bigbcraig

TL;DR: I'm thinking about swapping to a 13B-MSP (Renesis) in my 1985 GSL-SE.

Hello all, I recently bought a 1985 GSL-SE. It's my second car, and will be used for a play car / autocross car. I'm in Iowa where there are no emissions laws at all.

I'm looking into different options for engines right now. I want to stay with a naturally aspirated, NA, 2 rotor. This isn't super negotiable, especially NA.

I'd like to have 200whp. 250 would be sweet but I wouldn't spend much money or effort to get more than that.

As above, I don't need to make emissions. I won't have power steering and don't need AC. Sound is not a huge issue, but it'd be nice to keep it below 100dB inside / nearby outside WOT. Fuel economy is not an issue - anything about 10 mpg or more driving down the highway would be OK.

BUT I do not want to sacrifice smooothness / drivability / tractability. As I've searched and looked around, this seems to be a very hard goal to achieve.

My car currently has a 13B with the stock RE-EGI intake, ignition, and fuel systems. It has racing beat headers full catless exhaust. It feels pretty good right now, pulls hard as high as I've revved it (up to 7600 or so by accident), makes good oil pressure and runs cool. Hot starts are not very good, it'll crank and run for a few secs at <500rpm then sputter out if I don't pedal it a lot. But I've always been able to get it running. I've read this indicates apex seals are getting worn. I have no idea how many miles are on the engine or what's inside it, and haven't run a compression test because I'd rather fix some other things (steering specifically) before I convince myself I need a new engine now.

The biggest problem I have with the car autocrossing is gearing - second gear @ 7000rpm is about 45mph. Last weekend my fastest run was done with the buzzer on half the time or more; shifting to 3rd didn't work very well. I was really inbetween gears. So, short-term I can put a longer rear axle ratio in it, but that feels very wrong.

I would love to have an engine with a wider powerband to be more flexible with gears; and I think the right way to do that in an NA rotary is to have an engine I'm comfortable with revving to the moon (say, 9k). Without changing gearing 9000rpm would put me at 60mph, much closer to where I want to be at the top of 2nd in an autocross car. (Of course I am also investigating different transmissions and rearends)

Now I've looked into sterrtporting, bridgeporting, and going PP and a lot of them read like they have lots of drivability problems (part-throttle bucking especially) that I do not at all want. I know good tuning with EFI can help a lot; but still isn't perfect. As far as I've seen the best way to make a PP work well is to do something like Peejay's old PP where the manifold and ports are relatively small and keep power at high revs down a lot.

From what I've read, the MSP is a big pain to swap in because it mounts differently, and the computer is very finnicky (the whole chassis CANbus runs through it). But, even in stock form, it has as much torque, revs, and power as most built NA motors (there are exceptions, yes...) and has better tractability and drivability than the stock motor.

So, if I'm willing to spend months planning/figuring out wiring and working with a standalone computer to basically run a stock, but bare renesis (standalone ECU and no accessories but alternator), is there something I'm missing on why I shouldn't do this? I feel like it would've been done more than once or twice if I wasn't missing something

diabolical1

iTrader: (3)

to be honest, I find nothing wrong with your thinking. the MSP is quite a viable option for building a HOT Gen I. I firmly believe that it may very well become THE option at some point.

I think the SE engine is probably my least favorite of the 13Bs, but that doesn't mean that I don't like it. I think it's simply the ancestor to some great engines that followed so now we the luxury of comparing it to it's progeny. it's still a good engine though and a few well-placed upgrades could produce a pretty hot setup, too. I just want to make sure you realize that that option still exists.

personally, I think you should consider the "built" S5 option though, since it's a little more straightforward than the MSP, but the MSP is definitely a great idea.


I have come to find that it is probably more common that you think. there are quite a few Youtube videos of them. however, my commentary on why it's probably not even MORE common is the fact that, as you said, the CAN-BUS (****) system runs quite a few things that contribute to HOW the MSP makes power in the Rx-8 and it is difficult to transfer that stuff to another chassis, and simply running the engine with a stand-alone will likely compromise some of that powerband.

samjaza78

The answer's pretty straight simple- dig up the cost of a full renesis swap. Then dig up the cost of a T2 swap. Then dig up the cost of comparable modifications for both engines.

diabolical1

iTrader: (3)

here's a couple of related links:

https://www.rx7club.com/1st-generati...ement-1040264/

https://www.rx7club.com/2nd-generati...ne-fc-1025482/

RotaryEvolution

iTrader: (30)

the renesis will actually bite back as hard and possibly harder if not setup properly than an earlier turbo engine will.

honestly i wouldn't expect a renesis to be a strictly track friendly engine. they'll show you how femenine they can be if everything isn't absolutely perfect.

hell, they don't even seem to handle the issues of starting and running on a daily basis very well...

bigbcraig

- I respect that the TII is a very good platform for my needs, but I really want to stick to NA for now.

-RotaryEvolution, can you elaborate? Other than flooding (which all rotaries seem prone to do), I wasn't aware of anythinglike that.
I know that Motec controllers are capable of actuating the valves in the intake manifold... and would be expecting to use the stock intake and then a simple exhaust - a la Star Mazda

RotaryEvolution

iTrader: (30)

apex seal chatter, even though they lightened the seals as much as possible i have seen renesis housings chatter and chew through chrome as badly as the old 3mm heavy seal 12A engines did.

add in that if you run a renesis lean for a moderate amount of time it will grenade, it leaves me not a proponent of suggesting using one as a strictly high performance engine option. you could run the early 6 port engines lean without doing much harm besides possibly melting your bumper. so if you say lost fuel at the top of the rev range, one engine will just sputter to a stop, the other has a high chance of spitting the seals all around the engine destroying literally everything.

even 60k mile renesis engines looked like 100k+ mile older 13Bs in the sense of internal wear. racing an engine just wears components faster to the point of failure, so you will be rebuilding the engine more often. the renesis is also more difficult to make all the peripherals work on, similar to installing an aftermarket EMS onto an FD and making the twins function sequentially, the 13B-MSP renesis intake system is about equally as complex, perhaps moreso with the stepper driven 5/6th port actuators.

bigbcraig

Well that's something g I hadn't read about the apex seals. This is in relatively normal operation (not a damaged engine)?
I knew they were more susceptible to damage in the case of an apex seal failure as the pieces don't exit the side exhaust ports as well as older peripheral exhausts.

I had also seen that everyone liked to tune them somewhat rich, but hat didn't strike me as too odd as I've spent a lot of time in the Subaru world. I guess the increased sensitivity to lean conditions is just a combo of light rotor / light seal / high comp. I hadn't thought about that but it makes sense.

I guess I'll start looking into modernizing a 13B to run full electronic control (spark and fuel).