Hi

The formula of linear velocity piston is based on the stroke of the crank and engine rpm, which is why they say that an engine can turn at … revs and another engine to some different revs.

The key is the stroke of the crank. The smaller, the linear velocity will be lower and therefore the effort for the engine will be smaller and may climb more revolutions

The formula is this:

V = NxCx2: 60000

Where N are the revs and C are the stroke of the crank. The result we will expressed in meters per second.

For a racing engine find that the linear velocity of piston can be around the 21/23 meters per second.

When we talk about competition engines, the speed is much higher, for example, we can speak engine rover series k.

If you see the different cams preparers (Pipercams, Kentcams), have done in all cases, the cams with a regimen of handing maximun power about at 8500 revs.

With the formula in hand, the engine rover k series in this case would have on its version 1.8 c.c, one linear velocity of piston of aproxx 25.3 meters per second.

This is a linear velocity of piston fairly high for a engine k series of prepared or modified for the competition, and the engine was designed as an engine standard, not competition.

The various developers that have made the evolution to 2.0 c.c. in the k series have had serious problems to get to design a proper fitting, since what maximum that can increase the piston diameter of 82.5 mm and is not easily.

You can see as JUDD has 2.0 c.c. k series, but his regimen of revs is set around the 7500 revs, another example is the engine of PTP, which with a piston of only 82.0 mm develop aproxx 235 bhp. In its engines due to the excessive stroke to reach 2.0 c.c. in the k series.

Another aspect to take into account the weight of the crank.

If the weight is too much, will have an engine very easily get to the torque at low revs, but uncomfortable when it comes to high revs.

We must find a good balance between the two, something difficult to obtain.

A good weight for a crank 2.0 for the series k, may be among approximately 12,800 kg and 11,200 kg.

Another aspect is the length of the connecting rod crank pin, as more shorter are the length, better support force exerted by the connecting rod and the least risk of breaking, because the effort is concentrated in a point of smaller length and significantly reduces the risk of breakage in the crank.

All these questions, I had very much present in the design of the crank to convert a 2.0 the engine k series.

Regards

Vicente