I am going to be making a bridgeport 12a and i am wondering if what i am planning to cut is to big or small? I have pictures of the port i have drawn up on plexi glass on top of the stock port to show the differnce, the pictures arn't great but the show the drawing on the port, Thanks<mike

mike_rudy,Dec 20 2004, 03:05 PM



I am going to be making a bridgeport 12a and i am wondering if what i am planning to cut is to big or small? I have pictures of the port i have drawn up on plexi glass on top of the stock port to show the differnce, the pictures arn't great but the show the drawing on the port,

Thanks<mike







Well Mike, the pictures are not clear enough to make much sense of, but that closing point is right up there in to 90 degree area, and that is late, as in all out road racing, no power under 7,800 RPM best power above 9,500 RPM. No fuel economy and not enough torque to shift out of low under 6,000 RPM.



The open side looks about right. The inner side looks as though it might be into the oil scraper track just a bit. Not good.



How about this:



Ink up the port area with a magic marker. Assemble the front iron with a stationary gear.



Place a corner seal in a hole on the gear side of the front rotor, with no spring but with a sliver of paper, so that the corner seal sticks in the bottom of the hole. Bend the end of a used side seal spring up at a 90 degree angle.



This so that it will make a mark exactly where the side seal touches the corner seal. you are interested in marking the path of the leading end of the side seal in the magic marker inked area as the leading end of the seal passes by the port.



You will have to cut the spring off so that is just taller than the corner seal.



Assemble the rotor and crank and turn the crank backwards to scribe the path of the leading end of the side seal.



Flip the spring around into the groove on the other side of the corner seal and turn the crank in the opposite direction to mark the path of the trailing end of the side seal. Take the spring out and install the outer oil scraper with two springs under the ring but no "O" ring. Turn the crank through several revolutions to mark the path of the outer oil scraper.



Now you have demarcated two of the limits to port to. You cannot move the inner edge of the port under the scraper ring track. You cannot move the open side (manifold side) of the main port much past the trailing end path of the side seal.



I don't even have a stock piece of iron to measure for you. Or, I could see where it closes stock and just say move it up 3/8" or whatever.



Read the posts with the TDC locating rig and measuring closing points with a big degree wheel, to mark your closing line. Practice on a junk iron. It is suprising how close daylight is when you move the bowl North to a later closing point.

Close the bridge port in the same place. Leave the face of the bridge 1/4" wide for good wear. Leave it full thickness, and sharp edged. Just sand smooth. Radius and polish like chrome the closing line.



Go to Paul Yaws web page (www.yawpower.com) and read the tech articles and look at his ports.



Here is a port that closes at 85 degrees. Best power is above 9,400 RPM. It would be dreadfull on the street.





Lynn E. Hanover

Ok i just went out and tried that and looked at my MFR PP housings and the closed at around the same degree lol, I changed it and now its at about 73-75 degrees, and i also moved the inside line because it was a little too close to the oil seal, Thanks alot, Mike

ok well everything went fine on my porting i will have some pics up soon, one problem i had was my die grinder slipped and in one spot on one bridge it is like 1.5-2 mm think the rest is all 3-3.5mm think, is this a serious problem???? hopfully not, thanks, mike

thats a small bridge.........

I know it is small but i am wondering just if in one spot like 2 mm long on the bridge it is 1.5-2 mm wide , i am wondering if i can use that or if i should get another plate, it sucks when you are cutting out the ports on a bridge and your cat jumps on your back with full claws out

I would get a new plate. Most all of my bridges have a width of no less than .150" i would not use one that is less than 1/8". It may just be me but anything less looks unsafe

here are some pics, in the one you can see a ruler beside it showing how thin it is(kinda blury)

i don't know how thoughs first 4 pics got in there the last two are the ones i was talking about

That looks fine.







Lynn E. Hanover