When approaching an engine rebuild, many hobbyists take the bigger-is-better approach. A larger displacement engine tends to produce more torque than a smaller engine, and that usually translates into a combination that's less sensitive to cylinder-head-port size, camshaft duration, and rear-axle gearing, and typically drives better at low engine speeds.
It seems that the threshold for large-cube Pontiac performance begins with the 389. While high-performance 400 rebuilds are still quite common today, an increasingly popular modification is the addition of a long-stroke aftermarket crank, which can transform a 0.060-over 400 from 412 ci to 467 in one swipe of the credit card. It's usually accompanied by a ready-made combination that easily produces 500 hp or more.
The "XU" stamped on the front of the block indicates that this particular engine is a 350
Just because big-cube performance seems more popular, that doesn't remotely suggest that big power can't come in small packages. In fact, Pontiac produced stout combinations using its smaller displacement mills during its heyday. The 326 H.O. and 350 H.O. were Pontiac's top small-cube options during the '60s; they were intended for Firebird and Tempest customers seeking large-cube performance without paying the higher insurance premiums associated with bigger engines.
Not surprisingly, Pontiac's small-cube hi-po mills were never as popular as their larger counterparts, as evidenced by their relatively low production numbers. That isn't at all indicative of capability, however. While the '68 350 H.O. used small-valve No. 18 cylinder heads, the '69 350 H.O. is essentially a small Ram Air III and used the same large-valve No. 48 heads and comparative camshaft duration. With a compression ratio at 10.5:1, it was rated at 330 hp at 5,100 rpm and 380 lb-ft at 3,200 rpm that model year.
You may recall from "Cylinder Sleeve Salvation" (HPP, Mar. '10) that this particular 350 b
Late-'60s Firebird and Tempest models powered by 350 H.O. engines are gaining popularity today. Jon Carbonneau of Beatrice, Nebraska, owns one of them-a '69 LeMans. He purchased it from a salvage yard after learning that the original numbers-matching 350 H.O. was still nestled between its framerails. The engine was in sad shape, but after a complete rebuild, it's alive and well-and HPP has the dyno sheets prove it!
Finding The '69 H.O. LeMans
You may recall some of Jon's story, which appeared in HPP ("Cylinder Sleeve Salvation," Mar. '10). His buddy owned a 350 H.O.-powered Pontiac years before, and Jon was intimately familiar with its performance capability. He located the LeMans, and recognizing its rarity and uniqueness, he purchased it with the intent of restoring it to its original condition.
The 350's main journals needed only minor honing to restore the saddle finish for optimum
Jon found that the LeMans was parked in 1990 with just 66,000 miles on it. At some point during its extended slumber, someone had stolen the original Quadrajet. The owner covered the engine with a sleeping bag in an attempt to keep out water, but that invited mice, and they soon infiltrated it and the engine's internals. Many of the exposed internal surfaces had corroded badly by the time Jon took possession.
Aware that internal engine issues existed, he enlisted the experience of Chuck Willard of Willard Auto Machine (WAM) in Omaha, Neb-raska, to assess its condition. After a thorough cleaning, Willard found that the engine had never been apart and the numbers-matching block needed two cylinder sleeves and some cylinder-head work. It seemed to be in excellent condition otherwise and a perfect rebuild candidate. The 350 H.O. rebuild was on!
With a sense of excitement toward the rebuild, Jon explained to Willard that he wanted the 350 H.O. to be as stock as possible. He asked for only one deviation: Since he planned to replace the car's Turbo-350, column-shift, automatic transmission with a floor-shifted, four-speed manual, he wanted the 350 H.O. rebuilt to manual-transmission specifications. That meant using a manual-spec No. 068 camshaft in place of the original auto-spec No. 067.
WAM owner Chuck Willard undersized the main and connecting rod journals of the original 3.
WAM machinist Beau Sheffield installed the Melling No. 068 flat-tappet camshaft and rear m
Original cast-iron connecting rods are more than sufficient for a rebuild of this level. T
Stock-replacement piston choices for 0.030-over 350 Pontiac engines are limited. Short of
Beyond measures taken to remove rust and scale from the intake manifold and cylinder head ports, WAM found that the 350 H.O. rebuild was relatively free of any unforeseen issues. The block received two cylinder sleeves, and new valves seats were installed in the No. 48 cylinder heads. Because it was destined for a restoration application and the owner wanted it as stock as possible, WAM reused the original cast-iron connecting rods and sourced a set of stock-replacement, 0.030-over, cast-aluminum pistons.
Once the 350 H.O. was complete, it was installed on WAM's Land & Sea DynoMite engine dyno. Chuck Willard broke-in the flat-tappet camshaft for several minutes and began applying various loads on the engine to properly seat the piston rings. After the break-in session was complete, the engine was pulling 19 inches of vacuum at idle and seemed to be in excellent operating condition. The dyno tuning session was ready to begin.
The wrist pins were pressed onto the connecting rods. With the rings installed, each pisto
In its first full-throttle pull in ready-to-run condition, the 350 H.O. generated 318 hp at 5,000 rpm and 380 lb-ft at 4,000 rpm, with 0.074 primary jets, 0.046 primary rods, and "BE" 0.041-inch secondary rods installed in the Quadrajet, and 36 degrees of total timing. The result was just a few horsepower shy of the original 330hp rating, but the computer shows that the carburetor appeared very lean. Several additional pulls were made, adjusting the carburetor accordingly.
Using 0.075 primary jets, 0.046 primary rods, and "CC" 0.030-inch secondary rods, horsepower from the 350 H.O. peaked at exactly 330 at 5,200, which was (coincidentally?) practically identical to the factory horsepower rating. Peak torque dipped to 373 at 3,900 rpm, however, but the mighty 350 produced more than 350 lb-ft from 3,000 to 5,000 rpm. An astounding feat considering its limited size!
Sheffield then torques the connecting-rod bolts to the manufacturer's specifications.
We were quite surprised to find that the 350 H.O. required an unusually rich mixture to produce peak horsepower. We reported the results with noted Q-jet expert Cliff Ruggles, and he remarked, "I'm not totally surprised at the finding. The 7029262 casting has primary Pull Over Enrichment (POE) holes, which may add more emulsion air to the secondary circuit than a conventional tube-type. It seems that the POE holes dilute the fuel supply to the secondary nozzles, and richer-than-normal secondary rods are required."
Considering this 350 H.O. was rebuilt to completely stock specs, it's not overly surprising to find that the small-cube mill generated horsepower and torque numbers nearly identical to Pontiac's original rating. The flat torque curve from 3,000 to 5,000 rpm was a pleasant surprise, however, and proves that the engine should pull very well throughout its entire power range.
This little 350 H.O. may not be quite as strong as a comparable engine that's significantly larger, but with 330 hp and 373 lb-ft of torque readily available, it surely isn't at a disadvantage!
Once the reciprocating assembly is completely installed, the original windage tray, Mellin
With the No. 1 piston at top dead center, a new Fel-Pro No. 8518 cylinder head gasket is l
The '69 No. 48 cylinder heads were used on that year's 350 H.O. and any Ram Air III engine
Combustion chamber volume of No. 48 cylinder heads generally ranges between 66 and 74 cc.
After complete machining, the No. 48 casting's airflow capacity was measured using a Super
Sheffield installed the No. 48 castings onto the 350 and reused the original head bolts, w
The camshaft lobes and lifters received a liberal coating of break-in paste during install
The freshly rebuilt 350 H.O. was installed on WAM's Land & Sea DynoMite engine dyno. A pai
The dyno session at WAM included various carburetor jet and metering-rod combinations. Eve
Engine Buildup Worksheet - 1969 350 H.O.
Engine Displacement: 359.3 ci
Horsepower: 330 at 5,200 rpm
Torque: 373 at 3,900 rpm
Bore/Stroke: 3.905 x 3.75
Bore/Stroke Ratio: 1.04:1
Rod/Stroke Ratio: 1.77:1
Block Description: XU-code No. 9790079 350
Preparation: Bored 0.030-inch,two-cylinder sleeves installed
Deck Height: Zero
Crankshaft: Nodular-iron 3.75-inch
Preparation: Main and rod journals undersized 0.010-inch, fully polished
Balancer: Stock Pontiac
Rods: Original Pontiac cast-iron, 6.625-inch length
Preparation: Fit pistons pins
Bearings: Engine Pro No. 11-758P-8-10(rods) and No. 12-4836-10 (mains)
Pistons: Sealed Power cast-aluminum, No. 357P-030
Piston Pins: Sealed Power pressed
Piston Rings: Hastings 2M660-030,ductile iron plasma-moly
Fasteners: Original Pontiac
Windage Tray: Yes
Crank Scrapper: No
Oil Pan: Original
Oil Pump: Melling M54DS, 60-psi
Casting Number: 48
Head Mods: None
Combustion Chamber Volume: 66 cc
Flow at 28 inches:
Compression Ratio: 9.85:1
Valves: Melling No. 1098 2.11-in (intake)/Melling No. 1097 1.77-in (exhaust)
Angles: Multiple angle with 30-deg intake and 45-deg exhaust seat
Retainers: Original Pontiac
Locks: Sealed Power VK-115R
Valve Guides: Bronze
Valve Seals: Positive
Rocker Studs: Original Pontiac bottleneck
Rocker Arms: Original Pontiac stamped-steel,1.5:1 ratio
Pushrods: Melling stock-replacement
Brand: Melling SPC-7 (No. 068 replacement)
Type: Hydraulic flat-tappet
Duration at 0.050: 212/224-deg
Lift: 0.414-in with 1.5:1 rockers
Intake Centerline: 113-deg
Lobe Separation Angle: 116-deg
Lifters: Melling hydraulic
Valve Springs: Engine Pro No. 813
Install Height: 1.60-in
Seat Pressure: 100 lb-in
Open Pressure: 240 lb-in
Timing Chain: Pro-Gear PG-3112 roller
Carb: Rochester Quadrajet 7029262
Size: 750 cfm
Primary Jets: 0.075-in
Primary Metering Rods: 0.046-in
Secondary Metering Rods: CC 0.030-in
Fuel Pump: Carter stock-replacement
Fuel Line: Original
Intake Manifold: No. 9794234 '69 cast-iron dual-plane
Points: Pertronix Electronic Conversion
Coil: Stock Replacement
Wires: Reproduction ACDelco 7mm
Total Timing: 36-deg
Initial Advance: 12-deg
Mechanical Advance: 24 deg by 3,500 rpm
Vacuum Advance: Adjustable
Spark Plugs: AC Delco R45
Manifolds: Reproduction Ram Air
Primary Diameter: 1.625-in
Downpipes: PYPES stainless-steel 2.5-in mandrel-bent (No. DGA20S)
Air Temp: 85 deg
Barometer: 28.80 hg
Humidity: 60 percent
Correction Factor: 1.092