Straight or Angled Bolt Main

[Lextreme II]

Hello Experts,

I have been reading Summit Racing Catalog and noticed Chevy and Ford have main caps come with eight straight main bolts or angled main bolts. What are the pros and cons on strainght and angled main bolts?

 

[Zuffen]

An angled main bolt will not only be relying on the shear strength of the main bolt in a longitudinal direction it will also be using the shear strength of the main bolt in a sideways direction.

As an example a 6" nail has around a 5ton shear strength across it but only a little more than a ton lenghtwise.

 

[TOBES]

The angled bolts support the block by pre-stressing the main webs in towards the crank, much like the side bolts in a 1UZ. They also help stop the main cap moving around by giving it some lateral support.

I once built a 400 chev small block and was advised to use a 2 bolt main block with these caps fitted as the result was much stronger than the std 4 bolt setup.

 

[JBrady]

We are talking two different engine designes. Short and deep skirt blocks. Old style small and big block American engines are typically short skirt (block stops at crank centerline) and all the cap relys on is the main bolts and a small step machined in the block to accept the main cap.

Deep skirt engines usually are crossbolted. Not only does the bock extend below the crank journals it also accepts the main cap between the skirts and allows for a MUCH stronger lower end.

In addition to the advantages of angled bolts that are given above on a short skirt engine the angle also allows the bolt to recess into the stronger part of the block wall instead of the usually thin casting around the main webs.