I'm building a 408 with a Scat cast stroker crank, Procomp rods, Icon forged pistons in a 360 block. I took the components to the machine shop along with a standard 318/340 harmonic balancer because its supose to be internally balanced to get it all balanced. The shop is telling me that they need to use an external balancer or they will have to put a lot off mallory in the crank to get it balanced. Has anyone else run into this problem?
Balancing a Scat cast crank
- Thread starter Valkman
- Start date
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i went to the Scat website and it was no help. According to Summit it's inernaly balanced https://www.summitracing.com/oh/par...-_-shopping-_-srese1-_-scat-engine-components
yellow rose
Overnight Sensation
It all depends on Bob weight. How does summit know what the Bob weight will be?
Most of the time there isn't enough mass in the counter weights of a cast crank to keep it internal balance.
I'd trust the machine shop. BTW, this is why I tell people to spend the money for a steel crank. If you do make it internal with Mallory, you'll eat up most of the savings anyway.
At this point, I'd leave it external and run it.
Most of the time there isn't enough mass in the counter weights of a cast crank to keep it internal balance.
I'd trust the machine shop. BTW, this is why I tell people to spend the money for a steel crank. If you do make it internal with Mallory, you'll eat up most of the savings anyway.
At this point, I'd leave it external and run it.
it doesn't really bother if it needs to be external, this a street motor, but I just to make sure what I'm getting is right.
nm9stheham
Well-Known Member
It depends on the rods and pistons you are using. The SCAT cranks are designed to internal balance with a bobweight below a certain limit. If your bobweight (which depends mostly on the piston and rod weights) is too high, then it won't balance internally without mallory or external weights. In fact, the catalog states for this crankshaft "Internal Balance, May Require Mallory". See here , on page 18 at the bottom:
http://www.scatcrankshafts.com/wp-content/uploads/SCAT_Crankshafts_Catalog_Nov2016.pdf
The SCAT rods are fairly light but the Icon forged pistons are not as light as you may need. Which rod and piston PN's do you have? (I am guessing PN 2-ICR6123-2124 for the rods but there are 6-8 PN sof the Icon pistons.
Also, look at any tech sheets sent with the crank? Does it specify anything about bobweights?
http://www.scatcrankshafts.com/wp-content/uploads/SCAT_Crankshafts_Catalog_Nov2016.pdf
The SCAT rods are fairly light but the Icon forged pistons are not as light as you may need. Which rod and piston PN's do you have? (I am guessing PN 2-ICR6123-2124 for the rods but there are 6-8 PN sof the Icon pistons.
Also, look at any tech sheets sent with the crank? Does it specify anything about bobweights?
yellow rose
Overnight Sensation
I'd be surprised if your shop was wrong. It's pretty hard to spin a crank and not know whether or not it's going to need a bunch of weight.
If you don't care (I've done 800 plus HP engine that were external balance) just do it external. Is it a stick or auto?
yellow rose
Overnight Sensation
What are you going to do with the transmission end? Is it going to be internal or are you going to use a weighted converter or a different flex plate?
nm9stheham
Well-Known Member
At this point, knowing whether or not the stock 360 damper weight at the front, and the stock type TC or flexplate weight imbalance at the rear, are going to have adequate external balance weight is unknowable. You have a 4" stroke, which will require more external weights than the stock rods and pistons. You have lighter rods; pistons are unknown; either being lighter is going to help lower the needed external weight.
So it depends on the exact rod and piston on whether the stock 360 external balance parts will be adequate.
Of course, you can take the stock 360 pats and modify them to have more external weight.
So it depends on the exact rod and piston on whether the stock 360 external balance parts will be adequate.
Of course, you can take the stock 360 pats and modify them to have more external weight.
nm9stheham
Well-Known Member
Yes, that is all well known. What I'm trying to explain is that in the case of the B&M flexplate for the 360, the external weight it provides may still not be enough. Ditto for the stock 360 damper external weights. The longer stroke changes everything.
So was there no datasheet showingdata with the crankshaft bobweight? Normally they have data somewhere as to the bobweight at or below which the crank can be internally balanced. I've looked on the SCAT site but no joy....
So was there no datasheet showingdata with the crankshaft bobweight? Normally they have data somewhere as to the bobweight at or below which the crank can be internally balanced. I've looked on the SCAT site but no joy....
would it be safe to say if the shop was able to balance the rotating assembly, would make it all good to use a standard flexplate and TQ.
nm9stheham
Well-Known Member
Well, the neutral balance damper and flexplate would impose the cost of adding the Mallory to the crank. If you COULD use the standard 360 damper and flexplate, or modify them, that would be cheaper. And I am with YR and others.... nothing wrong with the external balance weights.
I am not saying that they can't balance it with the stock 360 damper and a B&M 360 flexplate.... I am just saying they might not be able to do so, with these parts unmodified. Just be aware if you go that route.
That is why the interest in the exact pistons and rods and the SCAT bobweight data.... it might give a better grasp on what is possible.
I am not saying that they can't balance it with the stock 360 damper and a B&M 360 flexplate.... I am just saying they might not be able to do so, with these parts unmodified. Just be aware if you go that route.
That is why the interest in the exact pistons and rods and the SCAT bobweight data.... it might give a better grasp on what is possible.
nm9stheham
Well-Known Member
That is good to hear. That sounds like what the OP may have. May I ask the total balancing cost?
If you go to the CNC Motorsports web site, my kit cost $1501 internally balanced. Add $60 more for the Mallory. Not sure what balancing alone was.
We balance a lot of these 408 strokers to internal balance you need to get the bob weight down to about 1700 grams.
nm9stheham
Well-Known Member
Wow, that is getting reeeealy on down there. What off-the-shelf rods and pistons get you there? And do you need to lighten them further?
I use Scat rods, the Mahle pistons with 1.5mm rings and King bearings (they are a little lighter) The rotating assembly I am working on now came in at 1718gm
Morten Stroem
Cuda67-Mortens
Hi Valkman, I 'm into a similar situation as you was. How did this end?. What options/path did you choose and what was the outcome ? Reason for asking is that I have an internal balanced 408 stroker setup and I have unbalance in the engine/gear. My manchine shop advice me to arrange for external balance of the damper and the converter. Could it be that the the SCAT crank and the .Chrysler Rod 6.123 is a bad design? (means difficult to balance?)
Engine ....................................................Small Block Mopar 408 inches stroker.
Dyno Numbers .......................................452HP at 5500 RPM , Torque 308 lbft at 3000 RPM, 473 lbft at 4400 RPM
Cylinder Heads .......................................Pro Comp CNC Heads
Bore & Stroke ........................................4.000
Comp .....................................................10.5:1
Intake .....................................................Mopar M1 Single Plane
Crank .....................................................Scat crank, Stroke 4.000
Piston .....................................................Forget
Rocker Arms...........................................Procomp Electronics, PCE261.1085. Rocker Arm Ratio: 1.60, full roller, stainless steel.
Crankshaft..............................................Scat stroker crank
Camshaft ................................................ ISKY, .525 lift – duration 232, tappet lift at 050 on 112
Balanced ................................................Internal balanced, balanced assembly
Connection Rods ....................................Chrysler Rod 6.123
Engine ....................................................Small Block Mopar 408 inches stroker.
Dyno Numbers .......................................452HP at 5500 RPM , Torque 308 lbft at 3000 RPM, 473 lbft at 4400 RPM
Cylinder Heads .......................................Pro Comp CNC Heads
Bore & Stroke ........................................4.000
Comp .....................................................10.5:1
Intake .....................................................Mopar M1 Single Plane
Crank .....................................................Scat crank, Stroke 4.000
Piston .....................................................Forget
Rocker Arms...........................................Procomp Electronics, PCE261.1085. Rocker Arm Ratio: 1.60, full roller, stainless steel.
Crankshaft..............................................Scat stroker crank
Camshaft ................................................ ISKY, .525 lift – duration 232, tappet lift at 050 on 112
Balanced ................................................Internal balanced, balanced assembly
Connection Rods ....................................Chrysler Rod 6.123
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j par
Well-hung Member
My cast scat stroker crank was internally balanced with a boatload of Mallory....
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