Chev V-8 F.O. vs. Rod/Cam Clearance

[MadBill]

Given time I could probably noodle this out, but it's way easier to tap into the S/T Collective for someone that's been there and done that: Do the common alternatives to the original Chev firing order, namely the '4/7' or the '4/7 + 2/3' swap, help or worsen the potential rod/lobe interference with stroker cranks, or just move around the conflict zones?

[Newold1]

I have seen valve event timing and cam install timing play havoc in a stroker with that clearance and a bigger base circle camshaft with bigger lifts, but I don't think moving cylinder timing around makes a difference as it's a rod to cam lobe timing where the issue shows up.

[MadBill]

Right, the rod timing stays the same but either four or eight lobes move around and I don't know which if any are brought into or out of the conflict zones as a result.

[rustbucket79]

1,2,5 and 6 are the contact rods in a SBC. 7/4 swap changes nothing, 2/3 seems like it would change contact but who has used that exotic a grind other than high end stuff such as a raised cam block? I have a 4/7 cam in my personal 406 but I doubt my next cam will be anything other than a standard firing order, I'm just not convinced it makes a difference.

[MadBill]

Not to argue, just looking for clarity/certainty, but to understand the effects, we'd have to know (and perhaps such knowledge underlies your answer) which lobes made contact, not just which rods. E.g., if with the conventional SBC F.O., the #7 ex. lobe contacted the # 6 rod, going to a 4/7 swap would put that lobe somewhere else and likely move the interference to a different lobe and a different rod.

To put this question into a practical situation, if only the vulnerable rods had been clearanced for a conventional F.O by a previous owner, someone installing a swap F.O. cam without thinking to re-check for rod-lobe contact could be in trouble.

[Larry Salisbury]

1,2,5 and 6 are the contact rods in a SBC. 7/4 swap changes nothing, 2/3 seems like it would change contact but who has used that exotic a grind other than high end stuff such as a raised cam block? I have a 4/7 cam in my personal 406 but I doubt my next cam will be anything other than a standard firing order, I'm just not convinced it makes a difference.

My 2010 EMC SEFI 458 SBC (4.200b x 4.125s) did use a (Schneider Racing) 4/7 swap hyd roller cam, JE FSR pistons, Eagle 5.850 rods with the stroker cut, and an Eagle 4.125 stroke crank with undercut pendulums. Back then I used the PBM/Erson standard deck block. Raised cam blocks were not permitted. The block came from Erson with the stroker clearances already machined. A very smooth running combo when done correctly.

Larry

[ProPower engines]

the common 383 and 406 rod interference issues are the same rods every time.
however now the rod manufactures have taken this to heart when making rods and add clearance to the areas that are affected thus most times depending on how much cam is being used have no clearance issues.

Swapping the firing orders only change the issue if those rods were affected to start with meaning the common 1 2 5 and 6 lobes that are normally interfered with but now if you have a 4/7 swap #7 has the clearance issue that # 2 had.
There is reduced base circle cam available but I believe for the most part it depends on who's rod you are going to use will determine if you cave any clearance issues.
As for the 4/7 5/2 or the LS firing order cams while they are very commonly used today for serious engine builds they are definitely worth the extra cost for the increased power/torque and smoother running with less crank stress.
I have been using this combo in many different engine builds over the last few years with very promising results with the BBC marine engines seeing the biggest gains over a std. FO cam.

Again the rod choice has alot to do with any interference issues as the rod makers now have specific rods for stroker builds where compared to 30 years ago not so much in the option department because they were just plain big and heavy compared to what is out there today because of material used today is much better and stronger then yesteryear.