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...
The "XU" stamped on the front of the block indicates that this particular engine is a 350 H.O. from a '69 A-body. It featured large-valve No. 48 cylinder heads and a four-barrel carburetor, and was rated at 330hp that model year. Only 2,800 XU-code engines were assembled during the '69 model run, and Jon Carbonneau is restoring the '69 LeMans convertible this engine was originally installed in.
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...
You may recall from "Cylinder Sleeve Salvation" (HPP, Mar. '10) that this particular 350 block received two cylinder sleeves at Willard Auto Machine (WAM) in Omaha, Nebraska, to repair damage related to mice inhabitation. The rodents made it a home for a number of years, but beyond needing two sleeves, the 66,000-mile short-block was in excellent shape otherwise. WAM bored it 0.030 inch to a total of 3.905 inches.
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...
The 350's main journals needed only minor honing to restore the saddle finish for optimum bearing retention.
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!
The Rebuild
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...
WAM owner Chuck Willard undersized the main and connecting rod journals of the original 3.75-inch-stroke, nodular-iron crankshaft by 0.010 inch each. The journal indexes were blueprinted, the unit was balanced, and the journals were micropolished.
WAM machinist Beau Sheffield...
WAM machinist Beau Sheffield installed the Melling No. 068 flat-tappet camshaft and rear main seal, set the main bearings in place, installed the main caps, and torqued the main cap bolts to 100 ft-lb (rear to 120 ft-lb).
Original cast-iron connecting...
Original cast-iron connecting rods are more than sufficient for a rebuild of this level. The LeMans this particular 350 H.O. came from is a restoration project, and the owner wants the engine to be as stock as possible. After checking for cracks and installing new fasteners, the stock rods were reconditioned and resized.