Well Here goes....
The other night, I left work, and cruised home (20mile drive)... putting along in 6th gear, barely over idle, I started hearing a weird noise... like a knocking. Went to dip the clutch and I felt the clutch peddle tapping against my foot when I rested it on it. got the car home (bout another 1 or 2 miles), and parked it until I could tow it to the shop.
Figured maybe it was the throwout bearing.... pulled the trans and found soe issues with the throwout... but saw that there was ovaling of the bushing in the end of the crank... went to pull the clutch and found that as I turned the flywheel... there was some play, and the front of the crank was not turning with the back of the crank under small movements. with full rotations, the balancer did spin.... so I PULLED THE PAN......


I found that the crank had split.... now this is a fully forged 383 LT1 with a procharger/intercooler set up (I'll list pics and full build sheet below). My guess is the crank is stressed from the blower, and cracked, but in my experience.... they usually break off in the front, at the snout... I wanted to see if any of the blower GURUs on here could throw some advice at me...

#1. have you seen this before?
#2. Do I just replace the crank and appropriate parts, of look for a stronger one?
#3 Just give me your input PLEASE....
1996 Z28, 383 stroker running through long tubes, aluminum driveshaft and 4.10s in the rear (M6)
BUILD SHEET:

PSC1 Procharger 8.2lbs of boost
450rwhp
(approx 3,000mi on build)
INTERCOOLER
MSD 6AL
MSD Blaster coil
MSD BILLET OPTI
60lb Motron injectors
4 bolt main corvette block
cleaned
bored .030
align honed
square decked
cam bearings and freeze plugs installed
scat 4340 forged crankshaft
scat pro series I beam rods - 2-ICR6000-7/16
srp forged pistons - 14cc inv. dome
clevite 77 H-series rod and main bearings
Total seal rings
rotating assembly balanced within .1 gram
melling hv oil pump
melling pick up screen
melling hardened oil pump driveshaft
fel pro gaskets
custom ground hyd. roller camshaft
comp cams roller lifters
comp cams hardened pushrods
aluminum full roller rocker arms
chrome valve covers
clevite 77 hp cam bearings
pioneer brass freeze plugs
cloyes roller timing set
lt1 timing cover
lt1 oil pa n
arp head studs - 12pt.
fully ported lt1 heads
2.02/1.6 valves
stainless steel valves
isky .600 lift springs
combustion chambers polished
runners matched to heads
BBK 58mm throttle body
Cat bypass
Pacesetter LONG TUBE HEADERS
MAGNAFLOW MUFFLER
Whalboro 255 HV in tank fuel pump with external helper pump
Granitelli MAF
LT4 Knock Module
centerforce dual friction clutch

 

Whoa!!! Sorry to hear dude. No advice here, but i want to subscribe!

 

buddy of mine had an carbed olds 403 just over stock in his 89' z28 did the same thing in the same exact spot it could be a balance or alignment issue

 

thanks for ur condolences ... lol. As far as the balancing issue, all I had to go off of was the builders word saying it was balanced.... within 1gm or something like that (see build sheet.)

Keep up the comments, and Ill keep the thread up to date.

One of the other sites I posted this on, got the suggestio to go with a BEEFIER crank called "Callies Dragonslayer".

 

Not really a fan of the dragonslayer, especially for a 450 hp build.

Sucks but it seems that everybody has minor casting issues. A local guy just did the same on a NA motor. Seems to just be bad luck in some cases.

How do the main caps look? Pulled the bearings yet?

 

I would have a machine shop look at it and check the alignment of the mains. I personally think you were just unlucky and got a bad crank with a casting flaw. However a bad align bore could cause the stress necessary to break that crank.

 

Nah, had to much work at the shop today.... only got to pull the procharger and tubing and intercooler out.... Hopefully tomorrow, I will get a look at it.

As for the DRAGON SLAYER, do you think it is overkill, or not enough for a 450 build... and remember, im only putting 8 lbs of boost though it right now... I plan on pushing 12-15 lbs with the smaller pulley....

 

Just seeing if anyone has anymore input....

 

Cranks usually break for 2 reasons...either it was abused or it was a a bad crank from Scat. If you where the only one to put the 3000 miles on the new motor (we're presuming the rotating assembly was new) then unless you, at some point beat the snot out of your freshly built motor, it's fairly safe to presume you got a hold of a bad crankshaft. Unfortunately, when something like that happens, you will really want thoroughly check any parts you may choose to reuse, not to mention checking the block thoroughly as well. There is a reason a Callies crank costs more than a Scat and if you plan on putting 15lbs. of boost through the motor, I would seriously consider purchasing the best parts you can afford when it comes to the rotating assembly. There will be a lot of guys that will tell you how theeir motors run just fine with some of the lesser quality parts installed in them, but it's my opinion that you should buy the best parts you can afford and also know their limitations.

 

Thankyou very much, I appreciate u taking the time to write that. Yes everything was new, and I am the only one to drive it. I do not abuse the car due to tuning limitations (still not rite) other than all the dyno pulls it has recieved.... Honestly I have done less than one hand full of burnouts and as u know with boost, I never even needed to shock the motor by side stepping the clutch, Thankyou and keep the insight comming... I will be installing the BEST that I can AFFORD.