When discussing potential paths forward to
building a streetable track car in the 200-250hp range a tech at a professional rotary shop suggested putting a renesis motor in would be more cost friendly vs rebuilding and bridgeporting the S4 13b.

I did some searching and most discussion i found on this was at least 5 years old. Is this a swap people are still doing? Pros? Cons?

 

i'm not sure anyone has done it yet!

on paper its a great idea, its going to be about the same power as a bridge, but you can put a muffler on it, and if you used a cat it would even pass smog.

its like having an Rx8, and taking ~400-500lbs off of it. huge potential for a really fun car.

downside is that you'd need to make mounts, and an exhaust, and radiator hoses. you'd also want to use the Rx8 oil cooler setup, at least.

 

It would be a lot of work, but with a fresh Renesis, you could make a great car out of it. The Renesis has a fair amount of power and would move an FC nicely.

 

It would be a great combo and I thought about it for a while. I got stuck on the ECU part. Since the Renesis runs on a CANBUS system, you would need to replicate all the signal inputs in order to run the stock ecu. Lots of work to get that working.
If you went with an aftermarket ecu, it loses the factory developed refinement and have to do lots of dyno and road tuning. Neither of those options seemed worth it to me.

Soon afterward, I went to a dyno day and put down a dozen more horsepower than a stock RX8 with a very mild S4 turbo. Have not thought about it since.

 

I'm sure you could run a standalone and bypass all of that and squeeze a little more than 200whp out of it

 

Don't know of anyone dropping an RX8 motor into an S4, but it's been done on an FB. See this link to RCC for more info: http://*************.com/rotary_foru...ad.php?t=18993

If this forum doesn't allow links to other forums, just surf over to RCC and use the search term "FrankenB" to find the above thread.

 

It is very very hard to make 200rwhp out of the 13B-MSP. Much easier with the older 13Bs NA.

13B-MSP swap makes sense if you are happy with max 180rwhp and you need a swap that will meet emissions/ be CA B.A.R.ed.

My auto 4 port RX-8 put down 108rwhp and if I try hard I can get 19mpg.

 

a stock S4 puts down 116rwhp... so apples to apples the Rx8 motor makes way more power and stays legal in CA....

if you want more power, turbo swap with some CARB legal HKS/GReddy stuff is the way to go

 

^^
Yup.

In Texas though, OP can easily surpasss 200rwhp with an old 4 port 13B, some bridge or semi p-ports and a holley style intake manifold to suit and injector style 4 barrel TB/ECU.

If you dont do a high rev build aimed at 300rwhp you could get it done relatively cheaply too (no engine balancing or machining). I would like someone to come up with dyno proven turnkey budget rotary options (engine, accessories, manifolds, ecu) for the non emissions builds (old chassis or other states).

 

I have heard multiple reliability concerns from the renesis, but none first-hand aside from seeing an RX-8 smoking on an AX run. Is anyone familiar with the lifespan and durability of the 13B-MSP? Is it possible to do a 3mm apex conversion?

 

Cannot do 3mm conversion. Putting in taller old 2mm seals is iffy, taller and wider 3mm would put you in the "oil jacket" for sure.

Cannot put older rotors onto 13B-MSP side plates as side seals will fall into ports from what I unserstand.

 

i have three friend who bought Rx8's new, and between the three of them, they have had to replace 2 coils and a thermostat in ~90k miles

i have had three Rx8's myself, and even though i looked to buy broken ones, i have had to replace coils, a cat, a radiator and a clutch. in fact going out on a limb, the biggest wear part seems to be the floor mats (one is always missing?).

so far have not had to touch an engine, although one of the cars i bought had had three, and somehow Mazda can rebuild these with all new parts and still get half of them to fail, so there is a foot note to the perfect reliability part.

 

I bought a 60,000 mile "blown up" (wouldnt start) automatic RX-8 (dealership did the Mazda cleaning and compression test and pronounced it dead.)

Got it blowing perfect smoke rings and eventially running good enough to spit the Carbon out with starting fluid and a 200amp jumpstarter.

Raced it 4 years at autox/kart track and now daily driving. Had to replace a coil. Had to put water in the battery since the 18x11 wheels and 295 wide race tires from my FD sloshed half the acid out and the car develiped low voltage/hot restart issue.

It now has over 100,000 miles, so internet wisdom says it will blow up soon. I dont know, fellow racer has 230,000 miles on his original engine 2004 RX-8.

My opinion is if you want the 13B-MSP engine, get it and get the best chassis Mazda has made for the rotary engine to date as a bonus by buying an RX-8.

If you want 200-250rwhp you wont get it with the 13B-MSP, they make 180rhwp.

Road to 300rwhp is pretty well documented with the old 13B.

 

the Rx8 is actually a pretty good car, the Chassis is magic. it feels like a 1st gen Rx7, but everything is better, stereo is better, ride is better, handling is better, its faster, quieter, easier to work on (its built like a lego, everything comes apart without breaking, and you can clean/grease it and it works), etc etc.

the Rx8 has 3 fundamental flaws,
1. the steeply raked window means the dash is a huge piece of black plastic, and it acts like a heat sink. the HVAC system basically spends 90% of its effort cooling/heating the dash, and that leaves about 10% for you
2. gas mileage sucks. i averaged 19, and best tank was 23? the 1979 Rx7 did better...
3. the back seat can fit full size people, which is very nice, but the back windows do not roll down, so if they need to 'toss some cookies' the rotor shaped hole in the front seat is where it goes...
4. bonus flaw! a base model Rx8 is 2950lbs, with 232hp, and the Rx-01 was 220hp and 2400lbs, you would have to think that removing 550lbs (thank Ford for this), would have changed the car from so/so to life changing... Rx8 does share the chassis with the NC miata, so the Rx8 drivetrain basically bolts in, and you could come close

 

The RX-8 is no longer available new; so we don't call those flaws, we call them CHARACTER.

 

You almost make me want one. That and driving my wife's Mazda 3 sometimes makes me want something newer.

There's the deal breaker. I can average 20mpg in the summer( difference in fuel blends I think) in my '89. If I got something else to drive instead of it, it needs to get better mpg not worse.

 

yeah somehow 20mpg in an 89 Rx7 is fine, but 20mph in the Rx8 isn't...

 

Yeah, I know it sounds odd but my truck gets 15mpg and the Rx7 18 to 20mpg. I wouldn't care to have something else to daily and antique tag the 7 but it needs to get better mileage like at least 25mpg min and be somewhat sporty. If it gets worse than the 7 there's no point I could just drive the truck. I guess what I really need is something along the lines of an Acura RSX or last Gen. Celica GTS to drive to work.