Decreasing Port Size
 

This is a topic I've had little luck finding info on. Has anyone done, or seen, the larger ports decreased in size to match the smaller, inner ports?

I know your first thought, "Why in the hell would you want to do that?"

Will it decrease power? Yes. Increase MPG? Probably not. I would see it hurting due to lack of power. Then why?

I have my reasons, but I'm not sure if I'm going to go through with the plan or not. I would still need to find an engine or two. Your insight on this, unusual, question is greatly appreciated.

Jose

Nothing? Guess that should tell me there that no can do. Asked a friend, he said that there would be no way to partially fill the port safely...Oh well...

Jose

I've seen people use a type of JB Weld (not sure which one exactly) on motorcycle engine ports but generally it would have been messed with every year so I can't speak of the actual durability. You could always contact a company that makes epoxies and see if they recommend anything that can withstand heat and fuel.

It's been done with jb-weld(industrial type) and devcon. Mainly used in road racing situaions. Iirc Lynn E. Hannover as well as Carlos Lopez of CLR have done this and should be good point of contacts for Info.

What engine are you starting with?

On 12As, the ports are all about the same size. (the "tallport" intermediate housing) Incidentally, these appear to be the housings used to make short-shaft 3 rotor engines. I haven't heard about any problems with power balance due to airflow, just cooling issues.

On a GSL-SE, the primary ports are about the same size as the secondaries if you keep the aux ports shut!

I am personally curious at what you plan on doing, but I can attest that with 4 port architechture, you pretty much can't go too big with the runners, low end power doesn't seem to be hurt at all by larger runners.

Thanks guys.

It was an idea being floated around between some friends of mine and myself. Buddy of mine aquired a 3 piece 4-rotor e-shaft, but wanted to try something different then just p-ports. We wanted to see if we could use the side ports as secondaries to open up at about 4500 rpm for an extra 'boost' to try and move the torque curve down a bit. It's a wild idea. But seeing as how the front and rear ports would be bigger (plan was to use TII housings and irons) it would kind of be off. Again, it's an idea being floated around, more so to the point that the group of us don't exactly have the funds yet to go through with it, but we have the e-shaft which is a big step (if the shaft is correct is the next step!). Crazy plan, may never see it come to life, but, it's chatter. Just trying to see if we can get more info on the subject just in case (like win the lottery! ha...). Thanks again. I'll see if I can give the above mentioned a holler and get some opinions on it.

Jose

12A primary ports are larger than TII.

Problem is the shaft is for 13B housings, and if I remember correctly, the cooling jackets don't line up from 13B to 12A (although Renesis and 12A line up...). Please correct me if I'm wrong.

Jose

cosmo RE centre plate would maybe work, as the port is also larger with the same water passage ways. and a much larger intake port face to the LIM.

Are you going mid plate bearings for the shaft support ? and if so just on 1 mid plate or all 3 ?

interesting idea, cheaper then tying to get your hand on three 20b mid plates or PP's that's for sure.

The water jacket changeover happened in 1986. Mazda made many 13Bs before that.

Never thought about checking the RE centers. Hmm...Have to look into that. But them things are not easy to come by (tried when I had the FD, no luck then...)

As for the bearings. Don't know. There is still so much research we'd have to do. This will be a massive (and oh so costly) endevear. So right now we were just throwing ideas to get a good goal (have to have a goal to keep costs and errors at bay, right?).

True. But S4-6 are so much easier to find then good condition older 13B's. But it may be worth a try. I'm up here in Cape Cod now, so I don't have a lot at my disposal to work with (when I was in VA, it was as easy as going to Fayetteville, NC and hooking up with some PR folk. They ALWAYS have spare stuff).


But, 13B housings from say, an RX-4 with 12A irons. Seems like the ports would be close enough? May have to port the centers a little to match the outers...Hmm...

Jose

From what I remember reading, Lynn Hanover used to use JB weld or Devcon to fill in the bowl volume, to help increase charge velocity at the port face. I've never heard of anyone filling in the port face, though. I would be a little hesitant to unless it was welded properly, then surface ground again.

I am also interested, because I have a 20B center thick iron that's been bridgeported that I'd like to fill in, but wasn't sure about it either.

Fill... in... bridge port? *brain explodes*

I mean, I guess, if you wanted to. I personally don't ever want to go back to half or street ports, the full bridge makes more torque everywhere than either, and fuel economy is the same, drivability is the same...

Mind you I only drive the car 20-odd thousand miles per year, so I don't live with it on the street very much ;)

I only want to fill it in because I'd rather go semi-pp, and it just seems overkill to do bridge + peripheral on a turbo 20b :)

Well, I guess there's that... ;)

But now that I've said it, maybe I don't want a turbo.... Damn, that's why I avoid the N/A forum!!!

Anyways, if you know a good welder, they would be the one to ask about possibly welding the cast iron. A good machine shop can grind the face flat again on a surface grinder, and as long as they're only taking a few thou for the last pass, it leaves a really nice surface for your rebuild. Just don't take too much extra off or your water jackets will be too shallow.

The BIGGEST problem with taking too much off is the eccentric shaft bottoming out against the rear stationary gear, at least in a 2-rotor. You'll have to oval the intake manifold holes before you get to that point.

Interestingly, I did a Subaru where we had to oval the intake manifold as well. The engine was something like .100" narrower because of how much was decked from each surface, and we had to make an adjustable idler gear in order for the slack side bank to be in time.

Yea, but the problem with welding the ports is pitting and heat. If heat builds up there it will be different, and could possibly crack, causing all kinds of problems. This is what a machinist told me. And it made valid points. The devcon filler I guess doesn't really absorb the heat. I don;t know. Thoughts on this?

What do mean ovaling the intake manifold for the 2 rotor? Maybe I'm not quite following, but why would you need to do that?

Jose

He's saying that the engine is a given overall length in stock form, as material is ground away from the irons, the engine becomes shorter. If the engine becomes too short, then the manifolds mounting holes need to be elongated to compensate for the narrower spread of the threaded holes on the engine

Ah, I see. I've never personally had to rebuild a rotary, so wasn't sure. When you re-surface an iron, you're doing the whole iron? Not just the inside face? I mean, it makes sense I guess being that the side seals would still need to seal, but...OK. That's why I'm here. To learn (search first!).

Jose

just the sides of the iron that face the rotors. 1 side each on front and rear irons, and both sides for center iron. No need to resurface the other sides. But, as Peejay implied, you would have to take a good amount off the irons to have this be an issue

The only practical way is to do that, yes. Especially since you'd want the rotor housing to meet up with the side housing on the same plane that the rotor rides against, else you run into sealing issues. Well, more sealing issues than the engine already has, anyway.

I've never resurfaced a side housing. '86-02 side housings cannot be resurfaced very much since it takes away coolant seal depth. Resurfacing also removes the hardening layer, which makes them wear faster. (If the amount that needs to be removed to clean them up won't go through the hardening, then they're worn so little that they don't NEED to be machined) Not really much of an issue if you keep the engine fed CLEAN air and keep the oil changed frequently.

Might be a stupid question, but has anyone ever done this to the sec ports on a 6port engine?

By that i mean removing the bridge on the sec ports and then filling in the port in the shape of that on a 4 port engine?

Maybe fill the second port first then shape it? either way, that pretty much is what I'm trying to figure out. But it 'may' be easier to start with a 6 port. fill the secondaries, then port it to match the inner ports...doesn't have to be the same shape, as long as the volume and timing are the same (which may mean it needs to be the same shape, yes? lol).

Any thoughts on diviting (is that a word? lol) the stock ports, then pouring in liquid metal and having it cool to hardness? Then bore out the port size/shape you'd want? Is that possible? Sounds expensive, too!

Jose

There exist epoxies specifically for filling areas of intake ports. Not Devcon.

I've used JB Weld for intake manifolds but have never had the guts to try it inside a working port with its higher thermal stresses. Metal expands and contracts with temperature changes, I worry that this will cause the stuff to eventually come off. I have used it with success to completely block ports off, but the worst that could happen if it pulls away would be a slight vacuum leak when hot, since the "plug" can't go anywhere.

The specific epoxies I mentioned don't have this problem.