The 450whp Renesis engine - why it will never happen - theory
12-03-2020, 02:58 PM
#101
Brett.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are. And though numerically it may seem like an insignificant increase in compression, the effects are exponential. I admit I went super conservative with the 9.0:1 rotors as it was unexplored territory for me running them in an MSP-ONLY motor, but now that I have more empirical data the next step would be to test 9.4:1 and 9.7:1 rotors. Not sure if/when that will ever happen though.
Now on to my reply about the dyno results, RotaryMachineRX nailed it already on the rear gear.
Copied my reply from FB but applies here as well:
"The lazier than normal pulls and late/narrow power band with such a large frame turbo and small displacement motor is exacerbated by the ultra low 2.73 rear gear. We expected this, it's not exactly rocket science which is why we designed the setup to be nitrous-assisted but it hasn't been activated yet. The TPS was over-volting on these pulls (explains the throttle modulation you hear in the video) so we didn't get a chance to use it. If we were running a 4.88 or higher rear gear ratio that alone would significantly improve that graph to a much more "usable" power band, but our mph potential would go from ~200mph (w/ 2.73) to ~160mph (w/ 4.88+). Also keep in mind the turbo is sized more appropriately for our Phase 2 billet 3-rotor, so we're in no way implying that this is the optimal combination to achieve these HP levels, we know we can more efficiently do that with anywhere from a 66 to 76mm turbo. Anyways, the base tune is obviously far from done and we're more than stoked with these results at such an early stage in the tuning process, and more importantly with such promising telemetry. With this chassis, weight and aero combination we only need ~450WHP to 500WHP to go 200mph (Phase 1 goal) so the initial results have far exceeded any of our already high expectations of this "MSP-ONLY" #RENESIS."
Also, the motor is as solid as ever based on the increasing HP/TQ numbers per pull, post-dyno compression check, absence of any hairline cracks on the side housings and absence of any bearing material in the oil or filter.
We’ll know we’re nearing the flow limit of the motor or ports when increasing the boost doesn’t net any positive gains, or worse, we start losing power. The turbo certainly isn't going to be the limiting factor.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are. And though numerically it may seem like an insignificant increase in compression, the effects are exponential. I admit I went super conservative with the 9.0:1 rotors as it was unexplored territory for me running them in an MSP-ONLY motor, but now that I have more empirical data the next step would be to test 9.4:1 and 9.7:1 rotors. Not sure if/when that will ever happen though.
Now on to my reply about the dyno results, RotaryMachineRX nailed it already on the rear gear.
Copied my reply from FB but applies here as well:
"The lazier than normal pulls and late/narrow power band with such a large frame turbo and small displacement motor is exacerbated by the ultra low 2.73 rear gear. We expected this, it's not exactly rocket science which is why we designed the setup to be nitrous-assisted but it hasn't been activated yet. The TPS was over-volting on these pulls (explains the throttle modulation you hear in the video) so we didn't get a chance to use it. If we were running a 4.88 or higher rear gear ratio that alone would significantly improve that graph to a much more "usable" power band, but our mph potential would go from ~200mph (w/ 2.73) to ~160mph (w/ 4.88+). Also keep in mind the turbo is sized more appropriately for our Phase 2 billet 3-rotor, so we're in no way implying that this is the optimal combination to achieve these HP levels, we know we can more efficiently do that with anywhere from a 66 to 76mm turbo. Anyways, the base tune is obviously far from done and we're more than stoked with these results at such an early stage in the tuning process, and more importantly with such promising telemetry. With this chassis, weight and aero combination we only need ~450WHP to 500WHP to go 200mph (Phase 1 goal) so the initial results have far exceeded any of our already high expectations of this "MSP-ONLY" #RENESIS."
Also, the motor is as solid as ever based on the increasing HP/TQ numbers per pull, post-dyno compression check, absence of any hairline cracks on the side housings and absence of any bearing material in the oil or filter.
We’ll know we’re nearing the flow limit of the motor or ports when increasing the boost doesn’t net any positive gains, or worse, we start losing power. The turbo certainly isn't going to be the limiting factor.
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12-03-2020, 11:01 PM
#102
Brett.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are.
. I accept that the low compression rotors have had a major positive affect on the maximum possible whp result . What I also see though, is while it's a high peak number for a Renesis ..... it's not even close to a good result if compared to a pp exhaust engine. So you have to ask the question ...why ? I still strongly believe that comes back to the side exhaust port inefficiency as detailed here on page 1. Elliot has suggested it's to do with high IATs ... I can't see a 100whp lost due to that alone.Now on to my reply about the dyno results, RotaryMachineRX nailed it already on the rear gear.
Copied my reply from FB but applies here as well:
"The lazier than normal pulls and late/narrow power band with such a large frame turbo and small displacement motor is exacerbated by the ultra low 2.73 rear gear. We expected this, it's not exactly rocket science which is why we designed the setup to be nitrous-assisted but it hasn't been activated yet. The TPS was over-volting on these pulls (explains the throttle modulation you hear in the video) so we didn't get a chance to use it. If we were running a 4.88 or higher rear gear ratio that alone would significantly improve that graph to a much more "usable" power band, but our mph potential would go from ~200mph (w/ 2.73) to ~160mph (w/ 4.88+). Also keep in mind the turbo is sized more appropriately for our Phase 2 billet 3-rotor, so we're in no way implying that this is the optimal combination to achieve these HP levels, we know we can more efficiently do that with anywhere from a 66 to 76mm turbo. Anyways, the base tune is obviously far from done and we're more than stoked with these results at such an early stage in the tuning process, and more importantly with such promising telemetry. With this chassis, weight and aero combination we only need ~450WHP to 500WHP to go 200mph (Phase 1 goal) so the initial results have far exceeded any of our already high expectations of this "MSP-ONLY" #RENESIS."
I felt that they didn't go full throttle till the last 1000rpms ...why was that ?
My feeling about the narrow powerband is that the turbo is way too big for the engine and it's operating very close to the surge line. At any lower rpm it possibly wont hold full boost due to this. When you add nitrous to spool the turbo earlier you may just end up forcing the turbo into full surge ... will be interesting.
12-05-2020, 05:56 AM
#103
Thanks for posting here. Hope you don't mind the analysis ... I feel it's worth discussing and don't mind you proving me wrong again . I accept that the low compression rotors have had a major positive affect on the maximum possible whp result . What I also see though, is while it's a high peak number for a Renesis ..... it's not even close to a good result if compared to a pp exhaust engine. So you have to ask the question ...why ? I still strongly believe that comes back to the side exhaust port inefficiency as detailed here on page 1. Elliot has suggested it's to do with high IATs ... I can't see a 100whp lost due to that alone.
. I accept that the low compression rotors have had a major positive affect on the maximum possible whp result . What I also see though, is while it's a high peak number for a Renesis ..... it's not even close to a good result if compared to a pp exhaust engine. So you have to ask the question ...why ? I still strongly believe that comes back to the side exhaust port inefficiency as detailed here on page 1. Elliot has suggested it's to do with high IATs ... I can't see a 100whp lost due to that alone.You do see how that logic and therefore conclusion is clearly flawed right?
One is currently an apple and the other is an orange, but you’re treating them both as equals and drawing a conclusion between the two.
Now if that apple was to somehow more closely resemble the orange with a finished tune, an IC and a 4.88+ rear gear, then you could draw a more accurate conclusion between the results of one dyno to the other. But since there are no plans to turn the apple into an orange they can’t be accurately compared.
12-05-2020, 12:34 PM
#104
You’re comparing the dyno results of a handicapped setup (low rear gear ratio, big turbo, no nitrous) that has an unfinished tune to what the average dyno results would be of a fully tuned pp exhaust motor that is optimally setup (4.88+ gearing, big turbo, IC, etc.) and concluding that the MSP dyno is “...not even close to a good result if compared to a pp exhaust engine”.
You do see how that logic and therefore conclusion is clearly flawed right?
One is currently an apple and the other is an orange, but you’re treating them both as equals and drawing a conclusion between the two.
Now if that apple was to somehow more closely resemble the orange with a finished tune, an IC and a 4.88+ rear gear, then you could draw a more accurate conclusion between the results of one dyno to the other. But since there are no plans to turn the apple into an orange they can’t be accurately compared.
You do see how that logic and therefore conclusion is clearly flawed right?
One is currently an apple and the other is an orange, but you’re treating them both as equals and drawing a conclusion between the two.
Now if that apple was to somehow more closely resemble the orange with a finished tune, an IC and a 4.88+ rear gear, then you could draw a more accurate conclusion between the results of one dyno to the other. But since there are no plans to turn the apple into an orange they can’t be accurately compared.
However, you still have to massively improve your powerband width to reach your goal. So as far as the technical side of it goes. My thoughts. FWIW
Lack of an IC isn't going to hold you back ..... you have charge cooling via the fuels chosen.
The final drive ratio isn't holding you back ...... gearboxes have gears(you don't have to use 1:1) and dynos have ramp rates.
Oversized turbo .... yes definitely a problem ... possibly insurmountable IMO
Nitrous ..... will definitely raise your peak numbers but will it solve your ultra narrow powerband issue? If you went down a couple of turbo sizes ......maybe.
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JETS3T8 (12-05-2020)
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05-06-2021, 03:36 AM
#106
Brett.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are. And though numerically it may seem like an insignificant increase in compression, the effects are exponential. I admit I went super conservative with the 9.0:1 rotors as it was unexplored territory for me running them in an MSP-ONLY motor, but now that I have more empirical data the next step would be to test 9.4:1 and 9.7:1 rotors. Not sure if/when that will ever happen though.
I agree with you that a 100% 13B-MSP RENESIS is limited to somewhere around 450WHP, but not because of the size/shape/flow/placement of the side exhaust ports, I strongly feel it would be due to the 10:1 compression rotors. The elevated CCP/CCT/EGT/Blow-by created under boost is just too overwhelming on the hard/soft seals, rotors, housings, plugs, etc. Even 9.7:1 compression rotors have significantly less CCP/CCT/EGT/Blow-by under boost which is why they're the rotor of choice in almost all of the pro drag motors, many running 80+psi of boost. Granted those are all peripheral exhaust ports but the exhaust ports aren't "as critical" in terms of their effect on reliability & power as the actual compression & combustion events are. And though numerically it may seem like an insignificant increase in compression, the effects are exponential. I admit I went super conservative with the 9.0:1 rotors as it was unexplored territory for me running them in an MSP-ONLY motor, but now that I have more empirical data the next step would be to test 9.4:1 and 9.7:1 rotors. Not sure if/when that will ever happen though.
CNC setup and machining is underway and this will go into my next engine.
Edit : I'm not anticipating that this will unlock a lot more power TBH. My main objective is to allow 400ish whp on pump gas. But I will try and if it does that will prove your theory correct and mine............... wrong.
Last edited by Brettus; 05-06-2021 at 04:04 PM.
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05-07-2021, 05:44 AM
#109
I didn’t measure anything out as in actually parts, and I probably wasn’t even trying to be absolutely accurate, but let’s do that:
[displacement + combustion chamber volume ]/combustion chamber volume = Compression Ratio
for CR = 10:1
[displacement + combustion chamber volume ]/combustion chamber volume = 10
[displacement + combustion chamber volume ] = 10 combustion chamber volume
[displacement ] = 9 combustion chamber volume
displacement/9 = combustion chamber volume
**** theoretical combustion chamber volume = displacement/[CR - 1]
In theory a Renesis engine is 1.308L displacement
= 0.654L displacement per rotor
10:1 = 0.654L/9 = 0.0727L at TDC
9:1 = 0.654L/8 = 0.0818L at TDC
DeltaDisp = 0.0818L - 0.0727 = 0.0059L = 9cc
edit: so what I probably did was just roughly divide displacement by CR, but you have to subtract 1 to CR to get an accurate number.
however, I’m half asleep and maybe made a mistake. I won’t consider myself being belittled by having someone point it out, but would welcome having it corrected.
.
[displacement + combustion chamber volume ]/combustion chamber volume = Compression Ratio
for CR = 10:1
[displacement + combustion chamber volume ]/combustion chamber volume = 10
[displacement + combustion chamber volume ] = 10 combustion chamber volume
[displacement ] = 9 combustion chamber volume
displacement/9 = combustion chamber volume
**** theoretical combustion chamber volume = displacement/[CR - 1]
In theory a Renesis engine is 1.308L displacement
= 0.654L displacement per rotor
10:1 = 0.654L/9 = 0.0727L at TDC
9:1 = 0.654L/8 = 0.0818L at TDC
DeltaDisp = 0.0818L - 0.0727 = 0.0059L = 9cc
edit: so what I probably did was just roughly divide displacement by CR, but you have to subtract 1 to CR to get an accurate number.
however, I’m half asleep and maybe made a mistake. I won’t consider myself being belittled by having someone point it out, but would welcome having it corrected.
.
Last edited by TeamRX8; 05-07-2021 at 06:58 AM.
05-07-2021, 06:10 AM
#110
hmmm that's not the math I used ...lol . Not saying I'm right but if I do the numbers per what you worked out above and put them into the formula .
[displacement + combustion chamber volume ]/combustion chamber volume = Compression Ratio
0.654+0.0595/0.0595 = 11.99:1 CR (not 10:1) Am I missing something ?
Edit : was not trying to belittle ..... wasn't sure I'd done it correctly myself so wanted to make sure ...that's all.
[displacement + combustion chamber volume ]/combustion chamber volume = Compression Ratio
0.654+0.0595/0.0595 = 11.99:1 CR (not 10:1)
Am I missing something ?Edit : was not trying to belittle ..... wasn't sure I'd done it correctly myself so wanted to make sure ...that's all.
Last edited by Brettus; 05-07-2021 at 06:39 AM.
05-07-2021, 06:45 AM
#112
Anyway , I've managed to pull out approx. 5cc with confidence the rotor wont implode, which brings it down to around 9.4:1 .
I should add : The idea to do this came from that post of yours plus the one from Jetset8 above.................. But I'm not gunna say thankyou (just yet) cuz it's costing me a packet.
I should add : The idea to do this came from that post of yours plus the one from Jetset8 above.................. But I'm not gunna say thankyou (just yet) cuz it's costing me a packet.
Last edited by Brettus; 05-07-2021 at 04:20 PM.
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05-16-2021, 02:16 PM
#113
Anyway , I've managed to pull out approx. 5cc with confidence the rotor wont implode, which brings it down to around 9.4:1 .
I should add : The idea to do this came from that post of yours plus the one from Jetset8 above.................. But I'm not gunna say thankyou (just yet) cuz it's costing me a packet.
I should add : The idea to do this came from that post of yours plus the one from Jetset8 above.................. But I'm not gunna say thankyou (just yet) cuz it's costing me a packet.
05-17-2021, 05:21 AM
#115
which I know we discussed using lower compression REW rotors before, but that was non-hybrid and have since reversed my position on doing that after discussing it with Pettit Racing and putting more evaluation into it.
if you’re going to do this then sticking to a standard Renesis with it or just going with an REW swap is going to be your best chance for a successful end result.
.
Last edited by TeamRX8; 05-17-2021 at 05:24 AM.
05-17-2021, 07:41 PM
#117
It’s not “my” reasoning, it’s because the more intake-exhaust overlap an engine has, the lower the dynamic compression ratio it will have compared to it’s static CR.
It’s why piston race engines with high-overlap cam timing run 12:1 - 15:1 compression ratio. Except on a rotary it’s generally accepted that 10:1 CR is the highest practical CR due to the rotating bathtub combustion chamber limitation.
as I attempted to explain in the past (and was chided over no less), a hybrid Renesis already leaks like a sieve for the reasons I’ve posted about numerous times. Lowering the compression ratio will only make a bad situation worse. Go review the KMR/Mazdatrix dyno graph again and then take away more low-end output and spool response. For somebody toodling around on the street in their RX8 like Mr Youtuber there, it will really be annoying to generally drive around in and a dog that can’t hardly get out it’s own way most of the time it’s being driven sanely on the street.
As I also stated before, the only way I see a Renesis hybrid configuration having any chance to perform any better (a mediocre chance, it will never be great compared to the alternatives imo) then it’s going to need a big turbo with high flowing turbine housing to provide a lot more CFM and less emap. Lowering CR will be counter-productive to that end goal. Or rather, require even more of same.
Not going to apologize for being frank or hold back about it at this stage of the game going on over these ideas; most of these things are really basic combustion engine dynamics, with the exception of the Renesis’ zero-overlap intake-exhaust cycle. For someone who has a solid understanding of these principals it’s fairly easy to recognize when somebody else doesn’t.
.
It’s why piston race engines with high-overlap cam timing run 12:1 - 15:1 compression ratio. Except on a rotary it’s generally accepted that 10:1 CR is the highest practical CR due to the rotating bathtub combustion chamber limitation.
as I attempted to explain in the past (and was chided over no less), a hybrid Renesis already leaks like a sieve for the reasons I’ve posted about numerous times. Lowering the compression ratio will only make a bad situation worse. Go review the KMR/Mazdatrix dyno graph again and then take away more low-end output and spool response. For somebody toodling around on the street in their RX8 like Mr Youtuber there, it will really be annoying to generally drive around in and a dog that can’t hardly get out it’s own way most of the time it’s being driven sanely on the street.
As I also stated before, the only way I see a Renesis hybrid configuration having any chance to perform any better (a mediocre chance, it will never be great compared to the alternatives imo) then it’s going to need a big turbo with high flowing turbine housing to provide a lot more CFM and less emap. Lowering CR will be counter-productive to that end goal. Or rather, require even more of same.
Not going to apologize for being frank or hold back about it at this stage of the game going on over these ideas; most of these things are really basic combustion engine dynamics, with the exception of the Renesis’ zero-overlap intake-exhaust cycle. For someone who has a solid understanding of these principals it’s fairly easy to recognize when somebody else doesn’t.
.
05-17-2021, 08:19 PM
#118
For an N/A engine I agree entirely . But for FI ...not at all. You are way overstating the losses and downplaying the gains from lower CR......... IMO.
https://www.rx8club.com/series-i-maj...9/#post4944507
https://www.rx8club.com/series-i-maj...9/#post4944507
05-18-2021, 03:21 AM
#119
as I attempted to explain in the past (and was chided over no less), a hybrid Renesis already leaks like a sieve for the reasons I’ve posted about numerous times. Lowering the compression ratio will only make a bad situation worse. Go review the KMR/Mazdatrix dyno graph again and then take away more low-end output and spool response. For somebody toodling around on the street in their RX8 like Mr Youtuber there, it will really be annoying to generally drive around in and a dog that can’t hardly get out it’s own way most of the time it’s being driven sanely on the street.
.
.
Not much overlap will be added by using the GSL housings without any porting. You can always port the exhaust port up, following the same position as the side port if bigger exhaust port is needed. The way you talk about the drivability of this sounds worse like a semi PP setup (where the overlap is worse).
Low compression wise, as Brett mentioned for FI it makes sense, hybrid or side ports will help benefit from this.
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