RX8 Renesis Rotary eSC

B

brettus8

Member
Had been interested in doing this for years but It wasn't till I came across Alex's videos that I was inspired to give it a try.
However, I'm not interested in drag racing, I wanted a system suited for everyday practical use. So I had some challenges to achieve that but do now have a working setup.
specs :
Supercharger: Speedmaster P2
Motor : Castle Creations 2028 800kv
Electronic speed controller : Hobbywing Max4
Batteries : 2x 6s lipo (50.4v) 7000mAH 120C (better batteries ordered)
Charger : icharger x12 with maximum charge rate of 450W @ 50.4V (as tested)
System nominal voltage: 48v
Max boost: as measured - 3.5psi
Tune : Self tuned with Mazdaedit all stock fuel system / coils etc.

After some late night tuning the night before, I took my first shakedown test drive a couple of days ago.
System performed pretty well, but as expected there is lots to work on.
*The batteries I bought were fairly cheap LIPOs that did what I hoped (IE gave me a start) but are obviously not going to be satisfactory for this task. So I've ordered some more powerful batteries already. Unfortunately I was unable to buy the SMCs Alex recommended as they wont ship out of the US and their Honk Kong store wont be trading till well into next year - so they tell me. So I ordered two CNHL 9500 90c s - the brand seems to do ok in testing by this guy -https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons
*Performance isn't earth shattering and I haven't taken it past 6000rpm yet . But when batteries were at full charge there is definitely a noticeable bump in power at 3.5psi Boost.
* DC-DC charger I purchased is amazing- but is a little cumbersome to get going at startup.
*Battery/speed controller box is a major PIA to get to - but It needed to be out of the engine bay so I put it behind the front bumper.
*I knew the maf setup was going to be problematic - and .......... it is!
 
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Power gains look like they as I hoped - 57whp up top with 30-40 all the way through. Log was done on a fully charged battery- with new batteries I should get at least this consistently as they become discharged.
Red/blue is with eSC at 3.5psi
Green/yellow is the stock engine before SC was fitted.

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brettus8 said:
Power gains look like they as I hoped - 57whp up top with 30-40 all the way through. Log was done on a fully charged battery- with new batteries I should get at least this consistently as they become discharged.
Red/blue is with eSC at 3.5psi
Green/yellow is the stock engine before SC was fitted.

View attachment 815
Click to expand...
Great job. Do you have a blow-off valve and if so where is it located, before or after the MAF sensor. What are the details behind the challenges that remain to be addressed. What ratio to motor are you running on the blower and are you monitoring the current draw for peak current values?
 
No BOV - no strange noises so far so don't think I need one at this boost. Main challenge is getting batteries good enough to hold voltage over an entire pull. Hopefully these new CNHL9500 90c jobs do the trick. Ratio is 14 drive to 18 driven. Just borrowed a device to read max. amps. Was 100 on the bench with a 25mm hole ..... I think it's gunna be more than that though.
 
You're at a 1.33 : 1 drive ratio, that's almost 1:1, I asked about amp draw because that's a good way to assess whether you can go up or down in the ratio to either improve efficiency, or get more boost. In other words if you're still within motor and battery specs with the current setup, you can perhaps make that ratio 1:1 and get a little more out of it, not that there's anything wrong with your 30% power increase at your boost level of 3.5 psi.

Since this is not a traditional turbo arrangement, and the discharge from the supercharger is so close to the MAF sensor, perhaps a blow-off valve ahead of the MAF would be a good idea to make sure there is no air turbulence related interference with the MAF sensor from airflow pulsing that might be associated with the throttle slamming shut at times, basically a smooth airflow under all conditions makes for more accurate metering. It may even be necessary to install a honeycomb insert to make the airflow over the meter more linear, as many enthusiasts running traditional setups on modern engine management systems have found very helpful at improving drivability.

Have you considered using a hybrid battery from a car with much greater capacity in place of the small RC packs especially since what you have is apparently dropping off before you reach full potential?

Your hp curve climbs all the way through, but your torque curve looks like it starts to drop off way earlier than it should suggesting to me your supercharger flow started dropping off from perhaps battery drain, motor heat maybe. That low level of boost shouldn't create that much heat in the air charge. Regardless this is a great job and thanks for sharing info to help me and others plan better. Please keep us posted.
 
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Thanks maticulus. I actually do heaps of turbo tuning for these cars so am well versed on the nuances of getting the maf sensor setup right. I knew it would be a challenge to tune the way I have it, but seeing as I'm a tuner, I thought I'd give it a crack. The are some advantages to having it where it is.
I do have a honeycomb in place and have made some subtle mods to that to try and get a good reading. Suffice it to say, it's not perfect, but it is working satisfactorily.
My aim for this setup was - the least amount of modifications for the most power. So a 50whp bump in power with no mods to the fuel/ignition system is right in the sweet spot I was aiming for. Re the batteries - will try the new ones I have coming first - hopefully they meet my expectations.
Seeing 25C above ambient at the end of a 2nd gear pull. Not too terrible and within the boundaries for premium pump fuel(98ron) I think. But I expect that to increase with better batteries so don't envisage changing the drive ratio at this stage.
 
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Update :
Just came back from a test drive on a windy road.
Wanted to test viability to see if the eSC is actually worth having in this scenario.
1/ Still on cheaper batteries so I expect improvement once the new ones arrive.
2/ Was able to drive hard on and off the boost for about 10 mins before battery was drained and starting to overheat.
3/ Max IAT recorded 52C at ambient temp of 24C.
4/Max battery temp recorded 51C (high temp charge cutoff activated) but was in low 40s most of the time. Battery seems to be getting good cooling at speed where I have it, but starts getting hotter when stationary.
5/To get from 'storage' voltage to full charge seems to only take 5 -10mins which, by happy coincidence, is about how long it takes to warm up the engine. But from low charge to full it takes a LOT longer . Need to define this better with accurate times.

Overall , the extra performance was nice but I was spending too much time monitoring stuff to really enjoy the drive. Was encouraged enough to believe that this setup could indeed be viable for this type of use.
The suggestion to have the eSC partially spooled might improve the experience further. I have the eSC acceleration 'punch' at quite a low setting ATM so might experiment more with that first.
__________________
 
Update:
Fitted new CNHL 90c 9500mah batteries. Didn't really notice much difference but they do at least last a bit longer than previous ones and hopefully wont overheat when pushed.
Also fitted larger 15T pinion. Made a little bit more power, but in testing (after a short period of heat soak) I heard some engine knock. So I decided that without intercooling the 14T is as far as I should go.

Noticed that at top end the boost drops off by 1/2psi (from 3.5 to 3) . I assume this is because the engine Ve improves from 6000 to 9000 when an extra port opens. This must cause a sudden jump in amps with a corresponding drop in voltage. That's what I think is happening anyway.
 
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brettus8 said:
Had been interested in doing this for years but It wasn't till I came across Alex's videos that I was inspired to give it a try.
However, I'm not interested in drag racing, I wanted a system suited for everyday practical use. So I had some challenges to achieve that but do now have a working setup.
specs :
Supercharger: Speedmaster P2
Motor : Castle Creations 2028 800kv
Electronic speed controller : Hobbywing Max4
Batteries : 2x 6s lipo (50.4v) 7000mAH 120C (better batteries ordered)
Charger : icharger x12 with maximum charge rate of 450W @ 50.4V (as tested)
System nominal voltage: 48v
Max boost: as measured - 3.5psi
Tune : Self tuned with Mazdaedit all stock fuel system / coils etc.

After some late night tuning the night before, I took my first shakedown test drive a couple of days ago.
System performed pretty well, but as expected there is lots to work on.
*The batteries I bought were fairly cheap LIPOs that did what I hoped (IE gave me a start) but are obviously not going to be satisfactory for this task. So I've ordered some more powerful batteries already. Unfortunately I was unable to buy the SMCs Alex recommended as they wont ship out of the US and their Honk Kong store wont be trading till well into next year - so they tell me. So I ordered two CNHL 9500 90c s - the brand seems to do ok in testing by this guy -https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons
*Performance isn't earth shattering and I haven't taken it past 6000rpm yet . But when batteries were at full charge there is definitely a noticeable bump in power at 3.5psi Boost.
* DC-DC charger I purchased is amazing- but is a little cumbersome to get going at startup.
*Battery/speed controller box is a major PIA to get to - but It needed to be out of the engine bay so I put it behind the front bumper.
*I knew the maf setup was going to be problematic - and .......... it is!
Click to expand...
-3.5psi??

I am so new to all of this, that I make green grass look blue.
How do you turn on and off your DC motor?
Or is it like traditional super/turbo charge systems where it is just on as soon as the ignition switch is turned?

Traditional superchargers use the BOV? for low rpm, low torque, parts of engine operation; did you not use one because this is "electric boost"?
 
professional said:
-3.5psi??

I am so new to all of this, that I make green grass look blue.
How do you turn on and off your DC motor?
Or is it like traditional super/turbo charge systems where it is just on as soon as the ignition switch is turned?

Traditional superchargers use the BOV? for low rpm, low torque, parts of engine operation; did you not use one because this is "electric boost"?
Click to expand...
yes ..3.5psi
ESC starts the motor from a signal I'm taking off the car ECU for rpm. Put this in series with a vacuum switch so it's load/rpm based.
Only reason for not using a BOV is that I'm not running enough boost to need one - nothing to do with electric or not.
 
Took the car for a decent drive through the 'twisties' a couple of days ago to see how long the batteries would last etc.
Managed 24 mins of 7/10ths driving (public road so not going too wild) before the batteries ran out of juice. The ambient temp was 22C and the batteries reached 45C max. Logged the run and counted 70 times it went into boost at an average of 3.5 secounds /time . Approx. 4 mins total in boost. Pretty happy with that - that's a decent drive. New batteries were worth it!

I ran my charger the whole time including when in boost (unlike the torque-amp). It's only 400w which works out at 1C for the batteries. I don't see any problems doing it this way even though it's not recommended for lipos.
 
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brettus8 said:
Took the car for a decent drive through the 'twisties' a couple of days ago to see how long the batteries would last etc.
Managed 24 mins of 7/10ths driving (public road so not going too wild) before the batteries ran out of juice. The ambient temp was 22C and the batteries reached 45C max. Logged the run and counted 70 times it went into boost at an average of 3.5 secounds /time . Approx. 4 mins total in boost. Pretty happy with that - that's a decent drive. New batteries were worth it!

I ran my charger the whole time including when in boost (unlike the torque-amp). It's only 400w which works out at 1C for the batteries. I don't see any problems doing it this way even though it's not recommended for lipos.
Click to expand...
The most significant benefit to an electric turbo vs. a traditional is the efficiency. I don't believe I mentioned that regarding your posted dyno results previously. At sea level 1 atmosphere is 14.7 psi, theoretically if you apply that much boost to a motor it should double the power, until deductions are made for inefficiency particularly in a traditional turbo from excess heat, plumbing and exhaust restriction and intercooler if installed.

Your 3.5 psi/14.7 psi = 23.8% theoretical power gain, without any correction for expected efficiency losses. 189 hp baseline x 1.238% = 234 theoretical hp at 3.5 psi. Deductions for projected losses would bring that value to a lower actual by an arbitrary 10% at that low boost level so let's say the actual outcome should have been ~234 x (100% - 10%)= 210.6 hp after efficiency taxes if it was a traditional.

What you actually achieved was 246 hp. 246 boosted hp/189 baseline hp = 1.3016 % increase - 1= 30% increase in power from 3.5 psi of boost, which is less than 25% of an atmosphere. You achieved more than you put into it at that boost level by exceeding the unpenalized theoretical output at that boost level. I believe a hybrid battery from production vehicles with much higher amp-hr ratings would make these setups solid winners. If you end the day with battery power on the table, the setup is golden.
 
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That virtual dyno result was on a cool morning (18C) before the engine/eSC was heatsoaked. It's the best result I've seen so far so possibly it's a little flattering. Pretty much every log is over that 234 mark however so it does seem to be doing particularly well for the amount of boost there is.
 
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Thinking about why we get so much power for so little boost. ........... Saying 14.7psi should double the power assumes that all the things that rob power from an engine will still be doing that at the same percentage of the total as you raise boost. This isn't what actually happens. The water pump/alternator/AC , internal engine resistance to rotation, drivetrain drag all reduce as a % of total power the more you make. On my turbo car 14.7psi pretty much does double engine power to the wheels, so you would think the theory is holding true there ..... but actually it isn't. It's getting the advantages mentioned above but the negative of added backpressure which robs power. So it's just a coincidence where the positives and negatives combine to make it LOOK like 14.7psi doubles power.
With the eSC however you don't get any exhaust backpressure robbing power so each pound of boost is worth more and the 14.7 calculation goes out the window.
 
brettus8 said:
Thinking about why we get so much power for so little boost. ........... Saying 14.7psi should double the power assumes that all the things that rob power from an engine will still be doing that at the same percentage of the total as you raise boost. This isn't what actually happens. The water pump/alternator/AC , internal engine resistance to rotation, drivetrain drag all reduce as a % of total power the more you make. On my turbo car 14.7psi pretty much does double engine power to the wheels, so you would think the theory is holding true there ..... but actually it isn't. It's getting the advantages mentioned above but the negative of added backpressure which robs power. So it's just a coincidence where the positives and negatives combine to make it LOOK like 14.7psi doubles power.
With the eSC however you don't get any exhaust backpressure robbing power so each pound of boost is worth more and the 14.7 calculation goes out the window.
Click to expand...
The 14.7 psi theory base still applies as it relates to the amount of air flow/density going into the motor, and that's independent of the accessories involved. None the less, those parasitic losses probably fall under the exponential rule as power level increases. Still far greater return than a traditional turbo under the same circumstances.
The accessories generally are not counted anyway as factory motors are rated in full dress as if it was in the car so that base power includes those parasitic losses and they would be the same at 14.7 psi as they are at atmospheric conditions provided the rpm range for the power rating is the same. So except for the weight the boost components add to the platform, along with the charge temp increase, the gain should be right near 100%.
 
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