My worry (IMNHO) is taking so much away from the port might make a hot spot that could boil coolant or hole.

Vince

 

He put the pictures up does anyone have suggestions. This isn't a secret and he's not offended by any positive criticism. It's just I don't know what's good or not and people have ideas but after seeing what has been done what do people have to say.

Also what is parent metal Richard? And from what you or Dave know about epoxy will it withstand the temps?

 

Parent metal is the original metal that the piece is made from.....I would stay away from epoxies... don't like them just me :D

 

I can't think of anything that will live in an exhaust port. It's all basicly plastic and no plastic is going to work at 2000 F. Is there a ceramic? I don't know of one, maybe someone else does. For years Devcon was the standard for shaping intakes. But there must be newer and better stuff by now.

 

I still use Devcon on intakes. I haven't found anything better.

If you aren't using a proper weld for fill on an exhaust port (assuming you need it at all), it won't last. Epoxy will die at around 400 degrees F. Even if you do use epoxy in parts of the engine, you must pay very careful attention to prep work. You don't want it falling out.

One day when I get ahold of some Renesis housings, I'll develop a port profile on the flowbench. If I had a mold of the original, I wouldn't even need the real housings. I can make copies for flow testing.

 

I read on another forum where a 600 degree epoxy turned to dust, when the exhaust heated up.

 

You say Devcon is the standard for intakes but does that mean it will work on the exhaust ports? What temperature can it withstand?

 

NO epoxy will withstand exhaust temperatures. They are all only good up to about 400 degrees or so.

 

Aight I didn't know Devcon was an epoxy

What will work then? If it's just the parent material can you just go pick that up?

Is it cast iron or what not? Please excuse the ignorance

 

As much as I love expoy, I'd follow everyone's sentiment and stay away from it in this application. A quick patch of a hose to "limp" you home? Works great. Patching the crank cover on a motorcycle after making friends with the side wall of a tunnel? Yep... got that bad boy home (although I was sweating bullets about the epoxy not being able to hold under the temps from the cover and stopped at every rest area to check it)...

 

The only way you get parent metal is in a new housing. If you grind through, get someone with the ability and equipment to weld it. By equipment I think it should include an oven big enough to hold the whole part for preheat.

 

Devcon Alumax is an epoxy that I believe is still being used to fill intakes, but repairing cast iron requires special welding skills that include preheating the piece in an oven before welding.

John

 

If you are then you must know something I don't because welding cast iron is not as easy as other stuff is. You speak about welding like it is nothing and if this is aluminum or steel I would agree.

^ i know just about nothing about welding....so i take it to my friend, the certified welder
as i understand, true cast iron is almost black in color and near-impossible to weld on. maybe the side housings have a higher steel content? i don't know...just a guess.

and i should have made the epoxy a little more clear-- i don't intend to use it, in any way shape or form, in the exhaust port itself--my plan was to do a thin layer in the water jacket (similar to the way you'd bolster the coolant land on the older motors when the wall became too thin).

 

I doubt you can get the surface clean enough to make the epoxy stick. If you do you will then end up blocking the heat transfer.

I used to say if you can cast it I can weld it. After all that makes sense it was melted once in it's current form, right? Well it turns out it is not that simple. The control of heat in the part has to do with the material and some just fall away when you get close to melting temp. So it goes to the fact of heat transfer. Aluminum is an example, it falls away quickly. But it can be controlled easily when using a tig welder. Just takes practice. Cast iron cannot be welded at low temps, it melts higher up.

Now I'm getting to the point where I don't know the next procedures having never done it myself. I have done some cast iron repair in non critical parts with an arc welder. The thing is they were so uncritical that I can't say if they really did anything.

Everytime I have ever had a block welded it had to be preheated and welded by a very old welder. They are the only ones who seem to know how. One other thing, I have brazed up heads when I ground through. results were not consistant, sometimes it leaked, sometimes not. Don't recomend it.

 

i've used epoxy on intake ports with no problems ever, so i don't think the epoxy sticking would be an issue as long as it's properly prepared. but i don't know if the difference in heat transfer will be enough to cause a problem.

the engineers at mazda spent a lot of time developing these ports, and i've got 2 engines worth of experience. although i'm sure the porting will yield more overall power (and possibly slightly improved fuel economy), about the only way for me to find out what the negative effects are is trial and error. this is one of the reasons i was reluctant to offer this until i'd done a few, but curiosity got the better of me.

so now we're at the benefit vs. risk part. how about i don't go through the jacket with snoochies engine--since i already did with the other one i'm working on. when i get that one up and running, it'll be my guinea pig to see if the weld holds up. since it's gonna be turbo'd, it'll have a lot more heat and back pressure in the exhaust ports, so if it can hold up to turbo torture, it shouldn't have a problem with naturally aspirated life.

and i think we are going to be able to dyno that car n/a before we get the turbo on, so we may get a direct comparison of port 1 and 2. that'll allow me to see how much i've improved in just one engine. i plan on each engine getting better and better until it reaches a plateau of what i'd call "good enough", then i'll have i guess "my" port developed enough to start offering it and advertising. but until then, i'm still calling it experimental.

 

John, welcome to our forum. Your website is a wealth of good info. I made a rotary port mold as per your instructions for doing so in cylinder heads and it came out just fine. It's really neat to see what the air sees. I am going to make port copies off of this mold and work on shaping them rather than guessing on a good housing. I originally stumbled across your site while researching different flowbench designs. I like the size and simplicity of yours but ended up building my own pitot tube based design. I've learned alot from it in a very short time. You've got alot of very nice info on your site and I'm glad you are here. Welcome!

 

i'm glad both you guys are here

 

I'm really curious to find out what the flow rates are on these mods. From everything I've learned the trick is to figure out how to shape the port so it focuses the flow of air; not just increase the area. Like the power of a tornado, getting it to focus increases the velocity. This is why even a small change can cause a seemingly disproportionate increase in flow. From what I can gather, figuring out how to increase the velocity at the edges (or outside) which creates a high pressure area, while having a low pressure area in the middle is what causes the vortex effect. Work the corners; the successful ports seem to have corner shapes that increase the velocity of the air at those points, which begins the twirling vortex effect in the middle. If you're north of the equator, then of course the Coreolis Effect is creating a counter-clockwise vortex. It does the exact same thing a tornado does; sucking air at increased velocity down it's center.

As somebody said, the smallest port that will give the highest flow is the best port. The one that enables the vortex effect the quickest will flow the most air. If you are going to make molds so you can practice on models, then experiment with the corners of the port first to see what changes will cause the vortex to form the quickest. You want the air to "fall" faster in the corners than in the in-between areas. The Coreolis Effect automatically starts the twirling to begin the vortex. Obviously on an intake port you want the "tornado" going in, and for an exhaust port you want it going out to pull the exhaust out of the engine.

You can see this same effect on an arrow. The feathers (or vanes) are angled so they cause the arrow to spin as it goes through the air. The rifling in a gun barrel does the same thing with a bullet. This gives the projectile stability and better velocity as it moves through the air. Without it the projectile "flutters" and quickly loses velocity, accuracy and distance.

In an engine the "projectile" is air. You don't want it to flutter anywhere in the port on it's way to the combustion chamber or out. You want it to "spin" so it travels quickly with accuracy and power. Basically it's just natural forced induction using nature's own dynamics.

Great thread!!

 

Alright well say we stop now because we havn't hit the water jacket. If it turns out you're really close will this be a problem. Like being to thin will cause it to burn a hole through it anyways. Or will the cast iron not allow that. Hopefully this makes sense. Because if patching it up is such a tedious and troublesome area we might as well stay astray from it. seems like a lot of problems there.

 

i've never seen any part of the metal in the exhaust section melted, reduced, corroded, or in any other way diminished. now if it's getting to the point where the port wall is paper-thin, we won't know it for sure until i poke through. that's why i said it would almost be a relief--since once it's welded, i have a better idea of how thick it is.

so this is where the epoxy inside the water jacket comes into play...just something to slightly thicken up the wall as a little extra insurance. i honestly don't think we'll have any problems with this. there is always some risk, but if i thought that chance were anything substantial, i wouldn't be doing it.

 

Thanks RG.

I have to admit I haven't given rotories much thought until now. So these things don't have any cam shafts and valves?

John

 

No cams.. no valves.. no lifters.. just 2 rotors and an eccentric shaft.. it's quite simplistic.

 

a couple triangles spinnin' around inside a peanut shell

 

man, i'm not getting much done today... i've got a sickly stomach flu. hope i get it under control by tomorrow!

anyway, side plates are done except for the final cleanup and i'll get started on the intermediate housing after i have a nap. with any luck, the motor should be back together by tomorrow night, or possibly wednesday. as long as luck is with us, look for it beng in the car running by monday or tuesday of next week. unfortunately, i've got to take saturday and sunday off of this pj for work.

 

Who needs a flobench when you've got a stomach flu? I am pretty sure stomach acid isn't strong enough to eat the cast iron .