Dart Big M or Merlin III

What is a better cast iron block for my combo? I have ran a 10.2 marine block for the last two seasons but I'm at its limits(1600hp). The main caps are starting too move around a bunch. I would like to step up to the 1800-2000hp.

Blown alky BBC,4.310 bore,4.00 stroke,11.6:1 comp,Dart 360's ported,14-71 Littlefield/Kobelco,1/4 mile drag race application,2100lb altered

 

The fact is that either block will do the job with splayed caps. !0.2 is really tall for 4" stroke, just curious about what rod length and compression height do you use?

 

I don't remeber off the top of my head. I will dig up the info tonight. I'm going to switch to a 4.250 stroke when I need to cycle my parts out.

 

Just curious why you feel the 10.2 is too tall for the 4.00 stroke? Would a slightly longer rod not be a good thing from a number of points of view provided the motor package wasn't too high? Would be inerested in your thoughts either here or in a PM. We had wondered about using some 11.2 or 10.7 stuff we have kincking around here, with 4.00........

 

For what it is worth Jim Oddy and Billy built us a Blown BBC and they use the Dart Big M if going Iron block, we tried the Merlin 3 and it lasted one meet (4 runs) before splitting in the head bolt area, Dart Big M is still going with numerous seasons of low 6 second passes. (best is 6.06@225 in 2250lb altered)

Cheers
Marc
PIGFISH Racing

 

If your at 1600hp now the Merlin III would not be a good choice, it would be reasonably max out. The Big M would be a little better deal but you should be looking at the Merlin Pro steel or an Aluminum New Century block for longevity and a better investment.

As far as what's the disadvantage of using a tall deck when you don't need one? The taller the deck the futher the heads get out from under the center of the manifold. That's why you see the very short decks in very high output naturally aspirated motors. The closer you can get the heads to the center of the engine the straighter the air flow and closer to the source equates to improved flow efficiency. There's other advantages but that's the main one.

Blessings.........Ron Clevenger.

 

I have been using the Merlin pro block for 4 years (9.80 deck) and have had zero issues with it, running 1500 hp. I am stepping up to around 2000 hp this year we will see what happens.

 

I agree, but only in the case where common carbs and packaging restrictions apply. Current Pro Stock would be an excellent example of this thought process.

If the packaging restrictions were to go away, but common carbs remained, then one could still make an argument for the shorter rod (lower rod/stroke ratio), because of the better early vacuum pull imparted on the carbs [for drag racing or short burst applications].

In the remainging cases though, such as IR throttles or slide throttles or forced induction or a dry manifold or EFI/MFI, there is no dependancy upon keeping the heads close together and therefore running a short deck and short rod.

The rod length and rod/stroke ratio are then open for evaluation in terms of mechanical and combustion considerations specific to the application and fuel at hand. Piston velocities, thrust loads, piston dwell, inertia loads, mechanical efficiency, etc.

I don't have any data or experience one way or the other, but I can't picture why a supercharged 10.2/4.0 motor wouldn't be better than a 9.8/4.0 motor with shorter rod, all other things being equal? The supercharger might or might not move up a smidge depending upon what is done with the manifold, so the CG of the motor might or might not raise up a bit?

 

New Century Block

If I had the extra cash I would go with the New Century but I would need to buy a new oil pan and gear drive. Also if your going to order a New Century I would order it with .904 lifters and for a larger cam bore(55mm)

 

I run a 10.2" Merlin 3, 480" blown alcohol. 4.5" bore x 3.76" stroke. Done 46 7.0 ~7.3 second passes without any issue. Only thing I did to it was enlarge the 7/16 head bolts to 1/2" studs. Same bearings have been in for 20 passes and still look new. Damn heavy lump of Iron, but nice. I agree with previous post. if $$ isnt an issue, and weight is... the Arias new centrury block is a nice piece.

 

Or a nice shiney CN billet block for just a few $$ more. Can have it cross bolt or splayed, wet or dry, with options........

 

Merllin III's are not spectacular blocks. The Merlin pro's are way better than the Dart big M. But the Darts are better than the Merlin III's.
If you can't find a good Merlin Pro, then go Dart.

 

Are they still making the Merlin Pro? Its not on their website? Also what are the Donovan D500 blocks like?

 

block

I have a NEW C/N billet block...#1048Y... it IS the ultimate. 481x race ready w/ head stud kit. $7800.00
Steve 585 647-3492 or ss3raceteam@yahoo.com

 

I've had problems with the Merlin 3's cracking in the deck from the head bolt to the cylinder on a few blown engines. Never had a problem with the Dart Big M's. I also agree that for a more serious blown chevy, I would consider a New Century. There's plenty of advantages to gain from this style of block on a blown alcohol engine making over 1600+ HP.

 

The merlin 111 is really only a new block replacement with better than factory tolerances.The merlin pro block is a totally different block and much
stronger and is designed for 2000+hp configurations.As wannabe said the pro block would be my choice over a dart,but the dart is better than a merlin 111

 

Dart Big M

What's the first thing to give grief on the Big M?

deck cracking or what?

 

Usually a crack develops from the lower head stud hole between the cylinders and migrates over into the cylinder wall.

Blessings...........Ron.

 

Ron

I've cracked enough truck and Mark IV blocks that way, but not a Big M or Gen VI.

For a Big M, is this still the first place to fail?

 

That would be setting them up. What a friggin pain!
They come out of the box so messed up. Sanding like crazy on all of the freeze plug holes so they don't leak, tapping every thread and plug as deep as they should be, finding out how far tight the mains are, (usually 3 though tight on the rear and all over the ballpark on the rest), seeing if the cam alignment machining is close, the decks, then grinding to make your front cover fit, your flywheel room over the rear plugs, etc.
But once you get them right, they stay really true.
Then the grand-daddy of them all, trying to create a messed up- screwed up contraption to fit a starter to the proper (driver) side of the block to clear a real oil pan.
Every time I do a Dart, I curse myself for buying another one. I guess I never learn. Done about 10 so far.
No, Merlin pros are not in production any more, but there are lots around in good shape.