Re: BBC header size
The trouble with many 1.875" is you may have to open up the flanges to the port, so good deal on the stepped headers. Primary tube size sets peak HEADER torque, and with my 440" and 2" its near 5000 rpms, so a 427 with a peak at 6000 dont need 'em. 427s that spin to 7500 do. I base it simply on peak header torque. If I recall 1.75" was near 3500 rpms, and 1.875 just over 4000 rpms. You may have been able to use really small 1.75" tubes with good effect!
You would notice the 2" pipes coming off a stoplight slowly. Smaller pipes work slow best. What I noticed with the 2" were on, low speed got a bit rattier, yet over 6000 they were decidedly better. Other than that, the math here has a pretty marginal effect for the overall system, but you done right with smaller.
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