Does connecting rod length determine stroke?

A popular misconception is that rod length affects displacement, which it does not. Only cylinder bore and crankshaft stroke alter the displacement of an engine.

How do you calculate the length of a connecting rod?

Measure the length of the metal between the end of the connecting rod and its inner diameter, taking the measurement as close to center of the rod end as possible. Perform this measurement on both ends, then add the numbers together. Add the total to the sum of the halved inner diameters.

What are the dimensions required to design a connecting rod?

The literature review showed that there are three fundamental dimension to be take into account on a connecting rod design. These are; – Small end inner diameter, – Cross-section, – Big end inner diameter. These dimensions change with respect to type and properties of engine.

How long should a connecting rod be?

The length of the connecting rod compared to the travel of its stroke (called the connecting rod ratio) directly affects engine smoothness and performance. Most automobiles work best with a connecting rod ratio of 1.65 to 1.75.

What is the ideal connecting rod ratio?

Some engine builders say a “good” rod ratio is anything 1.55 or higher. Production engines may have rod ratios that range from 1.4 to over 2.0, with many falling in the 1.6 to 1.8 range. Four cylinders tend to have lower rod ratios (1.5 to 1.7 range) while many V6s have somewhat higher rod ratios of 1.7 to 1.8.

How do you measure the stroke of a crankshaft?

It is determined by the diameter of the circle traveled by the connecting-rod journals of the crankshaft as the crank is rotated. Total stroke can be calculated as twice the distance from the centerline of the crankshaft to the centerline of one rod journal.

Which formula is used in designing a connecting rod?

Rankine formula
A connecting rod is a machine member which is subjected to alternating direct compressive and tensile forces. Since the compressive forces are much higher than the tensile force, therefore the cross-section of the connecting rod is designed as a strut and the Rankine formula is used.

How do you make a connecting rod?

1. In designing a connecting rod, the following dimensions are required to be determined :
2. Dimensions of cross-section of the connecting rod,
3. Dimensions of the crankpin at the big end and the piston pin at the small end,
4. Size of bolts for securing the big end cap, and.
5. Thickness of the big end cap.

What is the preferred connecting rod to crankshaft stroke ratio?

We hear a lot of engine builders shoot for a ratio between 1.5:1 and 1.8:1 on a street motor, with 1.75:1 considered ideal, regardless of application. The most highly developed four-stroke engines in the world – Formula 1 and motorcycle engines – have rod ratios of more than 2:1.

What do longer connecting rods do?

A longer connecting rod will keep the piston further up in the cylinder bore when at BDC for a given stroke. The small end of the rod, which is connected to the piston pin, is further up the cylinder bore with a long rod as compared to a short rod.

What is the best way to choose a crank rod length?

Given the height dimensions of the block and how much stroke is in the crank, you have some wiggle room to play around with rod length. Stroker cranks require shorter rods to maintain the same deck height of the piston at TDC, but you can maximize rod length if you use pistons that have a higher wrist pin location.

Why do piston stroke lengths depend on the crank throw?

Because the crank throw rotates about its own center at the main bearing you can see that only half the stroke length is used when the piston is at TDC. The rest of the distance is taken up by the rod length and the pin height of the piston.

How do you calculate pin height from rod length and stroke?

Since the rod length and stroke are now fixed, the pin height is the remaining variable. To find the necessary pin height, add the rod length and half of the stroke and subtract the result from the block deck height. Blocks that have not been decked typically provide a fudge factor of about .020-inch.

What is crankshaft crank radius?

Crank radius is half the stroke plus half the rod journal diameter, unless the counterweights are of larger radius. The connecting rod should be as long as possible for mechanical efficiency, and no shorter than being able to ensure adequate clearance between the bottom of the piston and the crankshaft.