I know this has probably been discussed many times previously. However, Crane have agreed to grind me a replacement cam due to fault with my current cam. The only core available is a 4/7 swap. I know the Chevy crowd have been doing this for years, but I was wondering if it has any real world advantages in a SBM. I kind of don't have a choice in the matter as this is the only core available at the moment. Suppose I'm looking for opinions and to see if anyone has had any experience with only the 4/7 swap.

Thanks in advance.

In theory, it helps take some of the load off of the crankshaft. If nothing else, it won't hurt. My new cam for my big block is also a 4/7 swap.

The Comp cam in my 416 small block is a 4/7 swap. If I remember right Comp said it helps relieve some stress on the last crank journal. Something that was also interesting is they said it moves the hot spot created by 5-7 firing close to each up closer to the front where the coolant is removed faster due to being so close to the outlet.

Cool

Interesting......

Might want to try some different lobes while you’re at it.

Is what’s wrong with the current cam top secret?

it won't hurt
It's going to affect mixture distribution: where is the next vacuum pulse in the manifold? Not where it was, everything back to factory assumes 5-7 overlap. Is it important? YRMV.

You'll never notice the difference unless you hook up the plugs wrong. When you do a swap like that you need to make a little decal or something so anyone helping you knows what the firing order is. Otherwise someone will put the wires on wrong and you'll wonder where all the power went.

Do it. There is no reason not to, except when you can't get the cam core.

No mate.....

The machinist on the day failed to drill the bleed back holes in the rear journal. Hence, I kept blowing out the cam tunnel plug on the block.

Oh, and took your advice on the pushrods. Going to a straight 3/8 0.080 or 0.135 wall.

what were you thinking? 420 lobe?

Yeh, those older Crane race 420 lobes are pretty good.

THIS POST HAS BEEN REMOVED BY THE DEPARTMENT OF INSIDE JOKES

Cheers

So cam cores are pre shaped? I would have thought they all start out as full circle lobes?

There are some roller cores that are full round. They are called UGL for Un Ground Lobe.

All the cast cams are made with the lobes in shape. That's one reason why Comp made 110 the de facto LSA. It's easier to move the LSA a couple of degrees either way and still get the lobes on the core.

I've been begging people for years to start changing up the firing order on all the cores to the 4/7/5/2 swap.

No reason not to do it, other than they don't want to do it.

Any high volume roller camshafts, they will rough machine the lobes. Less time on the grinder that way

Actually, it’s not just grinder time but also the delivery time.

“Most” billet roller cams start as semi-finished cores.
They have a lobe lift, lsa, and duration in that configuration.

The bearing journals are done, along with the dist gear being cut........ and, the heat treat is already done.
The heat treat on a billet core doesn’t go all that deep(deeper on some material than others), so the finished product can’t be way off than what the semi finished core starts out as.

To do a cam from an UGL core, which is not heat treated, you burn up 2 roughing wheels(about $100/ea) getting the profile semi roughed in on the core.

Then it needs to be sent out for heat treating....... which is where the big time delay occurs.
After getting it back from heat treating it gets the cam lobes finished.

It’s a much more efficient process to get a cam done from the semi-finished core.

While it’s true, had I put it together I would have used 3/8 x .080 pushrods for that type of combo...... that sentiment is not shared by many(any?) top builders, who would absolutely feel that what you have in the motor now would be unquestionably superior.

I've spent hours writing down different firing orders based on which two pistons are at TDC at the same time, when you do the 4/7 swap all you have accomplished is to move the problem from the driver side rear block to the front passenger side of the block, correct
1843
6572 Standard Mopar V8 and early Chevy V8 firing order.
The 7-4 swap =1873
6542
if you change it to:
1543
6872 you then change the two cylinders firing in line from each other to the passenger side two rear cylinders, correct
I'm done for tonight on this but a custom built crankshaft could remedy the issues, correct