SCAT superlight crank

Got a new big block superlight crank from SCAT. This one is 4.250 stroke with the 8 bolt flange. The crank weighs 64 lbs which is 7 or 8 lbs lighter than the standard weight crank. It looks nice. I'm going to pair it up with some Molnar 7.100 connecting rods.

That's light. Does it have a horsepower limit?

I'm sure it has a limit somewhere but it is going in a stock block so I'm not worried.

I see they're still not sure whether American V8 engines turn CW or CCW...

Catering to the boat market. :-)

Andy would you be willing to give up the weight savings and have center counter weights?

AndyF,

I went with the 440Source ultra light crank and their 7.1 rods. My Ross pistons came in around 524G's. I was hoping the light weight would be easier on the stock block. So far, I am unable to detect any signs of walking. Which main caps are you going to use?

Do you think the lighter reciprocating weight reduces the stock blocks susceptibility to cap walk?

What steel forging?

Looks good! Is it for a B or RB , is there a part # available for it ? Thanks

Do you think the lighter reciprocating weight reduces the stock blocks susceptibility to cap walk?

I'm pretty sure it's "yes", but is it significant? IDK.

What I don't understand: we KNOW the crank manufacturers understand windage, pumping loss, and aero shapes at that speed in f/s. If they don't, the volume of information available is huge.
Assume they don't want to change the shape of their basic product on the shelf.
Why not offer directional profiling as a post-manufacture operation with a high markup? Even 2 hours of shop time with a grinding wheel (not a head porter or master machinist, just an adult) contoured to do only the nose is an improvement. Position it, feed in until the improved shape appears, back up, dil over to the next.
Remember, the bow wave and trailing wake are resistance (uses power to heat up the oil and crankcase vapor) regardless of power output - it's there with the spark off.

The question is how many people will pay for that extra work for what's on the shelf?

I agree at some point you'd think these guys would change the shape to a better form. But if what you have is selling, and 99.99999% of the buyers don't say a word, is it worth it?

1 HP less than the amount that breaks it.

The one in the picture is for an RB engine. Summit carries these or you can order them direct from SCAT. Here is a link to Summit: https://www.summitracing.com/parts/sca-4426015-3/overview/model/3

They also have low deck cranks. I have a fully machined superlight 3.90 stroke crank in my 470 engine.

Here is a couple shots of the SCAT superlight in my low deck 470 engine. The 470 crank was the first Mopar superlight and they fully machined it including gun drilling and profiling the rear flange. It looks like when they put the superlight into production they deleted some of those features. I worked with SCAT back in 2015 to develop the first Mopar superlight. Or maybe it was the first low deck superlight, I don't really know for sure. The engineer I worked with had some dimensions but not others so I had to round up some info for him.

Real nice looking crankshaft. The rods as well.

The picture seems dark compared to the work we've come to expect over the years. I have to wonder if the lighting wasn't adjusted from the usual, or maybe if something isn't sprayed on the journals to cut down on glare.

My point is that soliciting this as a feature DOES NOT EXIST. No one asks if you want it, or even mention that it exists. The effect is "our product is as good as can be made", when that's certainly not true.
A question never asked has no answer.
I used to offer it an a feature on the Harley-Davidson cranks I sell*, but (since it's not done by the manufacturer, but contracted out) it became $$$ long ago. I still encourage this work and give advice on where/what in the engine booklets I write**.

* http://www.victorylibrary.com/stroker-flywheels.htm
** http://www.victorylibrary.com/books1.htm

PS: really light weight crank also has the effect of raising its natural frequency (in Hz), and pushing every destructive harmonic order higher in the RPM range.
This is probably within the capacity of any good S.F.I. 18.1 damper, but it can be both good and bad.
Good: the harmonic order you now have at the top of your scale may no longer affect you.
Bad: you may inherit one from below your normal power range.

The new crank has cosmoline sprayed on it so the journals aren't shiny. I didn't adjust the light setting on the camera to brighten the image. I did place my usual white background behind the crank though. Always trying to provide good photos for Moparts.

4340 non-twist forging is what the catalog says. I don't know any more than that. I've used these cranks in several engines with good results. They balance without too much work and the rear main seal stays dry so I'm happy.

Back in the day, a crank's original forging (hot from the die) was flat, with the four throws opposed 180° apart. The two 3-dimensional 90° throws are obtained by twisting the crank: pulling one throw up and one throw down. The process was called "struck and twisted".
4340 is (IIRC) the frequent material of choice for cranks and other forgings that have large cross-sectional changes.

target bobweight?

I'm surprised no one has asked.

Bobweight for the engine I'm building should be around 2300 grams. I don't have the pistons yet so I'm just guessing where they'll come in at. The Molnar rods are fairly light for a 7.100 long rod.

Consider the shapes of the leading and trailing edges of the counterweights.

Experiments with shape run quite a while ago showed that the rounded leading edge and tapered trailing edge had the least amount of drag. So, I would say the crank manufacturer knew EXACTLY which direction the crank would turn.

R.

I bought a new K1 4.500 RB crank a few weeks ago, it has the same counterweight shape on the leading/trailing edges as described. This seems to be the conventional wisdom these days.

I'm sure that the engineer at SCAT was going with a tear drop design on the counterweights. So a rounded nose and a v shaped tail. I talked to the engineer a few times when he was working on the CAD file for the superlight but I don't think we discussed the shape of the counterweights.

The bob weight of my 572 with Molnar 7.100"x 2.200" rods, Molnar 4.500' x 2.200" crank, Diamond 4.500" flat tops is 2238 grams
Doug