What is the different between a 3.1 crank and a 3.4? I have a nice 3.1 crank and it looks identical to the 3.4 crank. Can I install it?

I could be wrong, but I think they're interchangeable. Now if you were swapping pistons, that would be a different story.

[This message has been edited by Blacktree (edited 08-24-2008).]

They're the same, though you might want to keep the stronger of the two, if you have one of the stronger versions. Casting #981 and 282, iirc.

quote Originally posted by RotrexFiero: What is the different between a 3.1 crank and a 3.4?

Nothing. They're the same.

The difference in displacement between the pushrod 3.1L and the pushrod 3.4L engines is attributable to their bores, the 3.4L having a larger bore than does the 3.1L. The "throw" of their crankshafts contributing to their engine displacements is the same because the crankshafts themselves are the same.

Good liuck with your 3.1L/3.4L project.

Thanks you guys are awesome!!!!

quote Originally posted by RotrexFiero: Are the head gaskets interchangeable....again they look very similar.

No; bigger bore on the 3.4; the gasket should be that much bigger too.

Edit: The diameter of the three large holes in the gasket, that is.

[This message has been edited by Stubby79 (edited 08-24-2008).]

If you can find one get the 981 variant part number 10110549

This is a standard 981 that has been nitride hardened. They used them in the McLaren Grand Prix Turbo 3.1

quote Originally posted by RotrexFiero: What is the different between a 3.1 crank and a 3.4? I have a nice 3.1 crank and it looks identical to the 3.4 crank. Can I install it?

While they are the same casting number, the 3.4 has larger, HEAVIER pistons, so the 3.4 crank should be balanced heavier than the 3.1 crank, by a little bit. Check the diameters and depths of the balancing holes in the counterweights.

[This message has been edited by Will (edited 08-25-2008).]

quote Originally posted by Will: While they are the same casting number, the 3.4 has larger, HEAVIER pistons, so the 3.4 crank should be balanced heavier than the 3.1 crank, by a little bit. Check the diameters and depths of the balancing holes in the counterweights.

You think a few grams each would make that big of a difference on a stock set-up? I know on racing engines, they are balanced very precisely for high power and RPMs. But then, I was told once by a junkyard parts engine builder that GM has their engines balance very good, like, being able to spin up to 7K RPM from the factory. But he was talking about late 60s through 70s V8s.

What is the weight difference between a 3.1 piston and a 3.4 piston?

A 3.4 piston has 6% more bore area than a 3.1 piston, so an educated guess would put it at 6% heavier.

quote Originally posted by Will: Check the diameters and depths of the balancing holes in the counterweights.

Ditto.

[This message has been edited by Will (edited 08-26-2008).]