panic

The one-piece (cast, forged, or billet) plain-bearing crankshaft is the backbone of all modern automotive engines. For long service, resistance to bending is essential, and the length, number and width of the main bearings as well as the method used to secure the main bearing caps to the block all affect the straightness of the crankshaft.
However, the absolute and relative sizes of the main journal diameter, connecting rod journal diameter, and stroke length also affect stiffness.
“Journal overlap” is the continuous cross-section of steel or cast-iron in the counterweight or throw cheek shared by the main and rod journals. Larger journals or shorter stroke increase this shared area and increase stiffness.
For example: if the main and rod journals were each 2.00” in diameter and the stroke were 4.00”, there would be no continuous cross-section connecting them. The two circles formed by the journals would be tangent with no journal overlap; the strength would be limited to only the counterweight web connecting the two journals along the crankshaft axis (lengthwise). If the stroke length is increased, journal overlap is reduced unless one or both journals is increased in size.
The common calculation of journal overlap is:
Journal Overlap = ½ (Main journal OD + Rod journal OD - Stroke length)

However, this is not the method used by GM engineers (click for more detailed explanation: http://victorylibrary.com/mopar/journal.htm)

I've written a short .xls worksheet specifically for the LS engine, in which these annoying trigonometric calculations are already done and the three different stroke lengths (4.8; 5.3/5.7/6.0/6.2; 7.0) are compared. E-mail me for a free copy: sales@victorylibrary.com

03EBZ06

so, are you the crankshaft whisperer?

Mongo510

Thanks so much for doing this!
I was concerned about using a cast crankshaft in my application( Roadrace, HPDE).
My choices were to use a stock 4.8L crank or a custom forged crank from Callies (very expensive).
This reassured me that my choice to use the stock crank was valid.
Thanks PANIC!

NIKDSC5

iTrader: (10)

Yeah, very few know this actually. The 4" aftermarket cranks are not, and were not designed for the LS engine properly. With exception to the LS7. Which in reality is why the LS7 is so sought after (or should be). It is the only LS to have been designed with the 4" crank properly.

With all that noise said, plenty of guys making TONS of reliable power with 4"+ stroke cranks. So that counter weight webbing is doin just fine.

panic

Bump for more readers.

KCS

iTrader: (20)

Can you elaborate on how the LS7 crank is "designed properly" and how the aftermarket cranks are not?

NIKDSC5

iTrader: (10)

It's more along the lines of the piston coming out of the cylinder and sleeve length also. I guess when I stop to think about it the cranks may be designed just fine. But it's the whole thing coming together that doesn't necessarily work right. The Ls7 was designed with the 4" crank where no other LS was. For longevity and decreased wear in the sleeve and piston. But technically if you wanted a stoker kit to work correctly you'd need to go to either a tall deck block, or a longer sleeve.

Again, I have a 4" crank in a normal LS and I could care less of the effects. The Pistons have been changed with that combo making it less prone to doing damage. But it's still not condsidered "proper" engine building by any means.

KCS

iTrader: (20)

Yeah what you're talking about has almost nothing to do with the crank.

With a properly designed piston, the 4" stuff works just fine. So do the 4.1" combinations.

kinglt-1

iTrader: (26)

^This

panic

So I'm not holding my breath:
Does the LS7 sleeve extend farther down the bore than the 92mm stroke blocks, or not?
Are the LS7 crank counterweights relieved differently for skirt clearance than aftermarket 4.000"?
Are there any different oil control/pumping loss differences (bay windows, scraper or tray design)?

NIKDSC5

iTrader: (10)

Changing the Pistons wrist pin location and all that is more like a bandaid then a fix.

Again those combinations have been proven to work over and over again. But if you ask any big name engine builder if they were to build an all out race motor, they would not go with that combination. And they would address the issue by either going with a longer sleeve, or a tall deck block. Reason being is they know that it is not the correct way of doing things.

KCS

iTrader: (20)

Shortening the compression height isn't a band aid or a fix, it's a requirement to keep the piston from protruding .200" above the deck at TDC.

You any big name engine builder will agree with you, but they're all using standard deck LSX blocks with 4" stroke cranks. SAM used a 433" LSX, Proline used a 440" LSX, and BES used a 440" LSX in their all motor drag race programs, each of which make over 1000hp. The standard deck LSX block has the same cylinder length as a stock LS block (besides LS7).

Why are you bringing up all out race engines when you were saying longevity is what's effected?

KCS

iTrader: (20)

The LS7 sleeves are longer; somewhere in the 5.8" range versus about 5.5" for the other blocks. The LS7 engines are also "dry sump" so yeah, there are some differences as far as the oil system. No scrapers, but I can't recall if they have a windage tray or not. They have bay windows too, but so do many of the other wet sump Gen IV engines (LS3 for example).

NIKDSC5

iTrader: (10)

^Yeah that. Just to bring it up really, did'nt have much of a goal. More because I originally confused piston rock with crank stiffness.

mebuildit

I'm gathering parts now for a nicely built 440. Since everything can get expensive buying everything all at once, I've been buying things here and there.
Since you are talking about cranks, I decided to order a Winberg center counter weighted crank. This is the nicest crank I've ever had over the years.
I'm curious about your thoughts on this crank?
Car will be driven on the weekends mostly, Callies Got a deal on a RHS block so that will be what I'm using as well.

panic

As the stroke is increased, bending resistance goes down rather rapidly. This is not significantly improved by choice of steel alloy or heat treatment, since it's not a product of physical strength. By comparison (with the same journal sizes), a 4.125" stroke crank has only 76% of the bending resistance of a 4.000" (LS7) crank. 4.250" stroke takes this down to 55% (and only 30% vs. an LS3 etc. 92mm crank).

machinistone

Apparently you've never seen large diesel crankshafts that have huge strokes with no journal overlap and make thousands of foot lbs of torque with cylinder pressures vastly higher than gassers and run for millions of miles.

The real world evidence and experience don't support your suppositions.

We use Winberg cranks in our Sprint Car 360 and 410 engines, they're one of the best you can buy.

panic

Fascinating.
The very moment I begin designing a large diesel engine I'll consider that comment relevant.
Until then, I'll use the method the GM engineers have used for 50 years, which resulted in the comparisons I posted.

KCS

iTrader: (20)

The center counterweights really do make a difference. They may not affect the stiffness of the crank like what's being discussed here, but they do seem to reduce the forces that cause bending/flexing of the crank.

I heard there was nice little seminar about it at PRI as a manufacturer released their new CCW LS cranks.