Any irregularity in a parts shape increases the stress and reduces the fatigue life of the part.

If an irregularity is in a thick section where the stress levels are lower the life cycle decrease caused by this ( increase in stress factor) does not reduce the overall life of the part.

However, it does imply that a section had to be made thicker to reduce the stress level in that area so that an oiling hole can be used.

That increases weight... increasing the overall stress on the rod and therefore reduces the parts life.

Every change in shape can be given what is known as a "K" factor. A sharp corner is the worst with a long smooth radius being the best.

When you drill a hole in the rod you get a stress point. For a race rod where the goal is maximum strength, maximum fatigue life and minimum weight. Since the anticipated loads are high it makes good design sense to eliminate the oil hole and reduce the weight of the part.

Also a typical race engine is not spending a lot of time at idle and will in general have wider bearing clearances that throw more oil.

As with any change the only real way to know is to test the setup and see how well it holds up. You can make an educated guess, but in the long run it comes down to testing.

Since your motor is not a high RPM NA cammed out screamer, rod strength and loading is less of an issue. ItÆs the forces generated with a change in direction that is really hard on rods and that force goes up with the square of the engines speed. With a boosted motor the new loads are mostly in compression and the force to pull the rod down does not increase significantly ( not like changing the RPM from 6000 to 9000 would).

As a reference I have worked on Ducati motor that titanium rods that did not even have tangs or notches to hold the bearing shells. They were held in place only by the compression of the bearing shells by the cap.

The also were not drilled for cylinder wall oiling and the motor held up just fine at 15,000 RPM.

If I were to put a hole in a con rod I would consider finding a mold shop with a wire EDM.

Also when the stress levels are below a certain level the number of stress cycles a part can take becomes infinite. In he case of our motors thats typicly the case.

On my Ducati example not so much.


Kevin