Turbo Con Rods: Seem Cheap

[bruce]

4 bolt Miata motor - hee hee!

Sounds like what they do with rotaries - extra dowelling.

[The Pupat]

Benny the '4 bolts' refer to the main bearings, not the big end bearings. Only reason they use them is because of the relative flexibility of the V8 block - the base of the block is a big open space compared to an inline 4cyl block, plus the diameter of the crankshaft is bigger. All these combine to allow lots of movement in a V8 bottom end at high revs, resulting in the bearings moving and destroying cranks or worse. A second pair of bolts into the main bearing caps, generally from the sides, helps to limit this movement. Stud girdles are often used for the same purpose (big flat plate with lots of holes that ties all the main bearing caps together). I remember working with a crowd that made stud girdles for race motors - unfortunately they didn't do their metallurgy sums very well and the girdles expanded faster than the block with heat resulting in some catastrophic engine blowups! In a stiff little 4cyl block these are not common problems, but can still be addressed the same way if they occur.

Yep what he said, quite common and a few factory motor actually have them, a good one to check out he the Datto VH45 main bearing girdle with 6 bolt mains... tough as. I believe Nizpro used to run girdles in there big HP RB's so it's not just V8 that it's common, basically any motor that runs big HP and doesn't have a super strong block will benefit, won't stop a rod bolt from letting go though so the only solution there is either custom rods with bigger bolts/studs and/or high tensile bolts/studs.

[Sean]

I may be mistaaken, but don't mazda use a girdle in some of teh B series engines?

[CT]

I may be mistaaken, but don't mazda use a girdle in some of teh B series engines?

Correct - BPs from the 98/99 models use a mains support cradle.