Running a motor with no exhaust manifold can be downright dangerous as there are 8 blow torches shooting flames and LOTS OF NOISE. The entire neighborhood would be up in arms, perhaps DEFCON 2 depending on your neighborhood.
I suppose you could hook up a couple of mufflers and do the run in at the house, with cooling water running through the block. Some of your neighbors would appreciate it, some would not
Me? If I were in your neighborhood I would be miffed if I wasn't invited over for this event, given a beer, and an opportunity to get a little oil or dirt on my hands!
Roy