Scat 4” cast crank?

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middleagecrisis said:
Seems to me like the cost to use the cast 4 inch crank would exceeded the value you will get back. I personally can’t see going to that expense and using cast pistons for a 450 hp goal. Seems like you already have a 408 that is built the way you want at the power level you want. Just my two cents worth.
Click to expand...
Pistons are Scat forged that I picked up a few weeks ago.
Goal is not 450 … that is just a guess . My goal is torque and smooth power . Since I have to address the bearing issue which probably includes a line hone etc why not spend another grand and do it right while its out ? It should be a kick with the 46rh and 3.55s
 
mgoblue9798 said:
I would use it for a street engine if it didn't wind up costing a bunch of money to balance with the rest of your parts.
Click to expand...

For what it's worth all Molnar Technologies crankshafts are internal balanced. I know of no one that's ever had to add any Mallory, but lots that had to drill balance holes in the counterweights.

Tom
 
PROSTOCKTOM said:
For what it's worth all Molnar Technologies crankshafts are internal balanced. I know of no one that's ever had to add any Mallory, but lots that had to drill balance holes in the counterweights.

Tom
Click to expand...
I think I remember seeing a video once where a shop reported the forged Molnar cranks do not have any balance holes drilled in the counterweights as delivered new. Is that true? I never had one yet and I am curious about that.
 
I have a scat cast steel crank. It's still alive. Is it the right crank for my build? no. But it's hanging on.

680-700hp @ 7-8psi
 
mbaird said:
Static compression ratio of 10.2:1.
Effective stroke is 3.83 inches.
Your dynamic compression ratio is 9.81:1 .
Your dynamic cranking pressure is 196.37PSI.
Click to expand...
That’s not right …. Cam card IVC is incorrect. Good thing I checked the events when I degreed it . He has IVC @ -2 when it’s actually 37 atdc.
Here is the correct dynamic compression.
Static compression ratio of 10.2:1.
Effective stroke is 3.72 inches.
Your dynamic compression ratio is 9.56:1 .
Your dynamic cranking pressure is 189.51PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.96 :1.
 
mbaird said:
That’s not right …. Cam card IVC is incorrect. Good thing I checked the events when I degreed it . He has IVC @ -2 when it’s actually 37 atdc.
Here is the correct dynamic compression.
Static compression ratio of 10.2:1.
Effective stroke is 3.72 inches.
Your dynamic compression ratio is 9.56:1 .
Your dynamic cranking pressure is 189.51PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.96 :1.
Click to expand...
What DCR calculator are you using? I've found that different calculators provide different results based on how it assumes you are entering the IVC event. Some assume you're using the @0.050" IVC and add 15* to the number entered, while others have you enter the actual IVC number, which should be more accurate, in theory.
 
mbaird said:
That’s not right …. Cam card IVC is incorrect. Good thing I checked the events when I degreed it . He has IVC @ -2 when it’s actually 37 atdc.
Here is the correct dynamic compression.
Static compression ratio of 10.2:1.
Effective stroke is 3.72 inches.
Your dynamic compression ratio is 9.56:1 .
Your dynamic cranking pressure is 189.51PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.96 :1.
Click to expand...
Can you list the specs your using to calculate your compression ratio?
 
mbaird said:
Static compression ratio of 10.2:1.
Effective stroke is 3.83 inches.
Your dynamic compression ratio is 9.81:1 .
Your dynamic cranking pressure is 196.37PSI.
Click to expand...
Race gas.
 
mbaird said:
Cam card IVC is incorrect. Good thing I checked the events when I degreed it . He has IVC @ -2 when it’s actually 37 atdc
Click to expand...
Be careful, the IVC at 0.050’’ duration isn’t accurate. I’ve made the mistake myself recently, need to go off advertised / 0.006’’ duration IVC.
 
I have my Dart with 408 W2 and solid roller . I want this car more as a touring road car with lots of low and midrange. Besides I have already gone far enough down this impromptu rabbit hole . If it turns out I will lose quench then I might consider it . Maybe a cam on a 110 or 108 .
 
NC Engine Builder said:
Can you list the specs your using to calculate your compression ratio?
Click to expand...
Maybe in morning . I am at work tonight .

image.jpg
 
mbaird said:
Yeah I might have to go thicker head gasket .
Click to expand...
You may be able to work the chambers on the heads a bit, bring the SCR down a little bit.
I did it a while ago, smoothed off the CNC marks by hand then polished. I gained 4cc each chamber. Requires patience! :)
 
Valman said:
You may be able to work the chambers on the heads a bit, bring the SCR down a little bit.
I did it a while ago, smoothed off the CNC marks by hand then polished. I gained 4cc each chamber. Requires patience! :)
Click to expand...
Brian polished the chambers when he ported them so probably closer to 67 cc
 
I was planning on reusing the rings since the engine only had 4 passes on it . What’s your thoughts on that ?
 
Make sure the torque converter doesn’t bottom out in the crank before you install it.

By making sure I mean mount the flex plate, attach the converter and check the measurement, don’t just measure the depth of the pilot hole.
 
NC Engine Builder said:
So no specs that you used for calculating your compression ratio? I'm curious, cause I'm just trying to help!!
Click to expand...
Block deck - 9.599
Piston cc ( -20cc )
Chamber volume 66 cc
Rod length - 6.123
Stroke - 4”
Bore - 4.03
Piston comp height- 1.465
Gasket - .040
 
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mbaird said:
Block deck - 5.599
Piston cc ( -20cc )
Chamber volume 66 cc
Rod length - 6.123
Stroke - 4”
Bore - 4.03
Piston comp height- 1.465
Gasket - .040
Click to expand...
I think you need to recheck that deck height.
 
RustyRatRod said:
Race gas.
Click to expand...
Maybe, this is running magnum heads from what I can tell, the closed chamber and quench will help a lot.

I'm running close to 200psi on 93 pump gas without any signs of detonation, on a similar setup. Zero decked at 9.573, -13cc, 65cc heads. Running an 0.40 cosmetic.
 
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