Most of you may recall the Chevy big-block buildup we did last year with a mid-'60s 396 at Speed-O-Motive (May '06). Well, while 385hp may be sufficient for some, this Rat wasn't satisfied with Mouse numbers. As mentioned in the story, the valvetrain would eventually be addressed, swapping out the mild cam and springs to give the now 440-cubic-inch engine more elbowroom. Well, eventually is now the present, and we're about to see what this workhorse really has in her.
We didn't want to overstay our welcome, so we decided to take the 440 out to Steve Brule at Westech in Mira Loma, California, for round two with the big-block. After seeing the numbers the engine produced, he was sure he could easily get an additional 75hp, if not more, with a relatively simple cam, valvespring, intake manifold, and carburetor swap. As a matter of fact, he was more determined than ever since he suspected something might be going on internally, something that limited peak horsepower the first go-around.
Once we dropped the engine off, Steve first performed a leak-down just to see if there was any truth to his suspicions. Later that day, we got a call from him with the news, "20 percent on all eight cylinders." Being relatively high, but not totally extreme, the rings weren't biting on the cylinder walls like they should, thus allowing compression and oil to leak by. Obviously, the heads needed to be pulled to further probe the situation-and once they were, Steve's intuition was dead on, as each piston was evenly coated with oil. There was no turning back from here...at least not if we wanted to move forward with the initial game plan.
After Steve pulled the first piston out, what had been holding the engine back was finally revealed. Without getting into too much detail, it turned out the individual who initially started the project had ordered, and subsequently installed, the wrong size rings (undersized, with a 0.120 end gap) before having Speed-O-Motive finish up the long-block. Had we run the engine on their dyno a few more times, we would have seen the peak horsepower numbers decrease each run, which would have tipped us on to any potential problems. However, we didn't want to bog down their dyno for too long, so we were content with the initial runs, paid our bill, and went on our merry way. (It should be noted that Speed-O-Motive offered to fix the problem when they learned of it, even though it was not their fault.) OK, so the problem was isolated and, fortunately, the fix was simple-install new rings and move on.
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Sometimes, more is good-at least in this case. Had we not wanted to squeeze more horsepower from our old 396, we would have learned the hard way that the undersized rings weren't clenching the cylinder walls with enough tension, thus allowing substantial leakby (20 percent on all eight). | 
The problem was caused by a .120 ring end gap, which was due to an error in the early stages of the project that no one knew about...until now. No harm, no foul. |