Are forged cranks necessary in performance engines?

The answer to this (for a real performance engine) is Yes... in many incidences they are.

Forged steel cranks are the way to go if you're building a hot street performance, or an all out racing engine. Many factory engines came with forged cranks. The stock small journal 327's and 283's ALL had forged steel cranks. Some of the early high performance small block Chevys such as the 67 & 68 Z/28's with the 302's, and 350's such as the 370 HP LT-1's came with forged cranks as well. So did some truck versions of the 350's. Ford did the same thing with the BOSS 302 and a couple of others. 

The BOSS 302 was only "rated" at 290 HP (mostly for insurance reasons) but they obviously made more than that, but they weren't making 500 HP or more like many decent performance engines of these days are making (or exceeding). If they thought a cast iron crank would hold-up in a street driven car, with the shock abuse of a 4 speed manual transmission, don't you think they would have tried saving money instead of installing a more expensive forged crank? On top of this, most of the engines I mentioned also came with forged pistons, so even GM & Ford thought an all forged rotating assembly was necessary in factory engines that made plus or minus 400 HP, and that came equipped with manual transmissions.

The question is; why would you consider wanting a serious performance engine built with a cast crank (and pistons) if it's going to make as much (or more) HP than what any of the factory "performance" engines came with? So yes, if it's going to see some abuse (burnouts, racing, clutch dumps, trans brake use, etc), then anyone building one with cast components in it, aren't even meeting the basic standards of what fairly anemic factory performance engine originally came with and are just asking for a failure.

There are many types of steel used for making cranks, be them cast or forged, and some cast cranks these days are stronger than original cast cranks because they are made out of cast "steel" rather than cast "iron". There used to be just cast iron, nodular iron, and forged steel available. Now, for the most part, there's cast steel, 4130 and 5140 forged steel, and super strong 4340 forged steel available.

If you are building a mild performance engine and want a cost effective way to add some strength (and reliability) to it without spending a ton, then a cast steel crank can be plenty strong for most performance and mild racing engines if you aren't "shocking" them very hard or don't have a manual transmission. I have seen forged cranks break in half for no visible reason at all, yet I have seen cast cranks survive season after season in mild race cars. It just depends on what kind of abuse it is getting. "Shock", such as clutch dumps, trans brakes, etc are what tend to kill cast cranks because they just can't handle the sudden "impacts" that those things put on them. 

Personally, I recommend using forged cranks in ALL serious street performance and race engines, strokers, etc, especially if you're using nitrous or a supercharger. You have to keep in mind, a supercharger drives off the snout of the crank. Cast cranks are notorious for snapping off the snouts with large superchargers. So-much-so that on more serious performance supercharged small block engines that in extreme applications one with a larger and stronger big block snout is used so it won't bust off under high boost conditions or with large superchargers, like 12-71, 14-71s. If you use a cast crank in a supercharged engine, you're just ASKING for the snout to bust off, or the very rear of the crank where all 8 cylinders are twisting the crank where the crank flange meets the "load" of the vehicle at he transmission.

Another VERY important time to use a forged crank is on cars that have manual transmissions. Automatic transmissions are "soft" on the drive train because of the slip of the torque converter. It's like the difference of pulling on a wrench to undo a bolt compared to using an impact gun. "impact" and "shock" are what bust sockets, bolts and nuts off, and the same thing pretty much happens to cast cranks when they go from a smooth load to a sudden and violent impactive load.

Clutches are brutal on the drive train and cause "impact" when they're dumped. This impact can snap a weak crank, so on performance engines going into vehicles with manual transmissions, unless it is just a street cruiser, I'd highly recommend going with a forged crank.

Again, GM thought it was necessary on engines making LESS than 400 HP to have forged steel cranks (and pistons) in ALL of the early 340 / 365 / 375 HP Vettes, the 302 powered Z/28's, the LT-1 350 Z/28's, and even some trucks, so why would you think it would be OK to use a cast crank in an engine that makes more power? Yes, a LOT of guys do it, and get away with it... but they're also on borrowed time and are just ASKING for a failure. I won't build an engine that I think is on borrowed time or that I think won't hold up to what it'll be put through, and blowing the tires off on the street, accelerating with the pedal to the metal, etc IS "racing", (the engine doesn't know the difference between the street or the track), so it has to be as strong as any "race" engine if you want it to last.

Stay away from the Chinese and Taiwan made junk. I am not a fan of the Mexican made forged cranks either. Those come in all of the late model factory crate engines. Comparing those types of cranks to a high quality crank is like comparing a Chinese made $10 set of sockets to a set of high quality / high strength $125 Snap-On or Mac Tools sockets. There's no comparison, especially when you find-out the cheap, Chinese sockets break the first time you try to use them. Well, "steel" cranks aren't any different except for the fact that when you go "cheap" in an engine, you're asking for a MAJOR failure that takes everything else out along with it, such as the rods, the pistns and probably the block too, so is that worth it? No way! That's why I never used any of that kind of crap in engines I built, but you sure see that crap in all of the "bargain priced" magazine ad engines out there. You get what you pay for!

On the flip side, you certainly don't need a $4,000 profiled, ultra light, billet steel crank like you'd find in a NASCAR or blown alcohol / blown fuel engine, or even an $1,800 high quality forged steel crank in a well built street / strip engine, but you also certainly don't want to run a $200.00 piece of crap crank in an engine that's going to make some serious power, or that has a manual transmission, or has nitrous, a supercharger, etc. Again, you wouldn't use a $2.00 chinese made socket to remove the lug nuts on a big truck because it'll simply break. You'll need a good quality, super strong "impact socket", but those cost a lot more because they are high quality and very strong. A decent quality, yet bargain priced forged crank (like a 4340 Scat or Lunati signature series), will usually run anywhere from the $750 to $1,000 range depending on the variables (lightness, big block, small block, etc.). Yes, they cost a bit, but it's an investment in the longevity and reliability of your engine. Just remember, like with tools... you get what you pay for.

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