SAE papers on the RX-8 Exhaust port design
05-20-02, 09:50 AM
#26
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Something I notice in the SAE article was with the minimalized overlap, and the cleaner exhaust, there was substantially less exhaust energy, in the sepr, versus the ppepr, which to me sounds like a signifcantly smaller exhaust side will have to be used in turbocharged applications of this new port. Are the days gone of having to run a 454 sized exhaust housing? or have the days arrived of being able to make 350 hp on a small t3/t4 combo like other engines?
The exhaust port no longer running through the cooling jacket should allow the rad to be smaller, and also the reduced heat in the exhaust should allow Mazda to not have to build the exhaust like a tank anymore, which means wieght savings as well..Looks like a good thing, I am however a bit skeptical of the the powerband, its not going to be a very nice engine to have in a everyday car if you have to drive it like ya stole it to get any power out of it.. The torque is dissapointing at lower rpm's to say the least..
If they could give that peak power, but with say 40 or more ft/lbs available , that would be the icing on the cake...Max
The exhaust port no longer running through the cooling jacket should allow the rad to be smaller, and also the reduced heat in the exhaust should allow Mazda to not have to build the exhaust like a tank anymore, which means wieght savings as well..Looks like a good thing, I am however a bit skeptical of the the powerband, its not going to be a very nice engine to have in a everyday car if you have to drive it like ya stole it to get any power out of it.. The torque is dissapointing at lower rpm's to say the least..
If they could give that peak power, but with say 40 or more ft/lbs available , that would be the icing on the cake...Max
05-20-02, 02:46 PM
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So, how much power does a "no-holds-barred" peripheral port 13B N/A motor make? I was poking around the web, and saw power in the range of 300 to 330 hp. Is this about right? Or is it more? Or less?
05-20-02, 03:23 PM
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Originally posted by Red Rotary Rocket
So, how much power does a "no-holds-barred" peripheral port 13B N/A motor make? I was poking around the web, and saw power in the range of 300 to 330 hp. Is this about right? Or is it more? Or less?
So, how much power does a "no-holds-barred" peripheral port 13B N/A motor make? I was poking around the web, and saw power in the range of 300 to 330 hp. Is this about right? Or is it more? Or less?
05-20-02, 03:44 PM
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Originally posted by 13BAce
That's what I've heard people say they get. Mazdatrix claims about 300.
That's what I've heard people say they get. Mazdatrix claims about 300.
Perhaps we need to open our minds a little...past experience would seem to indicate that a p-port INTAKE makes more power, but we shouldn't jump to the conclusion that the same holds true for the EXHAUST port. Maybe a p-port is not the most effective design on the exhaust side.
Last edited by Red Rotary Rocket; 05-20-02 at 04:04 PM.
05-20-02, 06:13 PM
#31
Banned. I got OWNED!!!
Originally posted by Red Rotary Rocket
So if a no holds barred P-port 13B makes ~300HP, and a PRODUCTION MSPRE 13B makes 300HP, then I don't see how the whole "p-port makes more power" arguement holds.
Perhaps we need to open our minds a little...past experience would seem to indicate that a p-port INTAKE makes more power, but we shouldn't jump to the conclusion that the same holds true for the EXHAUST port. Maybe a p-port is not the most effective design on the exhaust side.
So if a no holds barred P-port 13B makes ~300HP, and a PRODUCTION MSPRE 13B makes 300HP, then I don't see how the whole "p-port makes more power" arguement holds.
Perhaps we need to open our minds a little...past experience would seem to indicate that a p-port INTAKE makes more power, but we shouldn't jump to the conclusion that the same holds true for the EXHAUST port. Maybe a p-port is not the most effective design on the exhaust side.
PP engines today with 9.7:1 compression and 9000rpm with well designed induction manifolds make over 380bhp, and this is still with a lot lower compression than the RENISIS. The multi side port engine puts out 250bhp sot there is a big difference, when you take the effect of the extra compression ratio a full PP would be making well over 400bhp. The RENISIS will not gain as much from an open exhaust as does the peripheral design so I doubt that it will make any more than 30bhp over stock with a well designed exhaust.
So, You can see from the similar revs and equivalent compression ratio that a full Peripheral Port will make about 40% more power EASILY add to that that the Peripheral Port will have unbeatable power spread compared to any side port combination and from a "performance" stand point it is unbeatable.
Peripheral = performance
Side = slow
05-20-02, 07:16 PM
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Originally posted by peejay
Too bad people don't see that, they just see "my '86 made 146hp, and the renesis makes 250, therefore..."
Too bad people don't see that, they just see "my '86 made 146hp, and the renesis makes 250, therefore..."
05-20-02, 10:10 PM
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I find it funny that we are all talking about an engine we have no idea about, like any of us know what we are talking about!
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
05-20-02, 10:22 PM
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Originally posted by RICE RACING
You need to compare an "apple to an apple" the 300bhp figure has been around since 1980 ! and is for a PP running a 48ida weber and only 8000rpm and 9.4:1 compression ratio.
That's good info. Thanks for the clarification.
PP engines today with 9.7:1 compression and 9000rpm with well designed induction manifolds make over 380bhp, and this is still with a lot lower compression than the RENISIS.
Really? The SAE paper quotes the MSPRE compression ratio as 9.7 also. Is it going to be higher than that in the production version?
The multi side port engine puts out 250bhp
Mazda originally claimed 300bhp for the RENESIS. The one in the RX-8 is supposedly detuned.
sot there is a big difference, when you take the effect of the extra compression ratio a full PP would be making well over 400bhp. The RENISIS will not gain as much from an open exhaust as does the peripheral design so I doubt that it will make any more than 30bhp over stock with a well designed exhaust.
Hmmm, I'm still not convinced... Assuming Mazda isn't lying that the RENESIS is capable of 300bhp, if you take a 300bhp RENESIS and add a well designed exhaust to it, based on your suggested limit of 30bhp, that puts you at 330bhp...with stock ports. Compare that to 380bhp p-ported 13B (only 380 because I'm assuming the CRs are both 9.7, based on the SAE paper) and the difference between the two motors shrinks significantly, except that the RENESIS can idle at a speed significantly lower than 2000 RPM. Can the RENESIS gain 50 more bhp by enlarging it's stock ports to bridge ports? I don't know, but it doesn't sound unreasonable to me.
To be fair I'll admit that the above assumption is a probably somewhat optimistic... Mazda's 300bhp figure may have already included a good exhaust design, and part of the detune to 250bhp may have been in changing the exhaust system. But even if that is the case, then you are still at 300bhp with stock ports, a good exhaust, and the same compression ratio.
I think about it this way: The RENESIS with its stock intake ports (might be as big as a street port for all I know), stock side exhaust ports, and a 9.7 CR can make 300bhp. What is essentially the SAME engine (a streetported N/A 13B), but with a peripheral exhaust can only make 240bhp The only difference is the exhaust ports, but one engine makes ~60bhp more. I'm just not convinced that p-ports are the best for the exhaust.
So, You can see from the similar revs and equivalent compression ratio that a full Peripheral Port will make about 40% more power EASILY add to that that the Peripheral Port will have unbeatable power spread compared to any side port combination and from a "performance" stand point it is unbeatable.
Peripheral = performance
Side = slow
Well, like I say, I'm not yet convinced...but then again you don't have to convince me The proof will be in the pudding, and I'll finally believe it when I see some modded MSPREs popping up, and making less power. I have no where near the rotary experience you do, but I just haven't heard anyone put up a good rationalization as to why peripheral EXHAUST ports make more power. And rationalization is all that anyone has to work with here, because if I'm not mistaken, the only people who have any hands on experience with side exhaust ports are Mazda engineers
You need to compare an "apple to an apple" the 300bhp figure has been around since 1980 ! and is for a PP running a 48ida weber and only 8000rpm and 9.4:1 compression ratio.
That's good info. Thanks for the clarification.
PP engines today with 9.7:1 compression and 9000rpm with well designed induction manifolds make over 380bhp, and this is still with a lot lower compression than the RENISIS.
Really? The SAE paper quotes the MSPRE compression ratio as 9.7 also. Is it going to be higher than that in the production version?
The multi side port engine puts out 250bhp
Mazda originally claimed 300bhp for the RENESIS. The one in the RX-8 is supposedly detuned.
sot there is a big difference, when you take the effect of the extra compression ratio a full PP would be making well over 400bhp. The RENISIS will not gain as much from an open exhaust as does the peripheral design so I doubt that it will make any more than 30bhp over stock with a well designed exhaust.
Hmmm, I'm still not convinced... Assuming Mazda isn't lying that the RENESIS is capable of 300bhp, if you take a 300bhp RENESIS and add a well designed exhaust to it, based on your suggested limit of 30bhp, that puts you at 330bhp...with stock ports. Compare that to 380bhp p-ported 13B (only 380 because I'm assuming the CRs are both 9.7, based on the SAE paper) and the difference between the two motors shrinks significantly, except that the RENESIS can idle at a speed significantly lower than 2000 RPM. Can the RENESIS gain 50 more bhp by enlarging it's stock ports to bridge ports? I don't know, but it doesn't sound unreasonable to me.
To be fair I'll admit that the above assumption is a probably somewhat optimistic... Mazda's 300bhp figure may have already included a good exhaust design, and part of the detune to 250bhp may have been in changing the exhaust system. But even if that is the case, then you are still at 300bhp with stock ports, a good exhaust, and the same compression ratio.
I think about it this way: The RENESIS with its stock intake ports (might be as big as a street port for all I know), stock side exhaust ports, and a 9.7 CR can make 300bhp. What is essentially the SAME engine (a streetported N/A 13B), but with a peripheral exhaust can only make 240bhp The only difference is the exhaust ports, but one engine makes ~60bhp more. I'm just not convinced that p-ports are the best for the exhaust.
So, You can see from the similar revs and equivalent compression ratio that a full Peripheral Port will make about 40% more power EASILY add to that that the Peripheral Port will have unbeatable power spread compared to any side port combination and from a "performance" stand point it is unbeatable.
Peripheral = performance
Side = slow
Well, like I say, I'm not yet convinced...but then again you don't have to convince me
The proof will be in the pudding, and I'll finally believe it when I see some modded MSPREs popping up, and making less power. I have no where near the rotary experience you do, but I just haven't heard anyone put up a good rationalization as to why peripheral EXHAUST ports make more power. And rationalization is all that anyone has to work with here, because if I'm not mistaken, the only people who have any hands on experience with side exhaust ports are Mazda engineers
Last edited by Red Rotary Rocket; 05-20-02 at 10:31 PM.
05-21-02, 12:51 AM
#36
Banned. I got OWNED!!!
You do not have to be an engineer to understand that any engine that recycles exhaust gas from a finished cycle will make less power than one that does not.
side port exhaust recycles exhaust gases
peripheral exhaust does not
This means more room for a clean charge, it is very easy to understand.
I agree with what you guys are saying, we will be inundated with people such as myself using the RENISIS high compression rotors combined with Peripheral porting to make some serious power, easily surpassing 400bhp N/A
side port exhaust recycles exhaust gases
peripheral exhaust does not
This means more room for a clean charge, it is very easy to understand.
I agree with what you guys are saying, we will be inundated with people such as myself using the RENISIS high compression rotors combined with Peripheral porting to make some serious power, easily surpassing 400bhp N/A
05-21-02, 01:00 AM
#37
Banned. I got OWNED!!!
Red Rotary Rocket, what you are missing is that the RENISIS has a higher compression ratio & it is tunned for a higher peak power speed , 1500rpm higher 8500rpm v's 7000rpm for a street port.
If you use the extra 1500rpm on the lower compression engine your 240bhp goes up to 291bhp !!!!
With a lower compression ratio ! If you read the article again you will notice that they state that they are using an OLD generation engine and simply changing it from peripheral exhaust to side exhaust, this opens up a can of worms in that there is an obvious "exchange" of parts that I was not aware of, or they made their own side exhaust port end plates? If so the first thing I will be doing is ordering a complete rotating assembly from the latest generation engine, either that or modifying it to run full peripheral Intake and exhaust as this is the proven way to make the most power, may not be the best for the environment but for racing who cares
The RENISIS is quoted by Mazda to have 250bhp, no more @ 8500rpm.
Believe me when I tell you that this is what makes this engine, higher than 9.7:1 compression and tunned intake and exhaust to make peak power at 8500rpm, NOT THE DAMN SIDE EXHAUST PORTS.
There ONLY benifit is to reduce fuel consumption in light load low rev conditions. THATS IT
If you use the extra 1500rpm on the lower compression engine your 240bhp goes up to 291bhp !!!!
With a lower compression ratio ! If you read the article again you will notice that they state that they are using an OLD generation engine and simply changing it from peripheral exhaust to side exhaust, this opens up a can of worms in that there is an obvious "exchange" of parts that I was not aware of, or they made their own side exhaust port end plates? If so the first thing I will be doing is ordering a complete rotating assembly from the latest generation engine, either that or modifying it to run full peripheral Intake and exhaust as this is the proven way to make the most power, may not be the best for the environment but for racing who cares
The RENISIS is quoted by Mazda to have 250bhp, no more @ 8500rpm.
Believe me when I tell you that this is what makes this engine, higher than 9.7:1 compression and tunned intake and exhaust to make peak power at 8500rpm, NOT THE DAMN SIDE EXHAUST PORTS.
There ONLY benifit is to reduce fuel consumption in light load low rev conditions. THATS IT
Last edited by RICE RACING; 05-21-02 at 01:09 AM.
05-21-02, 07:50 AM
#38
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Originally posted by AJC13B
I find it funny that we are all talking about an engine we have no idea about, like any of us know what we are talking about!
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
I find it funny that we are all talking about an engine we have no idea about, like any of us know what we are talking about!
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
05-21-02, 08:20 AM
#39
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When comparing a modern PP or any NA rotary "racing" engine with the Renesis, they will have similar features; free revving, light hi-comp rotors, good induction, exhaust and ignition.
The limiting factor in NA power is the volume of air sucked into the engine. THe side exhaust ports will not increase this, but potentially reduce / eliminate the amount of exhaust gas re-circulation. RICE - what do you think of this supposition (I think its along your lines...)? Would you then feel that when using the mspre styled exhaust the sole source of power gain will be in the elimination of the recirculation? What else would improve power?
The limiting factor in NA power is the volume of air sucked into the engine. THe side exhaust ports will not increase this, but potentially reduce / eliminate the amount of exhaust gas re-circulation. RICE - what do you think of this supposition (I think its along your lines...)? Would you then feel that when using the mspre styled exhaust the sole source of power gain will be in the elimination of the recirculation? What else would improve power?
05-21-02, 02:17 PM
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Originally posted by RICE RACING
Red Rotary Rocket, what you are missing is that the RENISIS has a higher compression ratio
Do you know specifically what the compression ratio of the RENESIS will be? I cannot find any reference to the CR, other than that it will be higher than 9.0, except what is written in the SAE paper (9.7) If you can point me to some reference that says otherwise, I would appreciate it.
...modifying it to run full peripheral Intake and exhaust as this is the proven way to make the most power,
Who specifically has proven that a periperal exhaust makes more power? Who has any experience with side exhausts at all other than Mazda engineers?
The RENISIS is quoted by Mazda to have 250bhp, no more @ 8500rpm.
True for the version going into the RX-8. Not true for the RENESIS in general. The power was quoted as 280 for the RX-Evolve. (http://www.caranddriver.com/xp/Caran..._detroit_c.xml) and 300 for the RX-01 (can't find a quick reference right now, but I'll try to come up with one)
side port exhaust recycles exhaust gases
Nope. Read the SAE paper again. It says on the first page, second paragraph, "As a result, burnt gasses entering the next cycle of combustion are reduced." I think you're confusing EGR with recycling of the UNBURNT fuel that gets caught in the trailing corner.
You do not have to be an engineer to understand that any engine that recycles exhaust gas from a finished cycle will make less power than one that does not.
Red Rotary Rocket, what you are missing is that the RENISIS has a higher compression ratio
Do you know specifically what the compression ratio of the RENESIS will be? I cannot find any reference to the CR, other than that it will be higher than 9.0, except what is written in the SAE paper (9.7) If you can point me to some reference that says otherwise, I would appreciate it.
...modifying it to run full peripheral Intake and exhaust as this is the proven way to make the most power,
Who specifically has proven that a periperal exhaust makes more power? Who has any experience with side exhausts at all other than Mazda engineers?
The RENISIS is quoted by Mazda to have 250bhp, no more @ 8500rpm.
True for the version going into the RX-8. Not true for the RENESIS in general. The power was quoted as 280 for the RX-Evolve. (http://www.caranddriver.com/xp/Caran..._detroit_c.xml) and 300 for the RX-01 (can't find a quick reference right now, but I'll try to come up with one)
side port exhaust recycles exhaust gases
Nope.
Read the SAE paper again. It says on the first page, second paragraph, "As a result, burnt gasses entering the next cycle of combustion are reduced." I think you're confusing EGR with recycling of the UNBURNT fuel that gets caught in the trailing corner. You do not have to be an engineer to understand that any engine that recycles exhaust gas from a finished cycle will make less power than one that does not.
I still think side exhaust is going to be the berries.
If you can tell/show me specifically where it says the compression ratio will be higher than 9.7, then that would help toward changing my mind, but from what I've read, it seems to be 9.7 will be the number.
Last edited by Red Rotary Rocket; 05-21-02 at 02:20 PM.
05-21-02, 04:33 PM
#41
Old [Sch|F]ool
I saw a paper on an Australian website (Mazda of Australia maybe?) that showed the Renesis's compression ratio in the 11-12:1 range.
And yes the ports are ENORMOUS... they could do that because they eliminated the possibility for the crevice volume to freely vent out the exhaust. Mazda is limited in what they can do by emissions and fuel-economy standards, we aren't. We can just say screw emissions and open up the exhaust port to the side of a sewer drain
I don't think we can count on big gains by changing the exhaust... We culd see huge gains on peripheral exhaust engines because of Mazda's limitations. Peripheral exhaust engines have very loud forceful exhaust pulses, and for Mazda to quiet the car down to "new car acceptable" they had to use very restrictive stuff. The Renesis will have much quieter, softer exhaust characteristics, meaning Mazda can use a free-flowing exhaust from the factory and still have acceptable sound levels. It also means that there is less to be gained by a free-flowing exhaust. In short most of the power gain from a free-flowing exhaust is already realized when you pick the car up off the showroom floor and there isn't much more gain to be had! The days of gaining 30-50% more power just by bolting on a header and straight pipe are over
And yes the ports are ENORMOUS... they could do that because they eliminated the possibility for the crevice volume to freely vent out the exhaust. Mazda is limited in what they can do by emissions and fuel-economy standards, we aren't. We can just say screw emissions and open up the exhaust port to the side of a sewer drain
I don't think we can count on big gains by changing the exhaust... We culd see huge gains on peripheral exhaust engines because of Mazda's limitations. Peripheral exhaust engines have very loud forceful exhaust pulses, and for Mazda to quiet the car down to "new car acceptable" they had to use very restrictive stuff. The Renesis will have much quieter, softer exhaust characteristics, meaning Mazda can use a free-flowing exhaust from the factory and still have acceptable sound levels. It also means that there is less to be gained by a free-flowing exhaust. In short most of the power gain from a free-flowing exhaust is already realized when you pick the car up off the showroom floor and there isn't much more gain to be had! The days of gaining 30-50% more power just by bolting on a header and straight pipe are over
05-21-02, 05:24 PM
#42
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Originally posted by AJC13B
I find it funny that we are all talking about an engine we have no idea about, like any of us know what we are talking about!
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
I find it funny that we are all talking about an engine we have no idea about, like any of us know what we are talking about!
Everything works in theory, but the proof is in the pudding. We will all find out soon enough my friends, soon enough
05-21-02, 06:04 PM
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Amen AJC13B! But it's still fun to talk about it though.
Peejay, thanks for the info...I'll poke around the web some and see if I can locate that paper.
Peejay, thanks for the info...I'll poke around the web some and see if I can locate that paper.
05-21-02, 11:02 PM
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Originally posted by RICE RACING
Nothing makes more power from 2k onwards than a Peripheral Port...period.
https://www.rx7club.com/forum/attach...&postid=338746
It ALL depends on how the Intake/Ports/Exhaust/Ports are tuned, this has been known since 1960.
You can see this from the BMEP in the SAE paper in question, the only reason the RENISIS makes good power is due to the higher peak power rpm and the high compression it uses.
The test done in the SAE paper uses an earlier engine with 9.7:1 compression, it verifiies what I have been saying for a LONG time. The RENISIS is designed and made for economy and emmisions, use the higher compression rotors it uses and tune the intake and exhaust for higher rpm (like it does) and you will have MORE power with Peripheral exhaust ports, imagine how much power with Peripheral Intake as well
Nothing makes more power from 2k onwards than a Peripheral Port...period.
https://www.rx7club.com/forum/attach...&postid=338746
It ALL depends on how the Intake/Ports/Exhaust/Ports are tuned, this has been known since 1960.
You can see this from the BMEP in the SAE paper in question, the only reason the RENISIS makes good power is due to the higher peak power rpm and the high compression it uses.
The test done in the SAE paper uses an earlier engine with 9.7:1 compression, it verifiies what I have been saying for a LONG time. The RENISIS is designed and made for economy and emmisions, use the higher compression rotors it uses and tune the intake and exhaust for higher rpm (like it does) and you will have MORE power with Peripheral exhaust ports, imagine how much power with Peripheral Intake as well
05-22-02, 02:59 PM
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Originally posted by RICE RACING
You can see this from the BMEP in the SAE paper in question, the only reason the RENISIS makes good power is due to the higher peak power rpm and the high compression it uses.
You can see this from the BMEP in the SAE paper in question, the only reason the RENISIS makes good power is due to the higher peak power rpm and the high compression it uses.
05-22-02, 04:42 PM
#46
Old [Sch|F]ool
http://www.autoweb.com.au/start_15/s...1/article.html
"Unlike rotary engines equipped with peripheral exhaust ports, the side layout of the RENESIS produces clear, transparent high tones and powerful low tones. We recognize engine sound as a key element in any sports car, and we are working to ensure that the engine produces a satisfying roar as you depress the accelerator"
Translation: We can make the exhaust free-flowing because the engine isn't obnoxiously loud anymore. Between the lines analysis: There's less exhaust pressure to drive a turbo - there goes that rotary advantage.
http://asmic.com/collect/rx-8tm/pics/rx_8e.pdf Interesting info on the RX-8, some highlights of the Renesis. 15 pages.
http://asmic.com/collect/rotary1999/rotary_e.pdf Renesis, Series 8 RX-7, history of rotary.... 35 pages.
Can't find the article where it said the C/R. I remember it was an Acrobat file...
I can't wait until we learn this engine's true designation - Renesis is such a hokey name. I call 13C or 13K... 13C is the next model after 13B, but 13C might have been used already by an engineering engine seeing as there already have been "production" 13G (3-rotor) and 13J (4-rotor) race engines, meaning 13K would be the next assuming it also hasn't been used.
"Unlike rotary engines equipped with peripheral exhaust ports, the side layout of the RENESIS produces clear, transparent high tones and powerful low tones. We recognize engine sound as a key element in any sports car, and we are working to ensure that the engine produces a satisfying roar as you depress the accelerator"
Translation: We can make the exhaust free-flowing because the engine isn't obnoxiously loud anymore. Between the lines analysis: There's less exhaust pressure to drive a turbo - there goes that rotary advantage.
http://asmic.com/collect/rx-8tm/pics/rx_8e.pdf Interesting info on the RX-8, some highlights of the Renesis. 15 pages.
http://asmic.com/collect/rotary1999/rotary_e.pdf Renesis, Series 8 RX-7, history of rotary.... 35 pages.
Can't find the article where it said the C/R. I remember it was an Acrobat file...
I can't wait until we learn this engine's true designation - Renesis is such a hokey name. I call 13C or 13K... 13C is the next model after 13B, but 13C might have been used already by an engineering engine seeing as there already have been "production" 13G (3-rotor) and 13J (4-rotor) race engines, meaning 13K would be the next assuming it also hasn't been used.
05-22-02, 08:48 PM
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Originally posted by peejay
There's less exhaust pressure to drive a turbo - there goes that rotary advantage.
There's less exhaust pressure to drive a turbo - there goes that rotary advantage.
You aren't loosing the rotary advantage at all...it's just being used in a different way. The exhaust energy isn't being lost...instead of being dumped out the tail pipe, it's being forced to stay in the chamber longer so it can keep pushing on the rotor and make more horsepower. The same link you quoted says so: "the exhaust ports open later, resulting in a longer power (expansion) stroke and providing radically improved heat efficiency." That's where your exhaust energy is going. Before, you had to put a turbo in the exhaust path to make use of that energy, now you get to use that energy even if you don't have a turbo And if you still want to use a turbo, the picture is still rosey. While there is less exhaust energy going into the tailpipe (as compared to a peripheral exhaust), side exhaust ports make other conditions much more favorable to turbocharging: Turbo engines LOVE to have no overlap. To paraphrase your words, "There's less overlap to hinder the turbo - there goes that rotary DISADVANTAGE."
Thanks for the links. The first two I have seen before, but I hadn't seen the last one...it was pretty cool.
I too am curious about the designation. I thought that changing the letter (like 13"C" for example) meant that they changed some critical engine dimension, like rotor width for example. If they keep the same internal dimensions, and the only difference is the ports, I'll call 13B-MSP...following the 13B-REW line of thinking.
05-22-02, 09:21 PM
#48
Old [Sch|F]ool
Originally posted by Red Rotary Rocket
Man peejay, your such a pessimist You aren't loosing the rotary advantage at all...it's just being used in a different way. The exhaust energy isn't being lost...instead of being dumped out the tail pipe, it's being forced to stay in the chamber longer so it can keep pushing on the rotor and make more horsepower. The same link you quoted says so: "the exhaust ports open later, resulting in a longer power (expansion) stroke and providing radically improved heat efficiency." That's where your exhaust energy is going. Before, you had to put a turbo in the exhaust path to make use of that energy, now you get to use that energy even if you don't have a turbo
And if you still want to use a turbo, the picture is still rosey. While there is less exhaust energy going into the tailpipe (as compared to a peripheral exhaust), side exhaust ports make other conditions much more favorable to turbocharging: Turbo engines LOVE to have no overlap. To paraphrase your words, "There's less overlap to hinder the turbo - there goes that rotary DISADVANTAGE."
Man peejay, your such a pessimist
You aren't loosing the rotary advantage at all...it's just being used in a different way. The exhaust energy isn't being lost...instead of being dumped out the tail pipe, it's being forced to stay in the chamber longer so it can keep pushing on the rotor and make more horsepower. The same link you quoted says so: "the exhaust ports open later, resulting in a longer power (expansion) stroke and providing radically improved heat efficiency." That's where your exhaust energy is going. Before, you had to put a turbo in the exhaust path to make use of that energy, now you get to use that energy even if you don't have a turbo And if you still want to use a turbo, the picture is still rosey. While there is less exhaust energy going into the tailpipe (as compared to a peripheral exhaust), side exhaust ports make other conditions much more favorable to turbocharging: Turbo engines LOVE to have no overlap. To paraphrase your words, "There's less overlap to hinder the turbo - there goes that rotary DISADVANTAGE."
Peripheral exhausts love turbos and turbos love peripheral exhausts. Why?
The exhaust is very hard and forceful because the port goes from closed to fully open in 30-50 degrees. This hard, forceful exhaust pulse is EXCELLENT for driving a turbine, MUCH better than what a piston engine can offer. It's why rotaries can get away with relatively HUGE turbine wheels and housings. We can have big free-flowing exhaust sides and still have decent spool-up.
Have you ever heard of "blowdown"? That's opening the exhaust (valve/port) earlier to get the exhaust moving earlier, when there's more pressure in the chamber. The still-expanding gases force themselves out, and with a well-designed manifold/header the exiting slug of gases creates a low pressure area (vacuum) behind it which draws the rest of the exhaust out. This is PROVEN to make more power than opening the exhaust at BDC - the exhaust does all of the work and the (piston/rotor) does not have to push the exhaust out. It also assists the beginning of the intake cycle during the overlap period! Overlap is not (as much of) a hindrance with a rotary as with a boinger, because on the rotary the intake and exhaust ports are spaced well away from each other and the rotor is kind of in the way! Meanwhile in a piston engine the intake and exhaust valves are right next to each other and in many cases the intake valve's exit points right into the open exhaust valve!
Like I said - I'm a cynical realist. Peripheral exhaust have MANY performance advantages over the side port exhaust. Unfortunately for Mazda, performance isn't the only goal - they can't sell an engine that has poor emissions and fuel economy. So they sacrifice performance potential - and i don't blame them one bit. But it sucks for those of use who don't care about weeny things like emissions or fuel economy!
05-23-02, 01:16 AM
#49
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Originally posted by peejay
The exhaust is very hard and forceful because the port goes from closed to fully open in 30-50 degrees. This hard, forceful exhaust pulse is EXCELLENT for driving a turbine, MUCH better than what a piston engine can offer. It's why rotaries can get away with relatively HUGE turbine wheels and housings. We can have big free-flowing exhaust sides and still have decent spool-up.
The exhaust is very hard and forceful because the port goes from closed to fully open in 30-50 degrees. This hard, forceful exhaust pulse is EXCELLENT for driving a turbine, MUCH better than what a piston engine can offer. It's why rotaries can get away with relatively HUGE turbine wheels and housings. We can have big free-flowing exhaust sides and still have decent spool-up.
Have you ever heard of "blowdown"? That's opening the exhaust (valve/port) earlier to get the exhaust moving earlier, when there's more pressure in the chamber. The still-expanding gases force themselves out, and with a well-designed manifold/header the exiting slug of gases creates a low pressure area (vacuum) behind it which draws the rest of the exhaust out. This is PROVEN to make more power than opening the exhaust at BDC - the exhaust does all of the work and the (piston/rotor) does not have to push the exhaust out.
Think about it, the RENESIS exhaust ports open at 50 deg BBDC, while the peri port exhaust opens at 75 deg BBDC. If opening at 75 deg BBDC was really better for scavenging (and thus reducing EGR) what is stopping Mazda from just extending the RENESIS ports down some more so that they also open at 75 deg BBDC? I suspect they make the port open at 50 deg BBDC for a good reason... remember, there is such a thing as opening the exhaust too early, and I think that is what happens with the peripheral exhaust. The SAE paper confirms this. Thay say, "On the peripheral exhaust port RE however, it is difficult to advance exhaust closure timing because thermal efficiency factors determine, to a large extent, exhaust open timing, which, in turn, determines the exhaust closing timing" They're basically saying, we'd like to open later and close earlier, but we can't because the peripheral port won't allow it. The peripheral port is a compromise that doesn't allow for optimal power or emissions. The whole point of the side ports is that there is more flexibility with port timing and port area...you can do things with the timing that you just can't do with a peripheral port.
Like I said - I'm a cynical realist. Peripheral exhaust have MANY performance advantages over the side port exhaust.
Last edited by Red Rotary Rocket; 05-23-02 at 01:21 AM.
05-23-02, 01:37 AM
#50
Old [Sch|F]ool
What's stopping Mazda? How about emissions and noise? What do you do when you port... you make the exhaust open earlier. (Well, I didn't, but I was worried about increased noise)
"EGR" as you call it is really only a factor when intake manifold pressure is lower than exhaust manifold pressure. At heavy throttle and with a tuned exhaust, exhaust manifold pressure will be lower than manifold pressure during overlap. Likewise with a good turbo setup exhaust manifold pressure will be lower than the intake manifold pressure. Either way you get good scavenging! Not so good for emissions but good for power. How are you going to get good scavenging with no overlap?
Flip side of the coin... when you are at idle or otherwise have relatively high manifold vacuum, and you have lots of overlap... you cyclically get large amounts of exhaust in the intake, causing misfires and that brap brap brap idle! Even a stock port will get brappy under very high intake manifold vacuum - it's experienced as bucking/shaking when coasting in gear around 1500-2500rpm - that's why Mazda went with the somewhat bizarre shutter valve setup on '81-85 carby models in an effort to eliminate that. (EFI models naturally cut fuel flow at zero throttle/higher than idle RPM so it's not a problem)
So who cares about smooth running, good emissions, and fuel economy? Mazda does! Who cares about fully scavenging the chamber and maximum power (and rough idles ) ? We do!
What do you do when you port... you make the exhaust open earlier. (Well, I didn't, but I was worried about increased noise)"EGR" as you call it is really only a factor when intake manifold pressure is lower than exhaust manifold pressure. At heavy throttle and with a tuned exhaust, exhaust manifold pressure will be lower than manifold pressure during overlap. Likewise with a good turbo setup exhaust manifold pressure will be lower than the intake manifold pressure. Either way you get good scavenging! Not so good for emissions but good for power. How are you going to get good scavenging with no overlap?
Flip side of the coin... when you are at idle or otherwise have relatively high manifold vacuum, and you have lots of overlap... you cyclically get large amounts of exhaust in the intake, causing misfires and that brap brap brap idle! Even a stock port will get brappy under very high intake manifold vacuum - it's experienced as bucking/shaking when coasting in gear around 1500-2500rpm - that's why Mazda went with the somewhat bizarre shutter valve setup on '81-85 carby models in an effort to eliminate that. (EFI models naturally cut fuel flow at zero throttle/higher than idle RPM so it's not a problem)
So who cares about smooth running, good emissions, and fuel economy? Mazda does! Who cares about fully scavenging the chamber and maximum power (and rough idles
) ? We do!