blackenedwings

I have begun working on mods for my Rx8, including doing a lot of research on various forms of FI and reliability factors etc. I am incredibly happy with my Rx8's looks and handling but disappointed with the power. The car simply is not fast enough stock. One of the things I started doing was comparing modified Rx8s to other modified import "tuner" cars like Rx7s, STis, and Evos. Why is it exactly that modified Rx8s seem to top out in HP around the 350-400 range while there are so many 600-800 HP cars of other designs. The stock N/A Rx8 isn't that far behind a stock Evo or STi in HP discounting the turbos... with a turbo the 8 should be noticably quicker than a stock Evo or STi... why does it seem to stop there?

Are the mods simply cheaper for the more popular Evo, STi and RX-7? Given similar investment the only signifigant difference I can see is that Rx8s are not as popular so they don't get the same aftermarket support that the others get, and the Renesis has such high compression it makes really cranking the boost dangerous/impossible? I've seen a lot of high horsepower rotary cars built using the 13B motor from the RX-7, and of course the 20B. Is it the fault of the Renesis that signifigant horsepower upgrades are so difficult or impossible? What are any other major components of the Rx8 that make it difficult or more expensive to modify.

I'm just sort of typing out loud, because I love how my Rx8 looks and handles, but I don't want to start putting a lot of time and money investing in a car without seriously thinking about what is possible on the platform.

paulmasoner

iTrader: (1)

the Renesis is still "new territory" in the grand scheme of things.

tuning limitations were a big factor until the last year or so

compression ratio.

maxxdamigz

iTrader: (1)

Stock turbo cars are generally easier to get more hp out of because they were designed from the start with boost in mind. This makes the initial hurdles of getting significantly more power out of the car easier. A lot of stock turbo cars will gain more HP out of a simple down pipe change than an rx-8 or most well built NA cars will get out of pretty much every available add on.

On top of that, you have a higher compression which lowers the boost/heat/octane level at which you start to ping/detonate. It doesn't make it impossible - it just makes it a little harder. Also note that the number one selling point of the rx8 is either it's handling or looks. Horsepower junkies do not buy Rx8s in the same numbers as they do more muscular cars. Most Rx8 owners bought their cars knowing they would never put down 300 to the wheels and considering it still to be a good buy. The demand isn't going to be there. The dynamic is not quite the same as say a mustang crowd where if a generation of mustang wasn't capable of gaudy hp numbers it would be a failure.

Why is it so crucial for an NA car of the ilk of an Rx8, mx5, s2000 or other handling first car be capable of 400+ HP anyway?

paulmasoner

iTrader: (1)

but there are those that bought it knowing they would put 300 down

hehe

09Factor

One other reason that the Renny has to contend with, Air Flow out of the engine.
The exhaust ports can only flow so much. Since how the ports are cast in the irons, there isn't much room between them and the wather jacket for growth.

I know I can put more air in my motor than what it can expell.

Rotore_787

renesis (13b-msp) is just really the fuel economic version of the 13b. if you want to get over the 350-400hp range then swap a 13-re in it its basically the same platform just with turbo.

maxxdamigz

iTrader: (1)

Yeah - I did 300 whp already. We'll see where I get.

I've never heard of the Renesis flow capabilities being an issue. I've heard it basically out flows the REW top to bottom (hence why it can make as much hp as it does NA). Some reference the direction of the ports (side plates) and design (middle siamese port) as disruptive to turbo spooling and robbing of exhaust energy, but I don't think anyone has reached a power level where it is legitimately an issue.

All I've really seen is people start cranking up the boost and then screwing up a tune or overheating. If there were 10x as many people pushing over 300 whp (which is quite achievable now), you'd see a lot more progress at the higher power levels.

MazdaManiac

iTrader: (3)

Everyone that wants a 500 HP+, <3.0 liter car has never driven one on a daily basis.

tajabaho1

when we get ported side exhaust port kit we will own

Outkast187

Agreed, 500+HP on these small engines seems like a great idea if you have done it. Its no longer a car you want to drive anywhere, no roadtrips, etc. If you can hit 300hp, be happy.

MazdaManiac

iTrader: (3)

^^ I take it you mean if you haven't done it.

All the complainers and horsepower apologists need to do is take two drives - one in a twitchy, "500+ HP" RX-7 and another in a carefully tuned 300 HP RX-8 to get a perspective on what they are talking about.

Really, I'm just sick of people fixating on horsepower; it is complete crap and totally useless.

rotary.enthusiast

If you're not building a race car, anything over 350 HP in a 3000 lb. car is a bit silly anyway IMO. Hell, even in my slow-*** NA 8 I'm waiting on other traffic most of the time... granted every once in a while it would be nice to lay down a nice healthy patch of rubber, but you don't need any more than the 300-350 HP that many 8's are currently producing to do that.

I think the main reason for renesis engines not producing ridiculous HP numbers is that nobody cares enough to do it. If you really want to make 400-500HP, why try to figure out a new engine with new pitfalls and quirks when you can just do what's been done a million times before with a 13B-RE or something similar? Most people would rather stick with what they're familiar and comfortable with than try new things... when it comes to cars where things can get expensive and time consuming very quickly I can kind of understand that.

rotary.enthusiast

I know what you mean... way too many so called "car people" are fixated on peak horsepower, which is such a small part of the picture, especially if it's a street car

MazdaManiac

iTrader: (3)

Horsepower is a function of RPM. Most small motors making a lot of HP do it by more spin.
Torque curve area is the only thing that matters in a street car.

The only thing that matters.

Until your daily drive consists entirely of long, accelerated runs up to 200 MPH and no stops or slow-downs, you will never experience your car's horsepower potential.

MazdaManiac

iTrader: (3)

"Cares" is probably a bit loaded, but your point is correct.
No one that is serious about this car's potential as a lovable, livable, useable piece of hardware is willing to find that power at the expense of comfort and drivability.

rotary.enthusiast

Yup. I think many people use peak horsepower as a "quick measure" of their car's overall performance relative to other cars of the same model, and in that capacity it's alright... until you throw turbos into the mix where the area under the curve can change significantly depending on the setup. I think I'm going to get a massive turbo that doesn't spool up until 9000 RPM and see what kind of HP numbers I can get

blackenedwings

Thank you all for the responses, I really appreciate the legitimate responses and lack of flames. I do love my Rx8, I've just been a bit puzzled by the apparent lack of recognition by most car enthusiasts for what seems like such an amazing car. The torque and hp do seem low to me, but I come from the American muscle cars side of things. I've owned a Corvette and Z28 prior to my Rx8 so I'm used to a lot of low-end torque and high hp from a big v8. I've really come to appreciate handling, finese, and butter smooth acceleration from the rotary in my 8, but I still crave more torque/hp.

I love the sound and feel of the rotary engine, and I think I'm decided to stick with modding up my Rx8 and going against the grain.

tajabaho1

^ new sig added, from now on, if you ever say "you need hp, get my turbo kit" I will have you Jeff, I WILL HAVE YOU!!!

MUHAHAHAH

SlayerRX8

Sounds like you need an engine swap or a different car. Hopefully you have the money for the engine swap. I know I'd have a 20B or LS1 RX-8 if I had the money. I'm in college so I went with another car instead.

I love the "power doesn't matter" talk. Seems to me there are definitely people on this site who don't care about power and are truly enthusiasts of balanced cars. Kudos to you. But there are also plenty that come off like they are just saying it because they can't/don't have good power.

Rotore_787

power isn't really everything but some people enjoy taking their car to another level; not just seeking power but the pride to say yup thats my baby get where i'm coming from???

blackenedwings

Exactly Rotore, it's not just the raw power, its that I would really like to invest some time and money into my car and make it something special, but I see a lot of modded Rx8s that don't seem to get a lot of notice or attention in the tuner scene because they have low hp numbers. I mean, I don't give a rats *** what people think if I like it, but I do like torque/hp and was curious what was keeping 8s from showing higher numbers.

I would love to have a 20B swap because I think the 3 rotor engine is the best sounding engine I've ever heard... I mean, it sounds like it's trying to eat someone. *drool* That being said, I don't think that a 20B swap is doable for me atm just due to price of the swap. I would never go LSx with an Rx8 anyway, because I've had a Corvette and although it's a great engine it loses the characteristics of what an Rx8 is about to me.

Rotore_787

thank you

MazdaManiac

iTrader: (3)

No, I don't.
Saying you have "X" amount of power is meaningless. It isn't another level, its just nut-swinging.

If you have two cars - exactly the same in every way and both making 300 ft/lbs of torque - but one makes 500 HP and a torque curve shaped like "^" and the other makes 300 HP, but has a torque curve shaped like "¯", which is the faster car?

I will take a car with half the power but twice the area under the torque curve any day of the week in any form of racing - even bracket drag racing.

blackenedwings

That's true MazdaManiac (or do you prefer Jeff?), but I'm curious, isn't one of the issues with the rotary in general lack of torque? Even more than horsepower, I thought low-end torque in particular isn't one of the strengths of rotaries.

rotary.enthusiast

The renesis doesn't produce amazing torque at the crank, no, but it's torque curve is incredibly flat compared to most piston engines, and it revs higher as well. It's not quite the "electric motor" delivery Mazda makes it out to be, but it's damn good for an internal combustion engine. A 300 HP renesis (barring laggy turbo setups) will have more area under the torque curve than any other engine that produces a similar peak HP number. Then you just use proper gear ratios in your trans/diff to put the torque to the ground that you desire.

Peak HP is just a theoretical measure of the top speed of a given vehicle... it doesn't tell you how fast that car will get to that speed. It's pretty meaningless by itself... area under the torque curve (or HP curve if you prefer) is what matters.