DTECH-RX

Considering that the RENESIS already seems like a pretty well tuned product right from the factory, what are "bolt-on" power possibilities available other than forced induction (turbo / supercharger)? It seems like the RENESIS won't really benefit much if at all from typical bolt-ons like intake, exhaust, etc. because of what I've read and what has been mentioned about the RENESIS already being pretty well tweaked in stock form.

I personally would like to get a little more out of the RX-8 if possible while keeping it naturally aspirated and avoiding any internal work. Any thoughts on this?

Lensman

Another Renesis?! (Should fit in the boot/trunk.)

Sputnik

The muffler from the factory may be a little restrictive for noise emissions reasons. You might be able to open that up with a different/lighter muffler. But that requires some investigation and testing. Just slapping on any bling-bling coffee can won't magically give you anything.

---jps

babylou

The exhaust manifold looks to be a simple log. I bet this is the bottle neck in the breathing system. Other than that? Dunno.

tribal azn2

saving weight can act like increasing hp.

u can get lighter rims/ tires

lighter exhuast

lighter battery

alex

What brand of batteries are lighter? Just wondering what's out there other than the Sear's brand stuff.

--alex

neit_jnf

what about repogramming the ecu to activate the secondary and tertiary ports at lower rpms?? Some similar to what is done on vtec cars...

wakeech

won't do much other than hurt the volumetric efficiency of the engine (unless Mazda engineers are retarded and WANTED to bottle up torque in the low-mid rpm range), which will only hurt your torque down low... the lower velocity of the air coming through the port will reduce the induction system's effectiveness at filling the combustion chamber...
a possible reason some VTEC cars benefit from getting on cam earlier is that Honda has tuned the engines (like in a Civic, which i may remind you is an ECONOMY car, and not a SPORTS car like the RX-8) to be economical on fuel, and good on emissions, rather than going for 100% everywhere in the rpm spectrum.

but you have a good point neit_jnf, that the ECU might be able to be tweaked to kill ALL emissions and fuel economy for a few horsepower over stock, and when working with a better exhaust header (it'd be difficult to improve much on the intake system without serious coinage and significant low end trade-offs) and lighter/"less restrictive" muffler on the exhaust system might find it a few more.

really, without internal modification, the RENESIS is already pretty close to its potential in RX-8 tune...

wakeech

as far as Pb/acid batteries go, the "weaker" (lower voltage/ampherage) the battery you get, the less lead plates (and acid) is in the battery, which would obviously reduce the mass of the battery a lot...

if you're looking for those last 5lbs that will make your car just that much faster in a drag/touring/autocross race, then there are drycell (alkaline) battery, which negates the alternator, but they're probably (never looked into buying one) pretty expensive, but they're very small and very light.

DYT

I've used a tractor battery from auto zone for the past year in my car. No problem with cold startup granted the winter at Cali is pretty mild. Saved 15 lbs over stock, as a bonus the battery is cheaper too.

DTECH-RX

Thanks everyone, I just thought someone out there might know of some "rotary magic" that I might not be privy to were you can do some tweaks and adjustments to squeeze some more juice out of the RENESIS or any rotary by design, without messing with the internals themselves.

I actually don't have a problem with doing a supercharger at some point later on, especially if it is a Mazdaspeed kit (hint hint Mazda if you're reading ). I guess I'll have to take a look at the exhaust setup once I get it home and see what the possibilities are. I'm not in a rush to add things to mine, but it's nice to know there are some possibilities. If any of you are like me, which from previous interactions some of you are, I sometimes can't just leave well enough alone. :D

Boozehound

I would guess that a less restrictive intake would work pretty well. I'm sure that mazda worked at quieting down the intake, and you could get something by yanking the silencer / intake tubing (this is all a guess, I didn't look really closely) and add something better.

As for the less restrictive header, there's probably a drawback to putting something free flowing on there - cat life. The header is designed to have enough restriction to retain and conduct enough heat to the first cat, so that they come "online" quicker. By slowing that process down, you obviously blow more emissons out the exhaust, but I'd guess that eventually you might slowly foul the catylist somewhere down the road. As for those of us who don't live in Cali, or just don't care, its probably no biggie. Or better yet, do what I did with my 83, yank the cat and put on a straight pipe.

Other good mods I can think of are: increased diameter / decreased weight sway bars, removing sound insulation, true cold air box, low mass flywheel (fun fun fun), low mass rolling stock, bigger binders and eventually someone's bound to give it a sniff of the funny gas.

I dont see why most of the renesis mods would be substantially different than the tricks that people like Racing Beat have been using on NA rotarys for 20 years. Sure it's a different engine, and there'll be things you have to do differently, but this isn't the space shuttle or a F1 car - this is a mass produced PASSENGER CAR , and there's going to be tons of crap to do to it without cracking open the engine or adding forced induction.

Just wait for SEMA next year.

Cihuuy

if reputable rotary tuners are interested in the rx8, they will definitely have some aftermarket product available a couple of months after the release of the rx8! opening up the intake such as K/N filters and enlarging the exhaust side will definitely increase Hp. But not so much to make you say WoW... we have to wait untill those big tuners do R&D on this car...

HKS and other Japanesse tuners will want to benefit to get as much market as they can but will it be available in the U.S.?? MazdaSpeed is the only tunner that i know of that already have these basic performance upgrades.

wakeech

jeez... i think there needs to be a thread to dispel some of these very common performance misconceptions which are popularized by the stupid "aftermarket industry"...

actually, there is an optimal diameter, which i'm sure Mazda has already designed into the RX-8... without some serious modification to the entire system (did i already say this in this thread?), there WILL NOT be significant gains in this engine without major major tradeoffs (like fuel consumption, torque, comfort... important stuff) to gain almost nothing.

Boozehound

So we should all just keep our cars stock?

rotarynews.com

Again, it boils down to "Comprmise." Mazda has to make them in order to pass emmissions, stay quiet, etc... at the price of performance.

Going on the rotary community's 15-17 years of N/A 6-port FC tuning, an open exhaust will make a difference. But it will also increase noise, and possibly hurt emmissions. But, it will still be cleaner than any previous rotary. It is possible to have a 'quieter' exhaust on a FC, with the expense of a few horses, but to go fast, the exhaust will more than likely be louder.

For me, the RX-8 is way too quiet, and an exhaust will be one of the first mods I do. I love the sound of a less restrictive rotary. For others wanting a quiet car, it is unrealistic to expect more horsepower without tradeoffs from the stock form.

rotarynews.com

US FD owners have been going with Hawker Genesis 680 Motorcycle batteries.

N-Tech offers the kit, to allow for a larger intercooler to be placed up front without relocating the battery to the bins behind the driver (or passenger)



I've had this kit on my FD for 4 years, replacing the battery once. (Vegas heat destroys batteries, "normal batteries" last about 4-5years.)

The weight savings is almost 20 lbs.

wakeech

yeah, okay, that big-*** dual tip muffler might hold back 1 or 2 hp, and sure weighs a lot more than a smaller single-outlet one.
but i'm telling you: having a 3.5" exhaust pipe is not going to magically make more horsepower, there is an optimum diameter, and it doesn't make sense for Mazda to choke this car down at all (unlike a Civic, where this "increasing the diameter of the exhaust = power" myth comes from).

question about the battery: what kind of cold ampherage does that thing have?? i mean, if in the distant future i aquire an FD to fix-up and tune, would i be able to use that battery north of 60??

babylou

You want lightweight batteries. Look here: http://www.westcobattery.com/ and here http://www.performancedistributors.com/batteries.htm

Most factory car batteries are about 35 lbs. A Miata battery from Westco is 24 lbs and surely has enough juice to turn over the tiny Renesis during the winter. There are several 15 lb batteries but life will be less. Finally, since these batteries have less reserve they are not good for weekend only cars unless attached to a trickle charger. Also, they must be charged very slowly or they overheat.

Basically, if your car is a daily driver the light battery mod is great thing. One might end up using one extra battery over the life of the car ($100) but will reduce weight 10-20 lbs. $10-$20 cost per pound saved is about as cheap as it gets. It also seems that the RX-8 battery is near the nose and up high so there will be significant reductions in Cg and yaw moment of inertia.

wakeech

ah, spiffy links. many thanks.

Boozehound

So why does increased backpressure on the Renesis maximize hp? In full out race form, wouldn't it be much better to hack the exhaust off right after the header? Or should renesis powered race cars have restrictive cats and mufflers? If you're not concerned about ANYTHING but power, then why would you want restriction?

zoom44

you could strap a jato on the roof:D

babylou

Update:

I searched around and discovered that the Millenia and 626 use 24F batteries. Likely so does the RX-8. A 24F lead acid battery has the follwing specs:

Weight:............38-43 lbs.
Power:.............450 cca (min)
Reserve............90 min @ 25 A

An Odyssey 680 Absorbed Glass Mat (AGM, like a Miata battery) has 680 cca and very good cold weather capability. However, the reserve capacity is only like 15 min @ 25 A. The cool thing is 15.3 lbs weight for a savings of 22.7 - 27.7 lbs.

wakeech

heh, okay. fun fun... i'll see if i can get this done before i gotta go coach YMCA

the deal is that backpressure from the turbulence along the sides of the exhaust piping is neligible until you get really really really high speeds (like +220feet/second), and it's not even a problem until extremely high speeds (like +260ft/s) which means that oversizing the exhaust piping isn't doing what you're thinking it does.

as you know, a volume per amout-time (the volume of exhaust coming out of the car) devided by the cross-sectional area it's going through (pi*r^2, where r is 1/2 of the exhaust piping diameter) equals a length per time, which is the speed the exhaust is travelling.

say the engine is at 7000 rpm at full throttle, ignoring volumetric efficincy, that'd be 7000per min*1308cc/60 s per min= 152 L/s. assuming the exhaust diameter is 2.5" (63.5mm, which is a guess 'cause i don't know the real diameter), that's an area of 3167mm^2 (or 31.67cm^2, right? yeah).

(152716cc/s) / (31.67cm^2) = 4822cm/s = 48 m/s = 158 ft/s

that's no where even close to a high enough velocity to worry about the losses along the sides of the piping (which, with a smaller diameter means that there is less actual piping for the gases to rub against).

in any case, backpressure is bad. modern catalytic converters might add up to a whole 1.5psi of pressure drop, even at full throttle nearing redline. the muffler is where you'll get the most backpressure, but the coffee-can isn't always the best solution for that either.

over-sizing exhaust piping is stupid for a few reasons, one being that it's heavier, two being that with more conductive surface area along the length of the exhaust there is also more heat being conducted out of the exhaust before it leaves the tail pipe which is also bad, three being that the velocity of the gasses is reduced which is bad because the static pressure of a gas drops with higher velocity, meaning that there will be a lower pressure difference across the exhaust pipe and the charge coming out of the engine... as you can tell i've run out of time. sorry. there are more reasons, i'll bbl.

more questions, ask, bbl to answer.

wakeech

btw, what the hell are you talking about??