ringmaster72

iTrader: (8)

I know scat cast cranks are not great, but what about the forged? Any issues with a procharged 383 in the 600-700 hp range?

hrcslam

Eagle cast is bad, do not even look at, Medusa territory.
Scat cast is good, not great, keep the RPMs low.
Eagle and Scat Forged are both good for high hp high RPMs.

Always go forged if you plan on high RPMs (horsepower).

nitrous2fast

iTrader: (2)

That advise isn't always right. The rpms a crankshaft can handle are more involved than that. There is something I have always been taught and it seems pretty true typically. The more rpms in an engine the less HP it will handle i.e.( 500 hp at 7000rpms or 600 hp at 6000 rpms; both involving the same part) This is just an example though and not involving something specific and not always true but typically so.

Forged is the better of the two and I like scat more than eagle. IMO

Catmaigne

iTrader: (6)

There are a lot of variables. 600-700rwhp or flywheel? What RPM do you want to spin to? How good is your top end? How fast are you going to spin the blower?

A centri blower puts a lot of strain on the snout and it isn't uncommon for a crank to shear between main #1 and the first rod pin from excess belt tension and more torsion overall. A tight blower belt and too much drag from the compressor is bad news for a cheap 4340 crank.

Things you should also consider:
- More stroke = faster piston acceleration and the likelihood of breaking it
- The same goes for high RPMs (bc resonant peaks + acceleration)
- Most aftermarket cranks have bores drilled through the centers of each crank pin (this is where it will fail most of the time, see pic for what I mean)
- Gen I and II SBCs are already at a disadvantage compared to Gen III+ when it comes to crank deflection/torsion because of their firing orders

The Scat/Eagle stuff is probably going to need to be reground out of the box because their quality control isn't top notch. Add the cost of machine work in and you could have bought a nicer crank. K1 and Compstar are supposed to be better when it comes to machining but they're all inferior china forgings.

I'm sure the Scat/Eagle 4340s are adequate if you stay on the conservative side.

I went with an OEM GM forging (#532, from the ZZ4/LT5/HD Vortecs/etc.) for my current build. It's not 4340 but is pretty damn beefy and I'm not going crazy with RPM. It's also stock stroke.

waltsfastz

iTrader: (4)

Im using a eagle 4340 crank, im also shooting for that 600-700 RWHP. I know eagle is inexpensive compared to other components but go to some of your local machine shops and see how often they are used. Mine was within tolerance as far as journal diameters out of the box, The rotating assymble was balanced before assymble so I cant speak for that aspect of it.

ringmaster72

iTrader: (8)

This one is used, was in an existing engine from a member here and he is asking $250 for it. I was going to go dragonslayer when i got around to building it, but thought that if this crank would hold it it was a good price and would save me some coin.

hrcslam

I completely agree. There are many other factors. But, a forged Crank (or anything for that matter) will handle more horsepower and more RPMs than cast, everything else being equal.

And since Horsepower is the product of TQ and RPM's you need more of either, or both, to increase horsepower. TQ can be increased through stroke or pressure (or both). At a certain point VE limits are reached and therefore pressure maxes out for a certain combination of parts. Changing up the cam to move the max VE to a higher RPM to maximize horsepower is when cast is not so good and forged is.

NA will have a limiting factor on RPM's (which equals horsepower), Supercharged engines change the scenario as given an example above by Catmainge. Turbo or N20 will have a pressure problem (force vs resistance). But, in all scenarios the Forged will work better than Cast. And for high RPM stay away from cast (OEM might be fine though, but I'm not sure of too many people using OEM 400 cranks in an LT1), 7000 RPMs on a cast stroker isn't a good idea IMO.

So while there's more to it than what I stated earlier, it's also safe to say what I did earlier too in absolute terms. But conversely, it's not safe to say to run a high RPM cast 383.

ringmaster72

iTrader: (8)

Cast is not an option. I am either buying this used scat 4340 or I will just wait and get a dragonslayer later. I just wanted to know everyone's thoughts on the scat 4340 for 600-700 rear wheel hp

Purple Poncho

iTrader: (1)

True story: My last engine had a cast Scat 9000 crank in a centri supercharged application and I had the belt tight as hell. Ran it from 2001 to 2009. Ran mid 130's mph in the 1/4 with a high of 138 at 3850 lbs, so 600-700 I would say. I kept the revs under 6200 and had a good tune . I still have the crank and will use it again someday.
Was this the crank of the century, builder of the decade, assembler of the universe?? Dunno but it is a real life account.
Has quality gone down since 2001? Possibly. Who can say?
Having said that if I was spending money on a new stroker crank right now it would be a Scat forged.

ringmaster72

iTrader: (8)

That's what I am after, real world experience. I just don't want to let this deal go if it can handle what I am planning .

myltwon

iTrader: (1)

Truth of the matter, bad quality cast cranks aside, there are so many variables involved in the success and failure of a motor that trying to pinpoint any single part as the make it or break it point of the infinite combos out there is an exercise in futility. More than likely the percentage of survivability of all cranks is likely around the same. Rpm, tune, machine work, assembly, fuel, and an adequate valve train are points of greater concern imo. Quality rotating assemblies fail, but more often its a symptom of failure in another area of the above than a forged piece of metal actually being the cause.

hrcslam

Well said. I agree.