Crankshaft Developments In Race Engines - The Torque Starts Here

Written by on October 1, 2004 Crankshaft Developments For More Power And Durability From Your Race Engine
Crankshaft Developments In Race Engines - The Torque Starts Here View All 8 Photos
Ctrp 0410 03 Z+crankshaft Development Race Engine+outside Diameter 1/8 Most race crankshaft manufacturers prefer to balance with a smooth outside diameter. This means no holes drilled into the outside edge of the counterweights. Holes only increase windage. The solution is to turn the counterweights down to a minimum diameter and then add slugs of heavy metal to bring the crank into balance. In this photo, you can see three slugs of heavy "mallory" metal in the far counterweight.

The crankshaft is, by far, the most massive moving part in your race engine. There's a reason for that-the crankshaft is essentially ground zero for every bit of the torque your high-buck race engine is capable of producing. It's eight pistons connected to connecting rods, which in turn are connected to the crankshaft, pounding down intermittently with incredible force. Meanwhile, at the back, the crank is connected to the clutch-and eventually the rear wheels-which is trying to resist acceleration. The same thing is going on at the front where the water pump, alternator, and other power-robbing assemblies are providing resistance



Ctrp 0410 02 Z+crankshaft Development Race Engine+pendulum Cut 2/8 Here's another look at pendulum-cut counterweights. This design puts most of the counterweight's mass at the outer edge, which helps it mirror the center of mass of a piston on a long rod while still lowering the crank's overall weight.

Forged vs. Billet


Ctrp 0410 04 Z+crankshaft Development Race Engine+main Bearing 3/8 Rick King of King's Crankshafts recommends a main bearing with a 31/44 oil groove. This means the oil groove covers 31/44 of the inside of the bearing, or 270 degrees. This provides better oiling to the crankshaft's main journals.

The Crankshaft Diet OEM

For racing, however, acceleration is paramount, and every extra pound of crankshaft the engine has to spin is just that much more power that's robbed from the rear wheels. First, the crank can be gun-drilled, which is essentially hollowing out all the main journals. Rick King, owner of King's Crankshafts, says this can cut as much as 3 pounds out of the crank, but because it's in the very center of the rotation, the gain is minimal. The same thing can be done to the rod journals, which will shave a couple of additional pounds

Ctrp 0410 06 Z+crankshaft Development Race Engine+cnc Machine 4/8


"In a perfect world, you would want to have the maximum amount of material as far out as you could get it so that the crank would still fit in the engine block," explains Peter Lieb, the manufacturing manager for Scat Crankshafts. "That's generally the best-case scenario for balancing the crank. Now, what happens when you go with a shorter rod? You have to cut the crankshaft so that it takes material off of the bottom of the counterweight. You have to move the weight toward the pin (the rod end of the crankshaft), which makes it not balance as well."

Ctrp 0410 07 Z+crankshaft Development Race Engine+cutting Machine 5/8


King recommends using a pendulum-cut crank on applications up to about 600 horsepower. "After that," he says, "you start to get a little too much flexing in there because of the power."




Ctrp 0410 10 Z+crankshaft Development Race Engine+crankshaft Plant 6/8 The Crankshaft Process<br>After the grinding is completed, the crankshaft goes through several steps before it makes its way out of the plant. The lightening holes are bored into the crankshaft, which then moves to its machining step. From there, the oiling holes become a part of the finished product. The crankshaft is then packaged and ready to be shipped.

Bob Koch, owner of Race Engineering, says that in addition to the reduced friction, smaller journals also have another advantage. "Not only do you get less bearing speed, you are reducing your weights," he says. "The reduction on the crank side is obvious, but it's also minimal. It's the reduction in the rod weight that can be important. If the rod manufacturer does the job properly when they make rods with smaller journals, they will move the bolt locations inboard. Then, they can machine some of the steel off from around the pads where the bolts go, which gets rid of weight."



"A lot of guys will tell you that's not the smart way to do it, and they are probably right," Koch says. "You really don't want to throw another piece of steel into the engine [if you don't have to]. But if you have a large-journal block and want to go with a smaller journal crank, this will let you do it-and it works. You just have to watch your clearances like you would with any engine build."

Ctrp 0410 11 Z+crankshaft Development Race Engine+bearing Spacers 7/8 For situations where you may want to use a crankshaft with small main journals in a block with larger journals, Race Engineering offers bearing spacers. They look a lot like bearings but are designed to sandwich in between the block and the smaller bearings.


"The knife-edging takes a lot of weight out of the leading edge of the counterweights, which will make the crank more difficult to balance," King explains. "Plus, depending on how much material you remove to create the knife edge, the bearings also won't wear as well."

Expert Advice

Expert Advice
One interesting thing that the Nextel Cup guys have learned recently is that at high-rpm levels, overbalancing can cause problems. It's common to overbalance, or add balance weight to the counter weights, at 51 or 52 percent. What we didn't realize is that as rpm goes up, those counterweights get heavier and heavier through centrifugal force.

So, the Cup guys, once they went from 8,500 to 9,000-and even 9,200 rpm-started scuffing bearings. And they couldn't figure out why. Evidently, one guy said, "Let's try something different. Let's cut the counterweights off." I'm using that very loosely, but what they did was turn the counterweights down and then add heavy metal to get the mass back up. All of a sudden, the problem started to go away.

Ctrp 0410 12 Z+crankshaft Development Race Engine+lightening Holes 8/8 Lightening holes through the crank journals can shave at least 3 pounds of excess weight off the crank.


Expert Advice
With the V-8 motors, we never recommend a cast crankshaft, but that is something we've found you can get by with on the four-cylinder motors. From what I understand, they have a little more flex in them, so they seem to be able to take a pounding. They may not have the life cycle of a forged crank, but they are still pretty good.


We are also in the midst of testing to see just how much we can stroke a Ford 2.3 engine. We've got a highly modified crank out of another engine that we're trying. It's a factory steel crank, and we are looking to get somewhere in the range of 3.67 inches of stroke. That should result in about 2,800 cc from the 2.3-liter block. That much stroke will really help with the torque, which is what you are always trying to find in four-cylinder race motors.-Bob Koch, Race Engineering


Race Engineering
Scat Crankshafts
Redondo Beach, CA 90278

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