Port length BBC heads

[Little Mouse]

How does the port length of a standard BBC say an oval port compare in length to the average standard sbc. How much longer.

[Alaskaracer]

Without measuring it, quite a bit......
Length of port isn't determined by shape of port...it's by the layout of the head itself......but yeah, much longer.

[Stan Weiss]

These are from PipeMax / Larry Meaux
Int=5.339 Exh=2.818 Int=135.6 Exh=71.58 GM #3890462 SBC out-the-box shape 1.940-1.500

Int=5.975 Exh=3.380 Int=151.8 Exh=85.85 GM 781 BBC cast-iron Good-Port in ported shape
Int=5.820 Exh=3.380 Int=147.8 Exh=85.85 GM 781 BBC cast-iron Bad-Port in ported shape

Stan

[Little Mouse]

Thank you lots of useful detail. So it's hard to compare the two on volume as like in velocity.

[Stan Weiss]

Thank you lots of useful detail. So it's hard to compare the two on volume as like in velocity.

I do not understand. You should want around the same velocity.

No different that a small valve small port SBC and a big valve big port SBC should want around the same velocity.

Stan

[maxracesoftware]

Thank you lots of useful detail. So it's hard to compare the two on volume as like in velocity.

These are from PipeMax / Larry Meaux
Int=5.339 Exh=2.818 Int=135.6 Exh=71.58 GM #3890462 SBC out-the-box shape 1.940-1.500

Int=5.975 Exh=3.380 Int=151.8 Exh=85.85 GM 781 BBC cast-iron Good-Port in ported shape
Int=5.820 Exh=3.380 Int=147.8 Exh=85.85 GM 781 BBC cast-iron Bad-Port in ported shape

Stan

Stan gave you example of Port CenterLine lengths .

Example=> Roof= 4.200 + Floor= 2.200 Total= (6.400 / 2) = 3.200 Port CenterLine Length
( use Scotch 3M 218 Fine Line Tape to measure Roof and Floor Lengths )

Just measure your Port's CenterLine Length
then measure that Port's Port Volume CC's
then Flow test that Port to measure its CFM

plug all that Data into this equation to get Average CSA Velocity FPS

CSA Velocity FPS = ( Intake Port CFM * Intake Port CenterLine Length * 39.3289536 ) / Intake Port Volume CC
CSA Velocity FPS = ( Exhaust Port CFM * Exhaust Port CenterLine Length * 39.3289536 ) / Exhaust Port Volume CC

where Constant 39.3289536 = 16.387064 * 2.4
2.54^3 = 16.387064

[Little Mouse]

I have a better understanding of what size heads would work well in sbc for different size engines. I'm not to deep in SBC bought parts yet. Considering doing a BBC instead. Long time ago I had a 396 and a 454 but I have a lot more experience with SBC. I did build 440 chrysler for a friends son, does this count. Lol