SomeGuy_sg

Great stuff Ito , one question what kinda angel is the bevel at ? Would a larger more gradual bevel be better , to help the apex seal ?

Judge Ito

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

banzaitoyota

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?

andynogo

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?

pengaru

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



hopefully ito can elaborate on that.

rotarychainsaw

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.

Lynn E. Hanover

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

GTUs

can you provide more details on this?

Lynn E. Hanover

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.

Judge Ito

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.