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Like most people's dad used to say, "Don't do as I do (did); do as I say." :-)
Tracy looked at my box after it was built & pointed out what I should have considered: those big flat (thin) aluminum panels won't survive intake pressure waves. I knew better, but that part of my mind had gone on break during the entire construction of the box. Car makers don't waste aluminum making cast 1/4" thick plenums just to get rid of surplus aluminum. :-)
That box is now lined with 1/4" plywood and fiberglass, and weighs far too much. I'm doubtful that it will be a flight item.
I'd suggest doing what Tracy did, & start with plywood/fiberglass, or use a 4"-6" round aluminum tube for the plenum. I can probably dig up some 6" if you want to try it, or check local farm-market publications down there for surplus irrigation pipe.
I never did find any tube length/plenum sizing advice for the rotary that I trusted. Very few Renesis car guys ever touch the stock manifold, since it would be very difficult to improve on Mazda's design for a car.
Charlie
On 9/12/2019 12:02 PM, Finn Lassen finn.lassen@verizon.net wrote:
6 1/2 years later I'm about to do the same and would like to ask the same question before I make my "shoe box":
"I'm curious about how others have adapted the common Helmholtz intake tuning formulas to the rotary. Would anyone care to 'show their (math) work'?"
Rather than building it as big as possible, I'd like to know if there is an optimal size.
Finn
Charlie's photo:
On 2/17/2013 3:41 PM, Charlie England wrote:
Now that everyone's awake again, I thought I'd send a pic of my intake progress (RV-7 Renesis with James Lyc cowl). I played with a couple of different materials for the bell mouths. I tried gluing up some 1/4" plexi from an old windshield, but used super glue instead of proper plexi cement (which I wasn't able to find locally in a hurry). The 1st try popped apart on the lathe; the 2nd turned out ok. Next effort was with 3/4" MDF (medium density fiberboard). That went well, until I put a little too much side pressure on the ring (homemade cutting tool) after undercutting the center section. Overall tube lengths will be ~11 3/4" block surface to bell ends. The plenum is *much* bigger than most tuning sites recommend. I figure that I can experiment with plenum size by just stuffing it with rigid foam to take up some volume, if needed. Going the other way wouldn't be so easy. :-)
Since I don't have Mark's TIG skills, I thought I'd ask what others have used in joining thin wall tubing to 1/4" aluminum plate. Aluminum brazing rod? High temp epoxy? JB weld? I do intend to add bracing from the plate to the plenum assembly to take some of the cantilever & vibration stress off the tubes.
I'm using this length and concept because Tracy has had great luck with both HP & BSFC on his Renesis with a similar configuration. However, I'm curious about how others have adapted the common Helmholtz intake tuning formulas to the rotary. Would anyone care to 'show their (math) work'? Renesis users would be better for me, but any calcs would do. When I tried to adapt the common formulas to a rotary, I was getting 'interesting' results, so I'd like to know if I got lost somewhere while trying to plug rotary 'valve' timing into the formulas.
Charlie
(Sorry for the sideways iphone pic; I guess you can pretend that you're looking down on it...)
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