Cylinder wall thickness

[Speedy Squirrel]

Is there a significant difference in the wall thickness of the cylinders for the cases with the "original" stud spacing? For instance, are the walls of a 95mm 3.2L cylinder thicker than the walls of a 97mm 3.3L? After the stud spacing increased (964 3.6?) did the cylinder wall thickness increase?

[Catorce]

My guess would be that the cylinders would remain within a few percentage points of each other regardless of the head stud spacing; cylinder wall thickness would remain relatively constant to allow for appropriate heat transfer for air cooling. Only a theory however, I could be wrong.

What is the context of this question?

[Speedy Squirrel]

As the cylinder bore gets larger within a given bore spacing, I am wondering if the wall thickness decreases. The stud spacing has gone from 80 to 90 mm, while the bore has gone from 80 to over 100mm. Also, the nikasil cylinders are said to have the thinnest walls.

This is of interest because it limits the clamping force from the studs. The tighter they are, the more the bore distorts, even more so if the cylinder walls are particularly thin.

[Trackrash]

Interesting question. So are you wanting to put 100mm 3,6 P&Cs on a 3,0 motor?

[Walt Fricke]

Here are some measurements from a 95mm Alusil (since Nikasiled, but that doesn't affect wall thickness):

Where it sockets into the head 9mm, except by studs, where it is 8mm.
In the fins on the side 7mm.
Above the spigot 9m.
Skirt 3.6.
The inner part of the CE ring groove for an SC cylinder is ~2.6mm.
These are somewhat approximate - vernier plastic caliper and an outside "lock and measure" caliper with no accurate way to unlock for extraction for fin area measurement.

You can see why you can't use a CE ring on 100mm cylinders, and maybe not on 98s?

If someone can measure a cylinder for a 3.6, or a 3.8, some comparison could be made. But the limit is pretty much the sides of the cylinder - as the bore increases, when you reach whatever cylinder wall thickness minimum you shorten the side fin grooves, which has to reduce the air flow around the cylinder. Were the 3.6s the motors where Porsche introduced the taper bore to account for differential heat expansion?

[chris_seven]

https://www.researchgate.net/publication/245396925_Air-Cooling_Effects_of_Fins_on_a_Motorcycle_Engine