I've only ever seen one broken cast SBC crank, came apart at the front counterweight to #1 rod throw. But I only had the leftover parts and don't know what caused it, for all I know it could have been dropped on the floor.

Forged crank is 'stronger', yes, but there are different kinds of strong. Forged crank can flex and twist without permanent damage, but a cast crank is more rigid and if it doesn't see any shock loading that exceeds its tensile strength... I'll just say that there is a lot of money spent on fancy non-twist steel forgings that doesn't need to be.

 

Is this why cast pistons live too? brittle but high strength - and are rods a different story?

 

Yeah the crank came back with a clean bill of health and at the very least, its a nice 10-10 grind thats not too sharp in the fillets. Using shitty plastigauge, it said it had .003 clearance when i got it and i rolled in some "better" used lower shells that made it .0025. Dont really know but thats what plastigauge said. It hated the new shells and edge wore the lower pretty hard indicating that crank was flexing pretty hard under big power.

Im working on it now and am about ready to put it on the stand tonight and berry hone the cylinders using....beer for a lubricant. LOL

 

I think cast pistons can be better than hypereutectic units in the land of cheap ass. I never hurt a single piston but if i examine all of them really close down in the oil ring groove where its slotted for drainback, they all have a small crack from skirt torture but im just gonna reassemble it anyways. Seen lots of em like that and they rarely get bigger. Its a super sharp casting edge and prone to crack no matter what.

Also, stock old school rods are amazing in a compressive load but the fail point seems to be at a lower HP the longer the stroke gets. We proved a 383 and 3.75 stroke will bend a stock rod in a C shape at 820 whp where my 3.48 stroke 350 lived at 738 whp. I bet the 350 would have lived at the 820 whp fail point of the 383 motor but not by much. Non floating wristpins and the harder con rod angle in a stroker seem to grab the rod and bend it in an arc with stupid power. Being a compressive load i thought they would never fail but......they will at some point. 1000 crank HP is really pushing the stock rod and powdered metal later rods shouldnt even be considerd EVER.

I also bent the hell out of a rod in a 350 around 1100 hp when it leaned the carb on a 1.39 60 ft launch and it just nipped the spark plug and went into detonation which amplified the rod loading and stomped the rod 1 inch down in the bore at TDC. Detonate any stock rod turbo motor above 700 hp and its gonna buckle a rod. Once again, its all in the tune because there is no insurance policy.

 

Reassembled the GRENADE over the weekend and in the proper tradition, recycled every used part i had in the shop! New/used bearings that came out of a motor that lost its cam during break in. They looked great and were the right size so i used em. All the bottom end including the Erson TQ30H cam and lifters is all the grenade stuff and the heads, head studs, rockers, trick flow pushrods and chrome balancer are from my old chevelle blower motor that puked the block a few years ago.

The heads are massively ported 993 casting deals with 2.02-1.60 valves and Erson springs i have had since i was in high school. Hell of a lot better head than the pocket ported 487x ones the grenade ran 9.30's with. Plus some good used ARP head studs to step the ol' GRENADE way up into "race motor" territory. LOL

I set the ring gaps at .027 top and second and pretty much didnt measure a damn thing. It ran before so who gives a shit? I think its all going to end up in my kids 70 chevelle with a saginaw 3 speed manual transmission and some chineese 57mm turbos mounted to some flipped Patriot untra shorty headers. Its a decent turbo setup for Ebay junk and with a 100 shot of spray might make 900 hp. Probably not going to push it as far as it went before but it should still be fun just making the motor breathe fire again.

Its become like a family member to me so pushing it to the max and potentially blowing it up would hurt my feelings these days. Ha ha.

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Oh yeah.. i forgot the best part. The old GRENADE had plain cast rings worn to at least .090 gap and this buildup is sporting....wait for it.......moly rings. Holy shit this motors not gonna know what to do with all these "race parts"!

 

Sounds dangerous..

 

Its going into this car that currently has a weak suck 350 with a tunnel ram thats more for looks than any real power. The kids 18 years old and needed to learn how to drive something lame first. Were gonna swap the 4 speed for one of the 5 saginaw 3 speeds i have laying around and clutch dump em at 6 grand till we break every one i have all in the name of dragstrip fun!

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Alright i actually honed it with PB Blaster because i didnt want to waste the beer.

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looking forward to seeing it run

 

are those three speeds strong? ive got one laying around i thought about abusing

 

Are those ROL gaskets?

 

They are better than you might think. The sag 4 speeds like to blow up 1st gear pretty easily but the 3 speed places 1st out in the middle of the case and is much stronger. We beat one in a TT 66 Impala with a 5500 rpm dump on slicks and powershifted it to an 11.79 in the 1/4. It twisted the input and output shaft slightly but no teeth were cracked. The car had posted 640 whp so we were being really stupid with it and i doubt it would have lived thru too many hits like that.

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Enginetech generic rebuilder gaskets. Used em a few times with turbos and they seem to do as good as my favorite corteco white paper ones.

 

Its halarious to find this build still ticking, I love it.
Im curious though ever use a cast crank that was machined 10 or 20 thou?

 

If it helps..
I know of a .040 under gm steel crank ( not re nitrited either) run 7.7@ 189 389 ttsbc @ 3000lbs, glide

 

Reducing the crankshaft journal diameters does not significantly weaken a crankshaft. In fact, if the grind is done properly and the fillet radius is increased an undersize crank will be stronger than a standard crank.

 

I have a factory cast 400 crank that's been cut down by .200" on the mains to 350 size and .020" under on the rods, made 620hp in a N/A 388, still perfect.

 

Now id think thats pushing it because of the same reason GM increased the main journal size in the first place. Crankpin overlap. Those crank throws get mighty weak as a casting thats turned that far and if i ever heard about broken cranks was when somebody did a budget 383 based on a stock 400 crank. Yet most all aftermarket steel cranks are still based on the 350 journal size. A lot of people dont like the 400 journal on a high RPM motor because of excessive bearing speed on the face but it might all be baloney.

 

X2 the cut and radius is key .

And for cuts I didn't even know .040 bearings existed until I ran them in my boosted mule stock 396 back in the day.

Looking forward to the Chevelle Buildup--- start a thread in the Builds section - It's winter - we need entertainment

 

Sorry for the late thanks. Just curious since id like to try and use/save a crank that has been part of a balanced assembly but unfortunatly cut 20 on the rods.

 

20 on the rods wouldnt scare me. The grenade is 10-10 with a .040 overbore and a sleeve in #1 cylinder. That aint exactly cherry!