Collector headers on blower motor

Has anyone had any experience with running collector headers with a blown chevy. If so, did it make a difference in performance or tuneup. Seems like even though they weigh a little more, the improved scavaging would be worth it. Also, is there any benefit to running a larger header pipe 2.5in vs 2.25in on either a zoomie or collector header. With most big chevy heads having a port size of less than 2.5in what is the point of having a 2.5in header pipe. Seems to me that when a high velocity gas or fluid passes from small i.d. to a larger i.d. the gas/fluid would lose some of its pressure and velocity.

 

Seemed like ~20 years ago Les Davenport ran collecter headers on a BBC Rodeck TAD (I think he won Denver w/ them). I personally like the sound of zoomies. I too wondered (years ago) about the header to head match up (especially when we ran D ports); if there was some lost flow (I am sure an active alky racer can answer that).

 

We tried it with a custom built and engineered tuned step headers.
We spent lots of money on the project.
The problem was they worked too good and sucked raw fuel and air right through the cylinder during the valve overlap period.
With a custom ground cam to address the valve overlap period I feel that this still has potential.
The other problems were - they weighed to much, caused wind resistance and cracked a lot due to the vibration with the length and weight combined to keep the vibration going. They were a pain to take off and put on.
The sucking through during the valve overlap cooled the chambers to a certain extent but heat cycled the exhaust valves hot exhaust to cold wet intake charge. Made worse by the blower pushing air through So of course boost was lost too.
At night they shot really great looking flames 6-7 feet out with the fresh air and raw fuel burning inside and outside the collectors. But that showed us that we were disturbing the air flowing over the wing.
We gave up the project and put the zoomies back on. Now I can instantly tell where I have a dead cylinder again just by feeling the puffing.

 

Thats what I like about this site. People that know more than me. No really, thanks for the answer, when I have asked this question before all I got was ((because everyone runs zoomies). Informed answers like this are hard to come by on the street. Still wondering about header size though. Thanks Jody Stroud