Ok, so I've been reading a bit about aux. ports... and some site mentioned that turbo rotaries typically are of the "4-port" variety. Why is this the case, and is this necessarily the case? Will a 6-port high power Renesis engine be able to accept a turbo kit without changing the side housings?

 

Yes, in the FC (2nd Gen, the only generation with both NA and turbo engines), the NA engines had 6 ports, and the turbo engines had 4 ports.

This does not mean that putting a turbo or SC on a 6 port engine won't work, or won't work well. One thing to remember is that there is a tradeoff between 4 port and 6 port performance. For an NA engine, a 4 port works better at low rpms (idle/cruise/part throttle), while the 6 port works better at high rpms with a Wide Open Throttle (WOT, stomp on the gas).

When you are optimizing an engine, you do different things between NA and FI (Forced Induction, either SC or Turbo). With an NA, especially with a sports car, you want the engine to flow the best at higher rpms, WOT, for the most peak power. With the Renesis, you can actually have the best of all worlds in that it will only open up ports as the rpms increase. In effect, at higher rpms, all 6 ports are open for the best high rpm/WOT performance, at mid rpms, only 4 ports are open for best performance, and at cruise/idle/low rpms, only 2 ports are open for the best low-end performance.

With an FI engine, you are cramming air in at high-rpms/WOT, so for a normal, street driven FI car, there is little benefit in high rpm performance to having 6 ports vs. 4 ports. With an FI engine, especially with turbos, the engine is not always getting boost. At lower rpms/cruise/idle/part throttle, the engine is actually working as an NA engine, and it can benefit from low rpm performance gains from having 4 ports. So, since there was little benefit in making it 6 port, Mazda made the turbo engine 4 port to give the best low-end/cruise/idle performance. Basically, they traded off a little benefit in high-rpm power for a significant benefit in low rpm power, mileage, and throttle response.

With the variable intake system, there still is a little to be gained by having 6 ports at high rpms on an FI engine, so as long as the variable intake paths are included in an FI Renesis, 6 ports would be optimal.

---jps

 

...but there's also the port timing effects of the tertiary ports... i know that with high-pressure aspiration, timing which doesn't overlap any of the cycles much (no cheating before or after TDC/BDC) is better than heavy overlap, because of the tendancy for back-flow to occur (especially with high exhaust timing overlap... ie: slow to close) which only hurts the pumping efficiencies.

referencing rotaryengineillustrated (here, at the very bottom ) i see that all 13b turbo variants never had either of the primary or secondary ports timed any later than 50 degrees After BDC.

in the 6 port NA variants the primary would close at 40 ABDC, with the secondary closing at 30 ABDC, but with the tertiary port above it closing at 80 ABDC (which i think leaves enough delay that the intake port is already starting to open to the next combustion chamber just as the tertiary port closes). this is a major factor in the efficiency of an engine, and could be a reason why turbos and NA 13B engines don't really mix so well.

because it appears that the RENESIS's ports are located lower on the side+int housings, and the exhaust ports are located so that there is literally zero overlap, the timing will probably be different (closures closer to BDC on the intake side) but still maybe not as favourable to a forced induction system as the 4 port motors...??

time will tell

 

c'mon!! no other thoughts??? this thread has a lot of promise!!!

 

i think the 4 port motors will easier to design an FI system for. you don't have to design around the tuning of the tertiary ports

 

you could always just keep them closed... jk. Also though, i think its important to keep in mind because most of the people who will be modding their RX-8's will start from the 6-speed base, which is 6-port. Do you think it will be the case that the 5th and 6th ports will just be retuned to stay closed?

 

Personally, I don't see any reason to defeat them, and I see a couple of reasons to keep them operating.

---jps

 

KISS = Keep It Simple Stupid :D

Since the renesis relocated ports and the statement the engineer made "its made to be fitted for a turbo" then that means the ports should be running....we'll see when someone makes a good turbo or sc system...

 

how do you measure TDC and BDC on a rotary?? On a PIS-TUN engine :D its the highest and lowest point of the PIS-TUN in the SIL-IN-DER. But the rotary doesn't have a linear travel. So how do you measure it in a spirograph setup like the wankel?? Do you measure TDC and BDC by the position of the intake ports full open/full closed or maybe when the rotor just passes over the port?

 

Spirograph.......thats priceless ! !
Been wondering myself what TDC means to a 'rotarian'.....

S

 

it's pretty simple: TDC is when the combustion chamber face is on either "side" (meaning lateral extreme), as close as it can be... this is when compression is at its maximum on the spark plug side, or both ports are closed on the port side.

BDC is exactly the opposite: it's when the rotor face is furthes from the perhipheral housing, which is 90 rotor degrees (which is 270 e-shaft degrees of rotation) after a TDC event... it's when the rotor is "pointing" down or up... so, really, per rotor revolution, there are two TDC and two BDC events (which is 90 degrees * 4 = 360 degrees) per combustion chamber per whole rotation, just as there are in a 4 stroke piston engine per piston, but the e-shaft goes around 3 whole times, with three whole combustion events, per rotor revolution... pretty cool, i know :D

 

sweet. Hey wakeech, do you get all your car super powers from trog dor, or is he meerly inspiration?:D

 

heh heh, StrongBad actually imbued me with ultra-awesomeness for scoring more than 1100 points on my third go at Trogdor The Game.

 

Here's an additional link from Paul Yaw's webpage about port timing (did he fall off the face of the planet too ?).

http://www.yawpower.com/dectech.html

Is this why quick-spooling turbochargers are the best choice for the 6-port RENESIS? IMO, I wouldn't see any point in high-rpm boost; the opening of the tertiary ports would take care of the top end. Meanwhile, a small-frame turbocharger can take care of the bottom end, which is in need of some power. What about a large turbocharger, such as a T78, or something of that magnitude? Since these turbochargers, I believe, are best for high-rpm apps, its usefulness to the RENESIS wouldn't be much, right? Personally, I don't prefer high-rpm power. I want the best average power gain I can get.

Is it possible to set up large-frame turbocharger to fully spool at midrange? What would the effect be if this was possible? I've said this before in other threads, but what about a new intake manifold, one that utilized long runners for low-end power? Would I have to eliminate the S-DAIS in the process? I know it sounds confusing, but I am trying to explain the best that I can.

 

my namesake has been disrespected

 

This is what I was looking for in another thread. Thanks Wakeech!

 

BTW... the 4 port Renesis looks to be zero overlap as well...

4 PI
Intake
Primary Open (ATDC) 3 deg.
Close (ABDC) 60 deg.

Secondary Open (ATDC) 12 deg.
Close (ABDC) 45 deg.

Exhaust
Open (BBDC) 40 deg.
Close (ATDC) BTDC 3 deg.


Here's the 6 PI

Intake
Primary Open (ATDC) 3 deg.
Close (ABDC) 65 deg.

Secondary Open (ATDC) 12 deg.
Close (ABDC) 36 deg.

Auxilary Open (ATDC) 38 deg.
Close (ABDC) 80 deg.

Exhaust
Open (BBDC) 50 deg.
Close (ATDC) BTDC 3 deg.

 

holy shazbot.

man, with those 4 port housings, you could seriously SERIOUSLY make a hugely killer turbo motor. wow. just port match both of the inspiration ports to go 3* ATDC - 60* ATDC (which i'm telling you is an ENOURMOUS area... wow, THANK YOU NEW DESIGN APEX SEALS!! :D), and both exhaust ports 50* BBDC - 3* BTDC, you'd just be flowin' like mad. holy bee-jesus.

 

Does this contradict rotarygod's thread about why the 4-port RENESIS will never make power? I heard elsewhere that a 4-port engine will out-perform the 6-port engine, but the only trade-off is a boosted 4-port will peak at mid-rpm.

 

well that's kinda what i was saying at the beginning of it all.

it's not that the 4 port will "outperform" in such a broad statement, but it will more efficiently flow a great deal of pressurized air than the more fragmentented flow path of the 6 port, and can deliver it within a preferable phase of the rotor's path.

the inhereantly lower velocities associated with any given amoutn of air that you have with very large ports and paths is that at low rates of flow it is less than optimal, which in an all-motor application (especially with a small displacement motor) low range horsepower will be less than satisfactory. with a high performance engine where you don't care about the low end, why bother caring?? the high end of the rpm spectrum is optimized and you're making tremendous power.

peak torque can be wherever you want to put it. if you want it in the middle, you can design the systems of your engine to have the peak in teh middle. if you want it at the low end, design the systems to complement that. if you want your peak at the upper rpm ranges to make the most power possible, than design your engine that way. it's all just a comprimise: you can't have all of everything, a flat torque curve just means that there is a ton more power that can be found in the upper end. the 6 port is designed to do this, give up a little bit everywhere, but have a very nice driveable engine. the 4 port in its factory guise is fairly similar, just without the top end of things.

as it stands, the 6 port has the redline (only by virtue of the 4 port being on the transmission in north america: overseas you can get the 4 ports on 5 speeds... and if they're the old RX-7 5 speeds, they're stronger transmissions than the 6 speeds the RX-8's now have) advantage, and more port area: in the short term, without opening the engine you will probably be able to make more power on the 6 port. as soon as people get serious about tuning this engine with pressurized induction systems, the 4 port is the only way to fly.

 

Interesting. Wasn't the 13BT a 4-port motor? Assuming that is correct, I guess that explains why Mazda decided to go with that type of rotary engine rather than a 6-port. I heard the 13BT, if it was a 4-port, had excellent low-end power, but it lucked out on the top end. wakeech, are you implying that the 4-port RENESIS can withstand more boost than the 6-port? Your post explains a great deal . I like that. Also, is this why the 6-port engine is not suitable for high-rpm boost? What about overlap? Is that important for forced induction? You're right. It's about compromise. I just can't seem to figure out where to draw the line .

 

all turbo motors were 4 ports, and i'm certain they will continue to stay 4 port motors.

it isnt' that 4 ports can "withstand" more boost (you could build one way up on the other or whatever), but just that two large ports per cylinder are more efficient than 3 smaller ports per cylinder, especially the way that the tertiary port phased (closing at 80* ABDC).

the characteristics of a motor have to do with lots of things, not only the size of the ports but also things like the characteristics of the turbo, its compression ratio, design of all the manifolds... it goes on, y'know.

as for the suitability, well what you have to do is look at the characteristics of the port configuration in the context of each application. in an all-motor situation, the 6 port has advantages over the 4 port in its ability to be adaptive as each of the ports is optimized for flow through a certain range of the rpm band: more ports means more adaptability (it's like a VTEC system with 3 cam profiles over 2). also the port locations, notably the tertiary port as it's really the big difference, play a part in this as their location on the side housing determines when they open and close and the duration (which along with the size of the port, which are positively related, are like lift). note that as i said before, on all other turbo motors Mazda has never designated a motor than had its ports close any later than 50* ABDC. tertiary ports, however, move the timing up from 60* ABDC to 80* ABDC. in an all motor application, the delay allows for some obvious amount of gain... how, i don't know, i'm not very smart and can't exactly study a motor i don't have. i suppose it must have something to do with taking advantage of the momentum the gases generate as they are accelerated into the combustion chamber (the forces generated in pulling in the gasses can overcome the pressures building in the chamber as the rotor moves to TDC again up to some point, once you're getting into the 8000rpm range). anyway, the point is that the higher charge velocities of a turbocharged motor lend themselves to closing the intake path into the engine not too long after BDC, otherwise the compression of the motor will revert some of the charge back out of the chamber.

overlap between the exhaust and intake cycles when dealing with really high pressures isn't so good at lower engine speeds, and is a real no-no when dealing with a street driven engine. in racing *shrug* maybe there would be a tiny bit to find at a very high rpm.

check this thing out, it's pretty cool: http://www.rotaryengineillustrated.c...-ports101.html

 

Thanks Wakeech... that's some good stuff.

Now if only I could picture the inside of the engine (rotor position) at the various timings (60* ABDC for example)...

 

I read Rotary Engine Illustrated's article a while back. I didn't quite understand it, but now I do .

What about porting the auxiliary port? I assume this will lengthen the port closing angle. But then, since you said the intake port should be closed sooner for forced induction apps, this might not be a viable solution. Also, is port overlap similar to the overlap that camshafts can experience? Maybe that will explain why port overlap is bad at low-rpm. I'm not sure, since I'm still a newbie to RECT. From the looks of it, a rotary engine port characteristics are similar to throttle bodies; a large single port will flow more air than three ports equal to that of the single. However, from REI's article, since the area of the secondary port is larger, the velocity is going to be slower. I can prove this through some easy calculation, but I'm not here to bore .

You may be right about the tertiary ports taking advantage of the momentum of the gases. I don't know either. It's a matter of fluid mechanics, and until I have amassed as much knowledge as I did in thermodynamics, I'm clueless .

I wanted to say that the auxiliary ports are useless for forced induction, but I came to a conclusion that since these ports open at such a high-rpm, one could select a quick-spooling turbo, for example. With this said, I suppose the turbocharger can reach its boost threshold at some speed before the auxiliary ports open. Will that example work in a 6-port? I imagine the torque curve will be as linear as possible, with the best possible average power gain as well. I don't know for sure.

 

Back in town. Man I've missed alot!

Wakeech, if you look at the 4 port Renesis timing numbers, they look good on paper but they are in fact much smaller physically than the previous 4 port motors. Lets say you are staring at a rotor housing on a bench. The intake and exhaust ports are lying to the left which would make the rotation clockwise from this view. The left side of the port is the opening edge and the top is the closing edge. These two lines intersect at the top left corner. Because of this I could have a port that is only the size of that corner but with the same published timing spec. The new 4 port, secondary ports do not go down very far and are in fact only slightly bigger than the 6 port engine's secondary ports. That number may look nice on paper, but it is a really small and low flowing port. The primary ports are similar in size. You can't go stricly off of publishd timing numbers to think they will or will not flow more. You need to see the actual size of the ports.

Overlap is a bad thing when it comes to turbocharging. This may sound contrary to those who have ever had a highly modified RX-7. Those guys have lots of overlap and sometimes even bridge or peripheral port turbo motors. Even I have an engine on the stand that I built that has lots of overlap. These cars run fantastically quick, make tons of power, get zero gas mileage, and couldn't pass emissions if they were turned off! If can be done successfully this way as many have done it.

There is also another school of thought which I am a believer in. Run little to no overlap and less port timing. Stock is fine maybe with some cleaned up ports. Then run higher boost. Everyone is so caught up on the "how much boost are you running" syndrome. Why does it matter? When you have port overlap in a turbocharged car, there is almost always going to be some exhaust gas dilution of the incoming intake charge. This is because in all but the most extreme turbo systems, there is always more exhaust backpressure than there is intake pressure. It is possible to reverse this but is not very common in a street setup. Since there is mroe pressure in the exhaust and there is overlap between the intake and exhaust, some of the gasses will try to equalize the pressure during this period. The result is hot, oxygen free exhaust gas going around into the intake. This makes less room for incoming fresh air and heats up the intake side. This decreases efficiency. The result of overlap is that it will take more boost to overcome this efficiency loss. But I said I would run more boost on a low overlap engine? Since everyone ports for the sake of airflow rather than timing, a larger port can obviously flow more air faster. That is why these big ported engines make so much power. There is less flow restriction and air enters the engine much easier. Some people say that at a certain psi of boost that you can't get any more air into the engine once there is an equal amount of pressure inside the engine so port size doesn't matter. While this is true reality will state that due to less port timing we may not have enough available time while the port is open to physically get all of that potential air in if we have less timing. This may result in a manifold pressure of a certain psi but an effective compression ratio less than what we had hoped for. Just run more boost. There are pros and cons to each setup but this is best for the street. Remember that it is the effective compression ratio that determines power so what is stated on a boost gauge is really irrelevant. The engine doesn't know any better.

As far as running no intercooler for low boost levels like 4-6 psi, you may not need to. An intercooler is something else in line and it will have a pressure drop across it. Maybe not much. The larger the intercooler at this boost level the more accurate this becomes. If we use too big of an intercooler, we lose too much to pressure drop. If we use too small of an intercooler we will get little to no benefit. A small intercooler may do something but you aren't going to bet big power gains from it. The more boost you run, the more you need one. Remember also that different types of forced induction have different efficiency numbers. Some forms will benefit from it more than others.