Fuel Octane Test - Project Pure Poncho

As was covered thoroughly in the Sept. ’11 article, the octane of the gasoline is only one part of the story. The energy content in Btu, the chemical composition, and most important the burn speed, all impact how the engine performs. As the testing proved, the Mule was nearly benign to the fuel fed to it, and proved some wrong about Pontiac engines and octane tolerance, the author being one of them (see sidebar).

What our testing has proven is that if a Pontiac engine is built properly with the correct combination of parts, excellent power can be made with regular grade gasoline. Once octane creep takes hold, then these results would most definitely change. The trick is not to let the carbon build-up and your engine should be fine.

Other things to consider are during our dyno testing the engine only experienced peak power for around eight seconds. Driving a Pontiac is certainly different than that, but also it is not making anywhere near peak power. It is the author’s opinion that a properly tuned 9:1 Pontiac of substantial power can be very happy on regular-grade fuel for most if not all driving conditions. In this day and age of $4-per-gallon fuel, that little difference can go a long way.

How great is it to brag that your engine can run on regular and still make just shy of 500 hp? That’s why we love Pontiacs!

Three Pulls-Horsepower On...

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Three Pulls-Torque Only

The red plot shows the best pull with the 88-octane fuel (551 lb-ft, 488.6 hp), the blue with the 94 (554.2 lb-ft, 489.1 hp) and the green with the 100 (552 lb-ft, 493.0 hp). Not shown since it was covered in the last issue is the 92-octane test, which produced 551 lb-ft and 491.8 hp.

HPP Engine Buildup Worksheet

Engine displacement: 467 ci
Bore/stroke: 4.185 / 4.250-in
Bore/stroke ratio: 0.98:1
Rod/stroke ratio: 1.6:1

Bottom End
Block: Stock ’75 455
Preparation: Cooked, magged, line-bored, line-honed, decks squared with BHJ, bored and honed with torque plates
Deck height: 10.205-in
Crank: Butler/Eagle forged
Preparation: Balanced, polished
Balancer: Summit Street/Strip, steel, elastomer, 6.610-in, SFI 18.1
Rods: Eagle forged H-beam, 6.800-in
Preparation: Pin end honed to proper size, balanced, big end checked for proper size
Bearings: Clevite, plain shell, tri-metal
Preparation: Clean, check for proper clearance in rods
Pistons: Butler/Ross forged flat-top with valve reliefs
Preparation: Pin fit, check size, clean
Piston-to-deck height: 0.010-in below
Piston pins: Ross, 0.990-in floating, 0.155-in wall
Method used to retain pins in pistons: Spiro Locks
Rings: Total Seal; moly top; ductile second; three-piece oil; 1⁄16-, 1⁄16-, 3⁄16-in
Preparation: File-fit, clean
Rod bolts and head bolts: ARP
Balancing specs: Internal

Oiling System
Windage tray: Canton in pan
Crank scraper: Canton in pan
Oil pan: Canton Racing Road Race Series 5-quart, wet-sump
Oil pump: Melling M54DS high-volume

Heads
Casting number: 6X
Combustion chamber volume: 96.2ccs
Maximum flow at 28 inches of pressure

Lift	Int. Flow CFM	Exh. Flow CFM
0.100	66	55
0.200	133	106
0.300	191	149
0.400	224	170
0.500	236	182
0.600	250	186

Compression ratio: 9.1:1
Valves: Manley SS 2.11/1.77-in
Angles used in valve job: Intake—45, 60, 75, and 82-deg, 82 is hand blended into 75-deg., exhaust—45-deg, 12mm radius
Retainers: Comp Cams, steel, 10-deg Beehive
Keepers: Comp Cams 10-degee, 11⁄32-in
Valve guides: K-line bronze liner
Valve seals: Steel/Viton
Rocker studs: ARP 7⁄16-in
Rocker arms: Comp Cams aluminum full roller, 1.65:1
Pushrods: Manley 3⁄8x8.900-in

Cam
Brand: Comp Cams Xtreme Energy hydraulic roller
Duration at 0.050: 224/230-deg
Lift: 0.552/0.561-in
Centerline: 106-deg
Lobe separation angle: 110-deg
Installed Position: 106-deg
Lifters: Comp Cams roller
Valvesprings: Comp Cams Beehive
Seat Pressure: 137 lb/in
Open Pressure: 290 lb/in
Timing Chain: Comp Cams double-roller