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RGHTBrainDesign - Rotary Engine Development Projects
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.
After researching through Mitchell manuals and forum posts, it seems like there wasn't any solidified control strategy on RPM set point in which this solenoid would actuate the vacuum secondaries. It would open automatically via vacuum only (or rather, once it saw boost, it was going to be open). This is simply an ON/OFF flapper design, not a stepper motor, so as long as it's near flat when ON, and closed when OFF, it's good to go.
I'm surprised to see that no one else is manipulating this feature on their FDs when tuning on a factory intake manifold configuration using an aftermarket ECU. Haltech has a standalone style control for it even... "Dual Runner Control". What this control strategy gives us is the ability to create more power off of boost and realistically build it faster.
Before I venture into what my starting settings are, I'm interested to hear what everyone's thoughts are, except for the "Just remove that ****." comments. If that's your strategy, I suggest you spend a few hours reading a Fluid Mechanics book and your negative bullshit can be taken elsewhere. This is for development.
For this table, we have MAP on the Y-Axis and Engine RPM on the X-Axis. 0.0 = OFF and 100.0 = ON. This is the ON/OFF Solenoid attached to a Vacuum Reservoir, attached to the "Secondary Butterflies" of the FD UIM. The idea being that you want the secondary butterflies to open higher in the RPM band when you're producing more vacuum (less load), and open EARLIER when you're under higher loads due to the demand for more airflow being higher. As an example of this, Honda VTEC stages with the earliest operation at the highest load, and has a linear taper to higher RPM as less and less load on the engine is requested. VTEC might engage at 4500 RPM at 80kPa, and 5000 RPM at 40kPa. It's a linear sweep between there in which at 4750 RPM, it'll engage VTEC at 60kPa. Make sense?
Now applying these theories to Boost and control strategy you can see why the table looks like it does. I want the system to open no matter what vacuum I'm at over 4300 RPM because that small opening isn't enough, and if I can make boost at lower RPMs, I want the extra airflow to come into the secondaries right before it.
***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)."
My goal is simply to build out enough projects to do a discussion on something like this every month (using this same thread) and to see where some of you can contribute with your ideas. We can bounce off our experiences and wisdom to hopefully build a better forum community once again. All it takes is effort.
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.
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.
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 ****" 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!
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.
How would you propose we eliminate that variable or compensate for it?
***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!
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.
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.
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).
Originally Posted by Emtron ECU Manual
Using the throttle body size, pre and post throttle pressure, and the Navier-Stokes equation, the ECU has the ability to calculate air flow using this mode. TMF calculations are performed to allow accurate calculation of throttle plate position required during torque reduction requests. TMF calculations can also offer advantages when the throttle pressure ratio is low (partial throttle), and respond much faster in transient conditions.
Throttle Air Mass calculations report in units of g/s or g/cyl.Throttle Pressure Ratio is the ratio of Pre Throttle Pressure sensing vs Post Throttle pressure sensing (Boost Pressure vs MAP Pressure most commonly)Throttle Eff Area defines the actual effective area the throttle is at which does not have a 1:1 relationship with throttle position in nearly all cases. Effective area is based on air mass flow which is crucial to the ECUs Torque Management functions as well.Throttle Mass Flow measurement must be configured for use in the fuel model in order for the calculations to be used in the final air mass measurement of the ECU. Because TMF works best when throttle pressure ratios are low, it cannot be used 100% of the time. It must be blended into other forms of air mass measurement.
So after the light/transient fueling, the model simply reverts back to MAP vs. BAP (Barometric Pressure) with reference to EMAP (Exhaust Manifold Pressure).
Last edited by RGHTBrainDesign; 09-13-18 at 05:12 PM.
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 ******* 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.
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 truck and taking a spin on the monsterbox nascar-style cabledrive rear mounted mechanical fuel pump and just mounting the ******* 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!
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.
You're going to be my new best friend, I can tell.
"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.
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
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'm not mixing anything. Not once have I mentioned the FD throttle body in this project, at all. I'm purely talking about a better way to control the UIM's Double Throttle Control System and outlined it thoroughly.
Anyone running a DBW LS3 90mm TB will see the largest gain over doing this sort of modification due to the fact that they're losing the progressiveness of the factory FD TB and regaining control of the Primary/Secondary functions of the intake manifold as originally designed.
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.
I'm not mixing anything. Not once have I mentioned the FD throttle body in this project, at all. I'm purely talking about a better way to control the UIM's Double Throttle Control System and outlined it thoroughly.
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?
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.
09-11-18, 03:43 AM
RGHTBrainDesign - Rotary Engine Development Projects
