What is core shift and why is it detrimental?
How a clever concept remedied misalignment in competition engine blocks – By Archie Bosman: No other engine deficiency would have irritated racers, particularly professional drag racers of the last century, like core shift. A bitter source of anguish, they would describe it in a way not easily forgotten. “We used mostly Hemi blocks,” commented “Mongoose” McEwen. “Often we would test fifteen-to-twenty blocks before finding one with consistent cylinder wall thickness. Keith Black had a method of measuring them, which typically demonstrated core-shift variations from around 0.090in or 0.100in to 0.040in. Consequently, if we raced those engines, the severity of the internal pressures usually split the cylinder walls.” As you can guess, the impediment of core shift didn’t debilitate just the racing Hemi; Funny Car racer “Wild Wilfred” Boutilier’s reject ratio with big-block Chevrolets was similar. So there they were pencil and pad in hand, slavishly enumerating cylinder wall thicknesses, one engine block at a time. The term core shift relates to the deviation of a foundry core during the casting process. That is to say, the core moves from its original position, perhaps as a result of inaccuracies in the machining process or the setting of the mold, and leads to alignment problems when the mold is closed. Mold temperatures or pressure differentials on opposing mold walls also cause deflections of the cores. Whatever the cause, the result is evidenced by undesirable variations in wall thickness, which affects the final shape and, thus, the mechanical performance of the part. The Remedy: The problem has now been resolved by substituting multiple conventional foundry segmented cores with a one-piece major core....
To intercool or not to intercool?
But first an amusing brief story involving a BBC, an intercooler, and Freon. By Sam Logan “I’m no authority on intercoolers,” admits performance carburetor specialist Dale Cubic of CFM, “but I do recall a memorable moment five years ago that involved one. Nothing too scientific,” he adds; nonetheless, it seemed an anecdote worth telling. The noted carburetor specialist had visited an engine builder’s shop with a carburetor for a 1600hp 565ci supercharged big-block Chevrolet. The engine was already installed on the dyno and suspended above it an intercooler. Unsurprisingly, with the intercooler connected, the engine improved by 50–80hp. But then the engine builder unexpectedly produced a can of Freon, purchased from a local parts store, and reached up and sprayed some of its contents over and around the intercooler. He then hastened to the dyno room and made a pull. “It gained a further 40hp! Spraying Freon on that intercooler was like feeding it with nitrous oxide,” remembers Cubic. But the mischief didn’t end there, to further mark the occasion it blew the plumbing off the supercharger! The engine was powered by a small Dominator and a Stage II ProCharger and the Freon had condensed the charge sufficiently to pack in more air than anticipated. Intercool or not to intercool? Racers, by instinct, explore every avenue that might lead them to more power. They know that the introduction of compressed air to the cylinders generates heat and excessive heat provokes early detonation. The common solution for expelling excessive heat is to install an intercooler. But what about hot rodders who enjoy most of their driving pleasures at part-throttle on...
Hammerhead Hemi peaks 928hp: 427ci SB Ford
By Freddie Heaney: The sound of the dyno approaching 8,000rpm was almost ear splitting. It was the first Friday of June and sitting in an open wooden-framed space at Charlie Pepper’s engine shop in Auburn, near Atlanta, Greg Brown’s innovative Hemi heads on a Man O’ War 427ci small-block Ford peaked at 928hp at 7,700rpm and generated a maximum torque figure of 674.0lb ft at 6,000rpm. Watch the video. When first tested in mild street form with around 9.5:1 compression ratio the combination yielded 602hp. Quite the accomplishment for unique and previously untested cylinder head designs. But it was not the main event nor might this be. Now, around six months later and using ported heads and intake manifold, higher compression ratio and bigger carburetor, but still employing the same stock-size valves (2.200-inch intake and 1.650-inch exhaust) the engine began the afternoon tests by generating peak power figures in the 850hp range. But with incremental timing and carburetion adjustments it eventually made its way up to a mighty 928 horsepower. Inevitable, I asked? “No, not at all, replied Brown. “Though we increased the flow in the ports from 382cfm / 260cfm to 435cfm / 290 (inlet and exhaust respectively), I would have been happy with peak horsepower numbers of around 850. Remember, ninety percent of all high performance wedge-style cylinder heads rarely exceed 800hp.” Of even greater significance, perhaps the 1250cfm Dominator-style carburetor had proved to be too small during the tests and will be replaced by another that’s capable of generating air flow of around 1450cfm. Was the 1250 carb an ill-advised choice perhaps? “No,” said Brown, “this...
Comparison: Testing a TorqStorm
But the best part was the TorqStorm’s ability to generate 400lb ft torque at 2000rpm; its rival reached 400lb ft at 2500rpm. At 3000rpm the ‘Storm generated 484lb ft compared to the Vortech at 436.
Recent Comments