I still follow another belief….aluminum caps DO work as a SHOCK absorber, but only allow more dimensional shift with the main bores when stressed - shifting the fall out to the crankshaft…..Best fix for getting all you can from a oem block @ 750 – 800 hp and get reasonable life? ……get rid of harmonics….or as much of it as you can.

Cap chatter is a vibratory frequency that actually transfers material from one surface to another, the bounce that is mentioned. This vibratory frequency is as much or more of the problem than anything else. The clearance with the registers is definitely important and once this cap walk problem generates, the registers will only get more clearance....blocks fail and ect.

A stock block, professionally machined with a good set of studs (properly installed), NO FILL and even stock caps.....yep......stock caps......have made many, many laps over many, many years doing this without ONE failure. A couple hundred passes were also made on a throttle stop killing ALL throttle at .001 - .01 out…..nothing worse on hammering the bottom end than that.
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Yep.
I think most of the aluminum cap supporters don't think into it deep enough, and you stated it very well.
Kenny D says it best... keep the crank rolling forward(not downward) and your engine will live a long life regardless of how much power you're making.

Alum. caps seem like a Mopar thing only. Am I correct about this and if so why?

Because everyone else has an abundance of aftermarket block manufacturers

Personally I don't think the cross bolting will hurt and will help it live. Yes the Hemi is beefier in the skirts for their cross bolt arrangement but I still I think it's an improvement for Wedge, even with the skimpier skirt.

I guess that makes sense.................

Lets see, the B and RB motor wedge was design in 1957 with no intent of racing those motors, the 426 hemi blocks where designed in 1963 with the full intent of being a all out race motor so they designed extra material in the oil pan rails and main ribbing for cross bolts I disagree with drilling through the sides of the wedge blocks through the main webbing support to add one skimpy bolt per side

I'm not using that style w/ the intent of it "beefing up" the load capability of the caps; IMO, and as I've seen described elsewhere, the ability of the girdle to tie the #1-4 main caps together and also to the pan rail should improve torsional rigidity of the mains.

Especially since the aluminum caps do crack on occasion (I've seen three different ones do it, and they weren't all the same brand, either):
1. If the aluminum helps absorb some of the shock and...
2. The girdle keeps the mains tied together so they're not swaying back and forth as much which would contribute to work hardening...
3. it should be a win-win band-aid on a stock block making under 700 HP.

FWIW, I have done some digging online for documentation that might describe in more detail the types of stresses crankshaft main caps experience, but haven't found anything that really covers it like I'd like. You'd think somewhere out there that somebody's done FEA and simulations of those loads, or figured out some way to attach sensors to various parts of the bottom end to detect and/or measure the extent and directions of the typical loads, to help people understand the nature of the beast better.

The crank is ALWAYS trying to push itself out the bottom of ANY motor. So the more power you make, the more force you have trying to help it push itself out. That is the only direction the cap sees any stress.

The other problems are crank flex and harmonics, but those two can be addressed with better cranks, lighter components and balancing.

I am wondering if the 4 7 cam lobe switch does any
better on the cap issue... its suppose to run smoother
which to me should help.. since it changes the firing
order.. maybe you would know Monte

I always run a 4-7 swap cam and in some instances even the double swap, which ends you up with a Chevy LS firing order. If you just look at the motor and run the firing order in your head, the LS order makes perfect sense from a balance standpoint.

Now, do we SEE any differences in the parts, that's hard to quantify, but they usually pick up power, which should tell you the motor runs "easier".

Again, it is just strictly a lack of clamping force and you will not fix that...........but anything that makes the assy lighter and smoother can't hurt

And, of course, NOBODY wants to be the guy in the magazine w/ the blowed-up 440 on display for the whole world: http://www.hotrod.com/how-to/engine/1405-breaking-news-dusted-plymouth-duster/

Yep, 2 broken caps AND 3 cracked cylinders =

That pic says alot for busted blocks, I had read this through and thought maybe if people posted pics of there busted blocks and there combo maybe we could get a grip on what really might work and what doesnt and whats alot of wasted cash.

To me its when the push on the crank is happening... at
the top of the firing stroke or the bottom would be the
points that would lift a cap.. anything on a angle of
the crank throw just causes it to spin.. so if the firing
order is smoother it would tend to spin easier(from what I
heard)... it would have the other cyl firing at better angles

You can use girdles, cross bolts, alum caps, billet caps but you still only have 2 bolts holding / clamping the mains. Ive ran um with stock caps and alum caps. they both cracked. Both engines were a half fill and used ARP studs.

You can make them live for awhile, but if you detonate or push 600hp+, eventually they will crack.

Being that I run SB I dont worry about it.. the SB doesnt
have a issue like the BB... I was trying to discuss what
the issue might come from... yes the cap is lifting.. but
is it the angle of the throw(top and bottom).. basically
trying to figure cause and effect.. even some of the 4 bolt
(not the side bolts) still have it... so is it the angle of
the throw that gives all the lift to the cap(or lack of angle
I might say)... but if the different firing order might help..
just thinking out loud
EDIT
ANd I dont lkie ductile iron caps... if I'm running a
aftermarket cap I prefer steel or alum.. ductile iron
cracks easy

From the looks of this, I will GUESS that the caps broke first. Then the stud is trying to hold the half a cap on the block. That will put a lot of side loading on the stud which transfers to the block. Cast irons are weak in tension. I'm not sure what grade gray cast irons were used in a block. This link has an interesting chart on the SAE grades with the Brinell hardness.

https://en.wikipedia.org/wiki/Gray_iron

Assuming we are using the SAE J431 G3000 grade, median hardness of 214 HB, then the tensile strength should be around 32ksi. I'd never seen that chart of hardness to tensile strength. I guess that's why my machinist engine builder in Tampa hardness tests every block he does.

Compare those values to Austempered Ductile Iron (ADI). Here the Yield Strength is around the 30ksi level, but the Tensile Strength is in the 55-65ksi range. Cast irons don't yield much, hence the brittle fracture on the main caps. Stretch a steel bolt and you can measure the elongation or necking of the bolt shank. I'd say that the ductile irons are a better main cap material than gray cast iron.

http://www.ductile.org/didata/Section12/12intro.htm

Feel free to disagree. I welcome an intellectual discussion, just keep it professional and not a bunch of name calling that is common on here. Hopefully the idea is to put our collective knowledge together and hopefully we can all learn from this thread. One of those synergy deals.

Big Block Chevy's have the same firing order as a Mopar and this is a non issue...........Why, because the HP blocks are 4 bolt with the outer bolts splayed. More clamping......it's just that simple. All the other is just a bandaid attempt to get a weaker designed block to last longer, as has been covered many times.

Kinda like Hospice..........will maybe make you feel better for a while, but the end is near

When I said ductile iron I might have been wrong.. I
was referring to the iron caps on a stock block...
they are brittle... drop a part of that iron and see
if a chunk breaks off vs a steel part that dents

I've seen stock 400 main caps break in two like that 440 did, I've also seen several RB blocks with the main webbing cracked between the #1 and # 3 cylinders and that #2 main cap I have built two different 400 stroker motors with both a 4.25 stroke and a 4.300 stroke crankshaft that took a lot of abuse with no fill and the old set of Mopar brand ductile iron caps with ARP main studs The first motor had 4 ductile iron sleeves in it due to deck damage on one side and pitting in two cylinders that wouldn't clean out at 4.375 bore size on the other side, it was a low compression pump gas motor that made over 600 HP at 5500 RPM using a stock type Eddy six pak intake and stock type vacume 440 6 pak carbs It started out with a set of mildy ported big valves 906 heads, it ended up with a set of Indy SR heads with a single plane Indy 400-3 intake and a Holley 1050 CFM #9375 Dominator carb, that combination made 727 HP on a DTS engine dyno in Klamath Fals, OR at 4300 ft. elevation I traded that car off several years ago and it is stll running with those main caps and studs The only reason I've tried the 440 source aluminum main caps now is that Mopar stop selling thier ductile iron main caps several years ago and I've used up the supply I had in stock I'm building another 400 stroker E85 motor now that should make over 800 HP on E85 with the CNC ported 440-1 heads with a set of paired shaft Jesel Rocker arms It has a set of the 440 Source aluminum main caps and ARP main studs, no fill or girdle on it It sonic tested oaky on the cylinders walls but it will end up with one sleeve in it also due to pitting

I agree. Cap failure, then comes the spread load on the saddles. A steel cap would not do this.
The fact that the crossbolt conversion caps shown are steel, gives me a warmer feeling about them. Add in the cross bolting, and how can you really say it's not a nice up-grade? If you can do the work yourself, it seems a sane as anything else.

I used the most ghetto of all "bandaids" (I hate that saying. Doesn't everyone have bandaids at thier house?) Anyway... I milled the humps off of the caps and built tool steel straps to hold all the pieces together when they failed. Guess what? They didn't fail. Know why? Accurate and late(relatively speaking) ignition timing. Roll that crank clockwise baby!!!!