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Engine is a stock RX8 with p-ported 2" intake rotor housings driving a propeller reduction gearbox (PSRU) ratio of 3.17. Max engine rpm is set to 8500 (2700 prop rpm), and cruise engine rpm will be around 7500.
The plane is out of commission for the summer while we rebuild the engine & redesign the front cowl for better aerodynamic performance. During the rebuild, I want to redo the intake / plenum system. Currently we are running 24" runners, with the injections underneath the 180degree bend. I found I would get pooling of fuel inside the plenum, not sure if the walls were getting too wet from the injectors being upside down and the opposite rotor was sucking back air from the runners during idle (high vacuum state). Pictures below are current setup.
Broken down into 4 discussion points.
-Runners (looking around 18" length)
-Plenum (pie shape, size unknown)
-Injectors (mount further away for better atomization)
-Throttle body (ITB or single TB,current 3" TB seems too big)
-Runners (old length 24")
The max engine RPM will be 8500, while we are thinking our best cruise RPM will be around 7500. Came across a few charts with different runner lengths. 18" looks more of a desired length.
From experience, peripheral port intakes do not work well with a common plenum. The intake pulses interfere with each other and you move almost as much air backwards as forwards. An independent throttle arrangement will greatly simplify things.
From experience, peripheral port intakes do not work well with a common plenum. The intake pulses interfere with each other and you move almost as much air backwards as forwards. An independent throttle arrangement will greatly simplify things.
With the ITB, they would still have to have a common filtered shroud that is being fed from the outside air. With the individual throttle bodies being in the middle (between the air filter and runners), that helps with the exchange of air? I haven't come across anywhere that talks about sizing a plenum.
The throttle body will still end up being the primary restriction in the inlet tract, especially at anything less than WOT. If the restriction is between the two ports, unless you have a really really good exhaust blowdown, the exhaust pressure during the overlap period will preferentially ping-pong the inlet flow backwards and up into the other chamber.
Having a common air filter is good. Much much better than individual air filters. Individual filters can cost 25% power on a NON pipey engine.
Running MegaSquirt. I like the ITB setup, as they have integrated injections bungs built in. I struggled making my own injector blocks and keeping them sealed and secure in my other setups. Idle isn't too much of a problem, because the prop is always turning and engine is under load. Roughly have to idle around 1800-2000rpm with P-Port.
Is EFIHardware the best place for ITB? I emailed them last week and haven't heard back.
That seems odd, I had the impression they were pretty good at responding, unless your email was filtered for some reason. They were the better option over injection perfection which may not be operating any more. Is the operating rpm based on prop/gearbox limitations?
on a side note, would be cool if you reached out to rotary aviation and they get you in contact with the retired founder who has a renesis in a rv8, might be able to pick his brain.
Yes the max engine rpm is based on the prop/gearbox. The gearbox is a 3.17 ratio planetary gear from a Ford rear end. You don't want the prop going past 2700rpm (8500rpm engine), as the prop tips could become supersonic. The prop I have now, makes better power around 2650. SO really, the engine isn't being pushed that hard at 8500rpm. Running stock OEM apex seals. The only mods are increase oil pressure and e-shaft jets / pellet removal. And ofcourse the p-port intake. I won't be going turbo, which is why I stuck with the Rx8 setup.
Have been building this plane for the past 7 years. The aviation world is good at aerodynamics, but when it comes to engine specific questions, the long history of RX7 members is worth its weight in gold. But yes, I'm all over their forums too.
I reserved a few posts under my main post, so I could edit and keep details in one spot. Looks like I can only edit my previous post, and not any earlier... Opss.
You’re pushing Renesis side seals pretty hard at 8500 rpm. That’s actually about as fast as you really want to push them despite the factory 9000 rpm redline. You definitely want EGT below 1650°F. Honestly though, imo you likely won’t make much more with a Renesis PP than a properly built Renesis with OE intake.
I agree the stock intake for the RX8 is properly designed, specially for a car from idle to max rpm. But it's too complicated and tall to fit in a plane. P-port simplifies the shape and length to allow us to tune to a specific rpm. 8500rpm is barely ever reached, maybe on the climb out once I pick up speed. Take off is around 8000rpm and cruise is around 7500rpm.
I have to get new rotors, so I'm looking at ChipsMotorsports getting the rotor side and face clearanced. (then balanced with my e-shaft and counterweight) Just waiting on an email back, to see if it's worth while.
Chips is good but add several weeks to your leadtime, its never what he advertises so getting that done early so its not the slow horse is a good idea.
Still no word back from EFIHardware. Tried their contact page, and email address. Very odd.
For top end HP, should I stick with my rx8 sideport exhaust & 2" p-port intake rotor housings? OR get the rotors scalloped and go back to a standard rx8 rotor housings? I have to re-design the intake, so I can go either way right now.
I premix the ethanol free fuel (1oz per 1gallon) with Super Tech Universal 2 stroke from walmart, and I'm getting a lot of carbon buildup on the rotors. Wondering if a bad intake design is causing the fuel to pool more then atomized.
Still no word back from EFIHardware. Tried their contact page, and email address. Very odd.
For top end HP, should I stick with my rx8 sideport exhaust & 2" p-port intake rotor housings? OR get the rotors scalloped and go back to a standard rx8 rotor housings? I have to re-design the intake, so I can go either way right now.
I premix the ethanol free fuel (1oz per 1gallon) with Super Tech Universal 2 stroke from walmart, and I'm getting a lot of carbon buildup on the rotors. Wondering if a bad intake design is causing the fuel to pool more then atomized.
Molson, I know it's about a year later, but I don't come here often. I'm on VAF more these days. How is it coming? I have a lightly boosted 450hp FD sitting behind the left wing of my RV6 in my hangar, but I don't have the cajones to pull the lycosaur out and put a rotary in yet.
07-05-22, 09:39 AM
