I like the idea of a Renesis swap for Lucy. Better fuel economy and interesting possibilities for power.

Of course, the engine management is a complete nightmare. But I have an idea.

With the auxiliary ports and VDI, the engine makes around 225/240hp. A Stock S5 NA makes 160hp. Does anyone know what a RX-8 engine would dyno if the aux ports and VDI were inactive? I'm thinking that it might be close enough to be a satisfactory interim until one could afford the necessary EMS hardware to properly run the RX-8 mill.

The idea is to have a Renesis installed and running with as little cost as possible. Perhaps modify the FC harness and run the Renesis with an RTek-7 2.0 and a wideband?

Just some thought experimentation. I know many of you will be thinking 'why the heck?', but I'm strange like that. just wondering if my ideas are out of line.

 

Wat about splicing the rx8 harness to fit the fc????
Ecu and all

 

A long time ago, SCC's Dave Coleman wrote about what a royal PITA it was to dyno the RX-8. Apparently, not seeing the front wheel spinning made the RX-8 ECU send the engine into limp mode (Coleman surmised that the ECU thought there was no air flowing over the engine and would overheat, thus the limp mode.) Upon trying to jumper the rear wheel speed sensors to the fronts, he was met with similar results. That sounds like a whole lot of tomfoolery I want nothing to do with.

 

yeah, dont use the rx8 electronics.

 

But if the thing with the dyno is true the how would u burn the tires????
Aka just sit and roast

 

standalone

/thread

 

Megasquirt can run it. You might be able to get away with an S4 OMP and the MS outputs can easily switch on and off the intake actuator solenoids at whatever rpm you need. MS-II even supports the stock RX8 crank signal (36-2-2-2). My thoughts say it would be harder to mount the Renesis than it would be to control it. The electronics would be the least of my worries.

I'm curious on what to use for the throttlebody since the Renesis uses drive by wire though and if the rx7 transmissions have the same bell housing patterns.

 

all your questions might be answered in this thread.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/renesis-powered-fc-saying-hi-uk-884483/

 

Nice, thanks for the link.

edit: He used the rx8 transmission with a shortened driveshaft and made all of his own mounts. I still wonder if it can be done with an rx7 transmission, it would make the swap heaps easier.

 

there is probably a reason why he used the rx8 tranny.

 

Some googling seems to suggest that the Renesis has the same bellhousing. Maybe its not as hard of a swap as I thought it would be.

 

Was looking for that. Thanks!

I think I could do MS. Didn't realize that it could work the aux ports and VDI. They're electrically actuated right? As for the TB, I figured that I could find a similar diameter piece and refit it to work on the Renesis intake pipe. I wasn't wholly worried about engine/trans mounts as I just finished a welding class and think I could make functional (read: ugly) bits. SCC used bent sheetmetal and hockey pucks to stick a VQ into a 240SX(I can't do any worse). I've been wanting to depower Lucy's rack, this would be a good opportunity. I figure grab a long-keg with the AC compressor still attached and I'm good there (R134 conv). And about the fuel system, I thought I'd just run new lines about the engine to feed the injectors and retain the return-style circuit.

Another advantage of the Renesis is parts. Some initial looking yielded a 13B-MSP rebuild kit for $670. If the new RX-7 and the 16G/X/B/whatever sells strongly enough...

Disclaimer; this is a thought experiment.

 

THOUGHT: I'd recommend using the turbo's drivetrain as I don't think the n/a drivetrain would be too reliable in the long run with the extra power on it.
EDITED THOUGHT: You could also use something like This if you didn't want to make your own solution for the omp.

 

The Rx-8's electronic throttle is vastly superior to cable driven designs in almost every way but the aftermarket is still catching up and few easy/affordable solutions are available.

 

They do about 30-35 HP in the s5 so i'd guess about 50 HP in the RX-8. Doesn't seem worth it unless you go all the way.

 

sv51macross wrote in the op post:
Seeing as how Lucy's aux ports don't work right now, and the engine is a little tired, 180ish horsepower and anything better than 12 mpg sound really, really good. Thanks though, for answering my initial Q.

 

im not too familiar with the rx8 motor, but from what ive read its not the most reliable. but thats just what i read.

now for the ports why couldnt you run like s4 or s5 manifolds? or are they too different?

 

The Renesis reliability problems are mostly due to a bad OMP design on the series I engines. If you premix you'll be fine.

the intake system is one of the main things that give the Rx-8 such a wide power and torque curve:





Now, compare the volumetric efficiency of a 6 port Renesis (which has the 4 actuators shown above) with that of the s5 nonturbo engine (which are all 6 port):



pink line is the s5. you can see it's gasping for air after 7000rpm while the 6 port keeps continues getting more efficient.

 

You're missing two things here. First, there is a variable fresh air duct which changes the length of the intake pipe before the throttlebody. That's a minor improvement in efficiency there that you can't easily implement if you are swapping engines.

Now here's the big deal. On all the previous fuel injected rotaries (turbo 12A all the way up to '99 spec 13B-REW), the secondary ports are opened in the throttlebody by the throttle cable. There are 3 butterfly valves in all the fuel injected rotaries. There is one big butterfly valve for both primary ports, and one small butterfly valve for each secondary port (total of 3). The secondary butterflies are mechanically connected to the primary butterfly. It's pretty simple.

The Renesis has electronic control over all of the ports. There is one big throttle butterfly. The secondary ports are opened by a valve in the intake manifold, which uses a vacuum chamber and a solenoid. Then the aux ports are controlled by a motor and the VDI and variable fresh air duct are controlled by a vacuum solenoid. Without the proper electronic controls you will be running on 2 ports out of 6 ports.