Have you ever had an engine that just didn't seem to run right? You know the kind-one assembled using a proven combination of complementing components that should run and drive much better than it actually does. There's almost always a root cause: It can stem from improper machining, poor assembly, an unmatched combination, or even unrealistic expectations.

Alan Fanning of Fremont, Nebraska, was one such owner who was disappointed in his Pontiac's performance. A previous owner had rebuilt his '67 GTO's original 335hp 400 four-barrel, but it wasn't operating to Alan's expectations. He rebuilt it again in the late '90s, reusing the stock components, but adding reproduction '67 400 H.O. exhaust manifolds, a then-popular hydraulic flat-tappet camshaft, and a set of dished pistons to provide a pump-gas-friendly compression ratio of 8.25:1. He wasn't totally happy with his new engine's performance, either, and spent the next decade searching for the cause.

Fanning enlisted our assistance a couple of years ago. The major issues we found included chronic detonation, occasional overheating, and continuous run-on. Even though the 400 hadn't been driven that many miles since its last rebuild, it was apparent that something was amiss internally, requiring yet another rebuild to correct the issues. This time, however, careful attention would be given to every tolerance. We reasoned we could also modernize the 400 with roller technology.

Follow along as we rebuild and dyno test an otherwise-stock '67 400. We'll cover the highlights of the build in this story. Complete assembly procedures, torque specs, and clearances can be found in the '67 Pontiac service manual.

Plan Of Action
Establishing a sound plan of action should be the first step of any rebuild, and it was extremely important in Fanning's instance. Not only had prior rebuilds produced less-than-desirable results, but Fanning's particular GTO was originally equipped with myriad convenience options, and retains its Turbo 400 backed by a stock-stall torque converter, 2.93 rear gearing, and functional A/C. This means the 400 spends most of its time operating at lower rpm, and has additional load placed on it at idle when the A/C is on.

Focusing on maintaining stock appearance and producing as much low-speed power as possible, we worked with Jeff Kauffman of Kauffman Racing Equipment (KRE) in Glenmont, Ohio, to obtain a mild hydraulic-roller camshaft, which would eliminate any chance of flat-tappet failure related to modern oil quality. We needed to maintain good idle quality and low-speed street manners, while producing strong horsepower numbers. We were less concerned with peak horsepower, but wanted to maximize average power from idle to approximately 5,200 rpm and have a wider lobe-separation angle to improve idle quality. A custom-spec Comp Cams grind was on our doorstep within days.

The Rehabilitation
During teardown we found many irregularities within the 400, but nothing that conclusively pointed toward the cause for its poor performance. We enlisted Chuck Willard of Willard Auto Machine (WAM) in Omaha, Nebraska, to perform all the necessary machining, careful assembly of the components, and to measure the engine's output on his Land & Sea DYNOmite engine dyno.

Willard planned to machine the block and crankshaft as if it was any other rebuild. The YS-code block checked out perfectly after being bored to a total of 0.040 over. The crankshaft required some additional attention, however. Its main and rod journals were at standard dimensions, which meant that machining wasn't necessary during previous rebuilds. While it's possible the journals could've been polished, Willard planned to undersize them by 0.010-inch, given the engine's history.

After installing the crankshaft in his grinder, Willard checked the rod-journal tolerances using a dial indicator and noticed a significant variance. The Nos. 2, 3, and 4 rod journals were out of phase when compared to No. 1. After equating, he estimates the last three journals were approximately 15 degrees retarded when compared to the first. Since no prior machining had ever been performed on the crankshaft, it seems to be an error that occurred at Pontiac-the 400 hadn't operated correctly since the day it was assembled in 1967.

With this severe degree of phase variance among the rod journals, there was concern as to whether enough material would remain after machining to use common undersized Pontiac rod bearings. A suitable replacement crank was located instead, and the build progressed with a sense of relief from Fanning, who was elated at the "smoking-gun" find. The rest of the rebuild went without incident, and once on the dyno, the stock-appearing '67 400 churned out 396 hp at 5,300 rpm and 444 lb-ft of torque at 4,200 rpm-outstanding results from a relatively mild combination.