I am always messing around and seeing what people are doing to make more power. My latest though is about the piston.

A while back I saw someone making a piston for a V8 with dimples on the top of the piston, more or less where the spark plug would point to. Dimples like you get on a golf ball. They claim it helps the intake gasses to mix better and therefore increase combustion and the end result is more HP.

So I went further and looked what those dimples actually do with airflow. Air flowing over these dimples tend to stick to the surface of the object and it reduces turbulence. So, what if you can do dimples in the intake system. It might not be a good idea between the carb and the valve, as the fuel droplets must not stick to the sides of the intake. Where it might help is before the carb, maybe after, but someone has to test it and see if it will help the fuel and air mix or not. Another thing that helps with airflow and it might work better than the dimples is to have ripples along the intake. Air flow speed up when they pass over curved surfaces.

Then to the last and final use of dimples.

What if the outside of the piston have dimples, meaning it has dimples where the piston and sleeve touch. I don't know the exact figures, put something like 50% or more of the power a motor makes is lost to friction inside the motor. Most of this is between the piston and sleeve. A normal piston have a smooth surface. A smooth surface piston will have more friction than a piston with dimples, purely because a dimple piston would have a smaller contact surface between the piston and sleeve. I also believe the dimples will fill with oil and further reduce the friction. The dimples can be very small, a couple of microns might do the trick. If you save just 10% on friction, you can convert it to HP. What if you save more than 10%... maybe 20%... then you are talking lots more power.

Just a thought, anyone like to try it for us?

 

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What you are saying makes sense.

I just have a BS in outhouse's so I am a little lost on this subject but if there was dimples in the bore wouldn't this make the ring loose unless there are arranged in a manner that the ring was always in contact at some point.

 

For part 2 of your question....why not just use a shorter skirt piston to reduce friction?? Or you can now get pistons w/a coating on them to reduce friction as well. Always like to see someone think "Outside the Box"

 

In car racing FI engines, usually smooth and consistent is better. Any change in the airflow path can create disturbances and turbulence. This is why porting and extrude honing is so popular. With carb'ed engines, you want smooth airflow, but retain some turbulence to keep the air and fuel mixed (not an issue w/ FI, since the fuel is injected in the head or close to it). Looking at all the engineering that goes into race engines, and they all use smooth intakes, I would be hesitant to try "dimpling" the intake for improved performance.

Colby

P.S. It seems to me dimples on the piston would create hot spots and provoke detonation...was that addressed in the setup you saw?

 

That's why the make short skirt/hyperutectic(sp) coated pistons to reduce friction. As far as the dimples are concerned -- that's why mfr's started swirl porting heads - similar effect......

 

I thought that the hyperutectic(sp) pistons were designed to help avoid the exspansion \ retraction of forged pistons but yet be tougher than cast pistons? Also, the majoraty of the short skirted pistons seem to be to make the piston lighter, therefore rev quicker, and then to cut friction. The problem with that is you loose some of the pistons abilty to stabalize itself in the sleeve. When I was drag racing alot of guys would machine off part of the skirts to get rid of some rotating weight, making the engine rev alot quicker, but pistons don't seem to live near as long by doing so. They can actually turn sideways in the bore and reek havic!
Your Idea sounds very interesting, but it would take some company alot of r&d to discover if it would be worth it.
P.S. I know dart and other companies make "turtles" to weld into the intake plenium's, and alot of prostock guys use them. Most carb intake tracks don't want a perfectly smooth surface because it won't flow as much air, go figure!

 

I dont believe dimples on a golf ball reduce turbulance. Not for a second. THey hinder boundary layer seperation. The boundary layer separates farther back on the golf ball. Essentially giving it a smaller wake. Dimples do create addidional turbulance. But I'm not sure how much it would help with fuel mixing.

Regarding a dimpled intake. The dimples produce tubulance, but boundary layer seperation is not inevitable. So the best thing to do is prevent it, not provoke it. So to make logical decisions, it helps to know what a boundary layer is, and what types of drag there are. That's fluid dynamics 101.

Now reagrding the piston and sleve, they never touch. The rings touch. The sleeve should have small grooves, that hold oil to the surface, causing the rings to hydroplane across the oil. That's why cylinders get honed in that nice cross hatch pattern when you rebuild and engine.

 

On some airplane wings they use little bitty holes to achieve the same affect. They cause a micro turbulence layer that the bigger volume of air hits instead of the actual wing (I think).

 

green700 your comment about the golf ball is correct. The dimples actually generate turbulence in the dimple and it helps with the layer separation. I b eleive it also helps with friction between the air and the ***** surface. The turbulence in the dimples actually causes a layer of air to be trapped between the ***** surface and the air flowing over it. The air flowing over the ball rubs against air trapped in the dimple and air against air have much less friction that air against ball surface. The air flowing over the ball therefore have less friction. This in turn reduces the wake behind the ball. The bigger the wake the more turbulence behind the ball, the smaller the wake the less turbulence. That’s what I mean with “dimples reduce turbulence”. Meaning less drag (caused by turbulence) behind the ball and making it fly further. I am not here to talk about golf ***** and my theory about how they work, just to get people thinking about how to reduce friction with the use of the dimples.

I believe that the air in the intake and maybe the exhaust system can flow with less friction. The dimples friction might also help with the fuel and air mixture. Meaning the dimples turbulence will not let the fuel droplets settle to the sides of the intake tract. That is a great plus for carb intake system. On carb intake system you cannot polish the intake tract. The polished surface causes the fuel droplets to settle to the sides of the intake. To get around it, people make the intake tract a bit coarse, but in doing so they create air friction which causes power loss. With dimples you can polish it to a real shine. The turbulence in the dimples will reduce air friction, plus help prevent the fuel droplets to settle to the sides of the intake. This is especially important when the fuel and air mixture have to go around a bend or corner. For fuel injection it might only help to put dimples in the intake port, just before the valve opening.

To answer your question about the piston and sleeve. The piston and sleeve do touch, not 100% of the time, but they do touch. You have a rotating crank and rod under the piston. It does not push straight up and it actually pushes the piston forward and backwards inside the cylinder. The rod is only 100% straight under the piston when the position is at its highest and lowest inside the cylinder. The rest of the time you have the rod pushing or being pushed at an angle. Meaning the piston must be pressed against the side of the cylinder wall. The rings cannot keep it straight and other parts of the piston have to touch. There is some play between the piston and sleeve. When the piston is compressing the gas it will move around and touch the cylinder wall. The front and back of the piston especially touch the sides of the cylinder wall. They guide the piston and a lot of the up and down stroke involve one of these sides touching the cylinder wall. Let’s assume the front of the piston is the side facing towards to exhaust and the back is the side facing the intake (Raptor motor). The back and front is always longer than the left and right sides of the piston. That’s exactly why you cannot use very short stubby pistons. The sides (Skirts) are there to guide the piston in the sleeve and therefore the two have to touch and generate friction. The longer these sides the more stable the piston is inside the sleeve. It has a drawback, that the longer the sides of the piston the more weight you add, and the lighter a piston the quicker the RPM and more HP. But short, light pistons have another drawback and that is its lifespan. Light short pistons are less stable inside the sleeve and it will cause more wear and tear. If you look at motors that are designed for durability, they all use long heavy pistons.

The dimple theory on the front and back of the piston will reduce the contact surface area of the piston and sleeve and hopefully will trap some oil to the side of the piston. The dimples only need to be below the rings, so it will still make a good compression seal. This in turn will hopefully reduce friction and less friction generates more power.

Then to answer you comment about honing a sleeve when you rebuild the motor. This is done for one reason only. The new rings have to settle and conform to the cylinder wall. Not for the oil to form a layer on the cylinder wall. The honing groves will only last a couple of hours until the rings set in and then they are gone. With the honing groves gone, there is nothing that will keep the oil to the cylinder walls. Oil is actually thrown or sprayed onto the cylinder wall by the crank or some other devise. The oil is then returned by the oil return holes in the piston. These return holes are located in the same slot as the oil rings. The rings actually scrape the oil of the cylinder walls. Not all of it, some pass, but only a very small amount.