Starfox07

Wouldn't the computer only receive resistance inputs from the sensors for, for instance, the wheel speed. Couldn't you theoretically ground it in such a way that the proper resistance is met whatever the condition? Or do new ECU's not work the same way.

BlackWorksInc

Theortically it is possible to just to replace the sensors with a resistor that would provide a false positive to the PCM. Though, in all honesty you could just as easily set-up the RX8 axles for the FB as well.

The RX8 Subframe has mounting point within the FB's Frame and is a plausible bolt in with minor modification. The problem is measuring where the Subframe needs to be exactly and reinforcing the frame if it needs it, which it probably will in other areas.

It is also possible to use the rear subframe to place the IRS in place of the rear axle as the mounting points also are within the Fb's frame, though doing such a thing is a lot more work than the front subframe due to the construction and purpose of the rear end.

Though you should be able to just fit the spindles in the rear with the RX8 hubs and rotors, which should have the speed sensors in them already onto the existing rear axle.


Another problem that will probably come up is speed, because the PCM calculates evehicle speed differently than our cable powered speedos and the vehicle speed can also be part of other subroutines in the PCM.


Its a bit of work and depending how much of the RX8 and its components you want to transfer over; it can be even more difficult.

Just my two cents...

purple82

I would suspect that the ECU is looking for a tach signal as opposed to a constant resistance. This would be the way it can calculate speed.

purple82

I really don't know what the ECU is looking for, but if it's comparing transmission speed and road speed to try to sense slipping, you'd also need to make sure you have the same overall tire diameter on the 1st gen as the Rx-8 uses.

I don't know about the front subframe from the rx8, but there was a member on this board that did a thread on fitting the rear suspension of a Miata to his 1st gen. It's not a minor effort by any stretch as the entire rear floorplan had to be removed and redesigned for the suspension arms to clear and for the shock mounting locations to be correct. I'd imagine the effort for an RX8 rear end would be similar.

Mark S

iTrader: (1)

The HKS V-Pro can handle the Renesis... Much cheaper than Motec. I believe you need to by their engine harness, though...

Starfox07

T2 swap is looking more appealing.

I'm still gonna keep looking into the Renesis swap, I KNOW it has been done before. How hard can it be?

djessence

Seen top gear? That seems to be their catch phrase. and usually its quite difficult lol

purple82

I think the reason this isn't done much is because the cost isn't worth the benefit to most people. Like I said above, there isn't much power difference between the S5 street port and a stock renesis (if at all), but it's soo much easier to drop in the S5 engine that the renesis doesn't make much sense. If your power goals were the stock renesis, you don't even need to go with a turbo engine.

purple82

That sounds interesting, but here's the drawback that I see:

"Programming is done via the HKS Power Writer software; which only Certified HKS Pro Dealers have access to"

It sounds like you can't do any of your own tuning, meaning they better have it right and it's going to cost you $$$ in labor for tuning or buying their map, which may not be tuned correctly for your specific set-up. I have no experience with the HKS system, but I can tell you from working with my car, the tuning is never quite finished.

Whizbang

yea i had the back asswards, but the point still remains, not a direct bolt together deal.

Starfox07

From the HKS site.

I just wonder if they have the RX8. I imagine disabling some sensor inputs would be much easier on that computer over the factory unit. Still...$1300 for an ECU is awfully steep.

Found this, apparently a guy put a Renesis into his plane, which would obviously necessitate a different ECU. Although I do see that he is using individual throttle bodies instead of the factory manifold, which you can easily do for a plane...not so easily for a car.

http://www.rotaryaviation.com/renesis_engine.htm

He is using the EM2, but I'm not totally sure what that is. Anybody know?

EDIT: A little more digging
http://sdsefi.com/prices.html

Looks like they have a unit specifically for the Mazda rotary, and its cheaper than HKS's, although it doesn't say whether or not its compatible with the renesis. I didn't see a throttle by wire facility on any of the listed ECU's

purple82

$1300 is dirt cheap for an ECU that controls everything that thing does.

Mark S

iTrader: (1)

You have to buy the harness too, I believe... ~$400 or so.

Also, I'm not so sure about the Street Port S5 making the same power levels as a Renesis swap. The power levels mentioned above on the SP S5 imo are only made with a very open exhaust system. Renesis makes slightly more power than an open exhaust Street Port while choked with modern emissions equipment. A Renesis is more comparable to a mild Bridge than a Street Port with an open exhaust.

And then, unlike a street or bridge, a Renesis would get pretty darn good milage in an FB, especially if you were to use one of the FC, NA transmissions with the .697 5th ratio. I worked out the gear ratios one time for my SE, and the combination -SE rear, -SE wheels and FC NA trans would yeild a much higher ratio than 6th gear in an -8. Add to that, the FB is like 700 pounds lighter, you tune the motor via your standalone to take advantage of not having all the emissions stuff, or tune for an open exhaust and it should do much better than the 22mpg highway the -8 makes.

I don't think you'd really need a TII trans for a Renesis FB swap, the FB is so much lighter than an FC or an 8, and you're only talking 160 lbft of torque... S5 TIIs were like 200 torque and 500 more pounds stock, yes? Unless you really plan on giving it to the car, I think the FC na trans should be fine. And if you swap tailshafts, it's a bolt in on an FB.

And if you can maintain the function of the Renesis intake, the torque would be plenty for an FB, even with the tall 5 th gear. And, you have the potential for an emissions legal swap --even in CA, as long as you could adapt the stock ECU.

I'm working on another engine swap right now (BPT GTR motor and trans into my 323 GTX) but if I ever finish that, (which seems doubtful at times) the Renesis into my FB would definitely be high on the priority list... Be a hell of an all around car...

Mark S

iTrader: (1)

EM2 does not have provisions for the oiling system or the intake, I believe. You'd need to premix and run a custom intake to take advantage. Also, planes spend most of their time in a very narrow rpm band. The difference between takeoff power and cruise power on a Cessna 172 is ~ 300rpm. Tracy Crooks Renesis setup is optimized for that narrow useful band. Not very good for a street car.

Starfox07

Yeah I noted that in my post, although not as in depth. Part of me wants do this swap purely because its uncharted territory, but then part of me realizes that I'm an architecture major and finding time to work on a project like this in the next 6 years will be very difficult. I think for the moment, I'm going to stick with my little 13b re-egi for a while, as it still runs great with 105k on the clock. It does feel a bit sluggish past 5500 or so, so I'm going to seafoam it when I get the clutch back in, to see if it helps the top end, which I'm willing to bet it does. After that I think it will be full exhaust and maybe an MSD setup, tokiko's, ss brake lines, hawk pads, RB swaybars, and just enjoy it like that. Hell I might skip the Renesis all together and wait until i can afford the 26B-PP + 300 shot fogger, hewland sequential, and full widebody with 315+ rear tires I've been dreaming about. Be kind of cool to put down over 1000whp with a 2.6 liter and no boost. Race gas most likely. [/dreaming]

purple82

My SP is limited to just a little opening of the exhaust ports. I have all my mods listed in the dyno thread, here's the plot (red line):

http://www.nopistons.com/forums/uplo...1083865442.jpg

Here are a couple more with different intakes

http://www.nopistons.com/forums/Stoc...-5-t65787.html

http://www.nopistons.com/forums/Na-S...no-t54928.html

http://phishcave.com/upl/eJAOcR9wBt.jpg

Now comparing that to other dyno runs isn't 100% accurate, but it's probably close enough for our conversation. Here are a couple of dyno sheets from stock RX-8s.

http://www.dragtimes.com/2004-Mazda-...aphs-8792.html

http://www.myrotarycar.com/portal/fo...7_rx8tx800.gif

They are not that different. I'm not saying that there isn't more power in the Renesis to be tapped, but with conservative stock tuning, there's not much difference with a tuned and ported peripheral exhaust.

Starfox07

The Renesis would still probably have better drivability and longevity though, which are two key things I'm looking for. Plus 9500rpm is really cool.

purple82

We'll have to see more high mileage Rx-8s before we know about longevity. The S4 and S5 are very stout motors in NA form. The Rx-8 has a lot to live up to there and they didn't start off too well.

As far as driveability, with the right tuning, you'll never know a street port isn't stock. The torque curve is what you should be looking at to tell you how every day driveable and engine is. How broad is the curve and where does it peak. Notice how my toque peak is 1000+ RPM sooner than the Rx-8s!

BigBoss

No dude, please, DON'T!

Mark S

iTrader: (1)

Please don't what?

Starfox07

Hmm I was thinking the Renesis would put down a little more than that. Was that a 6 port or a 4 port in those dynos?

purple82

There are 2 jumps in the curves, so I assume that means they're 3 different runners, which I believe translates to 6 port engines.

Starfox07

But thats nearly 30% drivetrain loss...that can't be right, even if it was awd.

EDIT: They all seem to be about the same though, I guess they are just over-rated factory. Kind of disappointing, considering I can make that power with MY 13b with some work.

Mark S

iTrader: (1)

The new SAE power rating requirements pretty much negate any chance of underrating from the factory...

j9fd3s

iTrader: (3)

i looked at the rx8 swap vs 12A PP

when i really started, the PP setup was cheaper, although a couple years ago finding the expensive stuff (rx8 intake manifolds are in the $3000range new) used wasnt really possible, now its different.

power and redline are similar, PP makes a little more at the fly and revs a little higher, but the rx8 engine will smog no problem, and well its stock!

they both have challenges to implement

1. rx8 ecu is networked, if you look at the JDM FB with the rx8 engine, you'll see they used the rx8 gauges and climate control and stuff, not to be cool, but because its in the loop with the pcm. the best option is either standalone, or a pcm thats reprogammed not to look for that stuff.

2. the rx8 uses a turbo 2 clutch, but the best option is just to use the rx8 trans, its got nice gearing for a high hp rotary

3. mounting in the car; it'll take some custom mounts. not a huge deal

4. the FB rear end should be fine, you're increasing torque from the 130lbsft to 150lbsft...

i'm doing the PP, but its mostly due to costs. ($2000 vs $5000+)