Piero wrote:Hi, I have only just found this topic,
but here is my input if it helps any.
I used to own and fly a microlight, and as such, we were expected to learn about areodynamics etc.
I am NO expert in areodynamics, but what I will say is, it is very easy to confuse this topic with whats been discussed here.
A wing of a plane or the prop of the same, have very specific jobs to do.
A wing must give lift, and leave stable air behind it to keep the plane going in a line. A prop must produce a pulling force etc.
A crank needs to do none of this.
Lets take a crank running in the block, and assume that it does run out of the oil for a given time, ...
Yes, modern wetsumps with positive pressure lube systems have the running fluid level below the swept area of the rotating assembling -- this even holds through a fair amount of inclination. This neglects vehicle movements and the effect of the windage on the surface/body of the oil.
... as it spins in the confines of the block, the amount of turbulance it creates and consequently the way the air is now moving inside the block is a thing that I feel maybe being overlooked.
Yes, there is a spinning and also pumping from bay to bay (inline) or across a bay (V configuration). Makes for complex turbulence.
If we belive it does run in oil for a given time, then it is here that the most benifits can be had if we try to reshape the crank webs.
The turbulence actively draws oil into it that continually comes from a number of sources so there is definitely oil in the path of the crank. More so if the car is driven with heavy acceleration, turning, braking, etc.
I personally beleive that as the crank spins, the air in the block spins with it (whirlling effect)
Yes, exactly. The pressure differential in the vortex is what suspends the oil.
I would look to the shape of the inside of the block, and reshape where posibble to reduce anything that might cause this whirlling effect to be interupted, all we can hope to do is to keep it all moving freely as one, (Crank and air).
Because the phenomenon is so complex and varies in nature over the rpm range this is not the best solution in isolation. The pumping of the cylinders which is commensurate with the rpm of the crank, of course, ensures that there will always be forces acting to decelerate at least some portion of the turbulence which the crank and rods must then pass through (friction). Also the beam of the rod will be in the way for much of its path again slowing a portion of the turbulence.
If you disrupt the pressure differential it allows entrained oil to be released axially and radially decreasing both mass and friction. Yes, disturbing the turbulence does cost power in and of itself but there is more energy saved than lost so a net gain over parasitic loss. Disturbing the turbulence for no good effect is not desireable and is why girdle structures can cause a net loss in horsepower. Unpublished research by Nismo indicates the girdle in the SR20 engine costs 5% power -- quite significant.
Reducing the atmosphere present in the crankcase is a better solution but more expensive. Dry sumping does this as well as dedicated crankcase evacuation pumps.
Here is a link to an article by David Vizard detailing how very minor crank profiling and various coatings can save horsepower. I think you can trust this data:
http://www.circletrack.com/techarticles ... echnology/