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In a message dated 12/3/2007 12:21:18 AM Eastern Standard Time, philwhite9@aol.com writes:
For those who have done porting on the cast iron end housings; what
bits/stones/burrs did you use to open up the intake ports? Does it take
several types? Which for rough cuts; which for polishing up?
I'm ready to work on my 20B, and want to do a mild street port on the
intakes. I have a 'dremel' hi-speed tool, but my bit selection is down
to 1 or 2 left. What to buy??
Phil in IL RV-10 in process
I use a selection of carbide bits in cheap Chinese air powered die grinders. I have many such grinders, so I don't have to stop and change bits. There are course and fine spiral design flutes for rough and finish work. Then I use sand paper rolls on short mandrals.
Most hot rod shops have porting packages with all of this material.
Read all of the tech articals on Paul Yaws web site WWW.Yawpower.com. Determine the
opening and closing points you want. Make a poster board mask of one set of ports. Set it asside.
Grind up a junk piece of iron to what you want the open and closing points to be. Lay on the mask, keyed with two of the case dowels. Copy the port by tapping gently around the edges of the port hole with a ball-pien hammer. Lay down three layers of duct tape all round each port. Go out from the port about 3 inches. This is to protect the irons when the grinder slips and the bit dances across the iron.
Do not unsupport the leading end of the side seal when increasing open timing.
Do.....raise the outer end of the closing line, so that the side seal comes back onto the iron from inside to outside. The side seals droop into the port a bit at idle and when the intake open point is moved, the trailing end is unsupported at the closing line.
Do....radius and polish the closing line to a chrome like finish. The side seals will love you.
Bernouli will love you...........
To establish where the open and close lines need to be. The call outs are from known locations like TDC and BDC. To determine where such things might be on a piece of bare iron, you need to pick an iron that has a stationary gear feature. Assemble that and a crank and a rotor. I use a rotor with a big wedge cut out of one corner so I can see the seal tracks while I grind. This is a big help.
You need a big (there is no such thing as too big) degree wheel. Like 11 or 12 inches or bigger. A modified flywheel nut, so you can move the wheel about and then clamp it to the crank so as not to move again. A rigid pointer that can bolt to the iron.
A piece of aluminum angle stock with a pivot point on one end you can clamp to the iron.
A magnetic base dial indicator. These parts ar used to establish TDC inside of one degree.
Then you can move the wheel to (say) 85 degrees after BDC and draw your closing line.
You soon discover the two BDCs and the two TDCs in this engine, and your mind may fog over for a while. But like riding a bicycle, it will come to you and you will be free for the first time..........
On the NoPistons list in the porting area there are pictures of many port jobs. Some of my stuff is there as well as a picture of my TDC rig.
Make little changes. Increasing runner and bowl volume reduces velocity. The bigger you make things the lower the torque at low speeds. Like off idle to 2000 RPM. The ports you may see in racing may have very poor low speed performance. My bridge ports work great from 7,500 RPM to 9,600 RPM with peak power (244.8 HP) at 9,400 RPM. Seal life is short at those speeds. However, my 12A has 170 HP at 6,500. We just cannot use it there.
Generally the longer the port open time, the more sensitive the engine becomes to exhaust system design and back pressure. You could put a perfectly ported engine with 350 HP into a plane with a homoginizing muffler and end up with under 300 HP, and endless tuning problems. If you cannot get it out, don't bother puting it in. For exhaust porting, where header and muffler design (in just about every case so far) is less than ideal, I would stay very close to stock timing. Just a nice radius on the open and close lines and polish like chrome. If you have those wedges in the liners, leave them there. Your muffler will last longer. Flow along the floor of the port is supersonic, and a polished surface perks things up nicely.
These engines tune exactly like piston port 2 cycle dirt bike engines. With the added feature that they displace so much per revolution, that you can missadjust intake lengths and exhaust lengths and sizes, and still produce an impressive amount of power.
The current E production 2 rotor engines ( limited to street porting) produce about 250 HP at 10,500 RPM. On the SCCA web site there are pictures of legal street ports. Where the junction of the side seal end and the corner seal may not be exposed in the port.
I am trying to get the new Florida house into shape, and my pictures and data are still in Hebron Ohio. I should have brought both computers down here.
If you are close to central Florida I can drive over and lay one out for you.
Lynn E. Hanover
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