'84 RX-7 half bridge 13b swap

I've already made some headway on this project but maybe making a build thread will help me push through the long list of small tasks that need to be sorted out before the new motor can go in the car. I've had this FB since 2006, it's my first car and the 12a has been running strong and without issue the duration of my ownership; a couple of years ago it made 102 whp on the dyno with a weber downdraft and a nice exhaust system. It currently has about 160k mi and I had no real intentions of ever swapping or building it.

However, a few years back a guy on marketplace was getting rid of a heap of 1st gen RX-7 stuff, including two mostly complete 12a engines, a pair of doors and fenders, and some other odds and ends. I bought everything for a song and proceeded to disassemble the motors to see how they looked. One was great, and the other had bad housings but good irons, so I took the good engine parts to my friend Logan at Defined Autoworks and told him to put together a fun bridgeport 12a for me at his leisure. Logan is a one man operation and at the time he was inundated with rebuild jobs, mostly RX-8s but a lot of RX-7s of every generation as well. I told him I wasn't in a hurry as my original 12a was still running happily, and I just thought it would be fun to have a rowdy sounding bridged 12a that made 160hp or so whenever he got around to it.

As time went on, a couple of customers came to Logan with FB RX-7s in need of partial restorations, including two that needed complete engine rebuilds with quality 12a parts, as theirs were unsalvageable. My irons and housings were already at Logan's shop, and I still had a good set of irons at home, so it was at this point that Logan asked me whether I'd be willing to barter some of my 12a stuff, and in exchange he'd build my engine with my 4 port 12a irons, but with 13b housings (probably from an RX-4) so that my good 12a housings could be used on the customer's restoration project, thereby saving them considerable money vs trying to find new old stock. 

If you're still reading this, that brings us mostly up to date, as last fall I brought home this lovely half bridge 13b. It has oem apex seals, an RX-8 oil pump, and a rotating assembly balanced within a gram (mostly because Logan bought a balancer and wanted to test it out). Since then, I've gently pulled the 12a from its home of 39 years (I'll clean it up thoroughly and set it on the shelf till I need it again), cleaned the engine bay (several times) and started fitting the new engine with accessories.

Some photos of the engine assembly:

RX-7 sans 12a:

The trusty 12a that's been putting up with me for 17 years now:

Weber 48 ida after extensive cleaning with my homemade soda blaster, still not perfect:

Recent state of the project, though since then I've installed the aluminum flywheel and new clutch to the 13b:

So the remaining tasks before the engine can go in include:

Install a pipe to hook up my heater core lines to the new motor.

Cut the leading header primary and extend it to fit the 13b which is 10mm longer.

I cleaned up a lot of the unused wiring on the harness, but I'd like to clean the existing wires and re-wrap in a new loom material which I got from Summit.

Install water pump housing, distributor and eccentric shaft pulley, and time them correctly.

Side quests that aren't completely necessary but that I'd like to do while the engine bay is open:

Clean up my electric fan wiring which is messy and probably a little shoddy.

Replace my fuel pressure regulator and gauge and actually mount everything safe and solid.

Order a 13b/FC starter, the 12a starter is fine but the 13b starter makes a cool sound, and let's face it half the appeal of rotaries is making cool noises.

Nice car! Excited to watch this unfold.

Does the 12A starter make a different sound? I've noticed the 13B does make a kind of unique "yin yin yin" noise when cranking, but I figured that was a rotary engine thing and not the starter itself.

Following for rotary goodness...

RX8 oil pump?

In reply to WondrousBread :

I'm told the 12a starter has a reduction gear, it doesn't sound nearly as cool as the 13b starter.

In reply to infernosg :

I didn't ask for the RX8 pump but Logan threw it in there to achieve higher oil pressure, I think he told me to expect 80-90psi. 

Also my rough estimate as to what kind of power this engine will make is probably anywhere between 180-200 at the wheels, depending on how everything is tuned. I would have been very pleased with 160 so the car should really be a riot. I'm still sticking with narrow tires so that traction is the weakest link in the driveline and so the car still has the classic 1st gen feel. 

In reply to dannyp84 :

I didn't think you could swap pumps from between FC and earlier, FD and RX8. Maybe he meant the pressure regulator. I think the S1 RX8 bypasses around 80 psi so perhaps that's what he used.

I would think a half bridged ported 13B would be over 200 hp to wheels. The 48 IDA may be a little small if my experience with similarly-sized throttle bodies is any indication. Although the exhaust (Racing Beat?) may be a bigger restriction. Regardless, I'm curious where this one will land.

In reply to infernosg :

You're probably right about the regulator. When I picked up the motor I was overwhelmed with how nice it looked and probably wasn't listening carefully. The header is a racing beat, everything behind it was originally built by Logan but I've had to replace the mid pipe section due to running it to low to the ground and smashing the first muffler. It seems like the correct intake and exhaust makes all the difference in peak power, but I'd be willing to give up some peak power for responsiveness, which is why I'm ok with the 48 ida for now, though I'm increasing the choke and main/air jet sizes.

dannyp84 said:

In reply to WondrousBread :

I'm told the 12a starter has a reduction gear, it doesn't sound nearly as cool as the 13b starter.

If you say so 

The FC starter is nice because it spins the engine up faster, but my rotary life started with an '80 and that is the sound I am nostalgic for.

It is the FC starter that has a reduction gear, which allows the motor to spin the engine up faster for the same current.  Pre FC starters are straight drive.

Now I want to dig up an old 12A topmount, just to know what it sounds like...

Was the top mount an SA thing, or pre RX-7 12a? We're getting deep in the weeds of rotary nerd stuff with starter noise comparisons, but obviously I support it. I love the look and feel of the SA/Series 1 1st gens, from the bumpers and shift knob to the dash layout and materials. At one time I had considered trying to retrofit SA bumpers to the FB, but for now I'd be satisfied just making my front bumper fit correctly - unless a 935 style bumper comes up on yahoo auctions for reasonable money. 

Top mounts were some time in RX-3-land.  My '73 twin dizzy had a bottom mount, which I was not expecting as the 10As had top mounts, as did RX-2s.  I'd like to say that very early single dizzy cars had top mounts because Mazda engineered the new bellhousing pattern for the single dizzy engines to TAKE a top mount, and a top mount from one of those years will bolt on to any RX-7 that has that opening, and work with the nonturbo flywheel.  I know Series 4 had the pocket, I know FDs eliminated it, I assume Series 5 still have the pocket because without it there is no way to get to the torque converter nuts on automatic cars.

There are TWO different 1st gen starters, I have forgotten the year split, but there are two different tooth counts on the starter.  What bakes my noodle is the starter is in the same location from 1974 to 1991 (nonturbo manual, anyway) and the starter housings are all the same but the different tooth counts mesh just fine.

I have an FC starter in my '84 because it needs to crank fast enough to start with a nearly dead battery.  I have the original starter in my early build '81 because of course I do.  It even has the '80 style steering gear, not the later one.

So, call me late to the rotary party, but it just clicked with me why you need the bridge in the bridgeport. Love it.

Specifically, this image. 

I have a fresh top mount starter in a box if we need a recording, lol.

Love this restoration.  We need more detail shots of the RX7.  Is it as clean as it looks in the pics?  How's the interior?  A buddy has a nasty big single 13B swapped FB that is an absolute animal on the Autox/Road Course.  

This thing looks great and looking forward to following along. 

I didn't realize the NA Doritos could put out that kind of power.
As a Mazda fan, I know some day I'll need a rotary car. This is definitely good inspiration. 
 

In reply to Cooper_Tired :

IIRC the drag racers are getting 450hp on methanol from a two rotor, as of about a decade ago, although those are a lot peakier than a 250-300hp (170-220whp) "torque flat" engine.

170-180whp feels about perfect as far as what the chassis and drivetrain will tolerate, it's a great target!

In reply to 84FSP :

When I got the car in 2006 it was very clean aside from the "pockets" at the bottom rear of the quarter panels. I've also had to replace the metal in the rear wheel wells as they tend to rust from the inside out, you wouldn't notice it unless you pulled the carpet and interior panels. My interior isn't too bad, I used to have T3 aluminum door panels but they were buzzy and uncomfortable so I put the stock panels back on last year, they're a little weather-beaten. I'll see if I can find some recent photos.

Cooper, I think information about NA rotaries falls by the wayside because so many people see videos of turbo 3 rotors making insane power, but I've always preferred NA. And Pete is probably right, I'm hoping that just under 200 hp is still mild enough that the rest of the driveline handles the power without issue.

I also wrote up a little appreciation post about the car on my blog: darkforestautohouse.com if you want to know a little more of its history.

I'm trying to reach a happy middle ground with the interior where the car stays simple and lightweight while not being completely void of creature comforts, for many years I ran without carpet and that was kind of miserable. The car currently weighs 2170 lbs with a little less than 1/2 a tank of fuel. It really needs some fabrication work in the rear to keep running this low and still have proper suspension travel, which probably means a tri link with mounts inside the car  and links that go through the floor. Or maybe I'll grow up a little bit and set it back to a more normal ride height ..

I also think it would be cool to fit the earlier series 3 dashboard if I ever came across one, they were available in black and look a bit more simple 70s sports car imo, but the '84 dash certainly isn't bad. It's a great car though, I've driven it the entirety of the Blue Ridge Parkway, as well as countless weekends where I drove it to and from a drift event and ran it hard on track all day without issue. The key is to upgrade to an FC oil cooler and respect the redline. 

If you're on instagram, there's a fair number of photos of the car on my friend's photography page: https://www.instagram.com/p/B4Ubf2WHg0o/?igshid=YmMyMTA2M2Y=

For the longest time the narrative was "you can't make more than 200 whp" N/A without crazy porting and you end up with an undriveable engine that makes peak power at 10,000 RPM and has no torque below 5000 RPM. I think a lot of this was perpetuated by the FC IT cars that were limited to the 6 port engines with stock port and intake/exhaust manifolds. People jumped straight to bridge ports without fully understanding how porting affects engine operation. Chasing maximum power without looking at anything else. Most people also run off-the-shelf exhausts from Racing Beat. These are great for a bolt-on street setup but they're not optimized for performance. IMO, it was only about 10 years or so ago that it caught on that N/As can make upwards of 250 hp to the wheels with a fat torque curve with smart porting, intake and exhaust design. Of course this knowledge was already out there in the racing community. Few people with street cars want to commit $5k+ into a custom N/A setup when that same money could be dumped into a turbo setup and make much more power.

In reply to infernosg :

Years ago when Logan was experimenting with exhaust runner length on his test mule car, he discovered some huge gains to be had when he found the sweet spot in exhaust tuning. I don't think he builds custom headers anymore, but someday I wouldn't mind replacing the RB header I have with something more optimally tuned. You've tried a couple of different designs haven't you?

Love this project sir!  I was unaware that you could make such good power with them.

In reply to dannyp84 :

Yeah, I'm on revision 2. The first was actually made by Logan but honestly I was a bit disappointed with the design and appearance. It looked nothing like the examples he shared online about 10 years ago. I assume you're referring to his FB with the 13B-RE? That's what helped me realize usable N/A power was a possibility and inspired my build. My current exhaust manifold wasn't made by Logan but it's inspired by his designs. Equal length primaries, gradual bends and a proper collector and expansion. I honestly don't know if Revision 2 affected overall power and torque because shortly thereafter I changed intake setups, which had a much more significant impact. I'm sure it could be further optimized but I'm pretty happy with the power the car makes right now.

Small update, I've been kind of stalling on this project because my water pump housing certainly didn't look clean enough to go on the new engine, and my at home cleaning methods weren't getting me far, so I took the housing and my eccentric pulley to a local sandblasting shop and after about 10 min the housing went from this:

to this:

I'll have to rinse everything off and flush out the insides once I remove the thermostat, but I'm pleased with the results. There is one small opening on the inside of the housing that I assume is for the emissions systems temp sensor which I no longer use, but I'll try and make sure it's clear of debris as well:

After that, a little bit of paint and I'll be ready to install it on the 13b. Also this week I continued cleaning up some wiring and put some new loom wrap on the remaining wiring, right now I have all the connections still used plugged into the 12a so I don't forget where everything goes.

I should try and get the plugs a little cleaner to match how nice the loom material looks. I'm still not sure where this plug down near the oil pan goes, but I'm assuming it was for the level sensor in the pan itself which had a broken wire, though I never got a low oil light on the dash.

Also on the topic of wiring, I'm wondering if I can delete this relay completely if I don't use air conditioning, from what we've found online it was used for the a/c system:

It's amazing how much a project can creep if you get really deep into the weeds of cleaning up unnecessary wiring or just flat out cleaning in general. Luckily, I've never been extremely meticulous about things being perfect, I normally just want something done safely and reliably so I can get back to driving, which is a far more preferable usage of my time than wrenching. With that said, I'd still like to redo some things a little bit better/cleaner this time around compared to when I was younger, less experienced, and far less patient.

Hopefully I'll have some far more exciting updates to come after this part, it's always the little things that become time sinks on a project. 

That little hole is an air bleed port so the pump area won't get airlock.  Any air in it can get to the thermostat side and up and out.

In reply to Pete. (l33t FS) :

Huh I never would've guessed, definitely want to make sure it's clear then.