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Did manage to see what happens with boost over a pull from 3000to redline.
2nd gear : holds 3.5psi all the way to redline
3rd gear: holds 3.5psi to 6500ish then drops to 3psi
If the compressor speed was constant (per flow map) it should hold same boost all the way to redline.
I can only surmise that the small drop-off happens after the APV opens (increasing Ve) and is due to the extra amps required to maintain boost causing a corresponding drop in voltage. Voltage directly corresponds to RPMs so RPMs drop and therefore boost drops.
Or to put it simply - the batteries aren't keeping up.
Did manage to see what happens with boost over a pull from 3000to redline.
2nd gear : holds 3.5psi all the way to redline
3rd gear: holds 3.5psi to 6500ish then drops to 3psi
If the compressor speed was constant (per flow map) it should hold same boost all the way to redline.
I can only surmise that the small drop-off happens after the APV opens (increasing Ve) and is due to the extra amps required to maintain boost causing a corresponding drop in voltage. Voltage directly corresponds to RPMs so RPMs drop and therefore boost drops.
Or to put it simply - the batteries aren't keeping up.
It’d be interesting to data log current (and voltage) into the compressor drive motor across RPM. From my understand current should be roughly proportional to flow. Not having as much experience with FI on rotaries I never realized the extreme mass flow requirements on the rotary due to the 2x effective air volume per rotation in combination with RPM.
I'd be curious how the e-charger would perform at like 5 psi (or so) from 2-6k rpm and either turning off when aux comes in or run like 1 psi boost to redline, etc. Personally like to see how much low end torque can be produced.
One of your early charts showed a gain of around 60 whp and 40wtq. Awesome results but I wonder if the figures could be reversed somehow. My best uneducated estimates would potentially put it somewhere around an approx 230whp / 200wtq instead of 250whp / 180wtq and if possible I think the low-end torque increase would be more beneficial than the additional top end hp. I do understand that you only made those top end hp numbers with some boost and would expect peak to come down (respectively) without it.
Did manage to see what happens with boost over a pull from 3000to redline.
2nd gear : holds 3.5psi all the way to redline
3rd gear: holds 3.5psi to 6500ish then drops to 3psi
If the compressor speed was constant (per flow map) it should hold same boost all the way to redline.
I can only surmise that the small drop-off happens after the APV opens (increasing Ve) and is due to the extra amps required to maintain boost causing a corresponding drop in voltage. Voltage directly corresponds to RPMs so RPMs drop and therefore boost drops.
Or to put it simply - the batteries aren't keeping up.
There’s one factor that may be a contributor; torque start dropping after a certain RPM. If you can get a “dyno” of the motor from supplier, or at least a RPM of where max torque should be given, it might be of relevance. If you are above this RPM when driving compressor, the equation becomes more complex. You may be at the edge of this…?
I do not know enough about this subject, but strongly suspect it’s because of Eddy currents internally in the motor.
I'd be curious how the e-charger would perform at like 5 psi (or so) from 2-6k rpm and either turning off when aux comes in or run like 1 psi boost to redline, etc. Personally like to see how much low end torque can be produced.
One of your early charts showed a gain of around 60 whp and 40wtq. Awesome results but I wonder if the figures could be reversed somehow. My best uneducated estimates would potentially put it somewhere around an approx 230whp / 200wtq instead of 250whp / 180wtq and if possible I think the low-end torque increase would be more beneficial than the additional top end hp. I do understand that you only made those top end hp numbers with some boost and would expect peak to come down (respectively) without it.
Keep it up, really promising project imo!
Cheers,
yeah I tend to agree, now that I've been driving it around for a while.
Have taken several people in it. It's a simple flick of a switch to go from N/A to boosted and most are very impressed with the difference. But for me personally .... it still feels underwhelming low down.
Although .............. just had my daughter drive it with me in passenger seat ..... gave me an entirely different perspective . Definitely feels strong AF!
There’s one factor that may be a contributor; torque start dropping after a certain RPM. If you can get a “dyno” of the motor from supplier, or at least a RPM of where max torque should be given, it might be of relevance. If you are above this RPM when driving compressor, the equation becomes more complex. You may be at the edge of this…?
I do not know enough about this subject, but strongly suspect it’s because of Eddy currents internally in the motor.
Will be interesting to see if dropoff is still 0.5psi when I go to slightly bigger pulley.
I'd be curious how the e-charger would perform at like 5 psi (or so) from 2-6k rpm and either turning off when aux comes in or run like 1 psi boost to redline, etc. Personally like to see how much low end torque can be produced.
One of your early charts showed a gain of around 60 whp and 40wtq. Awesome results but I wonder if the figures could be reversed somehow. My best uneducated estimates would potentially put it somewhere around an approx 230whp / 200wtq instead of 250whp / 180wtq and if possible I think the low-end torque increase would be more beneficial than the additional top end hp. I do understand that you only made those top end hp numbers with some boost and would expect peak to come down (respectively) without it.
Keep it up, really promising project imo!
The TorqAmp with a single turbo and bypass valve with max boost would get close to this type of behavior. The TorqAmp doesn’t have enough mass flow to provide boost past 5k RPM but can provide 5.8psi of boost max probably in 2k-3k range rolling off at higher RPM. After 5k RPM then you would just basically run NA through the bypass.
I don’t know how sophisticated the motor controller is, but with the right electronics one could program in to adjust boost based on RPM from crank (?) sensor.
Also a much simpler way would be to limit current into motor to establish a ceiling on mass flow effectively lowering boost at higher RPM. And then just crank the boost way up and let it limit down at higher RPM. In a way, I think Brett is seeing this with a slight drop off in boost at high RPM. Maybe just crank up the boost and see what happens even if it flattens out at the top end? Basically try to improve that low end torque and let the natural limitations of the battery/motor/pulley limit boost. I asked an earlier question if the Renesis could tolerate higher boost at lower RPM vs higher RPM alluding to this possibility…
I'd be curious how the e-charger would perform at like 5 psi (or so) from 2-6k rpm and either turning off when aux comes in or run like 1 psi boost to redline, etc. Personally like to see how much low end torque can be produced.
!
Well, I found the answer to this, at least in part.
Tried a slightly larger pulley (15T vs 14T) and boost increased to 4.3psi. Did some logging and it did make a little more power. But during one test after a short period of heat soak, I got some audible death rattle from the engine at around 4000rpms. Fortunately - no damage done.
After much thought I decided not to push my luck any further and dropped back to the 14T pulley.
So this will be my self imposed limit for the current setup.
Update:
did another circuit of my favorite twisty road and learnt some more:
1/Starting with a full charge I am now able (with the new batteries) to drive on and off the boost for 24 mins. Which, coincidentally, is the length of the drive. I count on the log 70 times the eSC goes into boost over that time with the average time in boost of approx. 3.5 seconds so approx. 4min total time in boost.
2/Batteries reached a peak temp of 45C at the end of the run. Ambient temp was 22C and batteries started at 3.9v were then fully charged to 4.15V/cell then fully discharged to 3.5V/cell over the 24min period of on/off boost. So these new batteries, while not increasing engine power, are much better for the job.
3/On the way home while recharging to storage voltage ( 3.9V) the charger got very hot (around 75C) and almost hit high temp cutoff. I did do several boost pulls on the way as well so charger was at max. (400W) for around 30 mins.
4/E-motor was too hot to touch at the end of the run. Didn't have temp sensor with me unfortunately but would estimate it at between 60-80C. I think a more progressive on switch will help with this.
Biggest takeaway from the drive : I have changed my mind : I definitely need to have a more progressive feel to the SC . With boost coming on harder as throttle is depressed further. AS is just feels too on/off and that does distract from the smoothness of the drive. so I think that's where I need to focus now.
Keep in mind that magnets/coils in hobby RC motors degrade terribly with heat. The magnets demagnetise and the coils melt(well not the copper but the enamel insulation) leading, in time, to less power being available.
Like so:
This is an engine that either got mechanically stuck in one position and the ESC kept trying to spin it(thus forcing a great current through a set of coils) or it was run too hot, too long. I would not heat an expensive motor past 70C....
As for more delicate control.... let me know. Can be MAF/TPS/RPM based and at the same time not bothering anyone on the CAN bus. See https://www.rx8club.com/series-i-eng...ssages-276101/ for a full list of parameters that are just there on the CAN bus waiting to be listened to and used. These parameters are NOT like those when you do logs with mazdaedit or any other logger... for those you literally bother the ECU to tell you what's the MAF flow at a certain point, what I'm talking about is already broadcasted on the bus automatically and you just... listen to that. The update rate is phenomenal!
Last edited by ciprianrx8; Jan 15, 2025 at 01:50 AM.
How about load ?
What would the wiring look like ?
What does the motor controlling have for I/O interfaces? Sure there’s a lot of data coming out the OBDII port but there has to be a microprocessor and CAN bus interface chip to sniff the port extract those values out of the serial data stream.
The wiring is easy - just T into or even just buy the connector to plug in if you don’t want to dink with your wiring. I’ve wired up a couple vehicles including RX-8 to connect to the head unit through adapter to Pioneer head units so I can get that streaming data along with engine codes and tire pressures. I can help you figure out what wires if need be.
But again not sure how you easily grab that data if there is not a port on the actual motor controller, but maybe there is…. Maybe there is off-the-shelf device or you could program an Arduino…
How about load ?
What would the wiring look like ?
Load = maf/rpm/displacement * some IAT/BARO compensation. We have maf, rpm, iat readily available on the CAN bus. I haven't done this on my car as the setup allows me to pool the ECU for abs load parameter, but on other setups this is a no-go. Because when you want to do logs, you can't have 2 devices pool the ECU for parameters.
The wiring would require a switched 12V, a ground, CAN high/CAN low wires, perhaps a tiny screen to show the power setting for the eSC and a boost sensor, and a 3 pin servo lead to feed your ESC (Electronic speed controller) with signal. Easy way out would be to put these in the ECU housing, or the cluster housing, or have an enclosure made to resemble a pod of the sorts, or in the ashtray...
Last edited by ciprianrx8; Jan 18, 2025 at 10:52 AM.
Load = maf/rpm * some IAT/BARO compensation. We have maf, rpm, iat readily available on the CAN bus. I haven't done this on my car as the setup allows me to pool the ECU for abs load parameter, but on other setups this is a no-go. Because when you want to do logs, you can't have 2 devices pool the ECU for parameters.
The wiring would require a switched 12V, a ground, CAN high/CAN low wires, perhaps a tiny screen to show the power setting for the eSC and a boost sensor, and a 3 pin servo lead to feed your ESC (Electronic speed controller) with signal. Easy way out would be to put these in the ECU housing, or the cluster housing, or have an enclosure made to resemble a pod of the sorts, or in the ashtray...
There’s a lot of electrical/programming work to do inbetween the lines…
Last edited by schm1347; Jan 16, 2025 at 07:10 AM.
You would be surprised how deep the rabbit hole of OEM drivability goes. Also the reason why most don't even bother to make their cars drivable past the point where they turn on and _maybe_ idle when the weather is nice.
Update :Decided to fit a water/meth system and refit the larger drive pulley.
Result shown below. It really has excellent midrange now but top end didn't really improve much. This seems to have again exposed the weak link of the setup - the batteries. By the time the engine has reached high rpm the batteries have suffered a severe voltage drop (down to 40V) and boost drops away as a result.
Even though it now feels super quick in mid range the top end fall off means peak hp isn't really that impressive. Was going to dyno but not sure it's worth the effort now.
Another issue that has appeared is that the P1 red injectors are maxing out at low rpm..... gunna need to swap in some yellows if I want an early switch point for ESc
Another issue that has appeared is that the P1 red injectors are maxing out at low rpm..... gunna need to swap in some yellows if I want an early switch point for ESc
No, merely the secondaries will come on and with them the SSV will open sooner. That is, if you didn't raise the minimum RPM for this past 0 (the stock setting once ECT > 0degc). Nesting conditions like this is bad.
No, merely the secondaries will come on and with them the SSV will open sooner. That is, if you didn't raise the minimum RPM for this past 0 (the stock setting once ECT > 0degc). Nesting conditions like this is bad.
The earliest the secondaries will come on (and SSV opens) is 3200rpm .... at that point the reds are maxing out causing it to run lean for several hundred rpms.
I know you found a map to open SSV sooner but after the latest epifan update -I don't have it anymore.
This can forbid the secondaries to come on, regardless of the required fuel qty. to be injected. I am not 101% sure of this but as far as I know this is how it works. Since in the factory tune it is set to 0 where it matters then the secondaries will come on as required, when the P1s have hit their maximum duty cycle(which tapers heavily with RPM increase). If you use this table to move the SSV opening RPM higher up, this is the worst way to do this.
This is the table for that:
You would set the 2500-3000 area to 40% and the secondaries would come on pretty much as soon as you touch the throttle. Keep in mind the SSV position is tied to the secondary injectors... at all times.
Update :Decided to fit a water/meth system and refit the larger drive pulley.
Result shown below. It really has excellent midrange now but top end didn't really improve much. This seems to have again exposed the weak link of the setup - the batteries. By the time the engine has reached high rpm the batteries have suffered a severe voltage drop (down to 40V) and boost drops away as a result.
Nice numbers! Looks like you added +40 lbs of torque throughout the entire power band; bet it's very rewarding having the additional midrange. This is with h2o/meth injection?
Nice numbers! Looks like you added +40 lbs of torque throughout the entire power band; bet it's very rewarding having the additional midrange. This is with h2o/meth injection?
It's starting to feel like the performance car it should be now.
Yes water/meth 50/50 (by volume) mix.
This is from last night when temps were a cool 19C, got more in the top end. Not 100% sure why but could definitely feel it kick more after APVs opened:
It's starting to feel like the performance car it should be now.
Yes water/meth 50/50 (by volume) mix.
This is from last night when temps were a cool 19C, got more in the top end. Not 100% sure why but could definitely feel it kick more after APVs opened:
What are the future plans for this, do you think you will bring this kit to market at some point? Seems like a great holdover option until one would want to do some sort of swap in the future, (rew/20b).
What are the future plans for this, do you think you will bring this kit to market at some point? Seems like a great holdover option until one would want to do some sort of swap in the future, (rew/20b).
It's not even close to what I would consider user friendly the way it is right now. I do have plans to rectify this and increase performance further so ...watch this space!
