2 Bolt vs 4 bolt Main Caps and Nitrided Stock Crank ... strong? ---

[alwayscode390]

I just realized that the crank was a Nitrided crank , and that the early lt5 engines used 2 bolt main bearing caps vs 4 bolt in the newer engines.

Is there any known failures from the 2 bolt engines that are more common than with the 4 bolt engines?

Is the crank Cast or Forged , then nitrided?

Whats the consensus on how many HP our bottom ends can handle?

I just picked up THE HEART OF THE BEAST ... figured I should start reading up on our cars , this is where I got this engine info from (stuff posted on the net from the book).

Thanks ---

[Kevin]

2 bolt vs 4 bolt makes no difference.

[rkreigh]

the LT5 is a "ladder bar" split block design and the 2 bolt blocks are plenty strong. the crank is a very stout forged casting

although the 4 bolt design is "marginally" stronger, (about 5%) the 2 bolt block set the endurance record and is plenty stout

when you look at the new LS motors they went to a deep skirt cross bolted design which is cheaper to manufacture.

you can't really compare a "2 bolt vs 4 bolt main" design with separate main caps holding the crank with a traditional chevy block

the ladder bar bottom case holds all the caps in a very rigid structure on the LT5

[Kevin]

i need to read up on the bottom end of the lt5. never really bothered before, not sure why

[alwayscode390]

Is the Ladder Bar Bottom sorta like using a "block girdle" ?

Thanks for that explanation ---

[Pete]

I will explain it this way.
two 1/2" inch bolts or four 1/4" inch bolts
They went with smaller bolts on the 4 bolt blocks
Let me add, some might say your spreading the load with smaller 4 bolts but the ladder frames have so many screws
all the way around i don't think 2 more smaller screws will make such a big difference to handle that much more power.
So if your building a 1000hp motor and the 4 bolt can handle another 25 or 50hp more at that point who cares.

To me makes no difference.
Some of the fast FBI Z's are 2 bolt blocks making 650-700hp

Stock crank is forged.

We know stock bottom ends can handle 600hp i think they could handle 800+hp.

Pete

[alwayscode390]

Awesome, Thanks Pete ---

[DaveK]

If I recall correctly the 4-bolt "enhancement" was a sop to GM after the supposed crank failure "issue" that was actually caused by an improper starting procedure during testing. Lotus didn't believe it was necessary.

Dave

[RHanselman]

My 2 bolt stock crank and rods endure over 700 chp and 660 tq.

[Paul Workman]

Something else...

The bolts sandwich the block between a ladder "girdle", into which the main caps are moulded, and the heads. The bolts of the 2-bolt motors are MASSIVE, and weigh over 21# alone!

To think of the LT5 2-bolt vs. 4-bolt from the perspective of a SBC (or even a BBC for that matter), is totally wrong. It is an entirely different animal - top to bottom. Looking at it dissassembled, it is one beefy mutha!

Standing around over brewskies with Dave Mclellan at a JVD BBQ during one of the recent Bowling Green GTGs, Dave said the LT5 (bottom end) "...should be good for 1000 hp or a little more."

FWIW,

P.

P.