TrueBlueGTO

Forgive my ignorance of the RX-x Rotary engines and their unique issues. However, I am intrigued to know why the new RX8 Renesis 13B doesn't seem to be receptive to boosted performance as the RX7 Twin Turbos. Those vehicles seem to have developed into brutal sleepers.

Is it a matter of tuning? Is it the redesigned ports and plumbing? Why does every other conventional internal combustion engine have several forced induction options, yet Greddy is "barely" the only one with with a kit for the RX8? Is a twin turbo kit that difficult to develop for the RX8?

Can someone shed a technical and accurate light on these questions?

J3

SomeGuy_sg

First of all the new Renesis engine is not 100% the same as the old 13B . The Renesis has different ehaust ports and different apex seal design just to name a few . Also the compression for the Renesis engine is now 10:1 , lack of space in the engine bay too . All these things contribute to the Renesis disapproval for boost .

Charles R. Hill

iTrader: (7)

The single biggest limiting factor in upgrading the power output of the Renesis is not mechanical in nature. The problem is dealing with the factory PCM and the fact that the PCM does not accomodate certain mods. On the other hand, there are other mods that the RX-8 is very receptive to, such as flywheels, swaybars, and such. Right now it seems that we are limited 50-60 h.p. boosts, whether turbo or nitrous, while using the factory PCM. Once we get the PCM to cooperate with piggybacks the horizon will widen considerably.

CRH

TrueBlueGTO

Is the Mazda PCM unique or a Ford EEC variant? Does it allow reflashes?

Based on your info, I'm assuming that basically the problem is no one out there has taken the dedicated effort to try and hack the Mazda system like they have with BMW, Benz or GM?

J3

therm8

Some are trying, but they've not been successful yet. The biggest problem is the sheer complexity of the car's maps and its abillity to learn and adapt. You have seperate maps depending on what gear you're in, and whether you're accelerating or decellerating or idling for that matter. And these are really just base maps. Add a piggy back that changes fuel mapping and timing, and the ecu eventually learns from the multitude of inputs that the car's not running like it wants it too, so it modifies its maps to counteract the piggy back and return to an overall stock tune. Maps seem to change based on IAT's, coolant temp, egt, cat temp and so on, which all ecu's do to some extent. But I've never seen one do it like the 8's. It's pretty amazing. There is now passthru equipment available, and you can download the factory tunes, so it's only a matter of time before someone breaks the encryption and makes it possible to write/edit maps directly to the ecu.

zoom44

racing beat can write maps to the pcm, so can that one race team in europe

Nemesis8

iTrader: (3)

Mainly due to the high compression and the PCM. Japanese tuner RE Amemiya is going to experiemnt with placing lower compression 13B-REW rotors in their 8, and then turbocharge it with a modified and upgraded Greddy turbo with higher boost - we shall see one day. Remember that RX7.COM told us:

"We have all heard the magic disappearing horsepower numbers from the marketing sources. The question we’d like to pose isn’t “where did the horsepower disappear to”? Rather, we’d like to ask, how much more power does the Renesis make compared to its predecessor?

Keeping in mind that Mazda did not increase the displacement of the Renesis, and they managed the amazing engineering feat of reducing emissions at idle to 10% of what the 13B-REW (the Renesis’ immediate predecessor) produces at idle, and 15% of what the 13B-REW produces at cruising speeds and loads.

The argument can be made that the Renesis produces higher peak power because of its ability to rev much higher than the old 13B. So to be fair, let’s compare the two power plants at the point where the old 13B is producing it’s maximum hp. In this chart, that happens to be at 7000rpm. At this point, the old 13B is making 125hp while the Renesis is making 175hp. That is a 50hp difference which translates to 40% more power (40% of 125hp = 50hp). For the sake of full disclosure, the 2nd generation RX-7 tested here is a 1991 with a fresh motor (less than 1000 miles), and the RX-8 tested is a 2004 with about 800 miles.

While we realize that 12 years has elapsed since the previous generation normally aspirated 13B was last sold; that there has been at least that amount of research and development devoted to the Renesis, we should not lose sight that Mazda is the only company actively perfecting and producing the rotary engine."

Reprinted from RX7.COM

Charles R. Hill

iTrader: (7)

I don't tend to think that the compression ratio is much of an issue as there are other engines with 10:1 that are able to take boost well. The matter is housing pressure under ignition which is really a question of fuel quality. If we can point out high h.p. FD's why don't we have the same optimism for the Renesis, which seems to take more abuse than the FD? How about we raise the boost pressure on a dyno Renesis until auto-ignition occurs? Then we'll know, roughly, what the ultimate dynamic housing pressure is and we can tune down from that. If I had money to throw around I would start taking bets as to how much boost the Renny can handle reliably. If I remember correctly, I thought I had read the particular ignition curve the Renesis uses and remarked to myself that it almost mirrors the curve I used in my small block Chevy. That engine had all kinds of room for tuning even though it was a strong runner that I frequently revved to 8,000 rpm with 87-91 octane fuel, and that was back in '86. I am often surprised as to how much my prior experiences are being replayed with the RX-8. Without nitrous I almost have the RX running as quick as my Nova with both on street tires.

CRH

fullsmoke

Doesn't the compression problem have something to do with the Renesis being a 6 port engine? Being a devout Rx7 owner and fan, I know that turboing the N/A 13Bs were an issue because of the 5th and 6th ports. However, the 13Bs that are turboed are of a 4 port design. Because of this, the nature of the N/A 13Bs would not produce as much power output as the 4 port engines (everything else held constant).

Am I right or blowing smoke out my ***?

FS