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I am wondering if anyone knows if the 20b front iron accepts a 13brew front cover. I am aware I would likely have to modify the oil pan. I am ok with this. I need to use the front cover from the FD so I can use the CAS for my rx8. I know blasphemy! Get this guy out of here. Unfortunately not many people on the rx8 forums have completed a 20b swap. None with what my intentions are. I am wanting to use my stock rx8 ecm for all canbus activities and a microtech lt16c for fuel and ignition duties. This way I can keep my ancillaries functioning ie tach cluster, cruise control, electric power steering etc. To do this I need to utilize the rx8 crank angle sensor and the rx8 drive by wire tb. The throttle body is easy. The cas a little more difficult. I can adapt my rx8 sensor to work on the fd front cover, but the mechanical 20b cas is a no go for what i want to do. I have nothing against Haltech, I just don't want to mount the haltech screen in my dash. If anyone could help I would greatly appreciate it. I'm holding off on purchasing parts until I get this sorted. If I cant get a wrap on it the car is getting an rew. I just really dig the 20b sound. As Im inching closer to retirement this will likely be my last big car project. If I go 20b the swap will be based on the Promax kit out of Australia.If I go rew it will likely be cxracing minus the turbo and wastegate. Either engine will be bridgeported. The rew single turbo. The 20b na at first. Mostly due to funds as the 20b is significantly more expensive. After I have the 20b swap done ill start sourcing the turbo bits.
The picture below is just to show that I have done a crazy swap before and know what I'm getting into. My swap car is not my dd. I did that whole thing myself, even down to the tuning of a maxima v6 ecm via open source. In fact as far as I know I was the first person in the world to do the rb26 swap into a twin turbo 300zx. I did this about 20 years ago. I had an fd in college, but I was on an anti cell phone phase then and pics don't exist. It wasn't anything crazy just a small single turbo and a halfbridge, but I did the whole rats nest and converted to nonsequential first. I will say those hard breakable hoses and brittle solenoids was one of the more painstaking tasks I ever did. I do hate wiring, but at least this project won't require translation from a Japanese wiring schematic. Thanks to anyone for any advice on the subject I greatly appreciate it.
People used the pre-86 front covers all the time for the engine mounting and distributor, so it's at least going to be compatible that far.
You used to be able to get a setup that modified a distributor for 3-rotor use, in the days before aftermarket ignition setups could control coil on plug, let alone control rotary style leading/trailing. So swapping on an early or even an FC front cover so you could use a distributor was not uncommon.
One of my friends had a Z32 and an R32 at the same time, and I was fascinated by how they looked like the same car except for the Z32 being a bit more cramped underhood.
It's not a competiton but that's not too crazy, it's the same drive type and engine manufacturer. When the weather stops trying to kill me, I've got more work to do on the EJ20-engined R53 sitting in my garage.
I get its not a competition. I just posted it as I am sure there have been hundreds of posts with zero post count with hey I want to put a 20b in ma car. I just wanted to show that I am aware of what I am getting myself into. Thanks for the info on the timing cover. That was really my biggest headache. Well that and I wont be starting with a complete engine. I plan on going with the Billet Pro stuff as needed and using 13brew stuff to complete it. This leaves me a litte worried as I am sure I may hit some stumbling blocks along the way for certain parts.
I have a couple 20Bs, at least one un-assembled front iron and (I believe) all front cover options at the shop if you'd like photos of some sort of combination. Sweet RBs, currently dipping my toe into an RB25 build for a personal car - still in the research phase though.
13BREW cover works just fine, you will need to modify the oil pan, or run the discontinued Xcessive oil pan like I did, or I think JDL manufacturing makes a pan.
13BREW cover works just fine, you will need to modify the oil pan, or run the discontinued Xcessive oil pan like I did, or I think JDL manufacturing makes a pan.
how do you check timing with the FD/RX8 set-up. I've been tempted to swap over as well, but it seems timing marks vs actual engine position vary based on style/year/phase of the moon/how much coffee the engineer had that day...
I verified top dead center of rotor one and used the circumferences to confirm the pulley marks where correct. Then locked the timing to -5 deg. BTDC and checked the leading timing mark.
I checked because I built a S4 motor once out of parts from 2 separate engines, and mixed the hub and crank pulleys and the timing marks were off.
They machine the crank pulley and keyway in the hub as a set. This threw the timing marks off by over 60 degrees, as the keyway was in a different location on the two hubs.
I verified top dead center of rotor one and used the circumferences to confirm the pulley marks where correct. Then locked the timing to -5 deg. BTDC and checked the leading timing mark.
I checked because I built a S4 motor once out of parts from 2 separate engines, and mixed the hub and crank pulleys and the timing marks were off.
They machine the crank pulley and keyway in the hub as a set. This threw the timing marks off by over 60 degrees, as the keyway was in a different location on the two hubs.
yeah, thus my question. Just out of curiosity, how did you check TDC when the engine assembled? I've been thinking of some cockamamie ideas with dial indicators and rotor position thru the leading and trailing spark plug holes, but it seems a very Wile E. Coyote way of doing it.
The TDC check I did was really a reference check, not a accurate TDC check. I checked the depth of both L and T using a small rod with the pulley set to what should be TDC.
Then compared the lengths to make sure they were not way different. Was not a true check but assured me that the pulley and hub matched and the timing marks should be close.
So. if you use a FD front cover on a 20B and utilize the crank position sensors, how does one go about setting up the correct timing trigger wheel and get the timing correct? Is this a FAQ written up somewhere?
So. if you use a FD front cover on a 20B and utilize the crank position sensors, how does one go about setting up the correct timing trigger wheel and get the timing correct? Is this a FAQ written up somewhere?
I think the only real "right way" to do it is to mock build up the front portion of the motor while having access to the rotor/eshaft to actually check the true position. you could use a tool like this, or this to accomplish this. After you know R1 is at TDC, you mark the pully. so you have a true TDC reference to check with a timing light.
Last edited by need-a-t2; Mar 25, 2025 at 12:15 PM.
I think the only real "right way" to do it is to mock build up the front portion of the motor while having access to the rotor/eshaft to actually check the true position. you could use a tool like this, or this to accomplish this. After you know R1 is at TDC, you mark the pully. so you have a true TDC reference to check with a timing light.
Need-a-t2 is correct. Checking with the motor assembled will only be as accurate as the factory pulley and hub that is used.
To be more accurate, you will need to have the motor disassembled and use a TDC tool, like the one that JBR sales.
you don't need anything nearly that fancy, place a rotor on the e-shaft and put a rotor housing in place with the e-shaft in and you can easily tell when you get to TDC as the compression pockets will be equal on leading and trailing, the front e-shaft keyway will be at exactly 9 o'clock. i mounted a degree wheel to a bare hub so i could easily mark any front pulleys for engine rebuilds. the method of finding TDC with the spark plug holes is innacurate.
i used to sell matched hub sets but i ran out because no one would send cores, i can mark pulleys for folks since i still have my degree hub set up but i no longer have matching hubs to sell.
i learned the hard way many years ago that the timing marks can be wildly off time when diagnosing other shops builds, because they ran like ***. you can't just grab any random pulley and hub from a bin and build an engine.
Last edited by notanymore; Mar 26, 2025 at 11:11 AM.
is that true though? I would think it were true, if the leading and trailing plugs were equidistant from the eshaft center line, but I don't believe that to be the case. I know the plug location has moved over the years, maybe not specifically on the 20B, but in a generic 13B sense. But either way, I believe both plugs are biased upward from the shaft centerline. Maybe the experts can chime in.
The leading and trailing plugs are not equidistant from the pinch.
This is actually one of the flaws with FD rotor housings, as when Mazda moved the plugs around for this engine, the need to keep the tension bolts in the same place (tooling is expensive!) meant that the cooling to the spark plugs was shortchanged a bit. I believe that there was a long thread examining coolant flow.
Note that Racing Beat's timing recommendations are dependent on the series of engine that the rotor housings came from. This is because Mazda kept moving the plugs around and the timing for an early 13B is going to be different than for others.
The way to find TDC to dead nuts involves a rig with a dial indicator and an eccentric shaft in the front end housing, stationary gear, and front cover.
