I popped this in this sub as it’s really the best place I can determine for it. Feel free to move it as needed.

So bear with me as let’s call this thread “for educational purposes.”

As this is more related to flows I can’t find jack, nor does flow benching seem to really be any topic of conversation here. Given the relatively significant differences here, I need to that that into consideration.

To those that have far better experience than I, if one were to take a 12A tall port center iron, could there be enough in said iron to get it to flow, as best as possible, to a 13B secondary. Street porting in this context. Which 13B variant? TBD from whatever comes out of this thread.

I’m aware of the timing differences and believe that there could be enough to get the closing of the 12A to match that of a 13B. But in this context, the 12A center is to be used as secondary ports.

Been away from this for a while. No idea who I could have a conversation with anymore these days.

 

13B and 12A are the same?

 

try this one https://www.rx7club.com/rotary-car-p...video-1147510/

 

One thing you haven't mentioned is which 13B? The 12A's had the water o-ring grooves in the rotor housings. If you've got a 13B from 86 or newer those seal grooves are in the irons. The best thing you can do is make all ports open and close at the same time. As long as you aren't using 4 individual throttle bodies the flow will balance itself out.

 

Well, I did and I didn’t. I did say which 13B is TBD as I can make that determination as soon as I figure it out.

As for the water grooves, that will simply be cut into the 12A iron and is a known.

I know what you’re getting at with regards to the flow balancing itself out, but given the pulsed nature of the flow, would that really work out that way? I would think that from a timing perspective, that should be achievable. I need to get an extra 10 degrees closing out of the 12A, and that doesn’t take into account any additional porting on the 13B secondaries.

I did forget to mention this is a forced induction application, so to your point about self balancing, I do understand how that would help the situation somewhat.

@j9fd3s thanks for that. Though that doesn’t go into the specifics of the question.

Does anyone flow bench these these days?

 

My point was that 12A and 13B before 1985 were the same size secondary ports. Usually even the same part number for the side housings.

The largest issue with the tall 12A ports is unless you have a tricky intake manifold, the intake port has to remain "short". The tall ports prefer a flat intake manifold like a TWM or Lake Cities so they don't have to curve sharply right in front of the port. This would preclude most forced induction unless you ran an electric water pump so you could sit the turbo in front of the engine instead of next to it.

This is a lot of why the FD intake ports are the way they are, they can clear a turbo without needing to have the airflow stop and drive sideways.

 

Check out Cosmo 13B-RE center iron as well.

Tall port, but set up as a 45 degree into the engine like 13B-REW and already has coolant o-ring groooves.

13B-REW front and rear housings for the stronger dowel lands and lower intake manifold clearance and 13B-RE center housing.

 

The challenge here is to match the “primary” ports of the 12A to the secondary of a 13B. The center iron is to work as secondary ports. The manifold will 100% be a custom job. I shall look into that further however.

I think the REW end housings are preferred. Again the idea being to try to get, as close as possible, a center iron’s primary port to flow/have timing to match that of secondary ports. The timing should be doable. Just the flow aspect that is in question.

For the record, while I have spoken with Jeff Bruce about this, and this is his recommendation, I’m just trying to get more details about how well this can work, and whether any actual metrics exist. I’d not gone into this level of detail with him.

I’m probably over thinking it, but I’m a numbers/detail oriented person.

 

So are you trying to do a 4 rotor with side ports and no peripheral port?

 

Math later. Tall intermediate ports 45mm high, about 17mm wide, constant radius top and bottom. End ports about 36mm high, 25mm wide, constant radius top and bottom

Back to work

edit: Math now. Tallports are the area of 17mm circle and a 28x17mm square. End ports are a 25mm circle and an 11x25mm square.

227mm*2 plus 376mm^2, 491mm^2 plus 275^2. Center is 604mm^2 area, ends are 666mm^2. Area difference of close to 10 percent.

I don't think that is different enough to really matter. Mazda did not think so, they made a few reversed intake manifolds with the primaries going to the end housings and the secondaries going to the intermediate.

 

Maybe.


Thank you for that. My google-foo failed me this go around it seems as I couldn't find any of that.

Many centralized resources, unless I just don't know where they've moved to, have disappeared over time it seems.

I've spoken with Jeff a bit more and gotten some additional color on what he'd initially alluded to. That will change up my plan a bit, but the above is great so thank you for that.

 

People used to make "short 20B" engines all the time with two tallport 12A intermediate housings. They worked fine, aside from the center rotor running a little hotter because there is no water jacketing in the side housings, just the rotor housing. In that case, a little less airflow might not be a terrible thing.

No pictures because I can't set Google Image Search to 1998

 

most if not all of the the billet plates have identical secondary port openings & timing on the primary side too.
.

 

Not going for the billet stuff. Trying to stay somewhat economical, and it doesn't need to make as much power as possible. It'll be more than enough.