Let me lay out the situation for you first. Someone in my area is about to do a V8 swap into an RX-8. (I don't get why, but whatever :P) As a result, he is essentially looking to sell/part out the whole powertrain.

The engine is in great shape apparently. Only has roughly 30k on it. I was wondering if there is anything on it that would be worth grabbing to use since I am in the middle of a rebuild. I found all kinds of debate on using the Renesis rotors and such, but not much on the external components of the engine such as fuel injectors, alternator, etc. Is there any real benefit to using these things off of the Renesis, or is it more trouble than its worth?

My build focuses on reliability, life of the engine, and livability on a daily basis. It's an '88 GXL (N/A).

Any constructive input is appreciated.

Thanks!

 

I should also mention that I'm not opposed to power gains. Any free power would be great! But nothing that will significantly effect the reliability or anything.

 

Yeah. Buy it off of him, then re-sell it and find a good 13BT.

Get to work son!

 

You can use the eshaft and stat gears/bearings which are all slight upgrades to the FC stuff and are direct swaps.

The rotors can be used if you mill the grooves deeper for rx7 apex seals. However you are then required to use the (crappy) keystone side seals that the rx8s require. The rx8 rotors are 10:1 CR and about 0.25lb lighter than S5 rotors. TO do this you'd need to custom balance the stock FC counterweights/flywheel.

The main benefit of using the rx8 rotors would be that the side seal position would allow you to drastically change the port timing and shape of your engine to match an rx8...several degrees earlier opening and a few degrees later closing. So you could pick up significant power that way...that is part of how the rx8s make their high rpm power. But then you have to ask yourself, "will my factory intake and fuel injection keep up?". Then you have to look at electrical and fuel system mods.

By the time all is said and done, you could have a turbo II swap or something cooler.

 

No external parts from the renesis are remotely similar to those on an FC, except for the clutch which interchanges with turbo II clutches.

 

I have a 13b with the primary s ported to rx8 shape, an exact copy off an rx8 iron. using s5 rotating assm. i originally assumed the rx7 side seals would hit, and so i put 10 miles or so on the motor before i yanked it out and apart to inspect why it had such low compression, and the apex seals were chewed up. but the side seals had no issue, i also heard of someone using rx7 rotor in an renisis, with no mods milling or anything.... so i threw a new set in the motor today, gonna break it in, and see how she does, this is in my 6 speed vert.
shooting for 150rwtq then going semi pp.

my biggest concern is that with the early intake opening of the rx8, and the peri exhuast of the 13b there will be far to much overlap, the rx8s have so much sooner closing of the exhaust that there is 4 degrees of "dead zone" between e close and i opening... not that i'm tell you these things Kevin.

to the OP, you could use the engine as a whole. but it's not a bolt on swap, you'll need a throttle body of some sort, and ecu, you cant use the fc front cover, so you can't use the Fc CAS and use the Fc ecu, or that would cheapen the swap alot.

 

like RR said, only eshaft, front and rear stationary gear is direct swap. ask me how I know

other than that ... if u wanna do a "complete swap", it's not really worth the "swap" if u ask me, too much trouble for the little gain u gonna get

 

i think a Rx8 engine/trans in an FC would be huge fun, but would be even better to do Rx8 engine in 1st gen, its 700lbs lighter than an 8

 

already in the works.. using rx8 (front for sure) suspention as well.

 

How easy or difficult is it to swap the RX8 engine/trany into the FC - plus you would also need the stronger T2 differential/axles, correct?

 

Compared to other more common swaps such as the NA to turbo swap, I would say that a renesis swap ranks much higher on the scale. Not only is the hardware far from a bolt in, but if you intend to use factory fuel injection and controls then you'll have a lot of wiring and parts to transfer over there as well. Unlike a T2 swap NOTHING will plug and play and you will have to identify EVERY wire and plug and what voltage/signals it needs to see in order to keep the rx8 PCM semi-happy.

To be honest I would say that such a swap done right is beyond the capability of the average FC owner. You also introduce yourself to all the common issues with rx8s. The ignition coils are garbage and need to be replaced every 2-3 years at $250/set unless you spend 500 bucks on an LS coil conversion. The PCM is not easily modified or tuned without a $700 cobb accessport. The engine is not easily modified and does not take well to boost. The rotor housing chrome layer is much thinner than previous rotaries and as a consequence engines with over 80-100k have housings that produce low compression and will not be reusable in a rebuild like we are used to doing on rx7s. Honestly for what they are, they get terrible gas mileage...worse than a properly running FC or FD (although some of this is no doubt due to the higher curb weight of the rx8; it's hard to say how much this may improve with the engine in a lighter weight chassis or with longer gearing).

Even though rx8s make more peak power than previous non turbo rotary engines, below 7000rpm they drive virtually the same and make similar power levels. So really you would only notice large gains between 7 and 9k rpm. In my mind all the effort would not be worth the expense and time.

 

RX7 rotors won't work in a renesis, not sure where you heard that.

in all honesty the PP exhaust port engines are more reliable and can be modified to make the same power as a renesis with less of the headaches associated with it and the higher than average failure rates.

i've built hybrid renesis engines with early parts to more replicate an early engine without the need to swap the engine and the problems that presents. the fabrication work involved isn't really worth it unless you have a reason for doing so, such as a turbo renesis.

if you want a chuckle, on the RX8 forum there is a "300whp club", most never make it into this club and even more of them drop out quickly due to engine failures. keep in mind this is 10 years into the RX8's life, and they are still only at that point.

 

Thanks for the input. You and RR said the eshaft and stationary gears would be the only direct swap. Im guessing that because of this similarity in the parts, there would be no real benefit to switching those out?

 

And I guess while we're on this topic of swaps, how much would you guys recommend that I take the plunge and go for the turbo swap? I always hear people talking about it, but my main goal for this build right now is to get a fun and different car that I can daily as reliably as a rotary will allow. Is there much/any difference in the reliability of the N/A vs the T2?

 

the turbo engines add in a whole nother avenue for engine failures, aka apex seal blowouts. losing an apex seal in an n/a engine is a much less common problem than in the turbo engines.

the difference is the requirement of maintenance to the car, a turbo car will be less forgiving if everything isn't ideal.

problem with swaps is they are usually not done properly, and with that comes reliability issues. as i often say, if you want a turbo car it's best to buy one that was always a turbo car.

 

I see your point. I'm not huge on the idea of having a turbo car. At least not right now anyway. So if it opens up a whole new can of worms, then i'll probably just keep on with the N/A rebuild.

Personally I kind of like the idea of an N/A build also because you just dont hear about them as much it seems like. Lately it seems what everyone wants is a turbo, and my original motivation for buying this car was that I wanted something different than everyone else.

 

every customer i have had who got the bug for power gains always eventually switches to a turbo.

one customer didn't even last 3 weeks from rebuilding his n/a to wanting me to make his 6 port high compression block to a turbo hybrid. now i just get complaints about how long it's taking, which isn't my fault since every week it is adding something new.

 

I would definitely buy it and swap it into my NC miata, since it just bolts in, but like most rx7 owners, I'm poor.

 

wat

 

Quit spending money on useless commas then.

 

Thanks RR & RE - great feed back. Like most FC n/a owners, additional low or mid range torque would always be welcome. S/c would make more sense than a turbo for additional power lower in the RPM range but I am just not sure I want to go the boosted route due to the reduced reliability of the apex seals. Short of adding more rotors (ie 20B or 26B) low to mid range torque is not a 13B strong point simply due to the design limitations of the engine. If you are looking for that, then I guess you really have to go another route.

 

but to gain more power on an n/a you have to sacrifice even more low end/midrange power. the whole powerband is shifted up, which also reduces the reliability of even the n/a engine.

the old saying "you gotta pay to play" is always the sacrifice you make for more power.

 

All the commas!

 

on the rx8 forum, i believe the guys name was roto8. so you have you put rx7 rotors in a renesis and it didn't work?

 

exact reason why RE FC/FD = 20b NA

remove the turbines, increase the displacement and engine power/response all at once.
no turbine(s) required

required : large budget.