What sets us apart - Quality Crankshafts and Connecting Rods.

A question I have heard a reasonable number of times recently is this "Why are your engines more expensive than Joe Blogs down the road?"

In short - it's the parts. Premium parts attract premium prices.

Below is a quick break down of the Crankshafts and Connecting Rods that we use in our motors. Our bottom ends feature Scat VolksRacer cranks and Scat Con Rods. This is one small part that makes a massive difference in our builds.

Crankshafts.

The manufacturing processes in a nutshell.

Casting is fairly straight forward process. A mold is made up in the shape of the required crank, and molten steel is poured into it. Once cooled, it is finished machined.

(Above, crankshaft molds being produced)

Forging on the other hand requires much more work. A piece of straight steel is heated until it is soft enough to be worked and then it is forged between different sets of dies until it is in the shape of the crankshaft and can be machined. This is a much more labor intensive process not to mention the set up costs of the dies are significantly greater. Depending on the crankshaft, as many as 24 sets of dies can be used to achieve the final shape. The strength of the forging is generally determined by the fineness of the grain structure, which is determined by the type of steel used, the grain direction and the number of processes it under goes to reach its final shape. All of our Scat cranks are fully forged.

(Above, the basic forging process for a 2 cylinder crankshaft)

Cast Vs Forged

Cast strengths:

A cast crank has only one advantage over its forged brethren. Cost. There is no other benefit of using one of these cranks.

Cast weaknesses:

1) The biggest issue that we have seen with cast cranks is the inconsistency of the casting. Some sections in a cast crank will be denser than others which leads to heavy balancing requirements just to bring a crank into spec. This unfortunately then leads to there being weak spots inbuilt into the cranks.

(Above, Heavy balancing was required to bring this cast crank into spec. It is the 'off the shelf' replacement part here now in Australia. This type of crank is commonly imported from China

and distributed widely in Australia.)

2) The next issue with cast cranks are the iron alloys. Cheaper cast cranks have a low wear resistance due to their alloy composition.

3) No VW cast crank has been made with nodular iron or cast steel. It may seem like a bit of a contradiction, but steel isn't just steel. Off the shelf cast cranks for VW's are cast in the lowest form of cast iron (Graphite flake cast iron) to be the one thing they need to be - cheap.

If they were cast in Nodular Iron, or Cast Steel, then we would not be seeing the issues that we are today with the cast cranks, but they would cost significantly more.

4) Flex. All crankshafts flex, but a cast iron crank will flex significantly more due to the casting inconsistencies which then exacerbates the issues surrounding bearing tolerance, cracking and harmonics.

Cast cranks also have a much lower elongation rating - Typically 2-3.5% - before failure. This is a measure of how brittle it is.

When a crankshaft flexes, the tolerance on one side of a bearing opens up, and the other side closes, so as you can imagine, maintaining these tolerances is critical to the retention of oil for bearing lubrication.

Harmonics become an issue as the amount of flex in a crank directly affects the amplitude of the harmonic wave travelling through it. The greater the amplitude, the more destructive the force of the harmonic.

Cast cranks are prone to stress cracking or having micro cracks straight from the mold. This is exactly the same as when you take a thin piece of metal or plastic and bend it backwards and forwards. Eventually it will crack. The down side is that when paired with a harmonic vibration, the effects can be catastrophic.

Some cranks are cast and then forged in China for example those labeled "Super Race". These cranks are less prone to failure due the subsequent forging processes evening out the majority of the grain structure and densities of the steel, but they are still a cast crank at their core.

Forged strengths:

Almost the complete opposite of the above.

1) Forging produces consistency, even density, fine grain finish, and aligned grain structure.

(Above, Scat VolksRacer - 69mm - Forged 4340 - 8 dowel, zero balancing required)

2) Due to the process costing much more for production, it is highly unlikely that you will find a manufacturer who is willing to use a low grade of steel. Typically 4140 or 4340 Cromoly steels are used.

3) They have low flex with a high elongation rating 20-22% before failure.

(Above, Side view of the VolksRacer crank. Full circumference main bearing lubrication

is a very nice addition along with the counterweights.)

Forged issues:

They cost more to produce, and as such, the end product is more expensive.

(VolksRacer crank once more showing the 8 dowel configuration used to locate the flywheel.)

(Above, Factory forged crankshaft. It is ALWAYS better to re-machine one of these cranks instead of using a cast aftermarket crank. Note the minimum of balancing marks required to bring into spec.)

Counter-weighted Vs Non-counter-weighted:

Contrary to popular belief, counterweights are not added to balance/smooth out a horizontally opposed motor as they are naturally balanced. What they are added for, is to reduce the dynamic stresses acting upon the cranks and increase the lifespan of the engines.

Connecting Rods.

All of the same issues regarding Cast Vs Forged apply to Con Rods.

(Above from the top, Cast Chinese, Forged Scat 4340 I beam, Forged Scat 4340 H Beam)

(Above, Cast Chinese Rod)

(Above, the section thickness of the Scat rod is far superior to the cast counterpart.

Not to mention ALL Scat rods come with ARP2000 rod bolts)

(Above, Scat forged H Beam con rods are as good as they come.)