[Tom Vaught]

Quote:

"like dude sez, some blocks do, some dont..there has to be a common denominator"

The ones with the good tune-up did not fail the block, lol. Explain to me why a 67 factory block with splayed caps can make over 1600+ hp for THREE YEARS and be as good as new three years later. "Everyone knows" the factory blocks will fail at 750 hp in most cases.

There were so many "tricks" in that block/engine: Proper Tune-up, Good Machining, Right Selection of Parts, Correct Fuel for the Power, Ford Guy working on the engine, LOL! Kaase makes a lot of power too, he knows how to build GOOD engines, he was a "Ford Guy". Same deal with a guy named Tony with a Cougar that runs 6.30s at 220 mph.

Tom Vaught

[Ron H]

"This is just my opinion of course, but I have studied the Pontiac block(and other successful makes) from all angles,and as a result have made a simple crossbolted type of mains girdle ,for my application,that ties the oilpan rails together through the caps."

Can you post pics of your main girdle please?

[taff2]

Ron, it's all stripped down at the moment,I've got the block in the hot tank to clean out the water jackets ready for the block fill. I'll take some pics when it's back together and post them.

[Elarson]

Originally Posted by 65nss4spdGTO

Eric,

What's the most HP you've made with a factory block?

Thanks.

We killed (3) stock 455 blocks when we were running at about 1000 hp. None of them split up the middle like this thread is discussing.

block 1) broke the main web around the main cap bolt which let the cap come open and it fractured the crank.

block 2) had a nitrous switch malfunction; oscillating the nitrous on & off a bunch of times and it split the block between two cylinders

block 3) had a major meltdown of a piston that burned/scored the cylinder wall deeper than we felt was repairable.

Indian Adventures introduced their block right about that time and the switch was on. We're still running the same (2) IA-1 blocks.

Arnie would regularly split stock blocks after just a handful of passes on his blown, nitro combinations. He thinks they were probably in the 1500 hp range at the time. The factory "funny car" block was designed to address that problem.

Eric

[440GP69]

Ive been Chamfering the Sharp edges of the Oil holes where they merge that go from the cam jrn down to the mains to get rid of sharp edges as It just seams to be a spot thats begging for a crack to start, I believe dude is correct about the Very litte Main BulkHead Material and Another suspect is 4-bolt blocks and How deep the Outer holes have been drilled, Several Stress Risers in stock blocks to tend to IMHO if they are to live at Power, Another point is Sollid Mounts are Very Counter productive! Especially with High rpm and Hi HP, Think about your 80lb crank with Heavy steel rods and TRW's spinning at 7000rpm Imagine the forces that are trying to rip that bloc in half!! Thats Why any Weight you can get rid of there will help as will shorter stroke's JMO

[BruceWilkie]

Originally Posted by 440GP69

Ive been Chamfering the Sharp edges of the Oil holes where they merge that go from the cam jrn down to the mains to get rid of sharp edges as It just seams to be a spot thats begging for a crack to start, I believe dude is correct about the Very litte Main BulkHead Material and Another suspect is 4-bolt blocks and How deep the Outer holes have been drilled, Several Stress Risers in stock blocks to tend to IMHO if they are to live at Power, Another point is Sollid Mounts are Very Counter productive! Especially with High rpm and Hi HP, Think about your 80lb crank with Heavy steel rods and TRW's spinning at 7000rpm Imagine the forces that are trying to rip that bloc in half!! Thats Why any Weight you can get rid of there will help as will shorter stroke's JMO

Glad to see you get the picture. We can speculate all day about what does or does not cause block splits and other block related catastrophies. I wrote the reply "stress relief" (post #11) because if you take PREVENTIVE measures you will be much less likely to find yourself discussing/speculating/analyzing why/how something failed. Yes some of what I said there seems unconventional. However, it is valid! If you take major twisting forces out of the block the less likely a failure. If you can tie the main caps to minimize walk and sway and spread some of the thrust loads across caps vs taking thrust on just one, you decrease the chance of a failure. If you can minimize or eliminate a stress source you will be less likely to fail something. Failure analysis is a look at failing prevention in the first place!

[INJUNTOM]

Originally Posted by Elarson

As combustion pressure is pushing down on the pistons (and trying to push the main caps off) it is also pushing up on the heads and pulling the top of the block off. Since this load is at a 45 degree angle, there is a vertical component (up) and a horizontal component (out). The main webs are resisting these horizontal loads, trying to hold the (2) banks of the block together. But cast iron is a brittle material, very notch sensitive.....and the oil holes drilled thru the webs are a big stress concentration.Eric

This is what I think as well.

Also have to wonder how much of an effect crank flex may be adding as well.

[Tom Vaught]

Quote:

"Also have to wonder how much of an effect crank flex may be adding as well"

Say you have an out of balance tire and wheel on your car and you try and run 100 mph for a while. How long do you think it would be before you fail the hub, the wheel studs, the bearings, or the spindle?

Most would say probably not long.

Imagine that you have the same deal with a flexing crankshaft where the forces are acting like the wheel out of balance. Most often the number 2 and 4 maincaps fail first in the factory blocks or the block splits up a not prepped factory oil hole due to a stress riser from the drillings.

Good parts and attention to details will allow some parts to live a long "Hard Performance Life".

Tom Vaught

[70 bird]

Tom, Would a forged crank help with stress issues in a stock block?

[Half-Inch Stud]

My opinion is,

1. The crank less-stiff-than-cast would promote PMD Block Splitting.
2. Steel Billet Main Caps, Thick Dowels, Main Studs do not prevent/lessen PMD Block Splitting.
3. Mech imbalance, Power Imbalance, Faulty Harmonic Damper promote PMD Block Splitting. Add Over-rev to induce the failure.

4. Sloppy Rear Trans Mount & cross member, Factory motor Mounts & Slicks promote PMD Block Splitting.

5. Rear Engine Plate is the most helpful aid I can think of to prevent PMD Block Splitting.

6. My Opinion: a 2.5" tall/taller Full Main Girdle that uses oil pan rail bolts looks nice. Probably helps restrain oil rails from TWIST that is part of the force-system that Split PMD Mains up to cam: see #3.
================================================== ==
Seems to me the Main Split failure is likely induced by Rod&Slug Accel at TDC, at hi-RPM, causing that Main-Cam zone to go into tension because Main Journal is pulled up-into that CYL, whereas the other Rod&Slugs are pulling-down on Mains and so-forth. Add a 1st gear TQ multiplier that is reacted at the engine mounts (not the Trans tail mount) and the recipe is set for "Main Web-in-tension go split". As can be deduced; the Most optimal Girdle would have no purchase on web-to-cam-to-web tension. Wishbone comes to my mind.

If so, then the best remedy is a solid rear engine plate-to-frame. Rubber motor mounts, and to keep it real a front plate.

Oh yea, I could be wrong. HIS

[BruceWilkie]

Originally Posted by Half-Inch Stud

My opinion is,


If so, then the best remedy is a solid rear engine plate-to-frame. Rubber motor mounts, and to keep it real a front plate.

Oh yea, I could be wrong. HIS

Adding front plate with mid plate induces chassis flex THROUGH the block not good. Dont use entire block to try to control chassis twist. Use a disconnected from engine front plate if you want to help fight chassis twist. Lower/front/center rubber mount and rubber tail mount merely keep engine from tipping and bending the mid plate. Twisting chassis forces at the bell only, cant apply twisting force THROUGH the block much similar to trying to open a jar by the lid without holding the jar. That twisting force of the chassis can only be transmitted TO the bell housing face. A very strong part of the block.

Perhaps the vectors of forces arrows were hiding when you threw that thought out there. Then you wouldnt be wrong because you were deceived.

[INJUNTOM]

Originally Posted by Half-Inch Stud

3. Mech imbalance, Power Imbalance, HIS

And imagine the imbalace and stress inducing loads that detonation may add?

[INJUNTOM]

Originally Posted by BruceWilkie

Adding front plate with mid plate induces chassis flex THROUGH the block not good. Dont use entire block to try to control chassis twist. Use a disconnected from engine front plate if you want to help fight chassis twist.

I visualize some way of having front and rear engine plate type mounting if possible that mount to the chassis in an insulated fashion. Seems a plate on each end of the engine would help tie it together as long as the chassis isn't twising the engine.

[BruceWilkie]

Originally Posted by INJUNTOM

I visualize some way of having front and rear engine plate type mounting if possible that mount to the chassis in an insulated fashion. Seems a plate on each end of the engine would help tie it together as long as the chassis isn't twising the engine.

But then greater chassis flex occurs vs solid bracing. Your idea great for a streeter but not optimum for a racer.

[BruceWilkie]

That 55 Pontiac engine mount design team knew what they were doing.

[INJUNTOM]

Originally Posted by BruceWilkie

But then greater chassis flex occurs vs solid bracing. Your idea great for a streeter but not optimum for a racer.

A racer should have an IAII

[Half-Inch Stud]

BruceWilkie, Yea you have a point. Gotta decouple from the pair of flexible frame rails.

Stiff:
Then an ideal would be: Solid Passenger-side only Mid Plate, Front Plate, solid Trans Mount, solid Pass Motor Mount.

Compliant:
Rubber DS Mount, some sort of compliant DS Mid&Front plate; mounted to a Big-Car Motor mount for give.
--------------------------------
IA II, IA I, MR-I, any sort of proven-safe mounting method with a PMD.
================================================
I just gotta say: Got the cam dialed-in, Rhoads in, torqued 1 head, HEI in, a huge slab of wild fish in the oven with sliced garlic all over, a bowl of garlic in olive oil, and me 2nd 16 Oz Yuengling Premium. Life is good. God is good. HIS

[taff2]

RonH, pics of the girdle in the race section. I was all ready to drop the block back in the hot tank when I remembered I'd painted the lifter valley area! Looks like the water jackets will have to make do with a pressure wash out.

[Goat-Racer]

Couldn't a guy just use the soft factory style mounts at front left and front right (instead of a single centered front mount), then add the mid plate to handle the load?
Seems like the result would be the same. The soft mounts just suspend the weight but really transmit no stress to the block casting.

Just shooting for a more factory look and less frame modification.

[NHRASuperStock455SD]

Has anyone seen a block split with no other apparent reason? I believe that the block splitting is a symptom of a worse problem. IE an end result, but not the cause. I know guys that have seen 3000HP on Pontiac blocks, they never split. The biggest problems on those old motors was crank snouts. Yeah they did block reinforcement, but who wouldnt? It makes power.

Lynn