What is meant by oval pistons and elliptical pistons?

On the other day of my class my lecturer did a wonderful lecture on oval pistons. So i am here to share it with you with some small doubts in it.
OVAL PISTONS- Oval pistons are first introduced by HONDA in their model NR 500 as they were forced to develop a engine to deliver high power output in motogp as number of cylinders were redtricted to 4 in that time.
Oval piston is not exactly oval but it nearly looks likw it with astonishing 8 valves per cylinder, two connecting rods per cylinder,higher output to increased air fuel mixture.It will be usually used in V4 and v8 emgines with 90degree apart.
Advantages :
*High power output
*Increased torque
*problem araised because there is no proper and efficient piston ring available for oval pistons.
*high cost
*high skilled technicians required

I know that it wad banned from MotoGp but why?
Why it was not commercially success?
Do you know about elliptical pistons?
if possible explian the working in a simple manner so that we can carry on the topic.


  • Velshankar MJ
    Velshankar MJ
    It was very impressive in terms of both technology and rule interpretation. It was actually evolved as V8 engine was banned from moto gp hence Honda combined 2 cylinders to from on which shapes as rectangular oval. The main reason for its ban is its reliability. It is un reliable though its power is high. Also many valves have to be fitted in one cylinder, Firing should be uniform enough in all sparks of same engine.

    The reason for its failure in commercial purpose is its cost. It cost a huge to manufacture this type of engine.

    Also the surface is not cylindrical so there will be uneven stress throughout the oval surface. Another major challenge in this is the manufacturing of piston rings for this type.

    Below image is NR 750 s Oval piston
  • Yougal Dhiman
    Yougal Dhiman
    good info,.. but why to use oval/elliptical shape in pistons?? when we get maximum surface are to circumference ratio in circular shape.
  • Velshankar MJ
    Velshankar MJ
    Both elliptical and oval pistons are used just to increase the power output and torque. Even 4 cylinder Oval piston engine s power matches the power produced by the V 8 engine. But as u told the fuel consumption will be greater due to higher circumference. 750 cc of this engine version can produce a maximum power of 125 bhp at 14000 rpm..

    @#-Link-Snipped-#:: Elliptical pistons are same as that of the oval pistons. Oval pistons have straight line edges on the side. But elliptical pistons have curved line structure at the side of the piston surface. By using elliptical piston some of the advantages can be achieved when compared with oval pistons. Wear on piston walls can be reduced when we use elliptical pistons over oval pistons.
    I would like to see graph of piston rings work in tnat engine (FEM)

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