Camshaft/Connecting Rod Interference

[Flathead]

Hi
I have been using the forum for gaining information for many years, so first off thanks for the site and the knowledge base behind it.
I have an issue with an engine (Flathead Ford V8) I am working on. I have increased the size of the cam to enable high lift and trying to maintain some rigidity given there are only 3 cam bearings, I am also trying to run a 4.375 stroke. The problem is that using the Ford cylinder numbering and the standard Ford firing order the lobes on cylinders 2 and 6 and 4 and 8 hit connecting rods, 1 and 5 and 3 and 7 miss by miles. There are a number of firing order options but trying to work out whether any of these would mitigate the problem is problematic for me anyway, just intuitively it seems most likely I would move the problem cylinders around. Has anybody got experience that would inform a new firing order that would create clearance or a way of modelling options?
I did endeavour to check this prior to starting build via a 2D drawing but must have messed that up somewhere. I have ended up with only .517" of radial clearance between the crankpins and the top of the cam lobe, I am using 1.850 BEs so no solution there.
It looks like running a flat plane crank would be a solution but will cross the first bridge re firing orders before asking questions about that.
Thanks
Grant

[mag2555]

I assume your running a steel Cam since cast iron is far more ridged ?

[CamKing]

Firing order won't fix the issue. No matter what firing order you use, the lobes will either be where they are, or 180 degrees from where they are on the camshaft.
Since the cam moves half the speed of the crank, changing the firing order will move the lobes 180 degrees, but that's 360 degrees on the crank. That puts them right back in the same place, in regards to the crankshaft.

[mag2555]

Also what the heck will the rod to stroke ratio be even if there was no clearance issue?

[Ks Fats]

1.6 ratio if it still has the 7" rod; is the .517 clearance at the crankpin or the cheek of the crankpin? Are the crankpins already at small journal? What connecting rod were you planning to use? Will this be a roller cam or a flat tappet? A bit more info might help....

[Flathead]

Hi Been away for a few days sorry for tardy response.
Questions
mag2555
Cam is made from Bohler M238 same as P20 tool/mold steel.
Rod/Stroke ratio is 1.66
Mike
Thanks you appreciate the input.
Ks Fats
Rod/Stroke ratio above 7.25 rods.
.517 is at the crankpin, crankpins are 1.850 Honda/Nascar size, rods are Carillo customs, cam is flat tappet.
Thanks
Grant

[mag2555]

The big question I have is with the limited air flow these motors with a stock amount of CID ( as in VE percentage) why are you making that even worse with such a big stroke increase?

[Flathead]

Hi I have done a lot of work on airflow I believe I have enough to support the displacement. The work on airflow compromises compression ratio with transfer space modifications I need displacement to gain swept volume.
Grant

[Ks Fats]

Flathead,
Since you are at a crankpin dia. smaller than the 2.00 s.j. there is nothing to be gained there. 7.25 rod is obviously custom so do you have any room to work with at the big end of the rod? It is sometimes necessary to work the big end (or beam) of the rod on the offending cylinders IF the design will accommodate it. You are in territory here that I'm not that familiar with; 4.250 stroke/.433 lift (stock core dia.), skinny 7-inch boxed rod is the maximum I've dealt with and (as mag has mentioned) struggled to get the port/valve area to feed it. Bear in mind I'm old and from an era in which cut and try was the development norm; you must have found something in the breathing area that eluded us in the past. There is a contributor here called "Pete" who has a lifetime of experience with big inch flatheads hopefully he will chime in...

[PackardV8]

Hi I have done a lot of work on airflow I believe I have enough to support the displacement. The work on airflow compromises compression ratio with transfer space modifications I need displacement to gain swept volume. Grant

Isn't that sort of a self-fulfilling prophecy? On flow-constrained builds, more displacement then demands more flow, which can't be supplied. FWIW, the Harley-Davidson Racing Department wrestled with this for forty years and found with flatheads, it always paid to give up compression for flow. Their most powerful engines were 6.5:1 compression.

[mag2555]

You beat me to the above reply!

First and for most any internal combustion motor in terms of it's power production must be looked at as a air pump