Dyno Room Exhaust, Zoomies don't work

We have 1600 HP BBC's that normally have Ø2.5" zoomies on them. The dyno room is only setup for back swept collector headers (car headers).

If my primary's remain Ø2.5", but are longer and go into a Ø6" collector, does it screw up the test?

What are your thoughts/experiences?

 

I've done a LOT of dyno work w/blower motors. Run the biggest tubes you can on your collector headers. Dyno will only give you a base line and tell you if changes make any difference (timing, etc) Its a whole nuther world when you bolt that bullet in the frame rails, TRUST ME! Have fun

 

Interesting topic AFC357.......

I have an engine from a dragster application that needs to now go into a door car. Was zoomies (2.5"x20") and needs to now be (X"x26'ish") with collectors. I was thinking of 2.75" pipe simply because a pipe of that diameter will nicely squish into a shape representing the odd exhaust port outlet that I have (with a bit of room to spare). For the collector, I was thinking either of a straight short 5.5" section, or, SPD have a beatiful 2.75" to 5" merge collector. Any thoughts about either the pipe diameter or the collector choice above? Open to thoughts at this point as we have not ordered any materials just yet.

In a general sense, have you found that pipe length, pipe diameter, or collector (or absence of a collector) makes that much difference in the tune of a blown PM or FC type engine? Does the difference seem to be from gas dynamics, etc., or does it all boil down to reducing back pressure and pumping losses? I've always wondered whether any of the conventional exhaust tuning theories applied when there is 40+psig boost in the intake and atmospheric pressure at the exhaust outlet?

SODAK, what about making an adapter that slips over your zoomies and then connects to the dyno room outlets? Curved runner adapters into a large trunk.

 

Great minds think a like!
I started building a sheetmetal "collector" that goes on top of the zoomies.
It's barely going to fit in the dyno room, it'll block access to under the valvecovers/port nozzles/etc and Mandolini runs collectors on his dyno. I think he uses Ø8", but I'm not for sure.
This stuff all got me thinkingThat's why I wondered what you guys thought?