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Are forged cranks necessary in performance engines?



Are forged cranks necessary in performance engines?


Yes they are in many incidences. 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, an engine rated at 290 HP, as well as a couple of others. Yes, they obviously made more than the rated 290 HP (which was for insurance reasons), but they weren't making 400 HP like most basic performance engines of these days exceed, and sometimes by far. If they thought a cast iron crank would hold-up to less than 400 HP, or the 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 less than 400 HP and with manual transmissions.

forged crank

The question is; why would you consider wanting a serious performance engine built with a cast crank (and pistons) if it is going to make as much (or more) HP than what any of the factory "performance" engines came with? So yes, sometimes our engines DO cost a bit more than other advertised engines do, but there is an obvious reason for it, and anyone who is building or selling cheap "performance" engines, with cast components in them, aren't even meeting the basic standards of what fairly anemic factory performance engines originally came with.

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. The new cast steel cranks are very cost effective and plenty strong for even most 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.

I recommend using forged cranks in ALL serious street performance and race engines, stroker's, etc, especially if you are 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 we order them with big block snouts to make them stronger. Use a cast crank in a supercharged engine and you are 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.

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. Clutches however are brutal on the drive train and cause "impact" when the clutch is 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 that much power or more? Yes, a LOT of guys do it, and get away with it... but they are 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 will be put through, and blowing the tires off on the street, accelerating with the pedal to the metal, etc IS "racing", 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 6 dollar set of sockets to a high quality / high strength set of 125 dollar 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 are asking for a MAJOR failure that takes everything else along with it. Is that worth it? No way! That's why we don't use that kind of crap in our engines, 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 engine, or even an $1,800 high quality forged steel crank in well built street / strip engine, but you also certainly don't want to run a $189.00 - $289.00 piece of crap crank in an engine that is going to make some serious power, or that has a manual trans, or has nitrous, or a supercharger. A good quality, yet bargain priced forged crank will usually run anywhere from the $750 to $1,000 range depending on the variables (lightness, big block, small block, material, etc.). Yes, they cost a bit, but it's an investment in the longevity and reliability of your engine. Just remember, you get what you pay for.

forged crank

If you want to learn more about this kind of stuff, in much greater detail, be sure to check out our Auto Shop Videos series by clicking HERE. We have one titled "Rotating Assemblies" that covers all of this kind of stuff and MUCH more. These make great Christmas, Father's Day and Birthday gifts!

forged crank

 

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