When building a motor with longer cylinders, using base gaskets, varied thickness head gaskets and heads that've been milled. The OEM width intake sometimes isn't wide enough. I drew a visual model of my last 124" from records I took when building it. The drawing is within 0.002" on the intake width measured at the heads.
I'm going to wait until I assemble this next 124" and will create a spreadsheet to calculate the width intake needed. Bore size or OEM head type doesn't mean anything, you just will need to know the overall cylinder height with gaskets, the head thickness after being milled, and the intake throat diameter and the calculation should be really close.
I want to build the next motor before putting figures to paper. I'll upload it once it's done.
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I did some calculations some years ago and posted them here.
If cylinder height is decreased by h, then the spigot on the intake manifold should be trimmed by (0.4142)h
I'm looking more at when a wider intake is needed, what to order.
How much taller will your cylinders be compared to your drawing above?
If, for example, you make the cylinders taller by 0.1000", then your new distance between intake port centers will be: 0.0765" + 3.6829" = 3.7594".
Jason
The calculation isn't the problem. It's determining what is the normal start point. I can't assume things based on one motor. So I'll wait until I assemble this next one and measure it.
The center to center can be used as a datum. I am assuming that is how you will compare stock to the other builds? They are multiple angle spigots which complicates things, as you know.
We simply machine the intake mounting surfaces in one of our vertical mills, as per calculations we have come up with many years ago.
Extremely common practice here.