Crankshaft Tech - Crank Call

Domestic versus overseas is... 

   

  read full caption

Domestic versus overseas is a hot topic, but the increased competition has definitely resulted in lower pricing for consumers. While best known for its premium cranks, Lunati recently introduced its Sledgehammer line of entry-level 4340 cranks. They're 100-percent U.S. made, and this big-block Chevy unit retails for $860 from Summit.

Alternative Makes
Traditionally, the aftermarket has neglected the Buick, Olds, and Pontiac camps. When it comes to cranks, this still holds true, but to a lesser degree. The efforts of engine platform-specific diehards have yielded a specialty market of just-released steel cranks in some markets. In others, there are specialists for each engine family that can modify factory cranks to get you the extra displacement you crave. Of course, companies like Winberg, Bryant, and Moldex will make a custom crank out of billet for any engine, but we'll assume most hot rodders are working with a real-world budget.

Pontiac
It's been 30 years in the making, but Pontiac enthusiasts now have both aftermarket cast and forged cranks at their disposal. In the late '90s, Butler Performance teamed up with Eagle to produce the first aftermarket Pontiac crank, a cast-steel 4.250-inch unit for 3-inch main 326/350/389/400 blocks. Just this year, Butler Performance released 4340 forged cranks in 4.000-, 4.250-, and 4.500-inch strokes for 3-inch main blocks. The company also offers 4.000- and 4.250-inch 4340 cranks for 421/428/455 blocks with 3.25-inch mains. "Before we released these cranks, the only option was offset grinding a stock crank, which netted an extra 4 to 5 ci," David Butler says. "Forged cranks are so reasonably priced these days, there's no reason to even bother with a stock piece."

These days, it's no longer... 

   

  read full caption

These days, it's no longer accurate to dub Mopars as "alternative makes." Companies such as Eagle and 440 Source have a full line of cast and forged cranks for Chrysler LA, B, and RB motors. Thanks to the big-block Chrysler's massive bore spacing, the modest 4.150-inch stroke of this forged Eagle crank nets 500 inches out of a factory 400 block.

Buick
Unfortunately, the aftermarket hasn't stepped up with a new Buick crank design, but there are still options for increasing displacement by a good margin. According to Buick expert Mike Phillips of Automotive Machine, all 400, 430, and 455 Buicks have the same crankshaft. "Up to '74, the cranks have an 'N' cast into them, which some people think means nodular," he explains. "These things have massive 3.25-inch mains, so you can put 600 hp through them without a problem, and with a 3.900-inch stroke, Buick cranks have more overlap than many big-block Chevys." Thanks to that overlap, they can be offset ground up to 4.15 inches. "With a crank offset ground to 4.150 inches in a 455, you end up with 494 inches, but I think it weakens the crank considerably. It's better to offset grind the crank to 4 inches, in which case you can still externally balance the motor."

Oldsmobile
In the walk of big-block Oldsmobiles, there's the 425 and the 455. Noted Olds engine builder Dick Miller says that all 425 motors came equipped with forged steel cranks from the factory, while the number of 455s with steel cranks are less than 100. The 455 is the most common engine amongst Olds buffs, which features a 4.250-inch stroke. "Some 455 cranks had 'N' cast into them and others had 'CN' cast into them," Miller says. "The 'CN' crank is the stronger of the two." Although Eagle makes a replacement cast-steel crank rated at 700 hp, the factory piece is very stout. "The stock 455 crank can be offset ground to 4.500 inches, which equates to 496 ci. These cranks can handle up to 650 hp."

Taking advantage of the 385-series... 

   

  read full caption

Taking advantage of the 385-series big-block Ford's towering deck height, Eagle and SCAT offer cast-steel cranks with strokes ranging from 3.850 inches to a jaw-dropping 4.850 inches. This rotating assembly is from SCAT

Ford FE
Never as mainstream as the Windsor or 385-series big-block, the Ford FE has been widely ignored by the aftermarket until now. Scat and Eagle both offer cast-steel cranks with strokes ranging from 3.980 to 4.250 inches. "The 390 is the most popular FE motor, and almost all of them had cast cranks," explains FE engine guru Barry Rabotnick of Survival Motorsports. "People used to get forged FE truck cranks and cut the nose down to fit into a car block or offset grind stock cranks, but there's no need to do that anymore. I've put over 750 hp through a cast Scat crank without any problems." Additionally, Survival Motorsports offers its own forged 4340 crank ina 4.250-inch stroke.

If All Else Fails
If you need something done to a crank that no one else can peform [or if you need a nicely-prepped OE crank for a fun street driver-ed.] give Adney Brown of Performance Crankshaft a call. His specialty is repairing and modifying factory and aftermarket cranks to standards few others can touch. "For applications where aftermarket cranks aren't available, we track down old forgings and put whatever length stroke the customer desires," Adney explains. In addition to simple services, such as fixing up burned journals, Adney can lighten a crank, alter snout diameters, and weld up different flanges. "Don't consider it junk or give up your search until you call us first."

Hierarchy Of Metals
Since the American Society for Metals allows for some leeway within each grade of metal, the tensile strength ratings listed in this chart and elsewhere in the story are approximate, not exact figures. Nevertheless, they do adequately allow comparison among the strengths of different metal grades. While these represent just a small portion of all the steel alloys established by the ASM, they are the ones most common in automotive applications. Here's a quick rundown: