Buger

Since there hasn't been any new and exciting rx-8 information coming out recently, let's discuss the not as exciting but very necessary emissions requirements that need to be met for the 2004 model year. Peripheral port rotaries are no longer an option for Mazda because of the emissions standards today and in the future.

Cars in the US were previously under the EPA "tier 1" emissions standards. These standards define the amount of Hydrocarbons (HC), Carbon Monoxides (CO), Nitrous Oxides (NOx) that can come out of the exhaust. Amount of particulate matter is also regulated but will not be discussed here. The emissions systems for the tier 1 standards are expected to last at least 100,000 miles.

The tier 1 standards to 100,000 miles are below (all #s are in grams/mile):

............. HC ..... CO ..... NOx
Tier 1 .... .31 .... 4.2 .... 0.6
LEV ...... .075 ... 3.4 .... 0.2
ULEV ..... .04 .... 1.7 .... 0.2
SULEV ... .01 .... 1.0 .... .02

Starting in the 2004 model year, there will be new standards called "tier 2". These new standards focus much more on reducing NOx than the previous ones. The emissions systems for the tier 2 standards are expected to last at least 120,000 miles.

The tier 2 standards (bin 5-a) to 120,000 miles are below (all #s are in grams/mile):

............. HC ..... CO ..... NOx
Tier 2 ... .018 .... 4.2 .... .07
[edited #s for bin 5-a]

The new standards are significant for rotary engines because rotaries produce less NOx than piston engines. In the 70's, a major concern was to reduce smog causing NOx. One of the selling points for the rotary in the 70's was the "great" emissions (NOx) performance. Mazda was the first manufacturer to follow the emissions standards from the 1970 clean air act (Muskie act) and they did it without even using a catalytic conveter! It is ironic that the fd3s left the US because of it's poor emissions (HC) performance. I read that the Rx-8 has already met the tier 2 standards.

Lean-burn engines have been identified by U.S. automakers as the next major technological step in combustion engine design and fuel economy. A problem with lean-burn engines is that they (up to approx 1.1 lambda) will produce more NOx.

The rotary naturally produces less NOx than piston engines and Mazda is perhaps the first manufacturer to solve the catalytic converter problem. See the below links:

http://link.sandiego.com/scripts/whe...e.idc?passin=1 (world's 1st 3-way catalyst for lean-burn engines)
http://www.repairfaq.org/filipg/AUTO/F_Gasoline5.html

From the second link, "Modern catalysts are unable to reduce the relatively high levels of NOx that are produced during lean operation down to approved levels, thus preventing the application of lean-burn engine technology. Recently Mazda has announced they have developed a "lean burn" catalyst, which may enable automakers to move the fuel combustion towards the lean side, and different gasoline properties may be required to optimise the combustion and reduce pollution".

Emissions regulations seem to be here to stay. Immediately after the regulations in the 70s, engines had to be made with lower compression ratios to reduce emissions. Unfortunately this also reduced power. Today, we are at the point where we have technology has allowed us to have 11:1 compression ratios in some cars which still meet LEV standards. What does the future hold for the rotary?

Brian

Hercules

I think the future of the rotary is wholly dependant on how popular the design becomes. If Mazda can launch it properly and keep it reliable, I think rotary will make a comeback in a big way.

The current horsepower war is all about displacement, and you look at the Renesis and its 1.3L rotary, and you wonder how the hell a engine smaller than a 4 cylinder can pump out 250 horses.

For other automakers they will look at it as an opportunity to increase displacement but get better results. Having a 3.0L rotary with 3 rotors spinning in the chamber? You're talking near 400 horses, plus a lighter weight than a I6 or V6.

It's a matter of time, and once the engineering is devoted to the rotary, then the accolades will follow. Mechanical engineers have always noted that the piston engine is a relatively poor design in a combustion engine. The Wankel is however, aching for its glory now. I think as time goes by and more dev time and money is given, the rotary, like the piston engine, will go through an evolution that will result in better emissions and gas mileage.

bwayout

Glad to see that I’m not alone in wondering about this topic. I'm no scientist or enginer, but I am really wondering about how this will all affect the fuel mileage of the RX-8. I hope that Mazda made this rotary their answer... so I can answer yes to my wallet when it comes time to buy the car.

Otherwise, I’d really love to get a hybrid, but as of yet, there’s no sporty 2+2 fastback/hatchback coupe that is on the market that is available … So, this is what I’ve been debating with myself – If I don’t end up with the RX-8 (due again to what I might have in my wallet and bank) - what other car has the best EPA Fuel Economy Estimate rating? This is what I've been looking at ...

(I skipped all of the torque comparisons simply because I got tired cutting and pasting everything in … I just wanted to focus on the EPA estimates. Of course actual mileage may vary blah blah blah - I just copied this from all of their websites)

Nissan 350Z (yes it's not a 2+2, but my wife thinks I should get one)
Its (V6 engine with CVTCS) horsepower is rated at 287 hp @ 6,200 RPM using Premium unleaded fuel – The 2003 EPA Fuel Economy Estimate (city/hwy) rating for the automatic at 19/26 and their manual is at 20/26

Infiniti G35 Sport Coupe
Its (basically the sameV6 engine same as the Z) horsepower is rated at 280 @ 6,200 RPM using Premium unleaded fuel – The 2003 EPA Fuel Economy Estimate (city/hwy) rating for the 5-speed automatic at 19/26 and their 6-speed manual is at 20/27

2003 Honda Accord Coupe LX V6
(Personally, I’m not that crazy about it’s “looks” at all – plus it reminds me of a much less edgier Mercury Cougar-which I liked better - but still it is a 2+2 coupe and cost less than a G35 coupe) Anyway, it’s horsepower is rated at 240 @ 6250 RPM using Regular unleaded fuel – The 2003 EPA Fuel Economy Estimate (city/hwy) rating for the 5-speed automatic at 21/30 and their 6-speed manual is TBA (Available in February 2003).


And moving down to smaller horsepowered engines:

Acura RSX TYPE-S and its (4-cylinder) horsepower is rated at 200 at 7400 RPM using Premium unleaded fuel – The estimated EPA fuel economy for the RSX TYPE-S 6-Speed Manual is: 24/31 mpg (city/highway). Plus for the regular RSX (which uses regular gas) is rated at 27/33 mpg (city/highway) for the 5-speed manual and 5-Speed Automatic: 24/33 mpg (city/highway).


Toyota Celica GT-S and its (4-cylinder) horsepower is rated at 180 @ 7,600 RPM using Premium unleaded fuel – The estimated EPA fuel economy for the Celica GT-S 6-Speed Manual is: 23/32 mpg (city/highway) and the Celica GT-S 4 speed automatic is: 23/30 mpg (city/highway) . Plus for the regular Celica GT (which uses regular gas) is rated at 28/33 mpg (city/highway) for the 5-speed manual and 4-Speed Automatic: 29/36 mpg (city/highway).


I’d love Mazda to come out with a hybrid rotary engine for the RX-8, but I’m sure that it won’t be available by this summer 2003

Here’s a past link (10/19/02) that covered the RX-8 Fuel Consumption question

http://www.rx8forum.com/showthread.p...&highlight=gas

In this thread, Hercules put out a guess that it might fall around 22/28, which makes it better than the Z or G35 coupe.

Has anyone heard anything else?

I’d love if it was similar to the Celica’s and used Regular gas

revhappy

I'm also intrigued by engines that can offer great performance AND decent fuel economy. Based on my unscientific, casual observation, Honda's VTEC/I-VTEC powerplant seems tops in this regards. The S2000 has an EPA estimate of 20/26 or a 23 average. The numbers floating around for the renesis seem competitive. Though, I'd be much more interested and seeing the "observed" fuel efficiency. A lot of cars seem to have competeitive EPA estimates with the S2000 (such as WRX, 350Z, G35, etc.), but the observed fuel efficiency during tests are always lower it seems.

How about a new ratio for the car mags to use? Fuel Efficiency- Performance Ratio: Observed MPG/0-60 or 1/4 mile time. Something tells me Detroit wouldn't like that!

wakeech

the whole deal with that is that the small displacement engines can simply just tour around using less gas most of the time, but when wound up can burn truckloads of it and make some really good power: it's all in the revs.

at low rpm, you're not using much gas in a 1.6L engine, especially when it's on the fuel-saver cam. when you're up at 6K rpm on the performance cam, you're not getting better than 10 mpg, but making decent power. that's the whole tradeoff. it's not QUITE that simple, as these new DOHC's with all kinds of crazy contraptions are more efficient at any and all rpms than some dinosaurs with carburetors and are better on gas in THAT respect, but you COULD, in theory, get better mpg's in a Corvette driven like a grandma than a brand-spankin' RSX driven like a maniac... of course, people with Corvettes often don't drive like grandma, and not everyone with an RSX is a maniac, but you get the picture. these numbers are kinda misleading: it's not the best of both worlds, the tradeoff is different (very low bottom end performance for good fuel economy in regular driving).

Hercules

Even at a 10% increase from the RX-7 you're looking at 20/25 for the EPA numbers. They always go down from that, but nonetheless it's not bad.

If you figure Mazda quotes most of the time a 30% increase overall efficiency (under certain conditions, which is always used).. put the increase from 10% - 30% and you're looking at reasonable gas mileage for its class. With its weight granted you are going to want better gas mileage but having a rotary will deduct you on a slight luxury of not filling up as often.

I'm not concerned myself, because it will be no different than what I have now (18 mpg in my Millenia ), if not an improvement. So I look forward to it

Buger

The ideal engine would offer great performance, great fuel economy and great (meaning less) emissions. Unfortunately these are in some ways contradictory things. In the 60's, it was easy to use high compression ratios to get high power. This increases the possibility of detonation but this was overcome by using richer air-fuel ratios. Richer air/fuel ratios leads to increased emissions but nobody really cared back then.

Fast forward to today and we have indeed come a long way. Carmakers are once again back up to 11:1 compression ratios but emissions are *much* cleaner today thanks to new catalyst technology, better fuel injectors and computers that adjust the air-fuel mixture God knows how many times a second.

The easiest comparison to the renesis engine would probably be the s2000 engine (f20c?). Both are small, lightweight engines with relatively low torque numbers and high hp numbers. I'm not sure what the final compression ratio of the Renesis is but I don't think it will be as high the f20c compression ratio of 11:1. The renesis will be smaller and lighter than the f20c while also putting out more horsepower and torque. The Rx-8 will also most likely be heavier than the s2000 so it will really be special if the rx-8 can equal or surpass the s2000 fuel economy.

I've never owned a Honda but most people will admit that Honda has been one of the world leaders in emissions and fuel efficiency. Can Mazda beat Honda at it's own game while using a heavier car with an engine that probably has a lower compression ratio and has *in the past* been less fuel efficient, less thermally efficient and more polluting? If I didn't know anything else, I would say no.

Despite the above reasons, I previously surmised that the rx-8 fuel economy *would be* better than the s2000 and come in around 19-20 city / 27-28 highway. Perhaps this is overly optimistic but rotaries do have characteristics that make it very different than piston engines.

Mazda has said that the renesis can run leaner than piston engines over a wide range of rpms. Mazda also supposedly has pioneered some new catalyst technology that could allow the engine to run lean while still passing 2004 US tier 2 and Euro Stage IV emissions requirements. Since the Rx-8 has a bigger tire circumference than the s2000, it's 5th gear will take it to it's top speed of around 155mph. This will allow Mazda to design 6th gear *strictly* for fuel economy at highway speeds.

How much of an impact will these factors have?

Brian

Mako

1997 Civic LX, 5-speed manual. EPA rated 32/38.

Driving home for turkey day and such is ~480 miles of freeway. (Santa Barbara to >100 north of SanFran via 101) I'm lucky if I can get 30 MPG. Granted this is because I make the trip in ~7 hours (passing through SanFran, 19th ave. is a time killer). It would be nice if there was a way to know (and perhaps there is and I am merely ignorant) how gas milege scales with speeds/conditions beyond that which the "highway" rating is derived from.

I say this because I know I am pushing my honda pretty hard (especially uphill). Usually fairly close to the limit of what the engine can happily produce power wise. It's very happy at around 85-90 mph in 5th gear (~3500-3750 RPM). Below that and it tends to want to speed up with just a little more gas, above that its really a matter of rapidly diminishing returns.

So my point is this, it would seem that different cars (different engine, gearing, drag, etc) would have different speeds at which they were most "efficiant" (not saying 85 in a civic is most efficiant for it, 38 mpg/<30 mpg quite clearly states that). But it makes sense that different cars would have different "sweet spots" in terms of fuel efficiancy. As well as speed/fuel consumption, it seems there would be a point where a plotted speed/fuel consumption chart would take a noticable turn.

A few closing remarks, as a civic owner and a college student I feel it necissary to point this out. . . The only thing not stock on my car are the tires, not the rims, not the. . . Just the rubber part. The part that keeps me friendly with the road.

And secondly, I am not the F*&Kwit that cut you off in the highway going 95. . . . I drive like I wish everyone would. This means I use my blinker, don't cut people off, and drive the speed of traffic. However at 3 pm in the afternoon, on a dry sunny day, on a 4 lane divided freeway that is pretty much empty (i.e. not passing people every 30 seconds), I find it perfectly reasonable to go 95. And wish, when looking at a future car (sometimes a comp sci degree can still land one a good job even in today's economy. . .) it would be very nice to have some idea if my MPG were going to totally tank when going 90, or if it was just going to take a bit of a hit.

revhappy

Very well said Wakeech. I certainly agree with you that the low displacement engines will get poor gas mileage if you rev the hell out of them. S2000s at the track get like 7 mpg! Hell, I routinely get in the low 20's in my Escort cause I drive crazy (well its got a low redline..but i hit it a lot!).

With that being said, when you look at overall driving, the fuel efficiency in the low displacement NA engines seems better. The road tests by the car mags almost always seem to verify this.

Quick_lude

During daily driving which includes city and hwy I routinely get 10L/100km so that is 2.6G/60mil or about 23-24 mpg. I think that is pretty good for a 200hp engine.. Keep in mind on the hwy I usually travel at 80-100mph (gotta love Canada! :D ) which translates to 4,000rpm and beyond. If the Renesis gets similar fuel economy in the same conditions I'd be very happy.
At the track, well who cares? Fuel economy is the last thing on my mind while I'm lapping.. Can't have it all, at least not yet.

Buger

Hi Mako,

I made a similar post awhile back after a trip from Denver to San Diego and back. I started reading about fuel economy and have learned a few things though. You will get your best gas mileage in your highest gear at the lowest speed (without lugging the engine).

I used Cartest to plot a rough estimate for the 1996 Civic LX (1997 data was not in the default database) and came up with the below mpg-speed graph:



You can see that (per gear) fuel economy is gets steadily worse as the speeds increase. Aerodynamic drag is the main factor here (Cd and frontal area). If you are going up a hill on the freeway, it is more economical to stay in your top gear (if you can keep up your speed) instead of downshifting. At any given speed, it is more efficient to be in a higher gear. I believe the main reason the government tried to mandate the 55mph national speed limit was because of fuel economy.

The bottom graph is used to estimate what the EPA highway test is like. The US Department of Energy website (http://www.fueleconomy.gov/feg/info.shtml) has more specific info on their highway test:

"The test to determine the highway fuel economy estimate represents a mixture of "non-city" driving. Segments corresponding to different kinds of rural roads and interstate highways are included. The test simulates a 10-mile trip and averages 48 mph. The maximum speed is 60 mph. The test is run with the engine warmed up and has little idling time and no stops (except at the end of the test). "

Brian

Mako

Thank you for a most informative reply Brian.

That's pretty much what I figgured, but I didn't think that the mpg graph would be quite so smooth. I know that the "peddle depression per unit speed" ;-) isn't that well behaved. Than again you did say it was a rough estimate. And it does seem a bit. . .idealistic in the low speed ranges at high gears.

I guess what is bugging me is that it seems that if we were to imagine two different scenarios. In one we are driving in the highest gear (say 5th in my case) and for some reason had it floored, and had topped out at say 95 (it's up hill, it's a civic. . .). It would seem that if we could go that same 95mph, in 4th gear, without having to floor it, that one would be getting better fuel economy. However this may not be the case, as the accelerator isn't exactly directly linked tot he fuel pump. . . and there other fators which I am sure I am forgetting or not aware of.

Yes I do believe that fuel economy was the reason for the 55mph limit, 70's gas crisis and all. But it was supposed to be a temporary thing. . . .

Anyway, this is the RX8 forum, so back to discussing the car we all wish we were driving today. . .

Buger

Hi again Mako,

I know *exactly* where you are coming from. About 10 weeks ago (Oct 5) I posted the below:

"If anybody here has ever taken a looong drive, you find that your mind often wanders a bit. We went on a trip from Denver to San Diego earlier this year and I found myself thinking about what the most efficient speed/rpms were in 5th (top) gear.

At the same time, if you are going about 65 mph in your top gear and start facing a small hill and start slowly losing speed, you either have to press on the gas more or downshift. At what point would it be most efficent do downshift?"

in the thread http://www.rx8forum.com/showthread.php?s=&threadid=929.

Since that time, I have learned a few things about fuel economy. I have to thank Grimace and Wakeech as two of the people who helped my views of fuel economy and rpms evolve since that time.

At first, it may not seem very intuitive at all but it is possible to use less gas by flooring the pedal if we are in a higher gear. At low speeds, engines can't suck very much air in. Let's say you are in your 1997 Civic LX in 5th gear on a flat road going at 35 mph. The engine rpms will be very low (something like 1400 rpms for your civic?), torque will be very low (torque curve is low at 1400 and 5th gear doesn't multiply your torque enough) and you will have to completely floor the gas pedal to keep up your speed.

You can also go 35 mph in your Civic in 1st gear, 2nd gear, 3rd gear, and 4th gear. Each lower gear will have the gas pedal pushed in less than the next higher gear but you will be using more gas in each lower gear. Note that the "gas pedal" more directly controls the air into the engine rather than gas. Of course, engines only run at a narrow range of air:fuel ratios so letting in more air uses more gas also. An engine's torque curve generally follows the amount of air that the engine can breathe for any given rpm (Note that the 3 raised areas of the renesis torque curve correspond to the rpms when the engine breathes the best from the 3 path intake). At 1400 rpms, the torque curve of your Civic is very low so not too much air (and fuel) are being used. The amount of gas burned between 50% throttle and 100% throttle at 1400 rpms is negligible compared to say the amount of gas burned between 50% throttle and 100% throttle at 4600 rpms (4600 rpms is the torque peak of the civic).

In 5th gear of your Civic LX, it takes approx 2.842 revolutions of your engine to turn your drivewheels once (4.06 diff ratio * .7 5th gear ratio). Lets assume that you have just enough torque to maintain your 35mph speed in 5th gear. Now think about if you were in 1st gear: it will take approx 13.195 revolutions of your engine to turn your drivewheels once (4.06 diff ratio * 3.25 1st gear ratio). Running in first gear @ 35mph, you will have *MUCH* more torque than you need to maintain your speed. If you just plan on cruising at 35mph, you are wasting fuel by burning it to produce more torque than you need. You can do the same comparison for 2nd gear, 3rd gear and 4th gear @ 35 mph. In each of the next 3 gears, you will also have more torque (because of gearing) than the amount you have in 5th gear @ 35 mph. This extra torque that you have in the lower gears does not come for free of course, you are burning more fuel because there are more power strokes even though the gas pedal isn't floored.

The highest gear is the most fuel efficient because you aren't making any *extra* torque/power to propel you at your speed.

Below are some things to remember:

1. Higher rpms in a gear mean higher frictional losses.
2. Higher rpms in a gear mean higher losses from aerodynamic drag
3. Higher rpms in a gear mean that you have more power strokes to burn fuel.
4. At any given speed, it is more efficient to be in a higher gear.
5. In any given gear, you will be getting better fuel economy at lower rpms.
6. Cars are most fuel efficient at the lowest speed that they can maintain in their highest gear.
7. Using your lower gears for acceleration means that you can get to your "cruising" gear quicker. You will spend less time in your fuel inefficient gears.
8. My posts are overly long, overly **** and overly boring.

Brian

Buger

The production rx-8 will have the below emissions classifications:

Japan. - E-LEV (excellent low emissions vehicle)
US...... - Federal Tier II bin 5-A, California LEV2-A
Euro... - Stage IV
Aussie - Stage III

Brian

wakeech

it is my duty and priviledge to bring the old terrific, classic threads back to life, like this one.

Smoker

Thanks wakeech.

I didn't remember reading this one.

Got any other personal favourites ?

wakeech

:D why yes i do.

How the RENESIS Makes More Power

RX-8 Gearing (that's a monster, but worth wading through... the middle bit is just fluff though)

ummm... a few others... search for anything with Buger in it, and it's nearly assuredly a good thread.

Mako

I meant to thank you Brian for the multitude of great replies, but I was unable to at the time due to temporary lack of net access and didn't want to go about reviving old threads. But since it's officially been resurected I'll gladly take the opportunity to make good on that intention. . .

A few points I have been wondering about that relate to this.

Is there a RPM where you would be extracting the greatest amount of useable power from a unit of gas? It seems that there ought to be, that at some RPM everything would be tuned juuuust right. . . But my knowledge of car engines is limited enough that I don't really trust it :o .

Let me attempt to paraphrase that huge post to see if I got the idea.

(Assumption)In general, fuel/air ratio does not vary wildly?

At any RPM, there are X number of combustion chambers that are in a position to suck in fuel/air mixture every second.

Because the fuel/air ratio doesn't vary wildly, this makes the volume it has to fill (i.e. number of open chambers per second) the primary determinant of fuel consumption?


Could you point me to a good resource on the specifics of how exactly the throttle works in a modern, fuel injected, ECU controlled, engine? If you've got a good link that'd be great, I don't want to ask you to write another book :p .


Wakeech, that gearing thread was good stuff. It's amazing the amount of knowledge on call in this forum. (As a ratio of smart people to annoying jerks it's probably tops among my regular reading)

I need to lurk less and post more.

wakeech

essentially, the system which existed in carburettors hasn't changed, it's just that the components have been moved throughout the engine, redesigned or evolved into something better, and are generally under computer control.

the choke is still there, as the main throttle plate: this is what really puts a restriction on the engine, purposefully hindering the engine's breathing so that it uses less fuel per rotation (combustion chamber isn't allowed to fill most efficiently), and rather than being a choke on the carb, it's way up at the business end of the inspiration system. rather than being mechanically conected to teh accelerator pedal, it is controlled via electric motor based on an ever-growing array of inputs and information through the ECU... basically, the ECU senses how much you're putting your foot into it, and it interprets that as some amount of torque you want from the engine at that rpm: the ECU then tells the throttle (and thus correcting for other things after it like the fuel injectors, ignition timing, and cams if you got 'em) what angle to be set at to best get that amount of torque.

the fuel rail too is still there in the form of the fuel injector: it's bigger and more obtrusive, but (obviosly) works far far better, and can be electronically controlled, not to mention directional (allowing it to SHOOT into the engine, rather than just bleed fuel into the airflow). with the injection point of the fuel as close to the engine as possible (to minimize loss of the fuel along the inspiration tract) fuel efficiency is enhanced, and atomization is maximized (less condensation). now that it's computer controlled rather than mechanically tuned with screws to set the rate of flow proportional to the throttle angle, it can now introduce a far more constant (or "correct") gasoline charge into the fuel air, being metered according to the information the ECU recieves from the MAF or whathaveyou.

ummmmmm... i'm missing things... dammit. but it's 11pm, and i should get some sleep. please, smarter-people-who-aren't-up-past-their-bedtimes, fill in my gaping blanks.

thanks in advance.

Buger

Who would have thought that one month after the release of the RX-8 in the US, the emissions would be a major topic for discussions. Since there has been a lot of discussion about US emissions standards as being the cause for the revised US HP numbers, it would be interesting to look at emissions standards around the world.

As posted earlier, the RX-8 is supposed to meet the following standards:
Japan. - E-LEV (excellent low emissions vehicle)
US...... - Federal Tier II bin 5-A, California LEV2-A
Euro... - Stage IV
Aussie - Stage III

The below #s are from a few different sources. If any of the figures are wrong, please correct me.

Japan - E-LEV standard:
10-15 mode (urban)
HC .04 g/km * 1.609 = 0.064 g/mile
CO .67 g/km * 1.609 = 1.078 g/mile
NOx .04 g/km * 1.609 = 0.064 g/mile

US...... - Federal Tier II bin 5-A:
After 50,000 miles (Intermediate Useful Life)
HC .015 g/mile
CO 3.4 g/mile
NOx .05 g/mile

After 120,000 miles (Full Useful Life)
HC .018 g/mile
CO 4.2 g/mile
NOx .07 g/mile

Euro... - Stage IV:
HC .10 g/km * 1.609 = 0.161 g/mile
CO 1.0 g/km * 1.609 = 1.609 g/mile
NOx .08 g/km * 1.609 = 0.129 g/mile

Australia - Stage III:
HC .20 g/km * 1.609 = 0.322 g/mile
CO 2.3 g/km * 1.609 = 3.701 g/mile
NOx .15 g/km * 1.609 = 0.241 g/mile

Note that the testing procedures are different for each of the above standards. Note that the US standards also require manufacturers to design cars that still complyafter 50,000 and 120,000 miles. I believe BWOB has previously posted about how difficult this is.

While the Japanese E-LEV standard seems to be tougher than the Euro Stage IV standard, it should be noted that "the [Japanese] emissions test drive cycle reflects slower average speeds, therefore [are] less 'challenging' to emissions control".

It should also be noted that the Japanese market gasoline has very low sulphur levels which helps keep in-use emissions/deterioration low.

Out of HC, CO and NOx, I would think that HC would be the toughest of the 3 for the renesis to meet for US regulations. Rotaries have historically been better than piston engines at NOx and the US standard for CO is more lenient than the Japanese and Euro regulations. Yet running the renesis richer would lead to worse HC emissions (unless a richer break-in would lead to better HC emissions in the long run?)

Anyways, I'm just throwing some of this stuff out for discussion. I don't really have a point today.

Brian

Buger

From multiple dyno results posted, we have seen that the current US spec RX-8s do not match the torque and hp of the presskit hp/torque graphs over ~ 6200 rpm. At least a couple of posts have compared graphs and things actually look good below ~6200.

Mazda has stated that the new tuning is due to US emissions regs (which test @ 50,000 and 120,000 miles). Perhaps early testing was within regs but late testing of production cars was marginal at higher rpms. Could it be possible that the production RX-8s were compliant at revs up to ~6200 and were marginally non-compliant with one of the specs over ~6200.

If faced with this type of problem, the quickest and easiest way to resolve it in the short term might be to just limit the output in some way at the high rpms. On a modern fly-by-wire car that doesn't have a mechanical throttle linkage, the ECU could even modify the throttle.

Whatever the case, this is still all speculation. there are many questions that will probably be unanswered for awhile. If people no longer have the same trust in Mazda NA, they can at least take comfort in knowing that there are some very intelligent people outside of Mazda that are also researching the case of the "missing" hp/torque.

One of these people posts here as yawpower. If anyone hasn't read some of his technical articles yet, I would suggest going to:

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

and spending some time. I believe that Paul [Mr. Yaw ] was going to have a writeup of some results of his testing of the renesis within the next month.

Brian

Buger

There have been many recent questions about the US emissions regulations and what effect they have had on possible tuning of the RX-8. I’ve found that the emissions regulations are much more complicated than most people may realize. Hopefully I understand some of this emissions stuff enough to explain it accurately.

As I posted earlier, there are new US emissions limits for 2004 model cars. Since the US RX-8 was released in July, it may have been the first (or surely one of the first) 2004 models in the US that were constrained by the new regulations.

I believe that the new regulations are also the main reason why the 2004 s2000 had a displacement increase. The previous s2000s would not pass the new SFTP tests (more about this later) without a redesign of the emissions systems. Honda didn’t think that potential s2000 buyers would appreciate a big drop in power because of a new emissions system so they used a bigger engine so that the peak power level would ultimately remain the same.

The previous emissions limits that were posted in this thread were all for the US FTP (Federal Test Procedure). The FTP has a test cycle that was designed to simulate an average LA commute (from the 70s). The LA4-SP test is about 7.46 miles with an average speed of 19.6 mph and a top speed of 56.7 mph. It is also known as UDDP (Urban Dynamometer Driving Schedule) or just LA4. A graph of the UDDP test is below.

After a “cold soak” (car sits without running) of 12-36 hours the car is started and idles for 20 seconds before the first acceleration in the test. EPA and CARB have determined that up to 80% of the emissions emitted during the test occur before the cat(s) are up to operating temperature (250^C – 400^C). Because of this, manufacturers want the cats to heat up as soon as possible and place the cats very close to the engine. Mazda has started to use a double-skinned exhaust manifold before the cat on their new models for this reason also. I also believe that Mazda tries to make the RX-8 idle as lean as possible after a cold start to help heat the cat up faster (lean a/f mixture leads to hotter temps, rich a/f mixure leads to cooler temps). Perhaps Syntrix can find out how much richer the RX-8 cold-start idle mixture is compared to the idle mixture when the RX-8 is warmed up (22:1 a/f ratio).

EPA emissions regulations are the reason for some of the main complaints about the RX-8. Lower fuel economy than expected, less power than advertised, cycling A/C. Surprisingly enough, the LA4 test is not the reason for any of these problems. If people are actually interested in this stuff, I will find the time to post more about the EPA tests that are responsible for the above problems. It would also be interesting to find out the temperature that the cats start deteriorating at huh? Who would have thought that EPA emissions regs would end up being so interesting and relevant on this forum?

Brian

wakeech

shmarty pants :p

MrWigggles

I think it is worth noting the unbelievable advances that have occured in emissions control.

I am all for cleaner air but this is getting ridiculous. We have seen roughly a 10 fold decrease in emissions in the last 5 years and at least a 100 fold decrease in emissions in the last 15 to 20.

If everyone drove new cars, then consumer autos would be practically 0 percent of the overall air pollution. The VAST majority of the air pollution due to autos is from older cars or poorly maintained cars (i.e. "gross polluters"). Yes the long term stratedgy makes some sense, but short term tougher emissions standards are just going to make engineers pull out their hair not clean-up the air. The cars from recent years simply aren't the problem.

What I am getting at here is that if we have lost power due to the Tier II (and maybe some fuel economy) then I want it back. However, I don't want to just straight-pipe my cat to get the power back - that is completely irresponisble.

However, I have 0 remorse for changing the ECU or reflashing the ECU with Japaneese code even if it means my HC goes from .015 to say .025. That would still be 4 times better than some parts of the world and many times better than the cars made just a few years ago (which were improvements themselves over previous gens). However, such a modification would probably considered a federal offense.

The FED's and the EPA need to stop beating a dead horse. It is ultimately costing the consumers money, fuel efficiency and performance to have the car manufacturers meet these increasingly absurd standards.

-Mr. Wigggles

Ps. In a congessed urban enviroment, where there a ton old taxis, delivery trucks, etc. pumping out fumes, I wouldn't be surprised if the air coming out of a Tier II car wasn't cleaner than the air going in!

revhappy

Buger,

I'd be interested to see some more posts about the EPA tests.

I believe you are referencing the EPA regulation regarding cats lasting 100,000 miles?? It seems like a silly regualtion if it forces the use of rich air/fuel mixtures. It should be a mandatory replacement in the warranty at x miles instead of an x amount expected life regulation. State inspections should catch a cat failure as well, I would think.