Will I break this crank?

-
Lurch59

Lurch59

FABO Gold Member
FABO Gold Member
Joined
Aug 7, 2021
Messages
162
Reaction score
102
Location
South Dakota
I have purchased a stroker kit with a Scat 9 360 4000 6123R crank. From my research this is a series 9000 crank, so a step above their stock replacement crankshaft. My build goal is 475 hp street and occasional strip use, with a 125 hp shot of nitrous at the strip. I know, a forged crank would be best but with limited parts available this is what I could find. My question is, has anybody out there broken a Scat 9000 cast crank? Hughes racing engines tell me they rarely see a broken crank. Probably the LA block is the weak link.

The RPM's will be modest as I am going to run a 3.55 sure grip. No sense in turning high RPM's in a stroker, IMO. This should help the crank live, methinks.
 
Lurch59 said:
I have purchased a stroker kit with a Scat 9 360 4000 6123R crank. From my research this is a series 9000 crank, so a step above their stock replacement crankshaft. My build goal is 475 hp street and occasional strip use, with a 125 hp shot of nitrous at the strip. I know, a forged crank would be best but with limited parts available this is what I could find. My question is, has anybody out there broken a Scat 9000 cast crank? Hughes racing engines tell me they rarely see a broken crank. Probably the LA block is the weak link.

The RPM's will be modest as I am going to run a 3.55 sure grip. No sense in turning high RPM's in a stroker, IMO. This should help the crank live, methinks.
Click to expand...
They all can break , here’s a picture of my cracked Eagle crank after a few hundred runs not going over 6,500 rpm and its a steel crank , IMO stay away from cast

39C8C272-0E76-4460-A18F-30D0B3E2FB41.jpeg
 
I'm 602hp on a stock crank. As you mentioend, i'd be more worried about the block
 
Get a good crankshaft damper something like an ATI Super Damper or Fluid Damper. These will reduce the torsional amplitude of the crankshaft. 65'
 
Make sure it's balanced properly. I ran a cast crank 408. Trapped 7200 regularly.
 
A good balance and a proper broad spectrum Hi performance damper (fluid or TCI rattler) will go far to avoid breaking any crankshaft. IIRC the stock cast cranks were 500HP capable.
 
pishta said:
A good balance and a proper broad spectrum Hi performance damper (fluid or TCI rattler) will go far to avoid breaking any crankshaft. IIRC the stock cast cranks were 500HP capable.
Click to expand...

yep, def gone 500hp on stock cast cranks.
 
From posts I've seen over the years, the problems seems to be the combination of "Eagle", "stroker" and "cast steel" cranks. I've beat on Eagle stock stroke 360 cast steel cranks for years without a problem and don't recall any pattern of failures with them or any Scat cranks. With a stroker, you naturally get less journal overlap which weakens them there and can promote flex. Then there is the quality of material and machine work.
 
I had a 357sbc with a Scat 9000 for several years sprayed to around 700hp, met its demise over a wiring glitch. Nitrous didn't come on, which caused a huge bog, but then in the depths of the bog, 225shot of nitrous comes on at about 1800rpm... on 87oct pump gas... on hyper pistons. It was pulling 2Gs when it came apart, lost just about everything except the 9000 crank!

Grant
 
weedburner said:
I had a 357sbc with a Scat 9000 for several years sprayed to around 700hp, met its demise over a wiring glitch. Nitrous didn't come on, which caused a huge bog, but then in the depths of the bog, 225shot of nitrous comes on at about 1800rpm... on 87oct pump gas... on hyper pistons. It was pulling 2Gs when it came apart, lost just about everything except the 9000 crank!

Grant
Click to expand...
I was at 539 hp and 502 tq. 9.8 to 1 comp. on pump gas with an ATI Superdamper , motor was balanced, thank goodness it didn't hurt the " R " block

7D3F7033-B477-4952-92E3-908A4717FAE3.jpeg
 
weedburner said:
I had a 357sbc with a Scat 9000 for several years sprayed to around 700hp, met its demise over a wiring glitch. Nitrous didn't come on, which caused a huge bog, but then in the depths of the bog, 225shot of nitrous comes on at about 1800rpm... on 87oct pump gas... on hyper pistons. It was pulling 2Gs when it came apart, lost just about everything except the 9000 crank!

Grant
Click to expand...
Yeah, I've got Icon forged pistons and forged rods. Things get spendy when the crank goes! At least if that happens I'll have some cool pictures.
 
Lurch59 said:
Yeah, I've got Icon forged pistons and forged rods. Things get spendy when the crank goes! At least if that happens I'll have some cool pictures.
Click to expand...

Thats just the twin gods of HP and Torque telling you it's time to move to a B or RB so you can spread the good word of Mopar.

:poke:
 
Locomotion said:
From posts I've seen over the years, the problems seems to be the combination of "Eagle", "stroker" and "cast steel" cranks. I've beat on Eagle stock stroke 360 cast steel cranks for years without a problem and don't recall any pattern of failures with them or any Scat cranks. With a stroker, you naturally get less journal overlap which weakens them there and can promote flex. Then there is the quality of material and machine work.
Click to expand...
I think the cranks are thicker at the main and rod journals that the SBC cranks. That has to help. SCAT claims cranks are 25 percent stonger than stock. The name scat needs to change though. I think of crap when I hear scat.
 
All of the cast crank issues I have seen over the years revolved around the a few years of the Eagle 4" cast crank. Scat didn't have the same issues. With that said, I have run both an Eagle 4" forged crank and a Scat 4" forged crank with no issues....my current low 10 second engine uses the Scat forged crank.

My point being, if you are throwing big money at your engine, why not spend a few hundred more for piece of mind....and, as my dad used to say "If you can't afford to build it right the first time, how are you going to afford to rebuild it when it breaks?".
 
A 4 inch stroke with 360 mains is much stronger than a 4 inch stroke on 340 mains. I wouldn’t even think of using a 4 inch stroke cast crank on 340 mains.
 
flyfish said:
All of the cast crank issues I have seen over the years revolved around the a few years of the Eagle 4" cast crank. Scat didn't have the same issues. With that said, I have run both an Eagle 4" forged crank and a Scat 4" forged crank with no issues....my current low 10 second engine uses the Scat forged crank.

My point being, if you are throwing big money at your engine, why not spend a few hundred more for piece of mind....and, as my dad used to say "If you can't afford to build it right the first time, how are you going to afford to rebuild it when it breaks?".
Click to expand...
flyfish said:
All of the cast crank issues I have seen over the years revolved around the a few years of the Eagle 4" cast crank. Scat didn't have the same issues. With that said, I have run both an Eagle 4" forged crank and a Scat 4" forged crank with no issues....my current low 10 second engine uses the Scat forged crank.

My point being, if you are throwing big money at your engine, why not spend a few hundred more for piece of mind....and, as my dad used to say "If you can't afford to build it right the first time, how are you going to afford to rebuild it when it breaks?".
Click to expand...

It's not a matter of affording it. I just don't like wasting money. If it's unlikely I'll break the crank, I'll chance it. It's like my lug nut analogy. You don't want your wheel coming off, so why not use 10 studs per wheel. Because 5 studs have worked well. Why spend money that you don't have to?
 
I run a scat cast 4” crank. 50,000 + miles over 1000 runs. Shift at 6300-6400. Pulled it apart a couple of years ago to change pistons. Changed bearings and had it balanced. The REALLY old talented crank guy said it was still straight. Probably making 400 hp at the crank.
 
rumblefish360 said:
Great advice below!
You’ll be fine IMO.
Click to expand...
And that is what I think. Take out the forces on the crank that are unbalanced parasitic and harmonic loads. Seems like compressive force from the cylinders transmitted to the crank are known,. but centrifugal forces due to poorly balanced rotating assembly at high RPM are huge. I seem to remember steel is very strong with regard to compressive strength, but comparatively weak with tensile loads. I am not an engineer, but it seems that is what I have read. I had a PhD structural engineer tell me one time, "try it, and see if it breaks"!
 
Lurch59 said:
And that is what I think. Take out the forces on the crank that are unbalanced parasitic and harmonic loads. Seems like compressive force from the cylinders transmitted to the crank are known,. but centrifugal forces due to poorly balanced rotating assembly at high RPM are huge. I seem to remember steel is very strong with regard to compressive strength, but comparatively weak with tensile loads. I am not an engineer, but it seems that is what I have read. I had a PhD structural engineer tell me one time, "try it, and see if it breaks"!
Click to expand...


If it were only that simple. Of course, crank balancing is incredibly important. But if you’ve seen how far the balance can be and not break anything you’d have a different opinion.

The crank is constantly twisting and untwisting. The damper is there to absorb those forces.

That’s why I said I wouldn’t do a cast crank 4 inch stroke on 340 mains. There isn’t enough overlap. When there isn’t enough overlap, the crank fails. Or, the crank is so thick through overlap that you needless added weigh when the better option was a steel crank.
 
You must log in or register to reply here.
-

Back
Top