I found a new Mopar siameese mega block, new in the crate. It was dated 6/7/2007 on the crate box. It's not a raised cam block. I'm considering another build, so i'm just starting to collect parts now. race engine only,

I also have some indy 440-1 cast heads. The engine will be heavy, but I will go with what I have.

Best cube size?
max safe hp level?

The block is cnc done it says, I see notches in the bottom of the bores. unfinished bore of 4.19 and box reads bore size up to 4.5

I'm looking for combo suggestions. compression suggestions to. This will be my winter project.

Any suggestions will be welcome. Block prep suggestions helpful, and any known issues.

You won,t hurt it with 440-1 or B1 heads. Go big on cubes to keep the revs down. A 4.375 or 4.5 stroke will yield enough cubes. That is 557 or 572 cubes. Go to as much compression as you want to run for the fuel you are willing to pay for. I run 15 to 1 and Methanol. My heads are cut down to 64cc to stay away from piston domes that are big. I only need about .080 dome to get the compression I have, and you may be able to run a flat top piston if you go 572 and still get very high compression. You will want to run a big roller if you want to make some real power. A great cam that is little known is an Isky rr735. The specs are 280/290/110 and I run it straight up. Lift is .761 with a 1.55 rocker, and that is what I ran the 8.77 with. Combine that with a 1.6 or 1.65 rocker, some very good rocker arms and springs, etc and a Dominator or Termintor injection on a 3x manifold and you are looking at 840 horse or more. I am running 8.90s at 3015 lbs in the heat at a DA of 2500 to 4,000 feet with only 528 cubes. Headers for mine are 2 1/8 by 30 by 4 inch collector that should be 12 inch long, but I can only get about 6 inches due to placement. A better combo for more cubes would be a two step of 2 1/8 to 2 1/4 or just 2 1/4 tubes with somewhere around 32 in primarys. A vacuum pump is worth 30 hp according to dyno study's. Run a 2.2 rod journal with GRP aluminum rods. This will be much easier on the motor because it is so much lighter than a steel rod 2.375 deal. I have been told by Crower that going to an even smaller rod of 2.1 (SBC size) will work and not be too small for my application. My pistons have .043 top and second rings, 4.50 bore. Low tension oil rings with a vacuum pump, standard without. Gap the rings at .022 top, .025 second.
If you need to keep the cost down, you can use a flat tappet cam with the biggest motor . The .650 lift Comp cam with 290 duration at .050 will work well and my guess is you can get 750 to 775 hp out of the package with fully ported heads.

Number 1 thing to do is sonic check... the older blocks
had core shift

Thanks MrP, getting ready for that now. I was wondering about a 4.5 bore x a 4.25 stroke for a 540 combo or a 4.5 bore x 4.375 for a 557 Maybe? I still consider a 572, but was wondering about the -1 heads for that combo. Is it better to have the bore larger than the stroke for making good power? I realize other factors come in to play. I do want to be close to 15 to 1 comp.

Does the mega block require a girdle?

an ole buddy of mine no longer with us had an older 2 bolt mega block with -1 heads and it showed signs of cap walk.

This is a 4 bolt block, but still would run a girdle if needed. Jason, do you run a girdle on your world block?

I have been running 817 hp on my mega block with cnc ported 440-1 heads for years with no problems. I have seen some running more power than mine.

I have ran an older megablock for years. Made 875 on a 4.375 bore x 4.25 stroke 511 with 440-1's. Now run 4.500 bore x 4.25 stroke 540 with B-1's makes 950. I had capwalk till I put studs in the mains. I would also sonic test real well I had to sleeve all 4 cylinders on the left bank after 2 years on 4.5 bore it cracked them and it was thin only in a strip about 1 inch wide the whole length of the block.

Is a 2007 considered an older block? I am having it sonic tested. I noticed no body has said they were running a girdle to.

Had to sleeve my mega -blk also last year also. left bank
first hole. 4.50 bore 300 runs

I guess I consider the pre world blocks to be the older ones. Mine has to be 2003-2005 vintage

testitmony is pointing towards a bore around 4.375.

I think the bigger 4.5 bore is worth fighting for. A thorough sonic check should rule out most issues. I have an early Megablock and can attest to the fact those blocks have cap walk issues if pushed hard enough. I have a heavy steel rod 4.15 by 4.5 bore setup and had cap walk issues till I put in a center weighted crank. The cap walk wasn't bad, But I wouldn't go beyond 900 hp with my old setup. Another issue I saw was block flex between cylinder banks. That might be why the newer blocks have those big ribs across the intake valley I had to go to just silicone on the intake manifold. I couldn't keep a gasket from pulling in towards the valley. Cudabin is making VERY good power with his 557 cube motor, so going bigger looks like the way to go. I have run some good numbers, but my power isn't to CBs level. Close, but not there.

alan no girdle. all
ARP hardware.

I just bought this block from Al. I think it was cast in 2007, and was probably cast by cummins. Can you guys tell me how to determine for sure who cast it, and any bugaboos to look out for? I'm still trying to decide what bore/stroke combo it'll end up with, and I have plenty of time as it'll be a good while before I have the money for a rotating assembly.