How much power can a cast crank support?

C

clutchdust

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I'm planning the build on the four bolt block I picked up. I'm estimating around 400-425hp at the flywheel. Surprisingly (to me, at least) the crank that came in that four bolt block was just cast. My local machine shop tells me that 400hp is about the most you can throw at a cast crank and count on it staying in the engine. I really don't like it that close.
Is he right?
 
yes

of course, I've had 750 on a stock crank without problems - but you do need to be careful.... and with how cheap 4340 cranks are, why risk it?
 
look at the price for balancing a new crank with existing rods. Most likely you want to bore the block and need pistons .030" over... so you need a set of forged pistons, you want a forged crank ... probably cheaper and less painful to buy a whole new rotating assembly that comes balanced....

what's your plan with the block? does it need to be bored or will a re-ring job do ???

I know the previous owner of my 79 beat the living crap out of his L48 with flat tops and Edelbrock heads.... CR was about 9.8 or so and he had the RPM cam in there so he was reving it very high.... the engine is still in good shape, the cast crank took all the abuse....

is this engine for the Vette?
 
I'm planning on reusing the +.030" Speedpro hyper pistons and ARP'd stock rods in my current engine. Current motor has less than <10k miles on it so I can't see throwing away perfectly good parts just because of that. I've been told that both should be sufficient for what I'm building.

Block is a junk yard take out, stock bore, so it will need to go +.030 just for my existing pistons. Block will get fresh bearings and obviously rings. Will be reusing my current Comp 276/282 roller cam but installing my AFR 190 heads with 1.6 rockers and Bowtie intake (until I go FI).

Like I said, I'm expecting around 400hp out of this combo and have been told that's pretty reasonable. I also don't think it's so much as to blow the bottom end out of things. Besides, I'm not drag racing, so there won't be any launches to speak of. Just the occasional "spirited" Sunday drives.
 
I think you'll be fine. It takes more than that to break a crank, Gbak for example is running a cast crank and 11:1CR and a hot cam.... I didn't think a cadt crank was a good idea for his combo but it seems to be holding up just fine..... and he's making way more than 400HP.......
 
Thanks. Kind of what I was thinking. I've heard a wide range of opinions on the issue. Seems like keeping it secure is a bigger issue than actually breaking it, hence the 4-bolt.
 
It'll be fine right up to when it breaks.

Really, harmonics and torsional load is more likely to break it than making HP- it's all about how the load is applied.
 
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