Im currently rebuilding my engine and wanting to push 15-20psi with a D1SC intercooled procharger. I was wondering how much power the stock, cast crank out of a crate engine 350 can take before i would need to got forged. I heard it will hold 700. Is this true? Any sueggestions are highly recommened. Thanks

 

700 crank HP on a stock cast crank? Nope. Well, maybe, but not for long, that's for sure.
You'd need a good forged one for that power level, cast steel shouldn't even be considered.

 

They claim that anytime forced induction is ran that it should be changed to forged. Some people have gotten away with doing without though. But with that Supercharger setup your already dumping some serious money into the setup might as well add another 800 or so (roughly) and add the best crank you can buy! Dont forget about the rest of your shortblock as well. What are you thinking of running for rods and pistons? If your planning on pushing that much PSI thru that motor you better get that blcok throughly checked and make sure that you have the TOP of the line fastner that you can buy!

 

Anyone have any pics of a crank bustin' for camaroracer85?

 

There's a guy on turbomustangs.com running 10.03s with a stock cast crank, but it's the exception not the rule. With a blower that pretty much clinches it IMO, you'd better go forged, perhaps even BBC snout. It also depends on wether or not you're afraid of killing the motor it's on. If it's a motor you don't care about a cast crank is fine, but if you're actually putting money into it get the forged crank.

 

I would think that the procharger system would be a lil less stress on a cranks snout though but then again I havent built up a procharged engine yet.

 

I have witnessed a friend of mine go 10.60's on a cast crank. The engine has been going for 3 years now. It's a 350 with a nasty shot of N20. That might not be a direct comparison to how boost works but I guess anything is possible.

 

It's not the boost that makes it an issue as much as it's the fact he's running a blower IMHO. If he gets a cog drive or something like that which will help reduce crank stresses he may be able to get away with it. Think about how much HP stock accessories take compared to a blower though, that's quite a bit of torque being applied to the snout.

 

I am running 6.60's @ 103 in the 1/8th on a stock crank. Motor has lived for 2 years so far 200 shot of spray with tons of bottles through it. However I dont have the added snout pressure of the blower.

 

Good point. I didn't think about the stress applied to the snout.

 

I have the stock cast crank and 2 bolt block with 140,000 miles on them. I have been running this setup for 3 yrs now. And i abuse the **** out of it. I drive the car regulaly. And not just cruising it around. I beat on this thing. I have tried to break it, holding it to the rev limiter for 30 sec at 15lbs of boost, wont break. (I'm just waiting for an ascuse to build a new engine combo, but no reason to yet.) The vacuum line feeding the wastegate has came off while i was driving it and i saw 25+ lbs of boost for a few sec. Still didnt break. Runs great still. But, turbo boost is alot less abuse on a crank than blower boost.

 

with arp main studs they can take quite a beating ive heard 500 horses with no problems. i dont believe they can take as much in a forced induction application

 

The power it can take, especially when you make it using boost isn’t the issue. As you increase power with boost you don’t increase peak cylinder pressure like you do with N2O or NA, but instead the amount of usable cylinder pressure is available longer during the power stroke (more area under the curve rather then a bigger peak). The result is that you don’t put as much more strain on the crank as you would if you made the extra power some other way and you’re less likely to break it (at some point you’ll probably bend it before you break it though).

The problem with your specific question is that the blower is crank driven and that is where you’re going to have issues, that I don’t know there is a good solution out there for…. I’ve seen cranks cut for double keyways and they still end up wallowing out crank pulleys/balancers and breaking crank snouts…

 

Excellent post! You are right on the money about longer useable cyl pressure being easier going on the crank. Im the guy Draconic refered to on turbomustangs. I dont recommend doing what i am doing on a stock motor but it does show you how tough a stock engine really is when turbocharging. On crank snouts, i used to blow the balancers off my roots blower SBC and the fix is to drill the crank snout out for a 5/8 fine thread stud and torque it down to about 200 ft.lbs. I didnt double key it or do a big snout at all. Just stock and tightened to hell. How do i know it works? I nitrous backfired at 14 lbs. boost on a 160 shot at 6000 rpm when i popped a head gasket and got flame where it didnt belong and BENT the three ribs on the balancer
. The key got a little loose and tried to shear but held. The crank was arrow straight still and is still in use 3 years later with no problems. When you tighten the hell out of it, the clamp load holds the power, not the wimpy key.

 

I think they have cranks out now with the larger big block snout on them for small block now.... maybe that would help?

 

Yeah, you can get a BBC snout on a SBC crank.

 

For what its worth I had a cast crank in a 60,000 mile goodwrench motor that broke at first journal with a Weiand 177 street supercharger after about a year. It was in a 67 pick up and rarely saw the high side of 5000 RPM. I think it depends a little on the particular crank, maybe a different GM cast crank would still be doing ok?