Interesting, thanks for the info scathcart

 

I was thinking the same thing. Thank you.

By %50 do you mean only half of the length is exposed? Some clarification please.

 

Thanks for the info, that makes me feel better about the port.

So what do you think about the shape of the bowl? I'm trying to get some feedback before I get into any of the other housings.

 

There is always a clearly scribed circular track on the iron from the outer o-ring, the same track that everyone tells you not to port into.
You can port up to halfway into it, so if its say... 3mm wide, you can port an additional 1.5mm towards the center of the iron.

What is important, though. is to actually mock up a rotor and spin it on the iron. Even with the stock ports, there are some sections near the bottom of the port that never fully open, and porting into the oil seal track in those locations will accomplish nothing.
As well, using a flow bench is a VERY handy tool when doing this, since we all know that porting is much more than just changing the port's 2-dimensional shape, but altering the entire runner and bowl. With a flowbench, even just a homebuilt unit, and grinding into the oil seal track and making changes to the port bowl can see some decent flow increases.
Even better is to take an entire scrap rotor housing, e-shaft, iron, and seals, set them all up with a sheet of coated plexiglass (to prevent the instantaneous scratching that would otherwise happen) and some very light cutting oil, and then use an electric motor to spin the e-shaft as fast as you can while you feed your choice of smoke/vapour into the intake port, and watch exactly how the charge enters the chamber.

Then again... who has the time for all that when an extra 1/2 psi can make up the difference?

 

First of all, take better pictures. Get better light, and turn the flash off. Hard to give advice when you feel like you're eyes are blearing like a hard night of binge drinking.

It looks like you just ground out the stack casting flash and didn't really try to alter the actual shape.

Let's start with the actual port 2-D shape. It looks like you rounded the top of the port quite a bit. If you look at a lot of porting pictures, you'll see that the top line (closing edge) of the intake port is quite flat. I've read a bunch of times that rounding the top of the closing line gives a broader powerband with a lower peak power. I've found this isn't true. A flat closing line does result in a higher peak hp, and a much steeper peak and fall-off, it does not necessitate that a lower mid-range power must be included. For equal port closing timing, a flat closing line will give the same low and mid-range power, but with a higher peak.

I'll post more tomorrow. There's lot to be done.

 

Thanks, that's good info. I'll take some better pictures when I get home.

 

Continuing on with the 2-dimensional shape alone: take alook at the opening edge of the port. This is the curved edge that is closest to where the intake manifold bolts on. For optimum reliabilty, it is best not to port into the leading track of the side seal so that the side seal does not flex into the intake port. This track is pretty easy to see on the irons, tho not in your pictures. Even better would be to mock up a rotor and a side seal to scribe a line into some machinists blue or the like.

Its obvious you ported that edge out, which is fine. This increases the intake timing and results in some significant higher-rpm gains on both N/A and turbo engines. It also increases port overlap, which lowers idle quality. My only problem with your port is the curvature on it: I think it is too much. It is usually best (bridgeports aside) to make the opening edge of the intake port match the exact curvature of the rotor face at the moment the port opens, without actually porting into the side-seal track. By making this curve match the rotor face, the intake charge opens a lot more "suddenly" than the gradual opening of the intake charge. With the "sudden" opening compared to the "gradual" opening, for the same port volume, the intake charge accelerates into the intake chamber much faster. This creates a more well defined charge pulse.

On your port, to achieve this, you would need to mock up a rotor onto the iron with the eccentric shaft and a stat gear and then spin the rotor on the iron while shining a light into the intake port. As you spin the rotor, the port will open, and you will be able to see the light. Back the rotor up until you just start to see light, and scribe a line along the rotor face on the iron at that point. Now, port as closely up to that line as possible (in your case, further outwards) on the top and bottom without actually going into the side seal track.

(Yes, I am aware you can port into the side seal track, but that's more complex than needs to be covered here)

The closing edge of the port, again as flat as possible, can again follow this same rule: to close the entire port along the face of the rotor. However, side seal longevity tends to be improved by adding a slight angle to the closing line, to allow the side seal trail edge to "scissor" the top of the port as it closes. For a street engine, put in the "scissor" angle. For a race engine, no scissor and bevel the hell out of the closing line.

The port runners:
You can start by gasket matching the ports. Stack the rotor housings and irons together and line up an intake gasket. Scribe a line around the intake port holes from the gasket, and then whip out the grinder and hog out the metal up to that line. While increasing the port runner volume does decrease charge velocity, the effect is pretty much made negligible by creating a uniform port shape and removing casting flash that inhibits flow, and decreasing any possible steps at gasket transitions.

Next, lets go back to the opening edge of the port. Newton's laws and all that jazz: any mass moving wants to keep moving in a straight line. The opening edge of the port requires the air to make a 90 degree turn. Make this as easy as possible by back-cutting the edge as much as you feel is safe.

The bowl itself is best actually experimented with, but without doing a lot of extensive testing yourself, just roll with this: Hog out the port so that it looks like a 1/4 pipe skateboard ramp. You want the inner edge of the port to gradually ramp up to 90 degrees, as the rotor face when the port is completely open will be 90 degrees to the intake port. By placing any sort of angle there, the charge is forced to make an instant turn... and this hurts flow. The closing edge of the port should attempt to angle the charge fairly straight from the start of the port bowl to the closing edge. When severely increasing port closing timing, obviously this is not possible without porting into the water jacket, leaving your options to create as slight a convex shape as possible, or partially filling the water jacket with steel epoxy. To prevent porting into the jacket, you can use your finger to feel behind the runner to gauge how much material your have left.

Lastly, the last little curvature between the closing edge and the inside edge of the port should be kept as straight as possible.

The port is best NOT polished. A slightly rougher surface helps with flow and fuel atomization. Only when building a nitrous engine should any portion of the port be a mirror finish. Leave the face somewhat rougher on the edge of the runner closest to the iron face. I tend to use 180 grit on the runners and the bowl, and 120 grit on the runner wall closest to the face. Simply put: the rougher edge helps to pull the charge around the corners.

Lets see your exhaust template, too.

 

Ahhh! Thank you. I have spent a lot of time spinning the rotor on the plate with the e-shaft. I think for us rotary noobs keeping the side seal completely supported would be a good idea. Especially for a street build. Am I wrong? I've done a lot of searching and have saved a lot of pics of what people on here say are good ports and am incorporating them into my porting. My question stemmed from the fact that even though the outer oil seal scribes a circle, the outer oil seal radius does not match the oil seal track. So even if the oil seal is exposed, it is not along the whole track. Does that make sense?

Thanks again for the information.

 

I think the leading edge of the side seal should typically be supported for a street engine.
I understand what you are getting at. Best bet is to just throw the plexiglass back on the and watch the oil seal itself. You'll be able to see how far you can go.

 

Better Pictures (Sorta):

 

Ports are looking a lot better. ^^^^

 

lots of work to be done on the runner to face transition

 

since the picture you pointed to was taken, I did a lot of work there, I'll take another picture from that angle to get your opinion of how well I did.

 

+1.

Imagine how the charge is going to work its way through the runner and into the outlet. The focus should be doing everything you can to retain the speed of the charge is it flows through and twists its way around and out of the port into the combustion chamber. The goal here isn't size; it's velocity. What can be done to retain velocity and remove or reduce the pressure drop points? Chamfer the entire underside of the short radius that Bastard is pointing at, both on the opening and closing edges.



B

 

FYI that's the main thing I was trying to tell you in my PM in the begining...I figured you didn't understand what I was saying though.

-J

 

Sweet statutory those look beautiful!

 

Thanks. I hope it helps elucidate more of what scathart's talking about.