2v crank - how tough?

[Dark_Horse]

A friend of mine (who is pretty knowledgable about mod motors) and I were discussing the toughness of the 2v PI crankshaft. I was explaining how I would like to upgrade the internals as well as upgrade to the cobra crank. He claims that there has NEVER been a problem with the crank on 2v's and that an upgrade wasn't needed. How can this be? I've read very few threads on spun bearings and even less on broken cranks from these motors, but I always assumed that the crank was also a weak component of the internals. I would assume upgrading to the cobra crank would be a good way to bullet-proof any upgrades performed on the internals. What do you guys think?

 

[squeak93]

Its the stock rods that are the issue in the 2v's. A cobra crank is GREAT insurance as long as you have rods to hold the abuse as well.


Tell your friend that cast vs forged is a no brainer.....

 

[2000GTdriver]

Stock 2v crank is usually good up to about 500hp.

 

[trinity_gt]

In terms of reliability, a forged steel crank > cast iron. If you want high-RPM durability, forged is the way to go.

Having said that, the 2V cast crank is a pretty stout piece and is definitely not the weak spot in that engine. I suspect Ford went to the forged steel part on their high-revving 4V variants (the automatic Mach1 has a 5800RPM redline...) because the steel part is better able to deal with fatigue associated with high-RPM versus the cast iron part, not because it could better handle outright cylinder pressure and torque. The forged crank has additional counterweights mid-length which suggests it's balanced dynamically differently than the cast part.

As has been said, the rods and pistons are the really weak parts of the engine. If you're building a stout street motor and expect limited RPM (i.e. 6K or below), the cast crank is probably a viable alternative to the more expensive steel part. But if you're going all out for a 600HP, high-RPM monster and you're that far into the engine, it only makes sense to get the stronger, more durable forged part for the extra margin it gives.

 

[Gearbanger 101]

Stock 2v crank is usually good up to about 500hp.

I've actually heard closer to 600hp provided the engine stays within or around stock 2V RPM limits.

 

[99RioRedVert]

I'd say anyone quoting you a number is just pulling it out of their you know what. There just aren't enough documented cases of cast crank failures to deduce an accurate failure level.

Part of it is that the cast crank is pretty stout. I have one in my motor, which makes 470 rwhp. The other part is that anyone building a 500+ hp motor usually puts a cobra crank in it as a matter of course, so we don't really have a lot of cases to look to. Building a 500+ hp motor costs a lot of $$ so why would you scimp out on a $700 part that is so vital to the motor's functionality?

 

[twogts4us]

In terms of reliability, a forged steel crank > cast iron. If you want high-RPM durability, forged is the way to go.

Having said that, the 2V cast crank is a pretty stout piece and is definitely not the weak spot in that engine. I suspect Ford went to the forged steel part on their high-revving 4V variants (the automatic Mach1 has a 5800RPM redline...) because the steel part is better able to deal with fatigue associated with high-RPM versus the cast iron part, not because it could better handle outright cylinder pressure and torque. The forged crank has additional counterweights mid-length which suggests it's balanced dynamically differently than the cast part.

As has been said, the rods and pistons are the really weak parts of the engine. If you're building a stout street motor and expect limited RPM (i.e. 6K or below), the cast crank is probably a viable alternative to the more expensive steel part. But if you're going all out for a 600HP, high-RPM monster and you're that far into the engine, it only makes sense to get the stronger, more durable forged part for the extra margin it gives.

EXCELLENT post!

 

[Dark_Horse]

+1, good info guys. My plan was to go all forged internals including the crank but thats a few years into the future As for my buddy who claims the stock crank is indestructible, it's good to know the reasons why forged internals always win. I thought this was ALWAYS a no brainer, so who knows

 

[TGJ]

Some facts to consider:

1) Forged Crank = More weight = Less HP than the Cast Crank.

2) The fastest N/A 2V cars run Cast Cranks, both KenB's N/A 2V and FastestN/A2V ran the stock cast crank.

3) 750 RWHP has been done on the Cast Cranks without issues.

4) 8000 RPM has been done on the Cast Cranks without issues.

5) Forged Crank = More money than the Cast Crank.

It technically is an upgrade but at what point do you need it?

 

[CobraRed_96_GT]

There have been many people running stage 3 cams/springs revving to 7k on cast cranks. Many people over 600 on them too. I did it for insurance due to the money sunk into a shortblock, and my forged crank cost as much as ARP head stubs so it's not that hard of a decision. More weight is a bummer though.