What to look for in a salvaged 302

[Neil]

BS, think about it, if the idea of the animation is to show the difference the two rods should have both big ends rotating around a common main brg center height and the long rod item should show a shorter piston comp height ( half the stroke distance ). No wonder the newbies get confused.

Right! Whoever created that animation did not know what he was doing.

 

[Ryan L]

I think it shows quite well how the different arrangements result in different piston positions for the same amount of crank shaft rotation even though the crank stroke is the same.

The greater the angle of the rod between the bore and the position of the big end, the higher the side load on the cylinder wall. What is also mentioned is that the shorter rod stops or spends more time at both BDC and TDC in comparison to the long rod configuration. For the same camshaft, this will allow for a higher volumetric efficiency (scavenging and cylinder fill). This needs to be managed against the increase in piston wall loads. Go too short, and the loads get too high and the longevity of the engine will suffer. Go too long with the rod and the weight gets too high and the whole assembly gets heavy and big.

I don't have enough experience to say which is wright. Still learning. I do see that things are constantly improving though. 30 years ago overhead cams and 4v per cylinder from the Japanese was where i thought things were at. Since then, there has been a lot of continuous development in all aspects of engine development. These days I have a lot more respect for the small packaging size and weight that is achieved by the cam in block v8 engines.