how far can you push cylinder pressure/or horsepower when using the older Mopar performance Siamese mega block with 3 cross bolt mains/arp studs/ with a good 8 bob weight crank/2400 bob weight, 4.375 bore, block in not filled, dont need to go over 7200 rpm - screw power adder. Is the boost the limiting factor ? Or can you scale it with a horse power like a stock 440 block ?

I have been told that a mega block is not that strong. That it can break when you go over thousand hp. So I would like hear how far others have pushed this mega block. Facts from people going over thousand hp with a power adder. Who has done it ? Have you had any stress cracks in the block from high cylinder pressure from using a blower without a crank support ? Do you have 300 1/4 mile hits on the block with no stress cracks forming around the webbing or any other area that would split the block? I know detonation will destroy any block. So lets assume you have a good safe tune up with 1200 hp from a big blower or 500 nos shot.. Hows is you mega block holding up when your way over 1000hp ?

I have not ran one myself at those power levels but dear God they have nearly twice as heavy of cylinder walls, decks and mains from the old blocks. One would think durability wouldn't be a problem. I wouldn't give it a second thought.

I have seen them split through the cam bores with a blower and no crank support at about 1000 hp.

Sum ting wong.........

Ok but can you rule out that it didn't happened because the engine was out of balance( harmonics) or detonation? Someone on this forum has to have pushed the block over 1000hp and made it live or is 1000 hp the limit to be on the safe side. Switching to an aluminum block is expensive.

Usualy when in tune the boosted motors appear to be easier on blocks. 3 examples; stock 340 block blown roots 650hp, stock 360 block (and cast crank) turbo 850hp, stock 440 roots 850hp. Non have broke. First two with many runs and street use. I run a N/A Mega block at over 900hp. I personally have 525 passes after buying used where it made similar power for yers.
Doug

Well, I've had no wedge megas, but a few hemi mega. I have one now that just dynoed at 1260, and I'm going to spray it with at least 400 on the hit. I've sprayed them with 500 numerous times at slightly less na power so I've had zero issues doing so, unfilled, and at 4.53 or bigger bore. The ones I've done in iron have no center counterweights either, and they all see 8200 + in the traps.

Breaking a good mega block at 1000hp sounds like a serious mistake on some part of the build, and or tune.

I agree, detonation is probably is responsible for any breakage. With a good tune I'd be confident it would handle north of 1500hp.

The original street and OEM "race" cast grey iron hemi blocks where used in both top fuelers and funny cars until Donovan and Milidon came out with cast aluminum blocks in 1971 or so.
I'm sure all of those old motors far exceeded 2500 HP even back then on nitro fuel
On your deal I wouldn't worry at all up to or over 1500 HP with a good tune

Yea but some teams retire the good BAE TFXtop fuel blocks after 50 runs....but we are not running nitro. The only reason I am concerned is because this information came from a reputable builder. Obviously the block could be less susceptible to stress cracks at a lower power level. The block would also live longer as long as the tuneup is not on the edge. No lean misfire to upset the load balance. Only 2 options - blame the block failures on a bad tune or a time related high load metal fatigue factor. Lets take into consideration metal fatigue because an engine is dynamic. Its cant be in perfect balance over the entire rpm band. Lot of people will over balance a crank if they know its going to operate strictly hi rpm band as a race engine. Have you ever stood next to an engine on a dyno when its at wot while making over 1000hp ? You can feel the ground shaking at high rpm. Its not like watching it on the engine on a video. The mean piston speed, rotating weight on the bearing increase as you turn up the rpm /boost/power. Keep turning up the power with a steel block... caps start to fret more on these non dowel main caps- lots of force trying to push out the crank out of the block. The firing order has some effect on flexing the crank in the block. Some people think a non Mopar firing order may give a v8 better load balance.. So no two engines are the same. Who can say why that mega block split in half? The other builder told me he seen the same type of failure at 1000 hp . What caused the metal fatigue or stress cracks before this broke ? These block could be tested for durability. I doubt its every been tested by the manufacturer to find out it limitations from a flexing metal fatigue issue.

You can get away with murder in an 1/8th mile, but keep bending the coat hanger back and forth without lifting and then what happens? Aluminum caps in the stock 440 block helped you get past 650hp. I Need more people to say the balance was off on these broken steel blocks to rule out metal fatigue flex factor over 1000hp. I asked Barton this question at one time and he said it would handle more but like anything you take your chances. Even a Carrillo rod can break for no reason. So this Mega block in a bracket car, the temptation to speed up the supercharger is a battle of the mind. One side thinks of going faster and the other side thinks about the cost of a broken block. Just one more pound of boost ! Of just 1/2 degree of timing... just leave it alone.


Thanks to everyone that takes the time to read and give their time, experience, or opinion .

545 inch roots blown,I am more concerned with melting pistons than making more than 1000 HP!!

I have been beating on a 572 Megablock for the past 12 years. Race almost every weekend all summer. Probably has close to 1000 passes on it. Also use Nitrous up to 400 hp during heads up events(5-6 a year).I'm sure I am way North of 1000HP during these events.
Still going strong. Bearings always look good on teardown every year.
Block is now 4.53 bore.
Mike

What blower and how much boost?

Its a Whipple 510R. The 510's are very nice efficient super charger. I am only spinning it 6 percent over and see 14 psi flat across the rpm band. It flows 3200cfm at 12000rpm . So 1500 hp is very doable. Car ran 9.0 at 3600lbs with a 3.5 gear last year. Mostly was a street car. Putting the 4.10 gear back in now. More fun to just race it at the track then play on the street.