Alright so as I dig into this rotary I got (rx8 13b RENESIS) I learn more and more about it, and what I've learned this weekend is this:
The lower intake manifold looks like this, as you can see it has lots of emissions garbage on it, mainly those big ol power sucking tubes. those are means to close off two of the six intake ports operated by vacuum actuator and some gears as I have deduced.
So I did some research on alternatives and there are zilch, as far as i know. I actually found a 1400 dollar flange:
but thats not an option for obvious reasons. So a call to my rotary brothers for help, alternatives? Is the 6-port on the older rx7 engines the same? Just remove the pipes and call it a day? they are not power suckers and I dont know what im talking about (likely) ? any help is appreciated.
The tubes opening and closing are to flatten out the torque curve, not emissions. Keeping them closed at low rpm shortens the intake duration and keeps runner velocity up. Above 3000rpm they open and you get much longer intake duration and more port area. Depending on gearing and tire, leaving the ports open all the time isn't all bad considering how infrequently you run in lower revs. I wouldn't pull the sleeves out though, they are contoured pretty nicely for flow and are way bigger than the old 6-port 13B sleeves.
The side exhaust ports on the renesis made for wider side housings which changed the intake flange pattern. Racing beat sells an adapter to convert to an older 6 port 13B intake to a Renesis engine. If packaging permits, the adapter and a 4-barrel style intake with EFI is a pretty good option. I really liked the 4 barrel / ITB on my 13B for the response and torque that just never dropped off.
http://www.racingbeat.com/RX8/Weber-Intake/16480.html
You can also just hack off the stock intake manifold and use it as a flange to fab from. That's what I did to make my 13B intake. The cast aluminum is just a little crappy to weld to.
An FYI, if you go custom intake and are stuck with just the two primary injectors, Injector rehab can "de-cap" your RX8 yellow injectors. The 2 primaries are plenty to feed an NA motor. For $25 per injector +S&H it's a sweet deal.
There are few alternatives to the OEM intake because it is so good and you're more likely to loose power by changing it.
In reply to RXBeetle : I actually did see that adapter when searching but I didnt think it was applicable to me. So let me get this straight, use the adapter, then up to (which manifold?) then ITB'S? With only primary injectors? Sounds interesting and I love me some ITB'S, but with only two injectors would power not be hurt? Related question: I know a lot of people don't like the RENESIS but it is the most powerful N/A, do you know why that is? What makes it so powerful compared the the others?
side note: I would fab my own intake but that is a little above my paygrade, I can do exhausts but intakes are a little to complicated
j_tso
New Reader
10/5/19 10:58 p.m.
The complicated staged intake on the RX-8 does a lot to make its power. Image below shows all the stages. The auxiliary ports actually open at 6250 rpm.
The intake adapters for a 2 or 4 barrel ITB are handy when installing the engine in another car since the factory ECU that controls the intake doesn't play nice when other components from the car are missing. I haven't found anyone who has done it and documented everything, but it's been on my mind since a lot more RX-8s are in salvage yards nowadays than 7s.
