Dart Big M 9.8 short deck

[Velocity Vector]

We dynoed these last week they did make decent power 632hp/573tq/5800rpms

[Geronimo36]

When I put the two side by side it does look like big pic is a tall deck and the small is short deck what do you guys see?

I can't tell from the picture on the right, it's too blurry for me but the pic on the left is a short deck.

[Velocity Vector]

Yea it's hard to tell and will make ya go cross eyed

[PatriYacht]

The other thing I'd be concerned about is the cranks. That's an item with a finite life expectancy in an engine that turns that fast. hard to tell if it's on it's first hour or it's last.

That was the problem Brian had. He puchased 2 used supercat engines and both of them broke their cranks within a couple of months. These engines are built to turn 7000 rpm all of the time so they really have a short life span.

[Chris]

That was the problem Brian had. He puchased 2 used supercat engines and both of them broke their cranks within a couple of months. These engines are built to turn 7000 rpm all of the time so they really have a short life span.

Built to turn 7K. But how many have been turned 7600?

[PatriYacht]

Throttleman thinking to himself," Dam I missed that wave..."

[Velocity Vector]

What the heck was that noise, I heard Merc puts them on the dyno at 7K & come back to check on them in 3 hrs.

[BUIZILLA]

yeah...
okkkaayyyyyyyyyyyyyyyy

[Chris]

Yeah- they're made to do that. But no rev limiter is friendly to ANY crankshaft so depending on how many misses...

Plus, Merc racing can tell you exactly what the service limit is on the crank. Crank breakage is rare as the average racer knows what that number is.

[Velocity Vector]

So the old saying "there is not a part made we can't break" still holds true.

[Chris]

Madara says it best "...could break a bowling ball in a sandbox."

[DAREDEVIL]

Instigator and others turned them all the time @ 7600-7800 RPM.
Crank is billet, and yes they do break ....LOL

[Chris]

Are they cut from billet or are they forgings? I thought billets were only used when a forged blank that would accommodate the application was unavailable.

[DAREDEVIL]

Are they cut from billet or are they forgings? I thought billets were only used when a forged blank that would accommodate the application was unavailable.

THEY ARE BILLET, maschined out of one solid block of steel !!!!!

[DAREDEVIL]

Ok, here is the little i know......

TALL DECK Bowtie block 4.500 bore ( also dart or merlin 10.200 are allowed )
Billet maincaps
Lunatti billet crank 4 inch stroke
Lunatti billet rods 6.585
Crower special ground cam ( merc spec for supercat )
JE dome'd piston ( merc spec )
Brodix BB2 heads
Brodix Single plane intake
Demon 1050
Drysump
12:1 compression
Thunderbolt ign.
Jesel valvetrain
Jesel cam belt
Merc aluminum valvecovers
dual cooler bellhousing
RPM range MAX 7800 RPM
HP 820+ on DYNO
Torque 700 +
Cubic inch 509

Thats kind of how the specsheet is to build the supercat engines for the spec class.

I may be wrong,,,,but i don't think so. i have 1 here.LOL

Also that kind of would explain the block change , hence the loss of the drysump.
A person just told me u can't run a wet sump pan on a drysump block ,,,oilinghole ?????? Don't know 100% but its what i have been told.

And they do turn up to 8000 + in some boats.

The best person to talk to on the supercat engines would be JD Byrider, team owner Tony Marcantonio !!!!
He still runs them in his cat and has a couple of spear ones ....LOL

[Velocity Vector]

Ok here's what I found out,
510 cid, 4.500" bore 4.00" stroke rods are 6.585", These are long rod motors so the Diamond pistons had to be custom made the pins go thru the oil ring lands.

12:1 Hammers that were taken out & 9.5:1 Hammers that when back in


Looks like both of these pistons intersect the oil ring on the pins to me

[PatriYacht]

Typical 540 uses a 4.25 stroke and 6.385 rods. That means that the wrist pin is .075 higher in the supercat engine. Doesn't leave a lot of room for the rings. And the short skirt makes for an unstable piston that will have less ring seal. This would work better in a tall block.

[PatriYacht]

I'm searching for a short-stroke (3.829") Callies Lightweight crank for Merc Supercat motor.

Anyone have one of these lying around? If so, please call me at 313 283-8148.

Thanks in Advance,
Brian

That's from the ad Brian posted. Put that stroke in a tall deck block and you have a lot of room for long rods.

[DAREDEVIL]

Ok here's what I found out,
510 cid, 4.500" bore 4.00" stroke rods are 6.585", These are long rod motors so the Diamond pistons had to be custom made the pins go thru the oil ring lands.

12:1 Hammers that were taken out & 9.5:1 Hammers that when back in


Looks like both of these pistons intersect the oil ring on the pins to me

If these pistons came out , then it was never a talldeck and /or a real supercat engine.
Per speca they had to be talldecks and they have a 4 inch stroke !!!!!!!!!

not 510........509 CI !!!!!!!!

[Geronimo36]

Ok here's what I found out,
510 cid, 4.500" bore 4.00" stroke rods are 6.585", These are long rod motors so the Diamond pistons had to be custom made the pins go thru the oil ring lands.

12:1 Hammers that were taken out & 9.5:1 Hammers that when back in

Looks like both of these pistons intersect the oil ring on the pins to me

Any idea how many hours were on the old engine? Also, look for scuff marks on the sides of the piston...

I'm running a 6.70 rod in my 580's compared to the normal length rod... Downside it it's harder to get pistons off the shelf and it puts the pin up higher in the skirt but it's a better rod angle ratio. 250 hrs on refresh and the pistions were perfect!