Great discussion guys. This belongs in techno forum asap! :D

 

here's some stuff i wrote in my thread entitled "Ahhh, the "weird" Bevel", and since it appears to me that very very few people have taken the time to read it, AND this thread is now in this section, i will simply snip and paste...

 

here's a link i made not moments ago (well, okay, a bunch of moments together) about ignition and stuff... mmm mmm, noobilicous... :DStuff on Rotary (13B) Ignition...

now, for those who're new, i'm Andrew, and all that i know i cannot back up with solid learning... i'm a 19 year-old university student, studying economics, and i yearn to touch wrench to bolt, but as of yet haven't...

 

Turbodyne and Garret are working on mass producing an Electric TurboCharger (e-charger).

Nissan is working on Bi-E-Charger for the next Skyline-GTR...

If TurboCharging the RX-8 is very difficult, how about an E-charger?

Also, I am very interested in the MPS RX-8 with 300 HP...

My CLS does nw low 14s in 1/4mile with all bolt-ons (more than 300HP @ crank)..Therefore, a low-rpm Hi-Torque is a must...

Hopefully we can see some 200+lbft of Torque on a RX-8 engine...

RX-8 is a very cool car... :D

 

on your question about "adding torque", well, there are a few ways you can do this: increase the displacement (the good ol' American way), increase the volumetric efficiency with some kind of magical inspiration and expiration system, or using forced induction get the same result (more air and fuel to burn at once)...

a wider rotor'd version of the RENESIS has been speculated, which would go a long long way to upping the low rpm torque, but this doesn't answer your question.

to increase the volumetric efficiency in an all-motor application, what you need is a system of inspiration and expiration that will automatically adapt to the needs of the engine. at low rpm, the induction runners must be long and small in diameter to maximize this, as there is an optimum velocity for the air being drawn in at a certain rpm, and this is affected by the amount the engine is trying to suck in per second (obviously determined by rpm), and the diameter of the induction runner. also, the length must be tuned to the rpm, as the positive and negative pressure waves (as the port is opened and closed) can be used to "suck" in more air at the opening (during a negative pulse), and can somehow deaden the effect of a positive pulse (?? Boogs??), i think... in any case, to do this at 100% efficiency, you'd need to have runners on both the inspiration side and the expiration side changing their diameter and length to every change in rpm, throttle position, and load. Mazda's done well, and has a system of three different RUNNERS ( not three different intakes), of three different lengths which are selected by the cpu to maximize efficiency.

as for forced induction, it's a fairly simple equation in theory, and unbelievably complex in practice (at least at the high-dollar, high-performance level). more air, plus more fuel, equals more pressure in the combustion chamber, which equals more force on the eccentric shaft, which equals more torque. more torque at the same rpm equals more power, and you go faster.
can you do it on the rotary?? why not?? no room?? if you were serious as a heart attack about making an 8 fast in the 400 (meters, that is ) throw stuff out of the engine compartment, onto the ground or into the trunk, or whatever you like. can you make it work with the variable length induction runner system that Mazda's put on the RENESIS?? depends. a supercharging system, i could see that working (specifically your e-charger, as it'd be easier to locate about the engine), but turbo charging?? i think you'd be asking for it, hard, and exactly where i'm guessing you're not ready for it... that's right, in the wallet.
seriously, it'd be a miracle for anyone to get the systems to work together, never mind fitting it in any vehicle short of a truck (a big, big truck). if you were gonna turbo the RENESIS, you'd probably throw the stock induction system in the bin, and pick a single length and diameter for the impeller to blow through. this'd absolutely kill your low-rpm torque (obviously), but you'd be pumping the horses up top.
i've just gotta add this: backpressure is bad, but that doesn't mean a bigger tip for your exhaust system is necessarily going to increase efficiency. think of the velocity, and this'll make sense. please, don't be a tail-pipe farter.

ah yes, now, as for adding speed in the quarter mile, it's as simple (as Rich and Sputnik like to say) as "adding plenty of lightness". the RX-8 will probably weigh between 2850 and 2950 as a rough estimate, which is considerably less than your CL with all that other stuff you've got on it (the sunroof, spoilers, etc etc)... how much does it wiegh?? probably more than the 3470lb estimated curb weight that Acura quotes. unless you already do this, you could shave a tenth or two off your ET by having less than a quarter tank of gas in it (with some in a can for a top up to get home), and leaving everything that you can take out of it back at the staging lane...

back onto the topic of the RENESIS, please remember this: it's a 1.3L engine. i'll write it again, because i like that number: it's 1.3L in displacement. if you didn't read it before (i suggest you do), this engine is gargantuanly oversquare (40mmx144mm) and it STILL makes 159 lb/ft of torque at peak, with 90% of that being made from 3000 to redline (right?? i can't remember... Boogs, you know)... even factoring in that it does have twice as many power strokes per revolution in an equally displaced 4-stroke piston engine, you'd still only be at 2.6L corrected. here's a little piece of info from the TSX (the latest Acura sports sedan to be offered):


think about that... horribly oversquare (more so than an F1 engine, i'd wager... they don't give out borexstroke measurements, so you can't be absolutely sure), an fundamental engine design which has existed for about half the life of the piston engine, making such incredible power at high rpms, with a wide power band (quite linear), and still makes nearly as much PEAK torque as one of the best 4-bangers in the world.

it's STILL one hell of an engine... :D

 

i dunno if the next GT-R is gonna be a Skyline... you've seen that thing, right??? nice car, but... i need my !!! :p

 

ahhhh, forgot forgot forgot...

torque at the flywheel doesn't mean all that much, because the flywheel doesn't push your car along, the wheels do, yes?? well, the gearing of the RX-8 is supposedly quite aggressive, which could possibly translate into sub 6.0s 0-60mph times (by Buger's fairly generous estimation in CarTest).

 

200 lbft of Torque from Renesis does not hurt? maybe the MPG...but that is oKay if your bills would increase like $100 per year.

It is nice to improve on excellent car to start with...a 13.5s $35K car that handles great is a great idea...

BTW what is the competion for RX-8 (less than $35k)

WRX STI..
EVO lanncer...
SRT-4...
S2000 Coupe/Roadster
G35c
CLS-6 speed.

The first 2 would beat the RX-8 in all categories excpet the aspect of luxury

The SRT-4 would accelerate and it is rummored to be a good handler... (It could be true but not sure about it) forget about luxury.

S2000 is as fast as the RX-8 Excellent handler (but 2 seater)

G35 Luxury and Performace and even Beats the 330Ci in every aspect

CLS-6 Excellen Acceleration... Front Heavy but suspesion mods (sway bars a lowering springs and good set of tires, headers, CAI) Still great 14s car for less than $35k!


Mazada has to convence the smart buyer that the RX-8 is an outstanging car and value and performance included..

Not Bashing the RX-8... I like the car.. howver, why not give light weight rims and Brambo Brakes... and bit more Performace ...at least as on option... I expect that such goodies would be on the MPS version... :D

 

Let me try to answer all your questions...

First of all, comparing an AWD or FWD car to the RX-8 is a bad comparison... they have very different driving characteristics. Sure speed and grip are noted with AWD but you don't get the feedback you do with RWD, nor can you gas it and get the tail out for some fun drifting (though I'd never do that! ) That takes the STi and Evo out of the comparison.

The CL-S, RSX-S, SRT-4, all FWD. Great handles AS front wheel drivers, but face the fact.. you have no control over that rear end. Driving wheels in the back are generally better for track use (which is why Miatas beat lots of cars at an Auto-X). So toss them out.

Now here are the right comparisons. 330i, G35 Coupe/Sedan, 350Z, S2000... these are the competing vehicles.

Let me first say that the G35 doesn't beat the 330 in much anything other than price and accelleration (and with the new 330's engine, doesn't do that any more either). Braking is better, steering feedback is better, handling is better.. skidpad... etc etc... If you drive the two cars back to back (I did one day) you will understand. Also, the G35 (and I don't care what people say) has a cheezy interior with bad materials thruout. While Mazda may not be BMW quality, the day I drove the G35 and stepped back into my Millenia, I was a happier camper as per the interior materials. But I digress..

You say the RX-8 needs Brembo brakes? Given the data available, and mathematical computations, the RX-8 will stop faster than an M3 can. Faster than the 350Z (With the Brembos). Brembos are great for the company that wouldn't like to invest money in developing their own braking system for whatever reason. BMW develops their own and as a result has better braking in class because they design their brakes for the car. Other companies that use Brembo get a 'fitted' design that isn't always ideal and while it may stop fast, a properly manufactured design from the company is usually better. So let's understand first out of all the cars, the RX-8 will have the best braking.

Next comparison will be accelleration and for lack of patience on this question, I'll simply say that yes, it's in the middle of the pack. It should beat the 330i (current engine) to 60 and in the quarter but the 350Z will probably beat the RX-8. The G35 Coupe with the 6 speed and RX-8 will be neck and neck (this is a guess, but a good one I think). Keep in mind that for most of the rev range aside from low end (3-5k) the RX-8 exerts more torque than the G35 and 350Z. That's where track driving becomes fun

Luxury I'll put the RX-8 second. Since they decided not to go with the cheezy silver trim the Mazda6 has in it and the G35 has in it, the car is the better for it. I think that BMW will be #1 here, with RX-8 not too far behind.

In the end the 'smart' buyer (as you put it) will see that the RX-8 can run with the best if not out perform them, has an appealing shape both inside and out, isn't cheap like the 350Z or G35 inside, and doesn't cost as much as any of them. That is why the RX-8 is a good car and in my mind, the best car overall in the pack. Granted I think the 330 will be a better handler (or maybe I'll be proven wrong with final production reviews coming out..), but for about 10 grand less... who can argue?

 

Bravo herc Bravo. that was excellent, i think you have summed it up quite nicely. totally agreement

 

Let me say this ... What does the MPS RX-8 should provide to make it a "smart buy"?

BTW, discounting 4WD , AWD is a mistake...

Handling, grip, and winter perforance for us living in the north... is a MUST.

Second rally cars are about performance, great traction, great handling...

WRX Stil and EVO are excllent track cars if you can forget about the luxo factor...

Yeah,... I forgot about the Z350 ... another excllent track car that handles like a Porsche...

 

Stiffer suspension, wider rotors (more power), lighter materials.

So you get handling and power upgrades to the MPS. Same thing as if you jumped from a 330i to an M3. Handling and power.

 

Discontinuing 4WD,AWD is NOT a mistake. These do not necessairly improve handling or grip. Suspension design and tires do that. Awd actually adds unnecessary weight and drivetrain complexity. Even the 911 Turbo system is primarily RWD and only sometimes it adjusts power to the front. The only time awd is beneficial is in powering out of a corner in slippery conditions. 99% of people do not NEED to do that while it's raining/snowing.. we're not rally racers. AWD would help in the winter, yes.. But a rwd car with dedicated winter tires can outperform an AWD car with all season tires on. Personally I can live without the added cost, weight and maintenance for awd.

 

I think people tend to overyclassify cars into ridiculously rigid categories. Now, that's not to say an individual shouldn't have their individual preference of cars to choose from, but I do not think its unfair to compare fun-to drive cars that are within a somewhat similar price range that a fair number of people will cross-shop. Based on objective tests (though IMHO of less importance than subjective feel), I think the RX8 will have a difficult time with the EVO, STI, 350Z and the S2000. However, this remains to be seen.

I do agree with you that AWD cars will have a much different (but not necessarily less fun) feel. The same goes for a FWD car.

I will agree, that in general RWD cars give more potential for sportiness (though some could argue this point for AWD too), but I think design execution and tuning are much more important. Hell, a RWD car can be desinged to understeer. Yes, you could upgrade the suspension, breaks, etc. to compensate for this, but to me it just seems like something that shouldn't need to be done (at least right away) when you throw $30K down. I would have taken an integra type r over most similarly priced RWD sports cars of its time (at least in terms of handling) because of its high limits, confidence inspiring cornering, and all over hard-core, no-nonsense nature.

My biggest concern has and still remains the possibility of its design lacking this soul or spirit. Like it or not, different design goals have been merged to form what we know as the RX8. Until, I see real proof that this car lives up to its claims, I will remain skeptical.

 

Sorry, but a 350Z doesn't handle ANYTHING like a Porsche.

 

Obviously I don't know for sure, but having seen the log manifold on the Renesis, I would wager that there are significant gains that would be possible simply by moving to an equal length header setup. How this would work with the side ports, I'm not sure, but I can guarantee Racing Beat already has a Renesis in their shop and are figuring it out as we speak.

 

yes, it's true you could probably gain a little bit of torque (for a whole lot more power) up near the redline with a shorter length header... the exhaust header would bolt on directly underneath the intake headers, and might make things a little tightish if you're doing a custom setup with great big flanges (like Racing Beat always does)...

i'm not sure why Mazda would use that "log" style of exhaust header, other than to more easily monitor it (O2 sensors and what have you), and to maybe slow down the velocity for the cat (enhance the reaction)??

the rest of the exhaust system, SEEMS at first glance, to be top-notch... the muffler is obviously going to hold back a little power, but i don't wanna guess how much could be gained by going to a "low backpressure" fart can...

 

hey Buger, math-wunderkind-and-idol-to-millions, i've got a good 'un for you...

what would the projected bore be of the "16B" RENESIS (hinted at by Dan The Man), supposing Mazda goes up another 10 or 15mm?? stroke is 40mm, as i've posted earlier...

i'll see what i come up with, and we can compare notes :D

 

buger 'keech and anyone else with rotor knowledge i read this from glenn butcher over on mazdarotaryclub.com:

"The RENESIS Rotor Housing (photo taken by Dan Mazzella) looks very much like it could be adapted to still use the Peripheral Type Exhaust Port.

OR you should be able to take an older style Peripheral Port housing and bolt it into the engine. Therefore having Side Ports and Peripheral Ports. More gas in and out means more power!

This is absolutely brilliant for racing engines! NOT RECOMMENDED FOR STREET USE OF COURSE!"

does this sound actually possible and reasonable?
:o

 

heh heh... boogs wanted to have an rpm+throttle sensitive perhipheral port...

but it COULD happen, but not with the Racing Beat style mega-flanges, 'cause they're huge.... or wait, duh, i'm stupid... they'd make one that fits all four of the holes that're comin' out of the engine...
that'd be quite sick, actually... look out SPEED World Challenge!!

hmmm... about that intake side though... how could you increase that without resorting to traditional things like a bridge port??

 

Hi Wakeech,

Hmm... I briefly read the thread on the autoweek forum that you mentioned a while back. I was going to post something when you originally mentioned the "oversquare" nature of the rotary but I think there are a lot of things that need to be explained before we can even discuss this.

The first thing would have to do with piston bore/stroke measurements and how it relates to rpms, torque, etc. Bore is the width (diameter) of a piston and stroke is the length that the piston can move up/down. If I understand it correctly, a piston engine with the same bore and stroke measurements would be called "square". Typically, engines with a long strokes and short bores produce more low end torque and don't rev as high. Engines with short strokes and wide bores have less low end torque but tend to rev higher.

If we are comparing rotary and piston engines based on their "squareness", we must know what how squareness affects a piston engine. Theoretically, some people say that the oversquare and undersquare engines should have the same torque characteristics if the displacement is the same. In the real world, a piston engine with a very wide bore and short stroke has more area to have larger valves than one with a short bore and long stroke. Short explanation is that a short bore/long stroke engine can breathe comparatively better at low rpms than high and a wide bore/short stroke engine can breathe comparatively better at high rpms than low. This would explain why the long stroke engines generally have higher low end torque than the short stroke engines. Short stroke engines can also rev much higher than long stroke engines because each revolution of the driveshaft on a piston engine means that a piston goes up and down the length of it's stroke. A short stroke engine has less distance to move so more revs can happen for a given time span.

It is true that you can compare the rotary engine by trying to give it piston measurements like bore and stroke. What I earlier found was that the eccentricity of all recent Mazda rotaries is 15mm (not the 40mm that JustinTX had?). You guys did a good job to figure out the calculations to compare the rotary to the piston however.

A piston displacement is measured by looking at the displaced cylinder volume. A cylinder can be thought of as many flat circles that are stacked so that they have height. The volume then can easily be figured out as pi * r^2 (area of a circle) times the height (stroke) of the cylinder.

To figure out the "piston related bore" of 1308cc rotary engine see below:

given: "stroke" = 15mm = 1.5cm
Displaced volume of one rotor is:
stroke * [pi * (bore/2)^2] = 654cm^3
1.5cm * [3.1416 * (bore/2)^2] = 654cm^3
3.1416 * (bore/2)^2 = 436cm^2
(bore/2)^2 = 138.78cm^2
bore/2 = 11.78cm
bore = 23.56cm or 235.6mm
1.3L rotary has a bore of 236mm and a stroke of 15mm?

The above result is even more "oversquare" than your previous calculation! After all of that work however, I don't think the comparisons are meaningful. The rotary and piston engines are very different in certain ways and I don't think that the reasons why an oversquare piston engine can rev high are the same as the reasons why a "oversquare" rotary can.

I think the redline of a rotary is determined by weight of the rotors (lighter weight means less e-shaft flex) and by breathing effectiveness. In the case of the Renesis, I don't think e-shaft flex was the limiting factor in the redline. If breathing effectiveness at high speed was the limiting factor, how can we get more air in at high rpms? Perhaps something I mentioned in an earlier post in this thread? A peripheral induction port/path that opens at high rpms would induce some high speed overlap and aid in volumetric efficiency yes? I'm no mechanical engineer however and Mazda has people that are far smarter than me. Whatever options there are, I'm sure that Mazda is exploring them.

The most obvious way to increase hp/torque would be the first thing mentioned in my original post in this thread. Of course we are hearing the rumblings about a possible 1.5 or 1.6L renesis for future cars. 90mm rotors will give the new engine a displacement of approx 1475mm and 95mm rotors will give the new engine a displacement of approx 1553mm. Hopefully SuperDan will have more info for us about this stuff.

Brian

 

thank you for the timely reply.

sorry to all, for ranting about oversquarness, whilst those not into engine design havin' NO idea what i was talkin' about. uh, let's see....

*sound of 200lbs of man falling over flat on the floor*
MORE oversquare??? :D heh heh heh heh... you're right this ratio doesn't apply to the rotary, mostly because it doesn't operate as a cylinder, but more how an orbiting and rotating "fat triangle"... the output shaft the rotor acts upon travels at a higher rotational speed than the rotor, completing 270 degrees of rotation for one "power stroke", which lasts only 120 of rotor revolution. for reference, piston engines have (piston-to-crankshaft) connection rods which act upon the crank shaft for a (theoretical) maximum of 180 degrees per power stroke. this extra 90 degrees of output shaft rotation (not to mention the rotary's inherent efficiencies with regard to maximizing leverage during the power stroke) must have a large role to play in the magically magnificant torque figures this engine, with a 15mm stroke, can make. i really hope i'm not repeating something that's already been said (on this board...).

shaft flex is something pretty easily overcome, with regards to evolving the engine, and as you said probably isn't the reason the RENESIS starts to choke at 8400 rpm... breathing.
actually, i've been lookin' towards the (horrendously) complicated intake system, which is really quite beautiful, but is really leaning towards the over-complexity of the 13BREW's twin turbo system... that must mean it's fast!!
the large airbox was said (by a member whose name i can't remember, sorry bud) that it created a slow flowing resevoir of air, ready to be sucked up by the engine when one gets on the gas "spiritedly"... so let's ignore inefficiencies in front of that, and let's look to the hind (toward the engine). the triple-path induction runner system is obviously not going to be as efficient at a certain rpm that an uninterrupted, single runner system would be (at the rpm it was specifically tuned for), but does deliver a pancake-esque torque curve.
from the display cut-away engines, i could percieve no difference in the diameter of the runners, but that doesn't mean there isn't any. if, in the instance that it is all the same diameter with the aim of reducing production costs, then when one thinks of the turbulence which would be present in the short runner at WOT operation, a runner of slightly (single digit mm's) larger diameter may increase the efficiency of the runner enough to get another few hundred rpm of useful operation. oh, to explain why this increase in diameter would help with the turbulence, the velocity of the air being inspired reduces (as it's a certain volume of air/min at maximum volumetric efficiency of the engine, and thus it's speed depends upon the area of the oriface it's travelling through), reducing specific momentum, and also the boundary layer (the turbulent layer of air which drags slowly upon the walls of the runner) may be inhibited in its ability to slow down the intake air. let's not also forget that this would hold true for a perfectly straight runner, and that the runner in the RENESIS is contorted... although it's probably not possible to help it, straightening the whole thing out would in fact help a little efficiency-wise.

again, thanks buger for your cool post... these always take me a long time!! i hope yours are all fast (they don't seem to take you much time to type...)

 

First off, AWD can have as much oversteer as you want. I can go buy a $150 adjustable rear sway bar that will have me spinning out at every corner.

Also, Audi AWD cars were banned from Touring Car Races after Dominating the everyone else, including BMW. Audi runs FWD now. Does this mean AWD is the ultimate answer? No, just means it sure isn't a mistake!

Now, on to the subject at hand. On the previous engines, the exhaust port Could be widened along with wider rotors to take up the extra exhust. No-one has mentioned that with the side exhaust ports, making the Rotor wider means the exhaust gases get farther from the exhaust port. More of the exhaust stays with the chamber when it cycles around for intake. Isn't this effectively the problem with older engines - Intake/Exhaust overlap? Great for racing maybe, but emissions would drop.

With the old design, the intakes and exhaust could scale with rotor width, while with the side ports the sizes are determined by the fundamental shape of the rotorary. With the side ports there is an optimum comprimise in size/shape for a given rpm range.

Tom

P.S. If you would like a good demonstration of AWD oversteer, the first Rally of the season (Monte Carlo) is coming up this weekend. Speed will have coverage Wednesday and Thursday after.

 

sorry Tom, but i don't follow you on almost any part of your post regarding the rotary engine... except that recycling partly-combusted exhaust gases (from the cool zones on the rotor) is better for emissions, not worse...

the Audi Quattro banning i think had more to do with engine size allowed than the 4 wheel drive, IIRC, but i could be wrong... it's not THAT big an advantage though, especially in road racing.
also, a poorly setup car spinning isn't the same as having oversteer... even FWD cars can spin, but not rear-end oversteer...

oversteer on a loose surface, however, doesn't really count as that's more related to momentum than power-on oversteer...

 

I tend to blurt out my answer without any of the steps I took to get there. Let me use an example for the side versus peripheral port thing - take the RX-8 rotor, and double the width. I know that wouldn't be done in production, but I need an example.

When the rotor width doubles, that means twice as much air needs to get in to take advantage of it. The intake and exhaust ports need have twice as much area to get twice the air in.

To let the engine breathe with all this new found capacity, peripheral ports means the port width can also double, to let the air in. The size of the ports aren't limited when the engine changes size, since the port width can scale right along with the rotor width.

With side ports, the shape of the port is increased to double the cross sectional area (roughly a 40% increase in each dimension). With this new area, the intake port intrudes either into the exhaust part of the cycle, or the compression part of the cycle. The bigger exhaust port would intrude either into the power cycle or intake cycle. That's why I was saying the intake port on the new engine is the best comprimise for the engine. I'd draw something up but I'm at work so I have to look like I'm working. :D

On the emissions, I'm still catching up on rotary design - I switched around some of the problems the old engine had, I think. with the RX-7, all the unburned stuff got scooped out with the periphery port, and I mixed that with carrying it over to the intake cycle. I guess the carryover of exhaust isn't entirely bad, to a point.

As for the sway bar, it affects both lift-of throttle oversteer and power-on throttle oversteer. My car isn't powerfull enough to over come the built-in understeer except in first gear. In rain & snow, this is easy, while on pavement it takes a lot of TLC and doesn't stay long (the limited slip kicks in and trys to steer me straight)

I guess it seems silly to say AWD has no oversteer when the major racing series that actually uses oversteer to a significant degree (World Rally) is dominated by AWD. As I said earlier, check Speed Wednesday and Thursday for coverage of a Paved Road Rally.

For a good video (12megs I think), Try this:
http://www.randyzimmer.com/video/mus...s/wrc-2002.wmv
Set to Linkin Park.

AWD Donuts (3.5megs)
http://www.oman-hp.com/videos/imprezadonuts.mpg