if you look back at the engines that used those separators you will notice they had a matching fuel pump. the fuel pumps were 8-9psi and worked with the .060" return orifice. i did some pressure/flow testing with this and found big low rpm pressure swings with return orifice sizes of .060" and up. the old factory pump set-up should generate 1-8lb swings at low rpm but will stabilize to around 6psi at about 2000rpm. when the. 060", or larger orifice is used with a more common street pump of 5-6psi the low rpm swings are still there, but hot running pressure may reduce to 4psi. i know from experience that using the .060+ orifice with a rated 6psi pump was definitely a power loss at the track but drove ok on the street. what i do now is solder the return hole up and drill for a .035"-.040" return orifice. this seems to work well with a 6-6.5psi pump. i've tested this using a factory original hipo 440 pump, a carter 6903 and 4862.
Great info! I'm guessing that since I'm feeding my motor with a Holley blue pump regulated down to 6psi I won't experience this (or maybe bump up my regulator slightly). Would you agree?
I bought one of the Goodmark fuel vapor seperators ($35) and it has 5/16" inlet & outlet. Can anyone confirm this is correct for 440 six packs & Hemis? (I think so, but I'm not sure). I ran a bread tie wire down all the holes and all the tubes extend to maybe 1/4" from the other end of the can (like a factory one I believe). I don't know if there's a screen in there or not. I will see if I can get a pin guage in the vapor return hole and let everyone know. It's certainly necked down a lot & probably in the neighborhood of .060" (the pin guage knows for sure)
