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.

[alwayscode390]

WOW, I just tried to picture that ... the bolts go from the oil pan up to the heads?!

I was definitely thinking of this setup like the SBC.

Can you take the heads off without having to take the engine out of the car ( taking the oil pan off? )

No wonder these engines are so historic :) ---

[Hog]

IIRC the LT5 architecture was used in the 3.5 V6(Shortstar) and 4.0/4.4sc/4.6 V8 Cadillac/Olds/Shelby engine from 1992-2011.

The V8 Northstar is/was part of GM's "premium V8" engine series. They are extremely durable and make great mid-upper rpm power. 4000-6500rpm is a fun experience, even in the 2 ton plus boats they were installed in. Add 1.1 liters and 100-125 hp to that party and subtract a ton of weight from the vehicle, and your arrive at the rip roaring LT5 experience.

They have a cam drive setup that is superior to the LT5. If GM had relaxed its max engine size by only an inch or 2, Lotus could have designed camshaft sprockets with a greater diameter which would have allowed greater durability over 7500rpm. The smallish LT5 cam sprockets cause greater chain action as compared to larger sprockets.

As it turned out larger sprockets could have fit during the Bowling Green chassis/body mate process where the body comes down over the engine on the line.

http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/northstar.jpg

Either iteration of the LT5's lower end is usually referred to in terms of being "bulletproof".

peace
Hog

[alwayscode390]

Thanks for that Hog.

I had a 2004 Cadillac DTS with the 4.6 Northstar and loved the engine.

What would be considered the "weak link" of our engines ... that usually cause a sort of engine failure, the head gaskets? ---

[Hog]

Here is an "exploded"view of a MY 95 LT5(actual my90-95). Look at all that lower end BEEF!
CAPWALK, whats that???

The crank is literally sandwiched in the middle, very very stable.

http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/lt5exploded.png

peace
Hog

[Kevin]

Thanks for that Hog.

I had a 2004 Cadillac DTS with the 4.6 Northstar and loved the engine.

What would be considered the "weak link" of our engines ... that usually cause a sort of engine failure, the head gaskets? ---

too much spray.

[alwayscode390]

Thanks for that pic ... #146 shows the extra bolts in the 4-bolt setup. ---

too much spray.

LOL ... whats considered too much? Sounds like the tune was off if these things can handle 500hp over stock specs :) ---

[A26B]

A color coded bolt size and comparison between the 90~92 & 93~95 engines.

http://i190.photobucket.com/albums/z224/A26B/DiagramLT5MainBoltConfig_zps16046b64.jpg

The nodular iron main ladder cast into the lower crankcase. #1 main area visible here.

http://i190.photobucket.com/albums/z224/A26B/OilPumpArea375hp_zps497e5785.jpg

[Kevin]

Thanks for that pic ... #146 shows the extra bolts in the 4-bolt setup. ---



LOL ... whats considered too much? Sounds like the tune was off if these things can handle 500hp over stock specs :) ---

whatever kurt was pumping into his 415 trying to run down supras.

[Kevin]

that is a great pic jerry.

[alwayscode390]

Thanks Jerry ---