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Merlin III vs Big Dart M. Im on the fence between the 2 blocks. Im building a blown alcohol motor and I need to decide between the 2 blocks. Any opinions on which way to go? Im sure this is a loaded question about the details.
 

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Merlin III vs Big Dart M. Im on the fence between the 2 blocks. Im building a blown alcohol motor and I need to decide between the 2 blocks. Any opinions on which way to go? Im sure this is a loaded question about the details.
i believe the merlin 3 has billet main caps as the dart big M does not, at least mine doesnt

i like the dart block but i didnt like having to have my brodix heads drilled and tapped for the additional head studs
 

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i believe the merlin 3 has billet main caps as the dart big M does not, at least mine doesnt

i like the dart block but i didnt like having to have my brodix heads drilled and tapped for the additional head studs
You can buy a Dart block with your choice of main caps, and there is no reason to feel like you "have" to have the heads drilled for the extra studs, but they are a good idea for an engine with lots of pressure in the combustion chamber, and that's certainly not specific to a Dart block.

A lot of people got turned off to Merlin blocks when they had a bunch that had oil passages machined wrong years ago. The ones I was aware of and exposed to were Merlin II blocks.
 

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Bill Mitchell sold the Merlin iron block tooling off to PBM years ago. Personally I wouldn't use one to built a lawn tractor.
Never heard of someone HAVING TO machine their heads for any block. All aftermarket blocks have the provision, its not exclusive to Darts. But the heads will bolt to them all just like a stock block.

If you don't need billet caps, the BluePrint Engines block is a excellent block at a great price, and USA cast in the same foundry that does stuff for the big 3, CNC machined, and dead accurate.
If you need the billet caps, the GM Race Block is my choice.



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I had a customer bring up 3 block last weekend a Merlin 2, Merlin 3 which are older blocks and a new Dart Big-M with billet caps.

As I have posted many times I have had issues with the World SBC with lifter bore issues ETC.

I had 2 customers in the shop and they were devastated on the condition of those 2 blocks once probed out.

The first block I set in the CNC machine and probed out was the Merlin 2 block the cylinders on the left bank were in spec but the cylinders on the right side were moved a head .034 and guess what the lifter bores would not even clean up at .904 had to bush them.

That being said I also noticed on both Merlin 2 and 3 block the intake lifter bores were only 1.250 tall because they had counter bored the lifter bores to deep as you can see in the pic.

I am sure the engines should make more power with the proper seat timing events and lifter bores corrected or to blue print.


I had to machine the lifter bushings to the length of 1.375 as both blocks for some reason has really short lifter bores like the Gen 4 BBC. To put a 55MM cam tunnel in those block you would have to use a tall lifter bushing to make it work. Also had to clearance the block on one side from the deck to the top of the exhaust lifter bore on the left bank.


The Merlin 3 block the cylinders were in spec but the lifter bores just made it at .904 no bushings needed.

I ran into these problems about 12 years ago with the World SBC and always I was always told they would take care of me which never happened.

Hope fully the new owners of World cast Iron have taken care of these issues I have found over the years.

IMHO In the long run your best to deal with a company that does all the machine work in house and has a way to check and qualify their machine work !!!!
 

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Discussion Starter #7
Thanks for the insight, great knowledge here. So Im scratching the Merlin off the list, Im going to go with the Dart. I talked with another friend of mine today that is an engine builder for drag cars and he said the same thing as GN7. Go with the Dart or Bowtie.
 

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Anybody try the Midwest Racing Industries blocks?
I have wondered about this block myself. For someone considering a nodular cap, standard cam location/diameter, I think the Blueprint Engine block is a much better deal.

The only benefit I see to the MWI block is if you were looking to run a raised cam, 55-60MM cam core and steel caps. But if that is the case, and you're considering those options, you shouldn't be looking at some import block.

The MRI block as some great "features", but if its at the expense of inferior machining and material, the features lose some glamour.
It doesn't take a lot of "fixing" to have the cost of the block to shoot right past the cost of a Dart or Bowtie race block. And your still stuck with an unkown/questionable iron.



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Google dart vs. Merlin. What l saw was the Merlin customer service was lacking.
As far as the Blueprint block and price. Im would guess they make a good block, but for 300.00 more why not get a Dart? And know that you are getting a block capiable of 1000+hp, because its been done a gazillion times before.
Be safe, schick
 

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I have wondered about this block myself. For someone considering a nodular cap, standard cam location/diameter, I think the Blueprint Engine block is a much better deal.
I actually had a Blueprint block in the shop and checked it out for cylinder placement, lifter bore placement and size, cam tunnel placement and sizing. Everything was spot on.
 

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So a bit off topic but at what power level do most of you consider steel caps "mandatory" in a BBC?
 

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My K motor is a Dart block with iron caps and I think you are familiar with the power level.;)
Yea, that's kinda what I'm getting at. My SS motor has billet on the 3 center mains at less that half of what your deal puts out...
 

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So a bit off topic but at what power level do most of you consider steel caps "mandatory" in a BBC?
TUNE TUNE TUNE! That said,
From personal experience of abusing stock blocks, I have come to the conclusion that studded mains aren't the weak link. We have failed a OEM blocks every way possible, but never the caps or webs. Seen my share of fretting, but never anything that led to bearing issues.

IMO, the point of steel caps becomes MANDATORY depends how the power is made, the RPM, stroke and use.
Drag racing verses circle racing would be a factor with me as well.

I think anything above 850 deserves at least splayed iron caps, and a stronger block, even if I have run more with OEM blocks, they are not really up to much more than that. JMO



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