In my first chapter I want to address APEX SEAL reliability in regards to exhaust porting. It's very crucial to the life of the apex seals. In this picture you will see the factory CHAMFER,BEVEL that is left by Mazda when the rotor housings are manufactured. This Bevel is very important to the apex seals reliability. I will explaine with pics as I go along.



below is a pic of stock port with a factory bevel

At this point you want to measure this factory bevel that is made by Mazda. It's 2mm. This will come into play later in my thread.

caliper pic showing the 2mm measurement

This picture is showing the rotor housing ported and the bevel is gone. When the rotor housing is ported to allow the port to open earlier and closed later this factory bevel is ported away. When this happens a super sharp edge is left behind.

If the exhaust is ported and this sharp edge is left behind the apex seal will crash right into the edge and create some serious damage when closing the port. Ill show were the damage will be done.

This picture here shows the exhaust ported to improve flow and port timing. When this is done the factory bevel is removed during the porting. I have found many engines done by other people that have left this sharp edge behind creating some serious damage and premature wear on the apex seal including radius lost on the apex seal.

When the exhaust is ported and after it's done you have to create to an exact replica the 2mm bevel that was manufactured by Mazda. Here I'll show some pics. This is done to protect the apex seal when the rotor is closing the exhaust port. The apex seal is being pushed in and out by the force of the springs and centrifugal force through rpms and that edge is a danger zone.



one more picture of sharp edge and apex seal. then the bevel replica

This picture shows the exhaust ported improving port timing and flow returning to the factory 2mm bevel.

When this is done correctly, you will improve port flow,port timing and apex seal reliability which is first and fore most.

I hope you guys enjoyed and learn a bit from this chapter in exhaust porting. Next week Ill go into my second chapter. Which will be port matching to the factory diffuser and port timing showing pictures of a degree wheel in before and after top and bottom dead center.

Great stuff Ito https://www.nopistons.com/forums/pub...1047683894.gif https://www.nopistons.com/forums/pub...1047683894.gif , one question what kinda angel is the bevel at ? Would a larger more gradual bevel be better , to help the apex seal ?

A 45 degree angle is enough to clear the apex seal from crashing into the edge.

Query me this Batman:



If the bevel is needed on the Exhaust port, is the same type (not neccasarily size)bevel need on the irons for the side seals?

Bevel not required on intake ports (well only a really small one so there's no nasty sharp edge) as there is less centripetal (is that how you spell it- I use centrifugal) force acting. The apex seals get pushed out as they speed past, whereas the side/corner seals etc only have spring pressure forcing them out onto the port, which would be waaay less force so less flex into the port...



Clear as mud?

centrifugal force is not driving the side seals into the side intake ports, so it isnt as important. but if you rev high and encounter flex / wobble of rotors I can imagine how a bevel might help https://www.nopistons.com/forums/pub...DIR#>/wink.png



hopefully ito can elaborate on that.

Yeah I was wondering if you could do the bevel like a 3 angle valve job? Well Im sure you could, but I wonder if it would do anything.

I make that a radius with special care at the junction of the upper radius and housing face. I have three sets of carbon apex seals and one set of ceramic seals that I have been using over and over for years. No damage and no detectable wear.



Judge Ito,



Do you have some pictures of a bridge ported turbo end housing or perhaps a Cosmo housing you could post. I am thinking Cosmo end housings to build a 4 port monster engine. There are several GT-3 cars running 12As based on turbo end housings and I cannot identify the center iron.



Also, what year and model center cast iron has the biggest port runners in stock form. I would be using them to build a 12A for SCCA GT-3 competition with a 48 IDA with 38MM chokes.



Thank for your efforts here.



Lynn E. Hanover

can you provide more details on this?

No problem.

The vena contracta formed at the top of the exhaust port is substantial, while at the bottom of the port where it first opens, there is little angle change in the exhaust stream so the supersonic flow tends to stay attached to the floor of the port for most of the exhaust event. Once the apex seal gets above the top of the port you have a ledge facing into the flow and a return angle with a sharp wedge shape.



As the apex seal traverses the port, the preceding rotor face is still connected to the port, and some exhaust gasses are still being scavenged by the exiting exhaust charge.



A larger radius at the top of the port not only protects the apex seal but assists in this scavenge flow off the preceding face.



I would prefer to over scavenge that face to a lower pressure to get a better charge started when the preceding face is exposed to the opening intake port.



So we loose a bunch of fuel mileage, but we cool the rotor face just a hair more,

and get just a bit more intake charge. In a periphery port or a bridge ported engine, the intake and exhaust ports are connected for quite a long time.



Intake charge dilution is a problem at lower rpm, so anything that gets the intake charge moving across the rotor face and even at slow speeds, out the exhaust port is a good idea.



The smaller the volume of exhaust gasses the rotor face carries into the intake cycle the better it runs.



Once the apex seal crosses the top of the port, there is only exhaust gas left to expel and the radius just helps flow. The port should look like the bell end of a trumpet. With a 1/16" radius along the sides and top of the port, flow can be increased dramatically without extending the port timing to any great extent.

So tractability is not affected.



Not such a big deal down low, but if you can get big port flow without the penalty of big port timing changes, then why not. So if you are in there anyway, just make the 45 degree chamfer a shinny smooth radius. No additional cost.



This works better with less back pressure. The improvement more obvious at higher RPM.



Lynn E. Hanover



Note the rather sharp edge of the exhaust in the factory periphery port VS my home made periphery housing.

Yes I do have pics of my bridgeported third gen. plates. I like them very much.. I think your Idea will work great I have seen it done before. Third gen. bridgeported side housings using 12A rotor housings and internals. Your going to need a custom intake manifold.

so what you are saying is that, in a high over-lap engine, when the first apex seal opens the exhaust port but not close yet, the exhaust scavenge effect from the supersonic-pulls (reminded me of my thermodynamic class, supersonic flow in a convergeing diverging nozzle) the remain exhaust dilution and some fresh intake charge from preceding cycle. Is that the reason you said a low pressure exhaust helps, or more specificly should I say, you mean a highly scavenged/collected exhaust helps?



more questions:

what do you mean by "over scavenge that face to a lower pressure..." ? Do you smooth the top radius and bottom radius differently? (different vena contracta angles)? from you picture provided, it looks to me that the bottom of exhaust port and top of exhaust port has diiferent radius, is it true? or just me?



How would you use this trick, for a S5 n/a with a medim street port(more over-lap on secondary and aux ports only)

Here's a new linkon how to swap exhaust port sleeves in my gallery:



http://bdc.cyberosity.com/v/Technical/RollPin-Removal/



B



Btw, here's a link to some pictures of the closing-edge bevelling that Judge Ito stressed so highly...



http://bdc.cyberosity.com/v/Porting/JasonK...veled1.jpg.html



I personally haven't had any adverse effects from not doing the closing-edge bevel, but I am concerned about whether or not it's a good idea if making an exhaust port much wider than stock, thereby leaving less area for the seal to be supported by, resulting in a seal that might banana-shape itself outwards... I've been making it a mandatory part of my exhaust porting ever since the subject became a hot one as I figure it can't hurt, but I wonder if it's necessary for stock applications or not.



Any ideas? Any other experiences?



B