Original GM
  • Primary: Center #64 adjust power valve spring for 12 Hg at 1,000 rpm
  • Secondary: Front and rear #70
  • Fuel pump: Will use 110-gph Carter
  • Fuel line size: 3⁄8-inch, 5⁄16-inch to carburetor
  • Intake manifold: Original ’64 PMD Tri-Power
  • Mods: Flow test indicated ’66 center carburetor would be required to improve total cfm, adapter made to fit ’66 center carburetor

Ignition

  • Distributor: ’61 Delco with cast-iron with direct oiling
  • Coil: GM
  • Wires: NAPA Belden 7mm
  • Total Timing: 36-deg BTDC
  • Initial advance: 18-deg
  • Mechanical advance: 36-deg at 3,200 rpm
  • Vacuum advance: Not used

Exhaust

  • Headers: Hooker Super Comp (for dyno test)
  • Primary tube diameter: 1.75-in
  • Primary tube length: approximately 31.00-in
  • Collector size: 3.00-in

Gaskets

  • Brand: Fel-Pro head and intake/SCE pan and timing cover

It Only Takes Two!

Dyno Results
Maximum power with three carburetors functioning
Timing: 36-degrees
Jets: 0.070/0.064/0.070
RPM TQ HP
4,300 493.62 405.28
4,400 491.89 409.34
4,500 490.64 418.14
4,600 489.66 426.64
4,700 488.94 435.50
4,800 487.48 443.07
4,900 484.75 449.82
5,000 480.63 455.54
5,100 473.27 457.08
5,200 467.99 460.81
5,300 462.70 464.87
5,400 453.66 464.28
5,500 443.57 462.56
5,600 435.73 463.03
5,700 431.45 465.85
5,800 426.33 468.43
5,900 421.34 471.42
6,000 416.18 473.30
6,100 407.49 470.91
AVG 460.39 450.83

When first exposed to the thought of testing a Tri-Power equipped Pontiac with the two outboard carburetors disconnected, the knee-jerk reaction is probably, why?

Jim Taylor’s reasoning behind this final test we did that day was to assign a hard number to the kick one feels when matting the throttle and allowing for the improved volumetric efficiency that the other two Rochester carburetors bring to the game. Well, with this engine that number is approximately 123 hp. The 421 made a hair shy of 350 hp when running on the center two barrel alone. Jim finally got his answer to a question he has been asking himself for decades.

As the author, this test not only satisfied Jim’s curiosity but also proved something I believe more valuable—it debunked the age-old myth that a Tri-Power manifold would offer poor fuel distribution during street driving.

For as long as I can remember, it was believed stunning performance and good drivability were not achievable with three carburetors. If that was the case then the engine would not have made 350 hp on the dyno with excellent loading and good fuel distribution. The only caveat being that the carburetors need to be set up properly, and Jim certainly knows how to do that.

The moral of the story is if you have a Tri-Power Pontiac that suffers from poor light-load performance, stop blaming the manifold design. When they are right, they are right, and when they are wrong—well, you know the result!

Dyno Results
Power with only the center two-barrel operational
Timing: 36-degrees
Jets: 0.064
RPM TQ HP
4,200 397.08 315.79
4,300 395.24 321.56
4,400 394.29 328.02
4,500 391.38 341.20
4,600 389.09 346.60
4,700 384.03 349.00
4,800 376.73 349.74
4,900 365.91 346.64
5,000 356.05 343.97
5,100 346.82 341.79
5,200 336.10 337.52
5,300 326.74 334.17
5,400 317.51 331.14
5,500 309.15 328.20
5,600 301.01 325.34
5,700 293.27 322.39
5,800 283.74 317.41
AVG 353.15 334.18

SOURCE
Jim Taylor Engine Service
P.O. Box 462
Revere
PA  18953
610-294-9707
UEM Pistons
800-648-7970
www.uempistons.com
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