Forgive me Jay, but I need to flex a bit.  This has turned into a pretty nerdy argument, but I don't want people reading this thread to come away with dangerous information.

Yes a standard inch-series steel socket head cap screw has roughly 20% higher tensile strength than a typical grade 8 bolt.  A big reason for that is so the head doesn't explode when you try to torque it.  (The internal hex drive wants to split the bolt head.)   You can't use anywhere near that strength to generate clamp load in the joint.  The small head limits the maximum clamp load too. 

Take that same 20% higher tensile steel and put a proper external Torx or 12-point head on the screw, or even a standard external 6 point hex head.  Then put it on a dynamic fastener "Junker" test machine.  The results will blow away the original Allen cap screw. 

I have a few qualifications too:

- Masters Degree in Mechanical Engineering - Machine Dynamics.
- Passed the Professional Engineer License Exam (which was full of questions about fasteners).
- Cylinder Head Systems Engineer at Ford.  A BIG part of my job was high performance fasteners.  No, you will never find an Allen socket head cap screw holding down a modern automotive cylinder head.
- 35 years experience in machinery design.
- Oh yeah, I'm a very experienced machinist too.  A big part of my current business is building prototypes of my designs using manual mills and lathes, as well as my Haas CNC mill.

In my opinion, Allen head screws do not belong anywhere near a connecting rod.  You won't even find those on a lawnmower!!  You can't get anywhere near the torque / clamp load needed for heavy use. 

Makes me scratch my head about what these were intended for.  The rest of the rod looks pretty stout, but the fasteners 

I live next to Long beach airport.  Boeing used to maintain a repair depot there for the B1-B.  They would replace the huge (truck tire-sized) Teflon pivot bushings for the airplane's swing wings.

I had a friend at Boeing who would tell me when a B1-B was going to be flying out.  They would usually leave in the evening at full military power (afterburners blazing).  Man the noise and the sight of those shock diamonds in the exhaust was something to behold!

I thought about that Renault   I wounder why Renault comit so much to racing and rally
when their customers consist of wino female shrinks and scoolteatcher with Marxsist ideas with zero interest in racing

Heo - Don't be shy!  Tell us how you really feel!! 

Those people in the US can't have Renaults, so they buy Subarus instead 

Re: Over-Amping

Charles Kettering first hit upon this principle when he invented the electric starter in 1912!  All of the experts told him that no available electric motor could provide that kind of torque in a reasonable size to package for a car.  Kettering realized you could over-drive the crap out of a small motor for a short time, if it had enough thermal mass to absorb the heat.

I remember around 1990 at Ford hearing about Polimotor  https://polimotor.com/ 

They were building a complete composite four cylinder race engine.  I remember seeing impressive pictures of engine explosions!  Usually all that was left of a failed crank was cotton candy in the block 

If you look at the website, they seem to have mostly given up on composite engine parts.  They are focusing more on metal 3D printing now.

Super nice pictures Heo!  Wishing you and your family a great Christmas season!

- Bill