Just out of curiosity what are the limits of a factory 440 block. Can they stay together at the 800 HP level? I have always heard that the factory blocks are only safe to around 650 HP and wondered if alot of guys are pushing that limit with good reliable results with proper block preparations (steel main caps,main studs,girdle,etc...)?

I had a 505 that did about 100 dyno pulls before it cracked the main webs.

Your better off starting with a good sonic tested 400 bock to make that kind of power
Your best bet is to buy a good race block to start with so you can turn it up some more later
Don't waste your money, time or effort on any girdle on a RB block It does nothing to strengthen the main webbing

No not very long so wouldn't even consider it. Start with a low deck motor, it will last longer, but it will still fail at that hp in a matter of time. How long, depends on the quality of the build.

Some haven't made it past the dyno, some, a pass or two, others built pretty good , 200/300, after that its just a time bomb, take your chances and expect a failure.

I’m not big on throwing out horsepower numbers because I’ve never had on on a dyno but my 440 (500 Stroker) lasted 275 runs going low 8.60’s @ 2500 pounds. No concrete, no gridle and when I took it apart to freshen it was cracked up through the mains. I bought a Keith Black block and a mega block after that.

Has anyone seen a correlation between block strength and stroke at say 7000 rpm for both?

ex. longer stroke = more prone to cracked main webbing?

Definitely.

The 3.75 crank seems to be perfect for the strength of the block. we've ran 650 hp 440s and hit them with big nitrous for years without cracking a single block. As soon as you introduce a big arm, things get dicey. Some of that is because the strokers are more prone to detonation with a narrower tuning window (although the same could be said of dome piston 440s).

Another consideration is piston speed, We prefer to keep the rpm down on our stock block strokers.

Bob wieght is part of th equation, and often you can reduce rpm if the build is head limited, like small ports on a bigger stroker. But in order to make the stresses equal, the rpm has to drop by the same percent that the stroke increases. If i read the formulas correctly, to any change in either bob wieght, rpm, or stroke will increase the stress by the square of the change. And it is cumulative of the answer. Double the stroke from 3 to 4 inch stress at 3 in would be a facter of 9. Double the rpm, you have to square the first answer, or 9 multiplied by 2 squared, or 9 x 4, equals 36!
With that info, a 400 with a 383 crank cut down to 3.54 stroke and bored to 4.375 makes 426 cubes and small port heads makes a lot of sense for a bracket motor.

I've observed the block breakage vs stroke thing within my local circle too, but no one seems to mention it when discussing block strength.

There also seems to be something in the aftermarket cylinder head chamber shapes (oem copies verses the better burn heart shaped ones) that has an effect on block durability within a certain power/rpm range.

To get this math i posted right, i had to do more than one edit. It is now correct as i understand the math.

Just remember there is a big difference between saying it worked for X amount of years or X amount of passes. For some guys 275 passes would be a lifetime but for a weekly bracket racer not so much. I had a good friend that would brag about his big block Chevy in his front engine dragster still being together for over 25 years every time he got drunk. He hasn’t raced the car in 24 years. True story.

I took over 7.5 lbs. out when going to the stroker assembly vs. the stock 440 stuff!

From what I've gather online from message boards and other member's posting thru the years is 650HP is "comfortable" 700hp is about the max for it to live an okay period but will eventually break. 800HP..will break sooner than later IMO

And like Pittsburgracer alluded to. Some guys will brag about how many years there stuff has been together, but yet might race 2-3 times a year...12 passes a year vs 200 passes is a HUGE different in the maintenance of a race car.

It's not the build that's important, so much as the tuning and driving. There's a lot of racers who tune by the "hold my beer and watch this" method and they also run their junk well after it should have been put on the trailer and taken home to figure out what's wrong.

How many A-holes blew up their junk trying to get "just one more run?"

Unsurprisingly, these are often the same guys you hear crying about "weak parts" and "bad builders."

Girdles and aluminum maincaps are beneficial because they dampen vibration and add rigidity, which is good for the same reasons as with fixturing machine parts. Vibration=chatter and broken tooling. S/F....Ken M

Isn't how you make the HP and use it important as well? 750hp turbo or procharged 440 in a light street car with a safe tune that doesn't hook would probably last forever. 750hp N/A 440 in a dedicated strip car is probably on borrowed time

With the heads and parts available today, you can trip and fall and still make 2HP+/CI.

I’m at 840 in a 400 block. We’ll see what happens this season. I watch things as close as I can and keep the tune in check. I’m sure one Day I let go of the button and that will be it. I hope that when the day comes I may actually be able to get my hands on a KB block. Here’s to dreaming.

Well Wookie, you have a B 400 block, so that's better. Nice job on the 840 hp

I'm sorry, I've wandered into the children's room.

I'll bet you are a lot of fun at a party. NOT!!!!!!!!!!!!!!!!!