Lock & Load

Reading September's issue of Motor Magazine there is an article called Renovation Renesis.

Here it is:

Rumors about a supercharged Renesis rotary engine for a performance special RX-8 can be confirmed as truth. Hungry for more torque from it's high-spinning rotary, Mazda is tweaking the engine using a small Eaton supercharger, tucked tightly on the engine's right side and an air-to-air intercooler bridging over the top, to boost power by 30kW (to nearly 210kW) and torque by a massive 120Nm (to around 330Nm).

There's no doubt the RX-8 could use more bottom-end urge. More damaging to Mazda's egos in Hiroshima is the blunt fact that Nissan's 350Z compehensively blows away the RX-8 over 400m.

Hopefully this supercharger will be available as an aftermarket part for our RX-8's. An extra 30kW and 120Nm would certainly put an everlasting smile on my face.

Racer X-8

What's that in HP & lb-ft please?

MrWigggles

Roughly 282HP and 243 ft-lbs

The sizeable increase in torque but only moderate gain in HP means that they are trying to get more grunt out of the car.

In other words, while on paper they might only be 17% increase of power on the top end, sounds like there is going to be a 57% increase in power in the "lower" RPMs (6000RPM or so) where peak torque is made. (By my calculations 277 HP at roughly 6000 RPM)

So you'll see considerably more than 17% HP in your 0-60 runs. Average HP over the last "octave" below redline is what's important (4750RPM - 9500RPM for the RX-8) not just increases in peak HP.

Also remember that IF Mazda is developing this for Japan, they also might be tuning it for more low end torque to keep the upper RPM power from going over the quasi-legal limit of 280 PS. A US version (if this supercharger reaches production) could be tweaked for more upper RPM power and less torque.

We shall see.

-Mr. Wigggles

WickdMonkey

That sounds good to me, but at what cost will this extra power be? Any ideas?

The Wicked MOnkey

Quick_lude

243 ftlbs! Can this setup work? Tech people, chime in.

RX-Nut

I dunno about this one.. Mazda has said time and time again that the RX-8 is not about flat out speed or horsepower. I'm not saying I dont like the idea.. In fact I love it.. I'd be first in line to put one in.. But I'm really a skeptic when it comes to speculation.

Anyone got any estimates on how much it costs to put one of these in... any car?

Tamas

iTrader: (1)

Gatting a supercharger (or turbo) is all nice and fun - the question is: how much worse the mileage is gonna get with any forced induction? It is quite bad as it is now, I'm not sure if I would want to have it any worse
In fact, mileage and the horrible numbers people are mentioning are my last major reason for reconsidering if I want to buy an 8 or not...

Lock & Load

Tamas sport cars use fuel if you a worried about the mileage and the cost factor you are looking at the wrong cars my wife drives a honda jazz { fit } in japan this gets 6.5 litres per 100 km ,but dont expect performance cars to give you low fuel figures .

ToRX-8orToZ

Ughhh, the 8 isnt a ferrari, or a super car. It is very reasonable for someone to consider fuel consumption when shopping around for a sporty car, or a sports car at the 30k price range. If the MPG drops to something like 12MPG with a super charger... well, I'd rather just buy an S2000 and throw a comptech on it and still make near 20.

mac

I'd be ok with the lowered fuel consumption if there was a switch to turn off the SC (like in Mad Max 1). That way you get your normal consumption and on those special occasions :p you flip the switch and zooooom zoooooom (and watch the gas gauge drop like a rock in free fall ).

This said, the fuel consumption is also my last reservation with this car. It's a small lightweigth car, it doesn't have silly numbers (ie 400 hp/400 ft/lb) so it should have similar fuel consumption as the others. It should at least meet the numbers published.

graphicguy

To say that the 350Z "blows away" the RX8 is a tad overdrmatic IMHO!

Having driven both, I can't tell (via seat of the pants) that there is much difference in the speed of the 350Z vs the RX8.

Even the trade rags have them both within a tenth or tow of each other.

Ike

The torque is really the difference, which the 350Z has a good bit of. Things like street start, and mashing the pedal in and out of turns is where it will help the most. So to say that the RX-8 is about handling is kind of silly because this would help is get around a track much faster, not just in the 1/4 mile.

I would estimate something like this will be a 4,000 usd add-on, give or take a 1,000.

Ike

MrWigggles

The Eaton supercharger is bypassed when you aren't on the throttle hard due to a built-in bypass valve. Much less energy is wasted. It won't be 12 MPG unless you drive the car hard.

Poor ecconomy will come from driving a Eaton supercharged car hard more than it does from the supercharging itself. Eaton superchargers in typical applications give a 6 cylinder engine the power of an 8 eight cylinder while it maintains gas MPG close to a normally aspirated 6 cylinder engine.

In some ways it is the best of both worlds.

-Mr. Wigggles

Ike

I've heard from pretty knowledgable car guys that the RX-8 really could not be FI from Mazda because of the new engine design and emissions standards, perhaps gas guzzling issues as well. But I don't have any hard evidence to actually back that up. If you keep out of boost after adding FI you're not going to see much of a difference in fuel consumption, but if you have that FI add on then why would you want to keep out of the boost range :p

Ike

Tamas

iTrader: (1)

Sorry Lock & Load, you're wrong. As it was pointed out, the 8 is not some kind of a supercar having 500 horsepower. It seems to have about 210-220 at the crank, according to those dyno numbers. I know the rotary uses more fuel by it's design (which is a pity on it's own), but not even meeting the published numbers is really bad. And it definitely shouldn't guzzle gas like it does. Coming with this 'sports cars use fuel' is a bit lame IMO... look at a Corvette (which otherwise I don't like so don't tell me to get one instead): if you don't drive it like crazy, it can get almost 30 mpg (or close to that) on the freeway. Show me just ONE 8 that is able to do that. Not even close. And the Corvette is MUCH faster.

I still love the RX-8 - but these fuel consumption numbers are frightening. I think Mazda needs to do some work there too (perhaps re-calibrating the ECU to make the car run leaner if that's possible) apart from figuring out why the car does not have the advertised 247 HP.

Sputnik

I would not put much stock in this rumour.

---jps

ProtoConVert

It isn't a sure bet that forced induction, whether TC or SC, will drastically reduce MPG. Light pressure TC's can increase mpg on cars that are otherwise underpowered, I think the common example is yugos, but I think current and prev. generation volvo's suffice as well. The value of these examples of course depend on how good my memory is, but I'd bet that Bell's Maximum Boost would substantiate. It's an arguable possibility to me that increasing low RPM torque can enable a driver to more easily get to cruising speed (low consumption), or in other words spending less time at increased throttle (high consumption), even if SC-induced torque requires more fuel.


Furthermore, it should also be noted that the Works' Cooper S package (which increases boost on the stock SC) actually decreases fuel consumption by 15%. So... this discussion is at best speculative and only answerable by hard numbers or a poster with both verifiable technical background and proprietary knowledge.


As ike said, staying off boost or switching it off (a capability i think is hardcore) will leave consumption probably close to stock. Also, as he says, WOT w/ boost will necessarily mean increased fuel usage through the injectors = hopefully you budgeted these extra fuel costs.


But I was interested in the discussion of torque vs handling. I actually find it admirable how often Ike takes advantage of any opportunity to rag on the RX8 and the things people like about it as it makes the discussion more interesting, but Ike I disagree with you here.

Better handling usually refers to suspension and chassis, not to torque. So, you see I was kind of surprised when you introduced it into a discussion of fuel consumption. Yes, low rpm torque helps powering out of a turn, but that's if you don't downshift. A higher (low speed) torque car on track with a better handling car will by definition have to brake more but will be able to compensate w/ torque, whereas the better handling car will need to use less brakes, this comparison being averaged over all turns over all tracks.

The comparison is really moot too, because it's relatively easy to modify both low speed torque (if you want) as well as suspension variables. It is much less easier to modify chassis'. But the point is, torque isnt a factor when you consider a car's handling.

Icemastr

With a turbo or supercharger, especially one this small, your going to see minimal losses in mileage driving normally. #1 From what I have read a lot of peoples gas mileage is getting better and better the more their cars are driven. #2 Your gas mileage could actually improve from the more amount of air forced in you will get better combustion and fuel will be more completely burned, although typically you would experience 1-2MPG drop for regular driving. When I first got my FD it had a downpipe and Power FC ecu, I was getting 24MPG on the highway with it, i did some upgrades and it is now producing over 80RWHP more, and I am getting about 22 on the highway. Its just when you start increasing injector sizes, fuel pumps, etc your going to see a lot more drastic jump as anyone who takes a car from 200RWHP to 500RWHP accepts this.

BOOSTD 7

Just more annoying, never-ending speculation ... not much else to help pass the day I suppose.

Sputnik

No it won't.

Remember, when you're considering a forced induction setup, you also increase the size of intake and exhaust to handle the significantly increased airflow. Even with a bypass valve, the increased intake and exhaust sizes will hurt idle/cruise performance. Since a car driving around the street or down the highway, spends a major portion of it's time at idle/cruise, this will still significantly decrease your mileage.

---jps

MrWigggles

Sputnik,

The bypass valve of the eaton supercharger is smallish an thus is designed help choke the intake some when boost isn't required.

Also IF the exhaust manifold needs to be changed, we are talking about minimal decrease in back pressure that comes from typical aftermarket exhaust systems anyway.

Most Eaton aftermarket kits leave the exhaust manifold completely stock and try and keep the intake side as stock as possible as well.

-Mr. Wigggles

neit_jnf

Doesn't forced induction increase the volumetric efficiency inside the engine? And turbos recycle what is otherwise wasted energy by using the heat and airflow energy from the exhaust, right? So then, if done right it may improve mpg theoretically? Or the increase in efficiency comes in the form of more power and torque? I have a headache :p

Sputnik

The bypass is small because that's all the larger it needs to be. A "choke" point is not going to make up for a large intake path, it will make things even worse (as in, act as a restrictor plate used in some racing series). If you don't replace the exhaust system, then it won't. But if you don't replace the exhaust system, you will significantly restrict the engine's ability to produce power, and you will not be able to take full advantage of your investment. The increase in efficiency comes in the form of more power and torque. At idle, the same issue with larger intake/exhaust still exists. And with a turbo, having an exhaust system sized large enough is not only important for power, but for spool-up response and other drivability issues. Again, at cruise and idle, the turbo is normally bypassed, so there are no gains from it.

But that's on cars with engines much more poweful than necessary for cruising at highway speeds. When you consider trucks and diesel-electric trains, they need all the power they have to maintain highway speeds, and turbos make a huge difference in mileage. Those of us with turbo Miatas have seen that the cars are normally under boosting (just under positive boost in my case) at highway speeds, especially at higher altitudes. I don't think that the RX8 Renesis will be able to use more boost like the Miata at highway speeds, and it won't help in city driving (as far as mileage is concerned).

---jps

Ike

This is important for any car, but especially FI cars, that doesn't stop manufacturers from putting rather restrictive exhausts on factory FI cars. The WRX has 3 cats and they are in horrible spots which make spool up times much slower, but the car still does alright. You will still get gains from a supercharger with your stock exhaust, and I'd be willing to bet your system is less restrictive than many others. How much in the way of gains has more to do with the engine internals and engine compression than the exhaust.

I never meant to imply that gas mileage will not be effected should someone with an RX-8 go with a FI setup, I think you will see worse gas mileage, but depending on how much you are in boost will effect how much worse greatly.


Ike


edit: Forgot to add that the cats of an exhaust will always be more restrictive than the configuration and pipe size of an exhaust, it's pretty much a given that if someone has the money to drop on FI for an NA car the exhaust will have already been taken care of.

mystrx8

I don't really know what all of the hullabahoo is about: add ~40 hp/ lose ~1-2 mpg. . . Hmmmmm. . . SIGN ME UP! :D