globi

Actually in this case you wouldn't encounter any idling problems since you don't fiddle around with overlapping. You just 'close' the intake port at a later point (which itself would reduce the power output of the engine if not supercharged, since it would pump less air).

In fact piston engines with variable valve timing reduce overlapping at low rpms by opening and closing the intake valve at a later point.

Charles R. Hill

iTrader: (7)

One of the things I think many people overlook when comparing the Renesis and it's side ports to the previous rotaries and their peripheral ports is that the Renesis in N/A form is making roughly the same h.p. as the twin turbo. I don't know the torque comparisons, offhand, so someone can enlighten me on that. What I wonder is if the side ports are actually a better way of modulating airflow through the engine because there is a more well-defined closing of the intake and exhaust events. We are tending to assume that the peripheral ports offer a better opportunity for quality airflow but might we be wrong? If not, then I suppose most of the numbers generated by the Renesis that eclipse the previous versions would appear above 7,500 rpm. Another thing to consider is that compression ratios tend to be a mechanical measurement and don't necessarily reflect the actual dynamic pressures an engine will generate. Of course, we have seen 10:1 engines deal with a turbo just fine and it has been said repeatedly that it is all in the tuning. As Maniac has said, the ECU and the fuel systems are the biggest hinderances. One more observation I have is that the 1300cc rotary engine is actually moving air in a similar fashion to that of a 2.6L. Since there are no cycles dedicated to only clearing the cylinder like a piston engine, every movement of the rotor is used to make power immeditely. Maniac pretty much alludes to this in his last sentence. I tend to think that the torque/h.p. figures for the Renesis are pretty much in-line with that of a similarly mannered 2.6L and, as well, the potential for ultimate power may be the same(with durability being the biggest factor).

A question for globi: How would lengthening the intake event cause a reduction of airflow? I think that the intake vacuum signal would definitely change character at lower rpm's but as the rpm's climbed higher we would see the same "supercharger effect" that the rotary is known for, only at a higher point in the rpm band. I read your last post and I tend to disagree with your conclusions because rotary engines don't experience the same reversion pulses/effects as do piston engines . Care to elaborate?

Charles

wakeech

the biggest reason the MSP is "making" nearly as much power as the REW is the increase in redline. this is actually a really dumb comparison as both motors are so different, so let's look at the numbers from an even older engine, the Series 5 13B (no fancy letters after it).

the S5 motor made a max of 160hp at 7k rpm, and (even though i HATE the implications made by quoting such a stupid number) a maximum torque figure of 140lb/ft at 4k rpm. the 13BMSP by comparison makes a claimed 238hp at 8500rpm (i'm sure that back in the day mazda was saying 247, it was probably closer to that number than what factory motors are to the new lower number), and 156lbft at, what, 5500?? (slipped my mind, torque figures are stupid).

the biggest difference, as i said, is in the increase in functional engine speed. this has come about with better internals (lighter rotors, stronger shaft, better machining, etc), way huger ports (stock ports are now at least as large as the most aggressive street ports executable on the S5, made possible by the shorter beam height of the apex seals), and massive improvements in the induction hardware (the refinement of the SDIAS system next to the ugly *** VFAD is like comparing the craftsmanship of a katana to that of a club made from a branch torn off a dead tree... from the big stuff to the tiniest details, it is wholly better). as is fairly obvious, it's a lot of small changes that have resulted in a rather huge improvement which can be qualified as a single characteristic improvement.

other stuff would be like the increase in compression ratio (from 9.2:1 at the highest IIRC, to 10:1), much better catalyst units, magic fairy dust, etc.

perhipheral ports flow the best, hands down, no question, period. a p-port motor with rotors clearanced for racing, balanced, lightened, studded, dowled, carbon sealed, and set to detonate with a 11-13k rpm redline make way over 300hp, all motor, no juice (and that was in the 70's and 80's, and amateurs these days). side ports simply have no chance against p-ports, which is why i have many times suggested someone with an engine apart and some ***** do some measuring, drawing, grab a hole saw and a die grinder to make a p-port induction side, side port exhaust side Renesis. it'd be magic, i tell y'all.

the deal with lengthening the intake event has already been addressed, decades ago, with the VFAD and now SDIAS systems built into the motors factory. the combustion chamber starts compression at 0 degrees ABDC, and is limited to 30 ATDC,40 ATDC and 80 ATDC (all IIRC, i don't have the patience to search for rotarygod's posted numbers, but i'm pretty sure they've stayed close) progressively as rpm increases. leaving the port open too long when the speed of the engine is low is obviously bad as the difference in pressure would drive gas out of the chamber before the port had closed, but as you say at high rpm the larger ports allow for a greater volume of gas to enter at a comfortable velocity while the motor is going nuts, with things like momentum and resonance tuning helping keep all the gas sucked, in. now because of where the ports are cordoned into by the sealing design on the mazda rotor, and what might be a non-linear rate of compressioon (i've never found any information on this, am not familiar with the matematics used for the geometry of this engine, and don't have one to play with, so i don't know but would love to find out) inherent to the wankel design, further increase to this phase in the cycle is probably not a great plan: mazda has probably hit the wall of deminishing returns with this experimentally, as this would be one of the easiest areas to make more power ('cause there's lots of room for port up there, but wouldn't benefit the motor).

to make myself more clear on that recent point, i was postulating on the rate of compression (whether it's a nice parabola on the volume vs. degree of rotation graph like a piston motor would have or not). if anyone has any ideas or information about this i'd be curious (i'm very sure it's known, it's simple theory, i just don't know it).

globi

As far as the exhaust ports of the Renesis go, I would assume that they were mainly put in place to reduce emissions since it recycles part of the unburnt fuel and it might somewhat increase efficiency since it reburns that fuel as well.
Here's a picture: http://www.der-wankelmotor.de/Techni...k_auslass.html
If it was just about generating maximum power, perimeter ports would probably be superior.

Regarding the lengthening of the intake side port and reduction of the airflow: It is basically as wakeech already mentioned, it would drive gas out of the chamber before closing the intake port and therefore reduce the airflow. You could also compare it with the Atkinson cycle which is used in the Toyota Prius:
The disadvantage of this concept is of course that the engine pumps less air. If the engine pumps less air it automatically generates less power. However since you pump extra air with the turbocharger you make more than up for it.
I guess ideally you'd have something like a third side intake port with a electromagnetically controlled valve. As long as you drive with partial load its closed. At increased boost it would open that extra side port and therefore reduce the compression ratio to 7:1 (for example) hence allowing a much higher boost pressure. (And this third valve is something completly different than a variable intake duct. It would be more like a turbocharged variable valve timing piston engine.)

globi

Btw the 26B has peripheral intanke and exhaust ports. (Of course in this case fuel consumption, idling stability and emissions didn't matter).
http://www.der-wankelmotor.de/Motore...mazda_26b.html

rotarygod

No you wouldn't.

First of all we need to understand that there are 2 different types of compression ratio that people get confused between. They are the static compression ratio and the effective compression ratio. The static compression ratio is the one that is quoted in all of the specs as 10.0:1 on the Renesis. The ONLY way to change this is to change or mill out the rotors. As of this time, there are no other alternatives for this engine. The effective compression ratio is what you are getting confused with. Yes at lower rpm's, you may get some reversion because the engine will begin it's compression stroke before the intake port closes. However, at higher rpm's, the engine intake air has so much momentum that it will not reverse but in fact keep shoving more air into the engine than normal and have a high effective compression ratio. It is possible (and pretty much guaranteed) that the engine will have less air in it at idle and low rpm's than it can hold. This would make the effective compression ratio less than 10.0:1. If the engine is only 85% efficient, you do th math. Let's say at high rpm's we hit 105% efficiency due to inertial ramcharging. Now figure it out. Every porting style has a compromise to it but the compression ratio that everyone refers to is the static compression ratio. Porting does not affect this.

rotarygod

The Renesis is not going to respond to turbo sizing in the same fashion as the 13B's. You can't only size a turbo for a 13B based on displacement. It doesn't work. The exhaust flow is so drastically different. A peripheral port opens fully much faster than a side port. It also closes more abruptly. This sudden opening causes a very sudden rush of exhaust gas. It is mroe of an impact on the turbo blades rather than a flow across them. This foceses more energy at the blades and really gets them moving faster. A good turbine blade design for a rotary is fairly flat in profile where a typical turbine blade is more curved. Unfortuately aftermarket blades are curved so we must use a bigger size than necessary. The Renesis on the other hand with it's side ports, has an exhaust flow that is more similar to a piston engines flow than it is a 13B exhaust port. The exhaust ports aren't open as long and they open and close more gradually which dissipates the impact effect. A more traditional turbine size and style is more appropriate for these engines. You shouldn't need as large of an exhaust wheel as the 13B. Something as large as a T-51Kai will just sit there and not work on a Renesis. They don't spool up very good on a ported 13B. If you consider full boost by 4500+ rpm good than so be it but this is really more functional as a dyno queen or a freeway car. They are slow on the street for everyday use. The T-51 is also out of its efficiency range if you are under 20 psi or so. Who needs this? Seriously, be realistic! A better choice would be a 60-1 HiFi or T-04B (very similar) for street use. If you want more power step up to a 62-1 or maybe a T-66 if you get into porting.

Big turbo Supra's may be capable of incredible power but at the dragstrip or on the streets, it doesn't take very much power to beat one. Get one on the freeway or try to outrun it in top speed and that becomes a very different story. They are dyno queens with a 2000 rpm wide powerband and nothing anywhere else. I still remember Ari at Rotary Performance when he dyno'd 620 rwhp vs Rhys Millen in their 1000 rwhp Supra. Toyota had all of their guys on hand and hyped up the show about how much power they had. Ari beat Rhys by almost a half a second in the quarter. If the track were a half mile, it would have been a very different story. The same turbo may spool up faster on an RX-7, but it doesn't mean it is any more streetable. It also doesn't mean that it will spool up on a Renesis.

Charles R. Hill

iTrader: (7)

Thanks, Rg, for affirming what I had been understanding/utilizing for the past 25 years. I am glad to see that several of my experiences in piston engines will translate to rotaries, as well. Re: your explanation on the differences between the nature of the intake/exhaust events between the peri and side ports, I would have thought that the peri port reaches full opening quicker but closes slower than the side port. To describe the closing of the side port's exhaust as more gradual than the peri has me somewhat baffled.

I am wondering if Wakeech is willing to take the time to explain his aversion to using torque as a measure of an engine's capabilites. I am having a hard time following that logic since torque level and rpm's are used to synthesize that imaginary figure we call "horsepower". Thanks.

Charles

Richard Paul

iTrader: (5)

Ya Wakeech, I'd like to hear that answer also. I'd sooner reject HP then torque.

I once was ordering a boat and had the option of Perkins or Catapillars. There was only 5 hp difference and many thousands of dollars. I was thinking of the savangs while I walked around the factory. When all of a sudden it hit me as I happened to see the size difference in the exhaust between to two engines. Then I hit myself in the head and said "torque you idiot". Guess which ones I bought??

globi

It's a question of a how large you size that additional intake side port. From a certain size on, you'll end up with a reversion at any rpm. Otherwise the miller cycle engine simply wouldn't work at higher rpms.
But of course if you size that extra intake port too big, you would lose lot's of low end torque, since you'd reverse too much air at lower rpms. Which is why I was suggesting an electromagnetically controlled valve on that extra intake port, so it only opens at higher boost levels and higher rpms. (This however wouldn't really be a practical solution for an aftermarket kit.)
Variable valve timing (eg. VTEC) on piston engines appears mechanically more complicated than what an additional controllable side intake port on a rotary engine would be. So I wonder why it hasn't been realized on a rotary engine yet, or has it?

Richard Paul

iTrader: (5)

Who says the miller cycle works at higher rpm anyway?? That whole thing is a waste. Now if you get electronic valve actuation, then you can get somewhere maping valve timing and blower pressure.

globi

Well you have to admit that running a supercharged engine with a lower compression ratio is also a waste. (Since the expansion ratio or work cycle is shorter.)

Richard Paul

iTrader: (5)

Globi, Say what???
BMEP

BaronVonBigmeat

Not to put words in his mouth...but it's probably because torque can be multiplied as much as you want by the transmission and rear end. You'll often hear people (usually the domestic crowd) throwing "torque at the engine crank" numbers around like that's all that matters, when they're missing half the equation. Likewise, you hear the import crowd tending to beat their chests about how many RPM's (at the engine crank) they can turn, which is also giving an incomplete picture of an engine's capabilities. Horsepower however cannot be multiplied by gearing.

For the boat motor example, or for heavy hauling in general, you'd be doing good to get a motor biased towards torque, because you don't want a motor that's constantly screaming, and you want good fuel efficiency. Plus weight won't be a factor for a boat or dump truck really. Of course, the additional cost may also have been due to craftsmanship, type of metals used, company reputation, etc.

rotarygod

It isn't so much a certain sized port as it is a certain timed port. If you keep the intake open too long into the compression stroke you can get reversion at any speed.

The Miller cycle is a very different approach. The idea behind it is that if you can have a compression stroke (not intake) that is shorter than the exhaust stroke that you can reduce pumping losses and gain mileage and reduce emissions. Their solution to this was to leave the intake valves open for a little longer into the compression stroke to ensure that the combustion chamber doesn't fill up as much. However to regain the amount of power back that is lost from this, they rely on a supercharger (a twin screw!) to force some air back in. In doing so they did increase the efficiency of that particular engine a little from an economy standpoint but power wasn't as high as it should be with a supercharger. They weren't using the supercharger to give the engine a kick. They used it to restore power back from leaving the intake open for too long. The idea sounded good but 27 mpg at 200 hp vs other engines that can eclipse that today just wasn't worth the effort and we never saw another example of it again. If it really worked so well, we'd see more of them.

Richard Paul

iTrader: (5)

BMEP=Brake Mean Effective Pressure. For those who have asked via PM.

Fred do you ever sleep?? Noting the times of your posts sometime I wonder.

rotarygod

Normally I go to bed really late and get up late. Last night I feel asleep on the couch watching TV at about 7 and woke up again at 10. If I'd have stayed awake, I'd have never fallen back to sleep so I just went to bed. Woke up at about 4:45 and couldn't sleep again.

MazdaManiac

iTrader: (3)

Sounds like my kind of schedule. I was out logging runs on the E-Manage at 3:00am this morning and slept from 5 to 10:30.
No TV for me though - it would take from my GTA-SA time!

Still awaiting wakeech's triumphant return as he explains away the value of torque as a true measure of power.:D

brillo

how would all of this apply to a super charger? I would think spooling should be faster but the compression issue would still be there....but, if what most of us really want is low end, and the compression in lower in the lower rev range, then I would think we could use a S/C or T/C that would spin up quick at the bottom and then tapper off as you get high in the power band.

globi

Actually another way to look at it is: Assuming you had that additional controllable side intake port, you could run a turbo at a much higher boost level, since the (apparent) compression ratio could be reduced to let's say 6:1. A higher boost level would make an intercooler much more effective (proportional to delta T) and therefore the engine would be less prone to detonation without having to reduce the actual compression ratio of the engine. However I'm not sure whether a turbocharger at much higher boost levels would still run efficiently enough?

Charles R. Hill

iTrader: (7)

Baron, I am thinking that your explanation has it backwards(although correct), in a sense. The reason I think this is because while torque can be multiplied, it comes at the direct expense of rpm potential. The thing is that torque is a direct measurable value while horsepower is a calculated(contrived) number. The way h.p. numbers become valuable is to compare the work potential of different engines and then designing torque converters, transmissions, and final drives that will best fulfill the purpose of the vehicle. All of this exludes particular characteristics of a given engine just for the sake of rhetoric. When we are able to evaluate the h.p. to weight ratios of different vehicles we may then begin to reasonably predict that vehicles performance and decide where, if any, changes or mods could be made. To use your comparison of domestic vs. import, I regularly explain to the Mustang owners that I have beaten in a drag race that because I have half as much torque as they do I also have almost twice as much gearing for a net h.p./weight figure to the wheels that is actually better than what they have. With a redline that is almost twice what they have available, we see that a slightly modded RX-8 will give V-8's a run for their money even though we only measure 160 lbs./ft.(+/-) at the crank compared to their 300 lbs. The great thing about the import engines these days is their relatively flat torque peaks when compared to the V-6/8 engines the domestics have. With the right tranny/gearing, import vehicles are really better cars for the money. And to think I used to be a musclecar freak.

Charles

staticlag

Would there be some way to use both a supercharger and a turbo on an engine? Using the supercharger for more low end quick spooling torque, then prehaps once the engine got into the effective turbo range, use a huge turbo on it and some valves to divert some of the supercharger pressure to the turbo spool path in the exhaust (it help spool the huge turbo at max rpm, and cool the exhaust temp)? If you used two intakes and worked out some dedicated airflow system, couldnt this be done?

merlin00gt

staticlag: I believe some older diesel engines had a similiar setup. I was watching a "Trucks" show on TNN the other day, and they showed an International engine that had a turbocharger feeding a supercharger. The turbo sat right on top of a "roots" blower.

My point is that it has been experimented with.

GeorgeH

iTrader: (2)

Yes, there is an experimental Miata kit out there right now that does just this. I know the guy who has it in his car, but I have not seen it yet.

Aoshi Shinomori

Why not just use the sequential twin turbo setup? The kings of the 90's, the supra, rx-7, vr4, 300zx all had this kind of setup. One small turbo that spooled quick so there was a bigger useable power band, and when the bigger one spooled the little one shut down. I might have a few things wrong here, but I'm pretty sure that's basically how it worked. I also don't know what the advantages/disadvantages would be over using two turbos or a turbo/supercharger. We'll let the experts sort this all out