Con rod ratio?

Question

does anyone know about the con rod ratio (it's bout ratio between con rod lenght and stroke lenght)

how it's affect your cars or bike engine caracterisric

how is the calculations

does you ever do such modifications

and where can i get more information about it

thanks before

Answer 1

here are some common examples off the top of my head, don't expect these numbers to be completely accurate, just examples.  

Chevrolet small block engines.

350 cid has 3.49" stroke and a 4" piston dia

302 cid has 3.0" stroke and 4" piston dia

305 cid has 3.49" stoke and 3.90" piston dia

The total cc of the cylinder head compression chamber effects the cid slightly.

Increase torque by increasing stroke

increase the capability for higher rpm by reducing the stroke.

An engine designed for relatively lower rpms would benefit from increasing the stroke.

An engine designed for higher rpm would benefit from a larger piston diameter.

Valve timing fuel intake and exhaust pressures must be addressed when making these modifications. Fine tuning of these three elements is crucial.

Ratios non specific. A larger crank journal circumference travel and shorter piston rods are characteristic of a long stroke.

Longer rods and smaller crank journal circumference travel is typical of a short stroke engine.

The best case is to build a long stroke engine with a maximum cylinder bore that will withstand high rpms and fuel management, intake capacity, valve timing and maximum usable compression ration fine tuned for optimal horse power and torque.

Answer 2

your rod ratio is pretty much your rod lenght/stroke. The rod ratio determines the piston speed and acceleration. The piston speed of the average car should be below 4500m/s at maximum rpm. Above that and the engine will experience faster wear and tare. Now the piston acceleration is what hurts and breaks the connection rods and the engine. The acceleration causes allot of force on the connection rod and bearings. So the lengh of the rod will affect the piston acceleration, longer rods will result in slower piston acceleration from TDC, and also longer rods will reduce the force the rods put on the sidewalls of the cylinder wall.