RGHTBrainDesign - Rotary Engine Development Projects
 

So while I am not quite sure where this is heading, I'd like to start a thread dedicated towards building out a set of projects intended on improving the rotary engine to modern standards of reliability and power output. A lot of my previous projects are covered elsewhere throughout the forum, but this will be a place where I intend on documenting via YouTube the concepts, developments, testing, and tuning of various parts of engine and control systems.

None of this is for the faint of heart, but I want to see your contributions.

Here is a post I wrote for Rx7 Group on Facebook:

"Wow. Let's talk engine calibration control strategies for a minute and the effectiveness of Intake Velocity on the drivability of a car. The FD Rx7 came with a set of Secondary Throttle Plates in which at around 100kPa (atmospheric pressure), they opened up. What this did was force all the air from the TB into ONLY the PRIMARY runners, increasing intake velocity dramatically at low loads/lower RPMs.

• Next I'm Covering Direct Fire with Smart Coils vs. CDI and the Pros/Cons of Each System.
• After that I'm thinking we talk Exhaust Manifold Design.
• Everything else will be open ended. We could do anything from suspension/chassis, to engine, to tuning, etc. Please be open minded and share your opinions.

Personal Use of This Configuration:

250 Views and no replies, huh? Well, I'm interested to see what you all have on your minds. Let's make this a badass discussion thread, rich with information.

I'm following this with interest!

Mine is a slightly different application to yours, as I am using vapour LPG as my fuel. This has different induction characteristics to petrol, as the LPG is already mixed with the air in gaseous form and takes up much more volume within the intake manifold (30% more from memory). However, like you, my system has a single large throttle body (through which LPG is added mechanically, basically like a carburettor).

Now, with the conversion from the OEM 3x throttle plate to a large single, you effectively lose the primary vs secondary intake staging and the benefits to low load throttle response and fuel economy that come with it. In this specific circumstance, I think your idea has a lot of merit, as it will allow you to re-introduce the primary vs secondary staging. If you kept the OEM throttle body, however, I'm not sure there's going to be a massive tangible difference compared to removing the restriction the double throttle system creates, especially for a vehicle that spends more of its time under load or in higher rpm. Modern aftermarket programmable ECU are also a lot more powerful than the OEM box in a FD and have lots of tuning strategies available that can help with staging and sudden increases in throttle.

I have a FD intake manifold setup and personally, I already "removed that shit" a long time ago. On the UIM to throttle body flange, I also removed the bridge between the secondary channels and opened it up to provide more intake volume (since I already knew I was going LPG). I then ported and polished, as shown below. I think this will provide better upper rpm performance. For the low down torque, I don't think I'll have a problem as I'm using a EFR7670 IWG on a shorty manifold, with stock ports, with LPG (which assists with earlier spool in the same manner as E85). However, if I find that low throttle / low rpm performance is unsatisfactory with the single throttle setup, you've given me a very good idea of how I might address it - stick the double throttle back in and control it electronically!

https://cimg7.ibsrv.net/gimg/www.rx7...f528fcbefb.jpg
https://cimg5.ibsrv.net/gimg/www.rx7...2ca92158a8.jpg

PS I found my old thread when I did this mod (in around 2004 - my project has been on the backburner that long) and found a link to this old thread on the subject: https://www.rx7club.com/3rd-generati...rflies-153158/

The specifics of pros/cons of removing the butterflies is light on, but I suspect for many people they aren't working properly and they may not an improvement but removing them. If you can control them using a more reliable/accurate method than vacuum, as you are proposing, you can tune the opening of the plates to your advantage.

As noted in the thread, the double throttle is there primarily to prevent going into the secondaries before the engine is warm. I checked the FSM and it appears that the system does not work exactly as you described (by reference to engine vacuum):

1. the actuator is vacuum controlled, but it only gets vacuum via a solenoid.
2. the solenoid is controlled by the ECU, based on coolant temperature.
3. to test the system, you check whether the vacuum actuator is fully returned once the engine has reached operating temperature. That is, the double throttle system is designed by Mazda to be completely inoperable once the engine is warm.

Now, that is not to say the system is not useful to introduce staging on a single throttle setup (for reasons explained above), but on a OEM setup, the double throttle only operates when the engine is cold. Based on this, I'd say it was not introduced as a performance feature at all, but for emissions purposes and as a guard against user error (driver punishing engine before it is warm). In normal conditions, the staged operation of the primary/secondary throttle plates in the throttle body itself is enough to take advantage of staging the primary vs second intake ports. Of course, if you go to an aftermarket throttle body, you lose this completely.

Very Interested in this.

Port design plays a big role in staging. How would you propose we eliminate that variable or compensate for it?

As always I've got dyno facilities open for testing :P

***These RPM points will need to be tested and tuned.***

We're simply applying this to our intake manifold configuration to optimize torque output. To find this point, you should be able to dyno the car with the butterflies entirely open vs. the butterflies entirely closed, and identify the crossover point when dyno runs are overlaid. You can then do this every 40kPa and continue following where it's crossed over to set that RPM/Load index properly. Estimate the values in between, and you should have a BADASS smooth transition that optimizes bottom end performance out of a small displacement engine.

You're finding the point in which the engine craves more air (crossover between OPEN and CLOSED at each given MAP pressure), and therefore aren't being wasteful by just dumping the secondaries open too early (lagging the system with reduced intake air velocity).

By providing Dave with a few parameters to test on his engine dyno, of course! :D

I think this is an interesting idea, and would like to hear your results when you get them. I did a little experimenting with controlling the Double Throttle solenoid on my car years ago, but I ran into a situation where my staged injection settings would start sending fuel to the secondary injectors (due to manifold pressure and RPM) while the Double Throttle solenoid was still closed. This made the engine run badly so I left the Double Throttle solenoid always open to avoid that problem and then forgot to revisit it again.

Right, which is why you always control them to open before the fuel starts injecting. That's a simple logic to add into the tuning of this whole thing. Again, that's why we are going to be experimenting and finding the optimal points at which to open/close based on various engine ports/configurations. Definitely thought about that before committing to the project. Glad someone else brought it up. :)

In one of your videos you mentioned you were using a double MAP configuration as opposed to IAT calculations. Seems interesting, could you explain this a little further, or send me to a good write up? I'm very new to tuning and am running ITBs, so I'm not sure if any of this is applicable to my setup exactly.

Your style of tuning should be TPS for Transient Fueling and Alpha-N for MAP x TPS on tuning. Let me see if I can find a better explanation.

It's something along the lines of using both MAP and TPS to blend a table. TPS is more dominate and accurate for you at low engine speeds and loads because ITBs don't generate a bunch of a vacuum, and MAP is more accurate once you're on the throttle more. It actually looks similar to the table I posted below.

My setup is throttle mass flow, which I'll quote here out of my ECU Manual. I'm still using an IAT, just relocating it. Double MAP (one Pre TB and one Post TB).
So after the light/transient fueling, the model simply reverts back to MAP vs. BAP (Barometric Pressure) with reference to EMAP (Exhaust Manifold Pressure).

Ok, that makes sense after reading it a bunch LOL. I find it interesting there is so many different ways to do a lot of the same things once you dive in and start doing it. My main fuel table is set on alpha N (tons of help from Skeese) but my target AFR page is MAP v RPM. I'm trying to figure out the transient fueling and I saw your og post on FB. It was an interesting concept I haven't thought into, just gaining overall knowledge I hope.

As an update, as of yesterday I think I've made arrangements to have access to a couple Dynapack hub dynos around 6 blocks away from my building available to whomever (may be rental fees for someone other than myself, haven't worked that out) though it would still be inexpensive. I'm also hoping to work out just being able to pick them up for semi extended dev sessions in my own space but we'll see. Hope this'll be helpful in getting some idears tested and quantified if they're already implemented in a chassis/I know not everyone has a spare engine to mule test on.

Given that good ole Nader of built2apex has now sent me 3 side mount alternator brackets that don't come anywhere close to fitting, I'm debating welding one of them into the trunk and taking a spin on the monsterbox nascar-style cabledrive rear mounted mechanical fuel pump and just mounting the fucking alternator back there and cable driving it remotely.

At this point, it isn't really as crazy as waiting on built2notfit to send another, that likely wont fit. How about that for unique random rotary BS.

Skeese

Rear Mounted Alternator. Hmm, I see that as a rotary engine development. Rearward weight distribution FTW!

Ohh, here's a proper *non-FD* unit. Contact them for the FD one: Franklin Engineering Side Mount Alternator Bracket

You're going to be my new best friend, I can tell. :ylsuper:

We run a driveshaft driven alternator on the turbo 3 rotor. It's annoying as shit.

Whhhaaaaaattttt? Pics are required.

Just to be clear this is a full tube frame GT car and its somewhat apart right now but sure I'll get some photos.

the FD actually has two systems, and you're mixing them.

the Double Throttle Control system, as posted by Kypreo is operated by a solenoid. these open simply based on temperature. if the engine is under, 70c (or something close to that) the Double Throttle Control solenoid stays on, and these stay closed.

the second part is that the stock throttle body has three butterflies, one for the primaries, and two for the the secondaries. these are staged like a mechanical secondary carburetor, so that the primary can open by itself some amount, and then after that all of the throttles open.

since its an old car, the secondary throttle probably does start to move at around 100kpa, but it is fully mechanical.

it would be very simple to switch this, although since the Double Throttle Control is not used as a throttle, it may or may not have some latency

I think the OP did have a bit of an error in it though - not your fault, as it was article that misdescribed the system. The double throttle only opened depending on coolant temperature and wasn't dependent on engine vacuum/boost. I haven't checked but I reckon the solenoid would have taken its signal from a location that was always under vacuum to ensure the double throttles close irrespective or primary throttle position.

Upon further thought, controlling this in the way you propose is actually quite simple - you could just control the OEM solenoid as a digital aux output and switch it via RPM/TPS/MAP, or you could put in a MAC valve or similar or have it a fully progressively mapped PWM output.

So you mean the the butterfly plates in the fd uim? The very first thing anyone does when they pull a uim off is rip those out and toss them in the trash...

Their entire point is to ensure you dont see substantial throttle when the engine is cold regardless of what you do with the pedal, which can be countered with the use of a modern ecu.

If you are going to do that anyways for the purpose of having independent control of the secondary throttle plates why not use a FD tb in the first place? Under what tuning scenario would you need it to be different than the way the mechanical linkage works as it is?

Skeese

I can see wanting to have a DBW throttle instead of a FD throttle plus IAC, if you didn't start with an OEM FD setup. I think the FD's second throttle blade begins opening around 30-35% throttle position, according to the TPS sensor. I can take some photos or video showing TPS volts vs throttle blade angle, if anyone would be interested to see that.

Skeese, I haven't seen dyno plots to prove or disprove this, but it sounds like Mr RGHTBrainDesign's theory is the engine might make better power with the Double Throttle valve closed at low-RPM, similar to the idea behind Honda VTEC. I think I've heard this claimed by Carlos Lopez, there are a few youtube videos that have been posted by some of the guys who work for him or maybe visit his shop often.

I can think of multiple if you're trying to build a fully functional oem-like build. Partial throttle lockout for valet modes, much easier and repeatable staging points unrestricted by the diaphragm used in stock configs, interesting traction control strategies that some OEMs are doing. It's just a nerd toy but I like the idea of DBW now that we have ECUs that are somewhat affordable to control it.

In the OEM setup, staging is done mechanically via the throttle body linkages, not by diaphragm (although I'm not disagreeing with you that doing electronically allows you set up staging points wherever you want).

People seem to be getting this confused. What RBD and I are referring to are the secondary throttle plates in the manifold that are pressure actuated, not the secondary plates in the throttle body that are mechanically actuated. Hence (and he corrected me on this the other month because even though I've been looking at my manifolds and deciding on the DBW setup I'm a 'tard) using a DBW throttle and some sort of stepper/solenoid to open the plates in the manifold.

You would think after three videos and a full explanation that it would sink in. I think it's laziness and lack of comprehension before "debating" this small project.

The thing this thread needs is MORE projects of value. I already have one figured out for us, so let's move on and continue progressing with engine control systems.

I'm not getting confused about anything. I'm clearing up confusion. If the merits of this modification are to be evaluated, it is important to determine the parameters of what is being compared. You referred to a benefit of RBD's approach being "much easier and repeatable staging points unrestricted by the diaphragm used in stock configs". The stock config, while involving a vacuum driven actuator, does not do any sort of staging via pressure. The secondary throttle plates in the UIM are purely on/off dependent on coolant temperature - that's all they do - so it does not present any kind of limitation or restriction on the staging of primary vs secondary intake port timing as your post suggested. The actual staging is done via the throttle body, mechanically. The secondary plates will transition from closed to open by reference to a fixed throttle opening angle, but even this could be easily modified/tuned by playing with the linkages (eg you have a ported engine and want to maximise low load torque). This is actually a simple, repeatable, 100% error-free method of staging and has nothing to do vacuum. Arguably it is also more reliable as the secondaries will never get stuck closed through faulty solenoid, vacuum leak, cracked hose etc (although I'm sure RBD will have those bases covered).

Now, in RBD's approach, because he has a single plate DBW throttle body, he loses the mechanical staging but could potentially reintroduce some form of primary/secondary staging by controlling the UIM double throttle plates. Therefore, the comparison being done is between primary/secondary staging by throttle position alone (the OE setup) vs primary/secondary staging based on (potentially) multiple parameters.

I suppose so. :)

I wasn't going to bring this up on here since I don't think anyone else is doing it, but the whole Throttle Mass Flow with the Emtron KV8 can utilize those Pre-TB and Post-TB MAP sensors as a high-flow Mass Air Flow, so my hidden agenda was to actually control this using throttle mass flow generated by those. The one that pertains to everyone though is MAP vs. RPM.

After hundreds of hours behind a laptop with the Honda doing secondary butterflies in the intake manifold and blending with VTEC, it became apparent to me that there should be more than just a TPS relation (mechanical linkage) to controlling primary/secondary transition. Going WOT on a factory FD throttle body will just dump open the secondary butterflies which as you can guess, will LAG the system.

I truly believe a 90mm DBW TB is superior to a factory FD or more specifically FC (in my case since I had a 13BT grafted into my 1st Gen Rx7), and therefore am building systems around it to give me power out of the hole on corner exit in tight mountain roads. That's what this ONE experiment is about. Just getting that low RPM torque out of a small displacement motor. Sure as fuck works for the Honda, so believe me when I say we can do it better for the Rx7.

So this is good and done. Let's move on and continue development on another project. Any ideas?

you might think about looking at how Mazda did this with the Rx8, they call it an SSV

If you don't mind a huge project, I think it would be interesting to try an intake setup similar to the E46 BMW M3. Those engines use DBW-actuated individual throttles near the intake ports plus a very large IAC solenoid. The IAC solenoid is so large they use it to supply all the airflow when cruising, the DBW throttles are completely shut. This seems to solve the problem of synchronizing lots of individual throttles at low throttle angles. If I had lots of time and money to burn I would try to build something like this for a peripheral-ported engine, possibly retain the OEM side ports but ideally I'd like to block them off completely.

On the more realistic side of things, I'm very interested to try an ECU-controlled exhaust cutout before the cat converter. If you haven't seen the Monsterbox build thread in the 3rd Gen section, it's one of the many cool things he's doing plus cheap enough that I could justify spending money on it. The car might have some hope of smelling OK at idle, and you could still have all the benefits of less exhaust backpressure at full throttle.

There is a seller in Australia who has been developing high performance rotary-specific mufflers and exhaust components for many years called AES. He also has a range of butterfly cut-out valves specifically for this purpose. They are engineered to tolerate turbo rotary exhaust temps. Some have been used to control EWG dump pipes, while others for reducing noise or tuning exhaust backpressure. There's some info here: Active Exhausts and Active Exhausts Information plus some of his more recent product developments are showcased on his Facebook page.

I feel like that's super easy. Just implement the exact same control strategy as the UIM Secondary Throttle solenoid and have it control a vacuum solenoid cutout or electronic motor. I was going to do this with my factory choke knob on the FB as an override.

Nice use of choke knob. I have been thinking of what to use mine for. I'm going to try to install a rotary potentiometer behind it and use it as a boost trim.

The next real thing in my to-do list is an overdesigned intake manifold heatshield.

• Tri-layer Design
• Covers Top of Turbine Housing to Protect Hood, Full Exhaust Manifold, Wastegate Pipes (Wastegates need fresh air), and part of the downpipe.
• Mica Outer (closest to exhaust)
• Ceramic/Fiberglass Inner (Air Insulator)
• Mica Inner (closest to intake)
• Standoffs from Intake Manifold UIM/LIM Studs and Shock Tower (either side)
• Full Heat Transfer Equations on here... I'll compare materials and placement with real figures. Might as well throw real engineering behind the efforts.

Heat shields are cool, but the intake manifolds are going to tend to get hot because they're strapped to the engine block. Nobody had had much luck with phenolic spacers on the lower manifold, but it might work with the upper. Even then, there's negligible heat transfer from hotter-than-ambient charge air and hot-as-the-block intake manifold, due to a relative lack of surface area and the sheer speed of the charge air.

Cool project though. Be interested to see what you come up with.

The phenolic spacers are just like polyurethane for suspension. Good for about a week before failure. Great point.

What I was referring to here was an exhaust manifold cover that's located between the shock tower, over the turbo, manifold, and downpipe, and connecting to the intake manifold.

Besides going with the HeaderShield cover for my entire setup, this will be a serviceable/removeable heatshield that is more for protecting paint and cleaning up the engine bay. I think the way Eric Xue (Corner Balanced) did his header heatshield is a perfect example. I'll link it here, just imagine it with two outer shells and a fiberglass/ceramic inner insulation.


I know he did a later video showcasing the work from my buddy (FFR Fabrication), but this is the one I could find.

Just as first hand feedback from a relatively repeatable exercise, i used to regulary notice a drop in torque while at "heavy cruise" up a steep hill near where I was living which corresponded with the engine reaching 70C. I had attributed it to charcoal cannister vent becoming active or a crude step in fuel/ignition trims in the apexi but the throttle staging makes sense, i would have to apply more throttle to then maintain speed. If I switch to a better ecu I will definitely map it. Even if the resolution on the combustion pressure sensors isn't great at those low loads being able to log 30 mins or more of data for averaging at lower engine speeds on the plex should give pretty decent results for genuine on road conditions.

I have been planning out my next build and was also thinking about how to use and control the secondary throttle to retain the progressive nature of the throttle. I was thinking more along the lines of an electric motor control them with the ECU but your much further into it. Wish I saw this sooner. With all the modern ECU's being used these days, I'm surprised this has not been tried yet that we know of.

In your video I see you can open and close the secondaries without interference with the FFE adapter and GM TB. Have you check for interference when the DBW throttle butterfly moving thru its range? I know you mentioned turning the TB upside down, which would change the way the b'fly travels. I would think you want it so that the b'fly opens inward from bottom so the air would be better directed to the primary runners.

wow this is a very interesting thread, i need to read and re-read it over to get my head around it.

looks like ill be visiting my tuner this week with a bunch of questions!

i am very lucky to have a dyno at our workshop so theres lots of ability to test the absolute crap out of this on my s6 intake