I have a ton of spare 12A parts lying around and a first gen without an engine and a background in mechanical engineering. I think I'm gonna make use of all three and build a peripheral port engine. The catch is, I'm gonna drive it on the street. Not everyday, just for recreational purposes.

Some info on the ports:
I will be starting with a 6" long aluminum tube with a 2" OD and 1.5" ID since it is a standard size. From this I will machine the external diameter to 1.75" for 3" of the tube. The internal diameter will be enlarged to 1.625" at the point where the runner will enter the engine. These sleeves will be SLIGHTLY larger than the holes bored into the housings and the sleeves will be dipped in liquid nitrogen to shrink them down and pressfit them. This will be more than enough to seal the water jacket permanently rather than placing faith in epoxy. I will tig weld the tube on the outside of the housing to ensure longevity. This setup will correspond to port timing of around 90deg BTDC opening and 60deg ABDC closing. Mazda Factory Racing housings open at 86deg BTDC and close at 75deg ABDC. The relatively earlier closing will help to keep the operating range lower so that I can run stock 2-piece steel apex seals to help with sealing at lower RPM levels and make the engine last more than a few thousand miles.

I will be dealing with the negative effects of overlap in the following ways:

1) the aluminum intake sleeves...
The internal diameter of the tube will reduce from 1.75" to the 1.625" when the runner meets the intake chamber. This will occur over a distance of 4 inches. This will improve the velocity of the incoming air and will combat reversion. Atomization of the fuel will be improved as well. Since this is a smooth, steady, small transition, the effect of maximum flow will be negligible.

2) another trick for the aluminum intake sleeves...
I will weld an injector bung in each intake sleeve close to the engine. These will be the primary injectors and I will probably use 260cc/min from a Miata (happen to have some lying around). These should be perfect to handle fuel delivery at idle and cruise and the fuel will be delivered at the point of high velocity. The ability to run longer pulsewidths will make a nice difference in idle and cruise, as well as the ability to have more precise control over the AFRs during those conditions.

3) wraparound intake manifold...
this will enable me to take advantage of longer runners, improving the pressure wave tuning at a lower RPM range. I will finish the setup off with a 48mm DCOE-style throttle body with 2 injector bungs, probably using 2 550cc/min injectors. I will incorporate the air filter assembly with velocity stacks to further improve the performance of the intake system.

4) tuning...
I will stage the injectors so that the 550s come on when needed. I will also run sequential injection so that the injection events for each rotor occur independently. The injectors will not open until the exhaust port is closed, eliminating any concern of fuel leaving through the exhaust port.

Its not going to be a record-setter in terms of power but it should be pretty torquey for an NA and reasonable enough to drive on the street. I will be having my best pair of 83-85 rotors clearanced and the entire rotating assembly balanced. I'll also be upgrading the oil system including upgrading to a MFR oil pump and running synthetic in the oil pan and premixing instead of using the OMP.

The car is an 85 GSL with grey interior. I have RB springs and Tokico struts waiting to be used and plan to upgrade the rear end to 4.88 gearing. I have 15" panasports as well so I have the rolling hardware to deal with the extra power as well.



Comments or suggestions?

 

good luck. sounds nice

 

Pics please!

 

sounds like a pretty interesting little project you're going to have on your hands. i like it. i really like your approach to the injector size, too many people seem to subscribe to the "let's-just-throw-fuel-at-it"- school of thought. as i said, i like your approach, but i can't help but be a little concerned with the overall (1620 cc) volume. do you have an appoximate HP goal in mind? yes, please post pics once you get started.

my only burning question so far is where do you plan to cut the RPM?

 

Sound like You've got it all figured out, sound right too

One question though, with the wrap around intake manifold the distance concerns me when You say you won't fire the injectors untill the exhaust port is closed. That leaves only very few degrees of open-duration to get the fuel into the chambers.
Are You sure the A/F will be mixed properly ?
To Me it seems like it would suck in alot of air for, lets say 90%(dont hold me to that) of the stroke and the add the needed fuel in the last 10% , which in my ears sound like a bad mixture.

Good luck, I can't wait to see the pictures and video.

 

I don't plan on revving past 9k. 9,500 absolute max if it keeps making power after 9 but I think with my earlier intake port closing that the operating range will be 6,500-9,000 with usable power from 4,500-6,500. Only time will tell.

 

The primary injectors will be right by the ports and will handle the idle and cruise demands. When excess fuel is needed the injectors will fire for the remainder of the cycle and then will begin opening earlier. At higher RPM and load the overlap won't be a factor so the injectors can open earlier. I just want to keep the idle under 1,500 and cruise MPG around 18.

I'll post up some pictures when I get to doing some of the port work. The cash situation is a bit tight right now and the time situation isn't much better but I intend to pick away at this.

 

Steel Apex seals will bounce and make chattermarks at those rpms, thats why You're supposed to use the light Carbon Apex seals in high rev engines.

 

Is there stiffer springs you can get?

 

This engine isn't going to see sustained operation at those RPM levels. Plus, with the fresh parts and perfect grooves in the rotors and premixing I won't have a problem. The carbon seals will basically destroy any real possibility of actually driving the car. With the right exhaust and intake setup the engine should be tame enough to use stock apex seals. I spoke with the engine builder that will be clearancing and balancing my rotors about the seals and he said that the steel seals would work best for my application.

 

Ahh ok then, I must have missed that part.
Keep us updated

 

Why would the carbon seals destroy driving the car? I have carbon seals in my large B-port and I drive it on the streets with no problem.

 

I didn't mean completely make it unable to be driven. I would rather lower the redline a bit and keep the steel seals for longevity and for a bit better idle. The engine may see some boost down the road as well, though not for a while.

 

Gottcha. Hey, can you post some pics of your 12app housings and what did you use to cut the pp hole? Also, what is the normal MFR housing pp intake hole diameter for the 12a?

 

What's new with your project? Are you leaving us hanging?

 

I'm doing this project as a senior design project for my engineering degree so I have a bit more busywork to tackle before I get right down to building it. The plus side is that I will have an excuse to work on the engine and call it "school work." I am also working on getting approval to utilize the engine dyno in the basement that just seems to sit around doing nothing. It sure would make it easier to tune for partial throttle and cruising, especially on the ignition end of things.

I will be doing a good bit of planning these next 3 months but you can expect to see some real progress this April or May. I will share the preliminary write-up of the project as I go through the various motions required for my degree in the mean time.

*SIDE NOTE*
I'm EXPLORING the possibility of designing a custom eccentric shaft and making a 12A based 3 rotor. Since I happen to have 3 perfect rotors and 3 good rotor housings and 4 great center irons (2 that I can mess up when installing a stationary gear) the only major obstacles are the eccentric shaft and the stat gear in the center iron. Chances are that this won't happen but I am going to explore the option in my quest for a high performance NA rotary.

I have tossed around the idea of trying a 4 rotor since it wouldn't be much more machine work than a 3 rotor but since I would need to track down another good housing, rotor, and seals for 2 more rotors it will cost way too much. Plus the weight would be so far forward in the chassis and mounting would be an issue.

 

Man, what a tease. I gotta wait 4 months for any progress? Why didnt' you just wait till April to start this thread?

 

You can expect some planning by the end of this month, if you consider that progress...

 

Well, I am cutting through the red tape with the university and am finishing up my initial technical specifications of the project, a written "abstract" of the proposal paper that I will be writing in April, and a project description. I will be exploring various types of aluminum to find which would work best for the peripheral port inserts and primary fuel injection and looking into the machine work to punch the holes in the housings for the ports and to machine the aluminum inserts to the proper shape.

I expect to send the housings and the aluminum tubing to the machine shop in may or June and to install the aluminum into the housings with liquid nitrogen shortly thereafter. Then will be the typical clearancing of the rotors, balancing of the rotating assembly, side housing lapping, and oil system mods. I will present the finished product in December but I would like to have the buildup finished in the fall sometime.

 

Expect pictures when I get to the machine work...

 

Run the apex seal groove clearance at the high side of the tolerance (0.006" for the 13B, IIRC). The extra clearance will allow combustion gases to get under the seal and help to push it against the rotor housing. Although this will slightly increase wear, that is easily combatted with extra premix. Doing so on a 13B engine and you should not experience chatter with stock steel seals up to 9,600 rpm.

 

You're talking about the 2mm seals, right? Not the older 3mm units?

 

Correct.


He's also going to need bigger fuel injectors.

 

I've got a CAD drawing that I threw together Thursday of the aluminum insert for the intake port. I have not decided what the final dimensions of everything will be but the geometry of the runner and overall layout is pretty much settled.

My thoughts on the intake port runner's minimum diameter (with some calculations):

The stock intake port runner area for each rotor is very close to 2.0 in^2. This is taking into consideration both the primary and secondary minimum runner area. I've used the measurement of the intake manifold for the primary ports as it is the smaller area on the tall-port 12A.

The peripheral porting configuration with a minimum diameter of 1.5 in will have a minimum port area of approximately 1.8 in^2, 10% less than the side ports.

If I machine the tubing to a minimum diameter of 1.625 in, the minimum port area will be approximately 2.1 in^2, a 5% increase from the side port runner area.

I am debating which size to use but am leaning very strongly toward the 1.5 in diameter because I believe that it will flow plenty of air, yet retain enough velocity under idle and cruise conditions to make the engine reasonable to use for more than just racing, especially with the right EFI and ignition tune.

I'm not shooting for a power record here, exceeding 200 rwhp would be great, I wouldn't even complain about 180 rwhp as long as the engine help up well and ran well. I do believe that the runner diameter will be sufficient to reach these goals considering the fact that the peripheral ports open and close almost instantly and are open all the time. If you look at how much rotation it takes for the side ports to be completely opened and how quickly they start to close again it will be pretty clear why a smaller peripheral port will outflow the big side ports easily.

Add to this the fact that the peripheral ports do not deflect the air 90 degrees to go into the chamber, only to have it turn again once inside. This results in more resistance to airflow for the side ports not to mention reduced momentum for the intake charge which reduces the "inertial supercharging" effect that is necessary since the ports close about 60 degrees after the chamber volume begins decreasing (in both a streetport and my peripheral port layout).

Also, the 1.5 in diameter configuration will shift my torque curve a bit lower, even if slightly, which will make the issue of the stock apex seals a bit less edgy, plus make it a bit more civilized. I still fully expect the torque to peak at 7k+, though have no basis to justify it yet.

This is going to be a fun project... All from spare housings and rotors! I even get to get credits for graduation from it!

 

40mm port ID works well for a 12A if you don't want to rev it much higher than 9500. I would use carbon apex seals over steel though, they are much less likely to bounce and chatter, and they still seal well. You'll get and easy 35k+ miles before the engine gets harder to start.