I've spoken with a few different techs on various cam help lines. I know it is possible to use big block lobes on a small block core, and it changes the duration specs, but not the lift. I can't get a definite answer on if the duration will be more or less. I know it's only 1-2 degrees, but I would just like to know.

One tech said that when you put the lobe designed for the larger journal (1.968") on a smaller journal (1.868") the specs will shrink by a few degrees. This makes sense to me. Say Comp lobe 3345B 230*@.050" will actually be ~228*@.050" and the lift will stay at .450" with 1.5 rockers.

Yet the guy today told me the opposite. The above lobe would end up being ~232*@.050. However, he also told me that you can also use a Ford lobe (2.080" journal) on a SBC. He said a 230* Ford lobe would be smaller by a few more degrees, which goes along with what the first guy said.

So, which is actually true. When you use a lobe designed for a larger journal camshaft (BBC or Ford) on a smaller journal camshaft (SBC), will the duration specs increase or decrease?

 

If the cam is ground 230@.050 it's still gonna be 230@.050, regardless of whether or not it's (the lobe) is closer to the cam centerline or not. The way I see it, moving the lobe further from the valve is just a matter of using a longer pushrod to make up for the distance... just like using a thicker head gasket. At least that's the way I see it.

-Mindgame

 

That's not along the lines of what I was thinking at all...

 

Mindgame is right. The specs will be identical.

There are no good big block lobes that can go on a small block cam that I know of. I know alot of Small Block lobes that could go on a big block cam.

We can get into this alot, but it's another novel. Basically there is a master blank for each lobe which is huge in comparison to the cam lobes on your camshaft. If the lobe of your cam is only .350 lift than even if the blank is 10" in diameter, it will still only have a max lift of .350, just like the lobe. Basically you have a base circle a certain size for the journal, the lift is going to be the same and the duration will be the same. The lobes on the cam and the lobe on the master will have the same amount of lift at every degree. So if you have a 230 degrees of duration at .050 lift then the master and the blank have it.

I hope that helps.

Bret