I have the Vetterman Crossover for Superior cold air sump on my RV-8.
I think 4 straight pipes are louder, and tune to a narrower RPM powerband.
If you run a constant speed propeller, 4 straight pipes may be the ticket.
For me, with a fixed pitch, I would like a bit more mid-range power I think the cross-over system affords.
I like the slightly mellow sound, some like the straight pipe bark!
(It could all be in my head?)
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing
-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)