Don Terrill’s Speed-Talk

what is the formula for milling the sides of a big block chevy intake manifold please.

I have a home made spreadsheet and if I mill BBC head .050 then Intake face gets cut .035 so it's about 70%.

jimjamm65 wrote:what is the formula for milling the sides of a big block chevy intake manifold please.

90° heads are 1 to 1

Formula courtesy of Master Panic
.707 ÷ (SIN (45 - intake face angle))
http://victorylibrary.com/mopar/intake-mill-c.htm

If you have 0.100 mismatch, take 0.100 from each side.
The manifold will drop 0.141.

I thought for sure I had duplicated the formula based on the dimension's I had found in the Chevy Power Book

I"ll have to check tomorrow to see where I screwed up. sorry for giving wrong info

thanks for the information, guys. i appreciate it. jimjamm65

This information is from Chevy Power book #6 for BBC milling can anyone check it out to see if it is correct.

This information is from Chevy Power book #6 for SBC milling.

The SB numbers are correct
I do not know where the BB numbers come from but they are wrong.
Could be empirical data just like I normally use 1 to 1 for a small block.
Even though I know it is not the correct number it works

Correctly done any angle other than 45° from vertical requires either more or less material removed from the intake surface to be "correct" & the multiplier is derived from the formula that I linked to by Mr Diamond (Panic)

Wolf , thanks for the clarification.

Here is the same model but adjusted for a 10 degree intake face like a gen-1 SBC

In this case to correct a 0.100 mismatch you remove 0.143 from each face, the manifold will drop 0.174

SchmidtMotorWorks wrote:Here is the same model but adjusted for a 10 degree intake face like a gen-1 SBC

In this case to correct a 0.100 mismatch you remove 0.143 from each face, the manifold will drop 0.174

Jon
Explain the .143?
Would it not be .123

.707/.574

I just make a parametric sketch, that way I avoid any possible mistakes in how I apply the trig triangles.

The CAD app just returns the values.

Intuitiveley 0.143 does seem high, I can double check it, in a couple of hours when I get back to the computer I did that on..


The trig way.
The intake face on a SBC is 35 degrees from horizontal
Tangent(35) = 0.7002 (opposite/adjacent)
1/0.7002 = 1.428
The mismatch is 0.1" so proportionally the correction is 0.1428 (rounds to 0.143)

SchmidtMotorWorks wrote:I just make a parametric sketch, that way I avoid any possible mistakes in how I apply the trig triangles.

The CAD app just returns the values.

Intuitiveley 0.143 does seem high, I can double check it, in a couple of hours when I get back to the computer I did that on..


The trig way.
The intake face on a SBC is 35 degrees from horizontal
Tangent(35) = 0.7002 (opposite/adjacent)
1/0.7002 = 1.428
The mismatch is 0.1" so proportionally the correction is 0.1428 (rounds to 0.143)

Thanks, math is not exactly my strong point

I have always used the difference from 45°, as in Jeffery's formula & it appears to be the same way the old Van Norman 570 broach manual showed it in their chart for different heads.
IE
SB
45-10=35
sin35=.574
sin45=.707
.707/.574=1.232

I think tangent is the proper function rather than sine in this case.