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I have never built a Merlin with that much HP. The last one I did build needed to be line bored and the lifter bores were off and had to be bushed. Basically re-machined the block, had to square it all up. If going BBC based I would use Arias. That is what I used when I built stuff that big. Go Hemi.
 

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Seen one of them in a 540 blown alky deal in the 1500 hp range.

Second pass in a drag boat, split # 2 main web.

Replaced the block with a Dart cast iron, same guts, made 1545 hp on the dyno ?

Didn't have any trouble after that !
 

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If you're truely building something with 2500 HP no cast aluminum block is gonna hold up. You will have to have a billet piece.
 

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steelcomp was here
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If you're truely building something with 2500 HP no cast aluminum block is gonna hold up. You will have to have a billet piece.
What about the New Century? The KB 6000series will handle it. So would one of the Trick Flow/Sonny Leonard blocks if you could find one. All there was up till not too long ago was cast blocks at more than twice that HP. There's more to it than just HP as far as what a block will handle.
I agree you'll need a dedicated-design race block if you're going aluminum and that much power, not just an aluminum BB Chev. reproduction, which is what the Dart and Merlin alum. blocks basically are. That kind of power will turn them into scrap, the Merlin especially. I don't think the Brodix 8B would be up to it either.
 

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Highaboosta
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Here's the Arias / New century block,

What makes this a better design is that it is a Y block with cross bolted main caps. Some call it a skirted block.

If you get the 10.7 " deck and use a tall deck manifold with spacers and 1/8" gaskets on one side and 1/16 gaskets on the other side, everything lines right up. That takes a 7.3" connecting rod.

I've got 12 years and many hundreds of hours on mine.

Here's the link to New Century Performance,
http://www.newcenturyperformance.com/
Great people to do business with too.
 

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I use a KB600 on my alcohol motor. Doesn't make anywhere near 2500hp, but according to the guys at KB a lot of the pro-mods use that block.
kb600.jpg
Donovan makes a nice block but for what you are doing I wouldn't use anything less than their HC800 block.
 

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If you're truely building something with 2500 HP no cast aluminum block is gonna hold up. You will have to have a billet piece.
They were using cast blocks well into the 5000 HP range. The original Donovan 417 could handle 2500 easy.
Like Steelcomp said, there is a huge difference between a "race" block and a alum replacement "ZL" block.

NOW, if you talking a stock GM alum LS series block, I heard they will handle 6000 HP on Nitro at 12,000 RPM.



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New Century is the maker of Arias.
Mine is a little older I think as it does say "Arias" in the front of it?
Seems to me, Lowell told me they don't have that cast in them anymore ?

Crossbolted mains on a skirted block, head studs pull from down at the bottom of the bores like a Chry !

Lowell is really good to talk to !
 

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They were using cast blocks well into the 5000 HP range. The original Donovan 417 could handle 2500 easy.
Like Steelcomp said, there is a huge difference between a "race" block and a alum replacement "ZL" block.

NOW, if you talking a stock GM alum LS series block, I heard they will handle 6000 HP on Nitro at 12,000 RPM.

The combo he quoted is a 565 which is a 4.600 bore, and at that bore no cast block is gonna hold up to 2500 HP. You may get away with it for a while but in the long run isn't gonna live. If he were to go with a smaller bore, then a skirted type block such as new century or KB would be fine.
 

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steelcomp was here
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The combo he quoted is a 565 which is a 4.600 bore, and at that bore no cast block is gonna hold up to 2500 HP. You may get away with it for a while but in the long run isn't gonna live. If he were to go with a smaller bore, then a skirted type block such as new century or KB would be fine.
That's a good point. Personally I'd never go that big of a bore on something like that on a 4.84, even billet, and if this is a Chevrolet/roots-based build, I don't see it making 2500hp, even with spread port heads. That's a lot of HP.
 
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