Hey this past month I’ve bought my second rx7, and I love it. But I find it’s just somewhat lacking in the power department. I’ve been doing quite a lot of research on how to get my 1st gen rx7 up into the 200-300whp range. But I can’t make a decision on which path to go down.


Options are:

Turbo the 12a engine

Swap in a 13b and turbo that

Attempt to make the power with a NA 12a setup (bridge port? Maybe semi P?)

edit: 13b Renesis swap?

(both turbo routes will likely involve FD oil reg, extended ports, machining the engine to accept dowels, rx8 hardend stationary gears, and clearanced rotors. As well both would be running off a standalone aka EFI)

I know that if I want to go the turbo route that using a 13b would be a better choice mainly due to the availability of parts/better condition of parts Vs the 12a. Question is if I got a 6port FC engine can I use my 12a irons to make a 4 port 13b? And if I'm not mistaken this would allow me to still use stock 1st gen front engine mounts? (Which I know is bad, but I’m not sure how to convert to mid or rear engine mounts).


Going with a NA 12a setup will likely end up costing a fair bit less than going the turbo route. But would the NA 12a setup still be streetable, and still get “okay” gas mileage while not ringing it out from every stop light? My worry is daily driving a bridge ported 12a won’t be as street worthy of a setup as a turbo setup would be. But then again I have no experience with any rotary builds.


If you have a different method to achieve 200-300whp in my 1st gen rx7 that’s better than what I’ve mentioned above then please share with me!


I have lots of experience fabricating exhausts and such, wiring, tuning, etc. So cost of everything is just parts + my time (other than machine work to the engine).

 

If you are adamant on keeping it rotary then I would go s4/s5 13b with a mild port and turbo. But if I'm completely honest the cheapest and most reliable option is small block Chevy or Ford. Also remember that either option will also require some suspension/brake work, ask me how I know. Your goal is completely doable, it just depends on what you want. As far as 13b engine mounts go I believe you would need to source some gsl-se mounts and a front cover, I believe racing beat has a mount also.
​​​Also if your 12a makes good compression it could very well pay for most of the swap.
​​

 

I definitely would prefer to keep a rotary in it, I'm not a fan of V8s. However I can imagine how much fun a stock Chevy 350 would be in a FB. I believe you can put the tii turbo on a s4/s5 13b NA engine along with tii wiring harness and ecu and run it like that? I definitely could be wrong. I currently like the idea of a renesis swap, it would make my power goal of 200whp on a stock engine (stock reliability) while keeping it a rotary.

Edit: my 12a does make great compression

 

I totally get it, I myself have no plans to ever non rotary swap my 84, but I have worked on V8 first gens and they are pretty nice.

​​​​​​I believe there are internal engine differences between turbo and non turbo. Also a stock s4 turbo ii engine would not meet your power goal. A s5 is a bit closer.

Renesis swaps are becoming more common especially with so many out there, although Mazda did lie about the stock power level.

 

The 12A irons won't work with the FC engobe because of the placement of the water seals. You can use GSL-SE 84/85 13B housings and 12A irons though. Best bet is either got S4/55 turbo 4 port engine. Depending on what you want to spend, S4 4 port complete engine is probably cheapest, You'll still want to rebuild any used engine. If I did something like this, I'd get a brand new factory RE 13B engine and change out the front cover to GSL-SE front cover and oil pan.

The other option, like stated, and cheapest, would be to go LS. A mild engine can get you 300hp without a turbo.

 

I have an RX-7 that makes a bit over 200whp. Bridge ported 4 port 13B with a barely streetably quiet exhaust. It is built using the homologation paperwork for a Group A 12A to get the bridge port shapes and dimensions, and transferred the exhaust dimensions to GSL-SE rotor housings. Because it is injected and I have an FC front subframe I needed to use a GSL-SE intermediate housing too, which hurts power a little since you can't make the intake ports very large before you hit coolant.

A Turbo II's intake ports are larger than the physical castings of the 12A end housings I used. You literally could not make the 4 port runners as large as Turbo II without hitting coolant all the way around.

All that said, I broke a lot of rearends so I swapped in a 9", which also broke a lot, but not catastrophically. Transmission life is extremely short and stock transmissions do not like shifting at high RPM. This is fine on the street as the way to drive a bridge port on the street is to shift at 2000-2500 to keep the engine loaded and out of the stutters.

I never drive it anymore. I have a stock '81 that makes stock power. It doesn't break, and is much more pleasant to live with.
In aiddition, I figure the 13B makes about 270 at the crank. I have a Volvo that makes about 300-340 at the crank depending on who you ask. It is quiet and comfortable and handles better than either RX-7

 

Other thoughts.

I never dynoed it, but by injector duty cycles I made the same power with a street ported 6 port engine. End housings were opened up into one large port (except for the port window) and the dead areas filled with epoxy.

The difference is that the bridge port did not have a torque "curve", it had a torque "flat". I set the tune to flood the engine with fuel over 9k so that it would not overrev when I would hit a slick spot or the transmission broke or something.



The 6 port did not have a torque peak I could find, it started low and just kept ascending all the way up to Dragonball Z on the tach. This is not a good thing for the competition I do, it means you are always in the wrong gear, and so without a 9000rpm capable CVT to put in the car, I rebuilt the bridge port and put it back in.

One advantage of the street port is that you could leave it in gear on the street. I wore out my left knee from constantly shifting the bridge in and out of gear because you cannot cruise a bridge port, it has to be under load. I can only drive manual transmission turbo Subarus with my right foot on the clutch because FHI can't figure out clutch ratios
​​​​​​

 

People ask me this pretty regularly, then start asking about piecing parts together over time and what tends to happen is they come back to me with a few boxes of parts that cost them 10k (somewhat hyperbolic), of which I can usually use about 1/3 to 1/2 and they'll still need to pay me to build an engine.

The most cost effective - and probably the easiest to drive - is going to just be a stock 13BT with a 1st gen front cover swapped on + all of the oldschool mods for ~250 horsepower with a very nice torque curve to boot. The problem is that people start getting feature creep during the front cover swap and it turns into the whole 'expensive box of parts' situation again. Stock engine, stock turbo (with a ported wastegate), some injectors, 3" exhaust (depending on some things) and an ECU. Set boost at 10 PSI and have a happy long lasting engine.

 

and anyone thinking a nice v8 swap done right is quick and cheap is cray cray

 

....and the last time I saw a Turbo II engine for sale, it was about $7000 shipped.

Ouch.

 

2,200 just posted. the keg at least

https://www.rx7club.com/market/1163136

 

That's an FD engine, not a Turbo II.

Plus the whole point of buying a complete engine is that you get the water pump housing, manifolds, injectors, fuel rails, turbo, and all of the other little parts that can be amazingly hard to find that will nickel and dime you do death.

 

where did the numbers come from? what are your goals?

honestly, unless you're planning to build a real brute of a car, i'd say you can build something affordable (relatively) and it will still be pretty fun, with less than 300 hp. a nice, simple 13B (streetported original recipe or a nice Renesis) will get you gobs of reliable (term used a little bit looser with the Renesis ) fun.

preach!!!
i'm over the barrel as we speak. i'm in the precarious position of having to look for water pump housings, intakes, oil pans, etc. and i wish they were just nickels and dimes.

 

A tuned FB with a weber carb, exhaust, and some shorter gears in the rear end is a ton of fun and not too pricey. Some of my fondest memories are from a stripped out 85 with a stock motor and all the bolt-ons. Wouldn't hit your target power, but all the parts can be re-sold easily if its not enough.

Beyond ~200whp, I'd be looking for a turbo engine. Much costlier, but a 300whp first gen is pretty damn wicked.

Really comes down to what you want to spend. 5k could build you a decent N/A toy, and you could probably get a turbo FB done for 10k if you are super thrifty and do all the fab work yourself. Realistically though, turbo is gonna cost ya some $$$.

I've done a number of swaps over the years, and while my 13B-REW is super fast; I often miss the character of my old 13B w/ 48IDA and 4.88 gears.

Unless its a race car, I wouldn't get too hung up on HP #s.

Alex

 

Sure, but the value add of those engines you're seeing are the ancillaries, turbocharger, manifolding, etc. It's just what it costs to build most cars these days - LS' and other cheap engines will catch up in price at some point as well.

 

I'll chime in here too. My street ported GSL/SE race engine dyno'd at 204HP at 7900 with 144 Ft lbs or torque starting at 6500. While it makes useful power (180HP) at 6500) I would not consider this engine to be very tractable. In other words not a street engine. I should add that this engine has a 51mm IDA that works more like a light switch.

Regarding transmissions, I could not make a stock transmission live behind this engine. Some can, just not me. On the street it might not be an issue but at some point this kind of power can turn a stock 3rd gear into gravel.

I would agree with the idea that a low PSI turbo setup makes the most sense.

 

If you want an LS, $2000 will get you an LS1 long block with no accessories. Even the fairly worthless LS4 (front wheel drive bellhousing pattern, 5.3l with DoD, goofy accessory drive, crankshaft shorter on both ends) is skyrocketing in price, what used to be $600 all day is now $1500. The newer stuff is $10k+.

Iron block Gen III/IV are not LSes and are boat anchors suitable for trucks, not 2200lb cars.

And none of them can accelerate. A 200whp rotary feels like a 400whp V8 as far as acceleration is concerned. V8s can pull like oxen but they can't run like rabbits.

 

OK? I'm not sure if you're following what I'm saying; I didn't suggest using an LS, or even that one cannot get one cheap. What I'm saying is that 5k for my original suggestion of getting a stock 13BT is not really much money in the grand scheme of things and that people that rail against that idea using things like cheap V8s as examples are failing to look at the big picture of supply VS demand and how it affects prices. For example 13BT imports used to be 1.2k all day long but supply has dried up - this WILL happen with LS' at some point - certainly not now, and not for a lot longer than it took for rotaries to increase in value but it WILL happen.

Anywhosit, not trying to hijack any sort of thread so I'll stand by my original idea that the best value for the numbers and drivability you're asking about is going to be a stock 13BT for ~5k, injectors for ~600, a budget (not MSx) ECU for $750, coils/fuel pump/other bits for another 1k and wiring + some exhaust bits. Call it 7.5k if you do all the work yourself.

 

Figure I might chime in here as well.

My 12A turbo car was probably making in the mid 200s for HP and eventually I'd like to shoot for over 300, but it'll need a better transmission and rear end before that happens. Like was said up above, some folks can keep the transmissions alive up to around 300HP, others cannot. Depends on the driver and how you treat it.

Engine-wise you'll have a much better time working with a 13B. Parts are more available, the later ones were designed with fuel injection in mind, and you'll have a far easier time finding intake and exhaust manifolds. The intake is one of my biggest issues with running a boosted 12A on fuel injection. There just aren't that many great options out there for it. I resorted to 3D printing an adapter from a standard throttle body to the carby intake, and while it does work, I'd really like to do away with it.

That said, 200-300HP is plenty attainable regardless of whether you turbo a 12A or 13B. Anything NA in those sorts of numbers will be a handful on the street however.

My two cents anyhow.


Edit: Forgot to mention that's it's not cheap any way you slice it. I had most of my engine parts and spent around 3k getting it ready. Another 4-5k for engine management related bits and bobs, 3k for the turbo setup, more for the fuel system, etc. You can certainly do it cheaper (and also much more expensive), but it's not an inexpensive endeavor no matter what route you choose. You have to keep in mind that these cars were carbureted and made barely 100HP; bringing them into the modern era takes some work.

 

I have a project that has ... escalated.

One odd bit of advice. Overbuild. If you think you are going to have 300hp, have a fuel system that supports beyond that. funny thing is each improvement or added insurance nudges performance up to where I'm chasing weak points. There is a chance I might break 400whp. At least the math works out. anyway, I'm focusing on the rear axle now. Its a GSLSE axle. The 4.076 ring and pinion is destroyed. This axle was in my kids SE, it blew out on him so I traded him to get him roadworthy. My turbo FB did not damage the gear set. Currently, I run out of gear quite quickly. At least when I had the 4.076 gears in it. The likely choice is the 3.63 gears from the MX5. Then there is rather or not to upgrade the LSD. Then off to focus on the next spot.

The purpose here is you don't just swap. its an organic process of planning, re planning . waiting. lots of waiting. At this point, in 2023, I'm not sure if strictly rotary is an economic choice. GM has a LS based v6 that hits 300hp or so. and that's just one cheap junkyard example. Im pro rotary, but it does require more fiscal commitment than in the past.

 

That LS (well, LT) based V6 is running $7k for a dropout, last I checked. Crazy.

The V6 swap to go to seems to be the 3.6l GM engine. They are plentiful, fairly reliable, make oodles of everywhere power, and unlike the Honda J-series V6 they seem to accelerate pretty well. The Hondas make power but they make truck power, they don't accelerate very well for whatever reason. Maybe because they have fixed cam timing (engine is essentially unchanged since the mid 90s) while the GM engine has variable timing on all four cams?

Technically the J-series is an easier swap because there are adaptors and such for swapping into Miatas, and if you use a Miata 5 speed trans with the RX-7 tailhousing, that eliminates a whole lot of grief because you have a bolt in trans and driveshaft situation.

Relevant to thread, the trans in my '81 that has maybe 2000 miles on new bearings is now screaming in 2nd and 3rd gear. I don't know how much power the car makes but it runs 16.8 at 82mph. So perhaps any commentary I have regarding drivetrain reliability should be taken with a grain of salt

 

I went the REW route.. $3500 for motor trans (6yrs ago) which was sold as a fresh build.. it popped at 8psi whiles logging with a known build/tuner.. pulled motor - drove it 28hr round trip to drop it off - spent $2K on rebuild with porting on useable used parts other than important parts like seals and some bearings.. did the 28hr round trip again.. taken the last 4yrs of random issues, frying ecu, updating cheap parts etc to be almost done... pushing well over 450 hp at the wheels and drives like a honda civic around town... be ready to spend $8-10k to do a swap right with porting etc.. can you do it a lot cheaper... sure... depends how much you can do yourself or how much to have a shop or reputable help help

 

As someone who has built one of the few RUNNING Renesis swap cars on here, and possibly the only carbureted Renesis car that runs (I know of one other in New Zealand, not sure if it still exists):
If you go this route, prepare for some serious pain. I think it was worth it, for me, but my situation was unique. I was able to get a freshly rebuilt street port Renesis for “friend prices,”due to a unique work situation i was in at the time.
A couple people have made this setup work with the stock ECU, one of which is on this forum (can’t remember his name, the car is cool though). If you are comfortable with wiring and modern PCMs, I cannot recommend this route more highly. You get your 200(ish)whp with a street ported Renesis. You get all the joys of modern amenities (a car that starts in the cold without having to perform a blood sacrifice, etc.) The only downside to this method is that you’ll have to fabricate new engine mounts, because the Renesis is a rear mounted engine, unlike the front mounted 12A. You cannot simply swap on a 12A front cover onto a Renesis and maintain the factory PCM, for a variety of reasons.

If you are a masochist like me, you can go the carb route. This requires an eclectic collection of parts that might be very difficult to acquire depending on your location, availability, phase of the moon and so on. If you do manage to get this collection of parts together, you will then spend the next two months trying to piece everything together with absolutely NO information on how to do so. Once you figure all that out, you’ll have an engine that makes less power than it would’ve with fuel injection, and you’ll likely have spent more money than you would’ve just keeping the factory PCM, or buying an aftermarket ECU. I have many reasons I chose to go this route, most of which are not logic based. I just *like* carbureted engines. There’s no good reason for it, but it’s what I like.

PM me if you have questions, and if you decide to go carby, please PLEASE PM me so that i can save you from wasting money and time on things that won’t work. I had to try a lot of different things to get my car to be a good daily driving vehicle. I’m not an expert, but i can tell you a whole lot about what NOT to do.


P.S. This is my favorite part about this engine setup.