what's stronger

[AC sports]

A 7/16 rod bolt of 8760 chromo steel with tensile strength of 180-190,000 psi
or a 3/8 rod bolt like arp 2000 rated at 220,000 psi?
Also why is a bolt only rod considered stronger than one with a nut and bolt arrangement like most oem ' s?

[modok]

It's not really stronger but it is lighter and more compact to eliminate the nut.
When it comes to rods.....which have to be light and fit in a limited space, that allow them to be stronger for the same weight/space.


you can look up the clamping force of bolts, probably is already in a chart.
Which one is stronger.....per unit weight, would be the higher tensile one!

[BigBlocksOnTop2]

You can do the math. The cross sectional area through the minor diameter of the thread and multiply by tensile. Its a good ball park approach...

[groberts101]

There are charts floating around but I'd think the clamping pressure of the 7/16" would still easily surpass the 3/8" bolt. As far as ultimate tensile strength.. probably a bit closer to one another than the clamping strength would indicate. Unless the rod is specifically designed around the larger bolt with more available material, sometimes a larger bolt is not always best. Lots of cookie cutter rod designs floating around out there using larger bolt size as one of their marketing ploys.

[Rick360]

Code: Select all

diameter	psi 	area	 lbf
0.375		220000	0.1104	24298
0.4375		180000	0.1503	27059

The 7/16" diameter with 180,000 psi bolt would be stronger.

Rick

[Nefario]

Code: Select all

diameter	psi 	area	 lbf
0.375		220000	0.1104	24298
0.4375		180000	0.1503	27059

This is not using the maximal stress root diameter of the threads but the method and conclusion is correct.

Also why is a bolt only rod considered stronger than one with a nut and bolt arrangement like most oem ' s?

The ultimate tensile breaking strength is the same but the longer bolt and nut assembly can stretch more for a given applied force. The shorter working length of the bolt creates a more rigid joint.