MacDizzy's Porting 102 - To Choose To Do

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- Porting 102 -

To Choose To Do

The question - Grabowski states: The easiest porting path to increased flow is to match the piston ports to "the sleeve". I assume he's talking about the obvious mismatch that we see between the cylinder ports (bigger) and the piston ports (smaller and factory mismatched and offset). Understand here, that we are speaking of piston port side-to-side opening rather than the piston port up-and-down opening which is in the area of port timing, correct? These are the ports we can see, down into the intake and exhaust, and it sure looks like (if the "boundary" layer of the incoming charge has to slam around a "wall" created by narrow piston intake ports) that a normal person could carefully widen those ports with a Dremel tool and a small vacuum hose for pulling the grindings out. The same thing holds true for the exhaust piston port, where you want to exit as much exhaust as possible. Comments??

The response - Could you provide me with the URL to the article you're reading from, I want to be sure I understand what he's talking about before I comment fully on it. Generally speaking the holes in the pistons of reed valve 2 stroke engines are designed with longevity (and hopefully timing) in mind. The part still needs to last a long time. I know with George, since he does so much personal watercraft work that this weighs greatly on his mind. It's bad enough to be broken down somewhere - it's worse if you have to swim to shore.

I can say without seeing the piece that I would never port without the cylinder removed from the motor.

Rick

The URL of George Grabowski's is http://www.hpt.sport.com/flowrivr.htm He was specifically speaking of the motor in a Yamaha PWC and of Yamaha's use of a 650 cylinder jug on the 701. And the porting options available for that engine. That's where he states that matching the piston ports to the cylinder ports would get excellent results. It was purely our idea to widen the piston exhaust and intake ports on our little Blaster 195 cc motor while the motor was out and the head off. We figured on taping a length of 3/8 plastic tubing along side of our Dremel tool and connecting that to our Shop-vac to remove (most) of the grindings. We would then invert the motor in a kerosene bath, spin it over, spray Yamalube 2R on everything, and reassemble it. We would only be changing the side-to-side openings on two ports, exhaust and intake and on the piston only.

Flyin' Ryan

I agree 100% with Mac on the "DO NOT PORT IT WITH THE CYLINDER ON". Once you do port a cylinder, you will have small metal particles (from chunks to dust)in places that you had no idea was even possible. And I have even sprayed carb cleaner into the ports to clean them only to find that they still had a fine aluminum residue left when they dried. Imagine dumping dry flour into your mouth. That is in effect what would happen to the piston from this dust. And this may sound funny but aluminum will break down aluminum. The cylinder MUST be cleaned thoroughly and the only way to do this is to have it off so that you can scrub every last part of its surface with a toothbrush and soap and repeat 100 or so times :)

Mac is absolutely correct when he says that simply opening a port wider does not always mean more horsepower. The port may be wide enough for the tuned (timing) characteristic of the rpm/power. If you go opening wider, all you are doing is slowing the velocity of incoming charge and changing the angle at which the incoming charge has the best potential to flow. i.e: If you pull the secondary transfer sleeve window forwards toward the exhaust, you would be placing part of the port window in front of its runner which would make the charge want to flow directly towards the exhaust port. Of course if the entire runner were opened too, then this would not be the case, but then the velocity would really die out as would Primary Compression. Although, the latest and greatest research says that the more volume under the piston - the better. It all makes for a very confusing and situational thing, so just HAVE a plan before you get into it... And when you are all done, POLISH THAT CYLINDER - It'll go MUCH faster! :) Good luck,

Trax310

There are some very good books available at places like amazon.com which provide information about 2 stroke engines which you may find very valuable before you start cutting. Go there and use the words "2 Stroke Engines" to find the publications.

In case I did not make it clear before - do not grind on the ports with the cylinder installed on the engine. Vacuum may not capture all the metal pieces. It is simply too risky to do. I know you said the motor would be out, and the head off - but I did not read anywhere that it said the cylinder would be off. For the price of a base gasket - take the barrel off. Though everyone has to start somewhere if they want to learn porting, it is probably not best to do it without some sort of a plan - and hopefully some direction.

This might include a simple cylinder mapping procedure to determine the starting size of the ports - the careful measurements from the top and bottom of the barrel to each port and the width of each port using an inside caliper. Additionally using AT LEAST a degree wheel to determine where to cut to (if altering duration). I can't recommend you just go and make the ports wider to get better performance from your motor. Porting is a thing that should be done as completely as possible - considering every aspect of the engine, its intended use and the target RPM. Simply making holes bigger is a fast way to become disappointed with the result.

In the "Flow Like A River" piece George is talking about the alignment of the iron SLEEVE ports to the aluminum cylinder port/tunnels. The liner protrudes in such a way as to restrict the port flow from the port tunnel. It is common for there to be a mismatch from the iron to aluminum, but on some cylinders there is more work to be done than others. Even two identical engines will show differences in their port alignment. When speaking of correcting this it is not always the liner or always the aluminum. The motor has to be measured to find out which direction the alignment should be changed in order to produce the desired effect. Many times I have found that the liner seems to be twisted or rotated a few degrees one way or the other. This makes for a lot of "fixing."

That engine had its displacement increased a few times. It started out with a 77 mm bore (650 cc and maybe smaller before that) and is currently at an 84 mm bore(754 cc). The basic lower cases are the same. The casting of the cylinders has changed very little with the increase in bore size. When they made the bore larger, because of the upward angle of the transfer ports into the cylinder, it decreased the angle area of the transfer timing. On the exhaust side, since the port is angled downward, its timing became milder. This was compensated for - to some extent, but not completely. The 84 mm version of that engine has transfer ports that are way too small and angled incorrectly for high output.

This says something about the lower end of the motor and 2 strokes in general too. Increases in displacement by changing the bore only are usually fine with no changes to the crankcase volume - other than what is increased as the bore is made larger. The modern 2 stroke cycle bottom end is small, compact and void of pockets or space which might hide or allow mixture not be used to produce power. The case reed design is probably better at lubricating the lower bearings than the cylinder reed.

Usually when an engine design is presented and put into production there are design parameters in place for future displacement increases. Especially in the area of the bore size and sometimes in the area of stroke as well. This is very easy to notice with V-8 engines. The Ford 260 grew to 400 inches as a small block. The Chevy 283 grew to 400 inches as well (did it start smaller than 283 - I forget). The bore centers of the block allowed for future castings to have larger pistons fitted.

All out pure racing designs usually have much less growth potential because they are specifically produced to compete in a particular displacement class. This gives them the freedom the pour all the technology they have into the design, pull out the stops and produce the lightest, most compact piece they can - without having to worry about the future. Engine tuners will extract all the power they can for the type of racing they are involved in. Development stops when it has been determined that it reached its full potential. You can be sure that when that development has stopped, the designers have already produced the next generation of "state of the art." They will give the new engine to their engine tuners to develop it until it outlives its usefulness - and the process starts over again. With current technology, the speed at which information can be gathered, sorted out and introduced into a new engine is faster and more accurate than at any time before it.

Rick

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To Choose To Do
The question - Grabowski states: The easiest porting path to increased flow is to match the piston ports to "the sleeve". I assume he's talking about the obvious mismatch that we see between the cylinder ports (bigger) and the piston ports (smaller and factory mismatched and offset). Understand here, that we are speaking of piston port side-to-side opening rather than the piston port up-and-down opening which is in the area of port timing, correct? These are the ports we can see, down into the intake and exhaust, and it sure looks like (if the "boundary" layer of the incoming charge has to slam around a "wall" created by narrow piston intake ports) that a normal person could carefully widen those ports with a Dremel tool and a small vacuum hose for pulling the grindings out. The same thing holds true for the exhaust piston port, where you want to exit as much exhaust as possible. Comments??
The response - Could you provide me with the URL to the article you're reading from, I want to be sure I understand what he's talking about before I comment fully on it. Generally speaking the holes in the pistons of reed valve 2 stroke engines are designed with longevity (and hopefully timing) in mind. The part still needs to last a long time. I know with George, since he does so much personal watercraft work that this weighs greatly on his mind. It's bad enough to be broken down somewhere - it's worse if you have to swim to shore. I can say without seeing the piece that I would never port without the cylinder removed from the motor. Rick The URL of George Grabowski's is http://www.hpt.sport.com/flowrivr.htm He was specifically speaking of the motor in a Yamaha PWC and of Yamaha's use of a 650 cylinder jug on the 701. And the porting options available for that engine. That's where he states that matching the piston ports to the cylinder ports would get excellent results. It was purely our idea to widen the piston exhaust and intake ports on our little Blaster 195 cc motor while the motor was out and the head off. We figured on taping a length of 3/8 plastic tubing along side of our Dremel tool and connecting that to our Shop-vac to remove (most) of the grindings. We would then invert the motor in a kerosene bath, spin it over, spray Yamalube 2R on everything, and reassemble it. We would only be changing the side-to-side openings on two ports, exhaust and intake and on the piston only. Flyin' Ryan I agree 100% with Mac on the "DO NOT PORT IT WITH THE CYLINDER ON". Once you do port a cylinder, you will have small metal particles (from chunks to dust)in places that you had no idea was even possible. And I have even sprayed carb cleaner into the ports to clean them only to find that they still had a fine aluminum residue left when they dried. Imagine dumping dry flour into your mouth. That is in effect what would happen to the piston from this dust. And this may sound funny but aluminum will break down aluminum. The cylinder MUST be cleaned thoroughly and the only way to do this is to have it off so that you can scrub every last part of its surface with a toothbrush and soap and repeat 100 or so times :) Mac is absolutely correct when he says that simply opening a port wider does not always mean more horsepower. The port may be wide enough for the tuned (timing) characteristic of the rpm/power. If you go opening wider, all you are doing is slowing the velocity of incoming charge and changing the angle at which the incoming charge has the best potential to flow. i.e: If you pull the secondary transfer sleeve window forwards toward the exhaust, you would be placing part of the port window in front of its runner which would make the charge want to flow directly towards the exhaust port. Of course if the entire runner were opened too, then this would not be the case, but then the velocity would really die out as would Primary Compression. Although, the latest and greatest research says that the more volume under the piston - the better. It all makes for a very confusing and situational thing, so just HAVE a plan before you get into it... And when you are all done, POLISH THAT CYLINDER - It'll go MUCH faster! :) Good luck, Trax310 There are some very good books available at places like amazon.com which provide information about 2 stroke engines which you may find very valuable before you start cutting. Go there and use the words "2 Stroke Engines" to find the publications. In case I did not make it clear before - do not grind on the ports with the cylinder installed on the engine. Vacuum may not capture all the metal pieces. It is simply too risky to do. I know you said the motor would be out, and the head off - but I did not read anywhere that it said the cylinder would be off. For the price of a base gasket - take the barrel off. Though everyone has to start somewhere if they want to learn porting, it is probably not best to do it without some sort of a plan - and hopefully some direction. This might include a simple cylinder mapping procedure to determine the starting size of the ports - the careful measurements from the top and bottom of the barrel to each port and the width of each port using an inside caliper. Additionally using AT LEAST a degree wheel to determine where to cut to (if altering duration). I can't recommend you just go and make the ports wider to get better performance from your motor. Porting is a thing that should be done as completely as possible - considering every aspect of the engine, its intended use and the target RPM. Simply making holes bigger is a fast way to become disappointed with the result. In the "Flow Like A River" piece George is talking about the alignment of the iron SLEEVE ports to the aluminum cylinder port/tunnels. The liner protrudes in such a way as to restrict the port flow from the port tunnel. It is common for there to be a mismatch from the iron to aluminum, but on some cylinders there is more work to be done than others. Even two identical engines will show differences in their port alignment. When speaking of correcting this it is not always the liner or always the aluminum. The motor has to be measured to find out which direction the alignment should be changed in order to produce the desired effect. Many times I have found that the liner seems to be twisted or rotated a few degrees one way or the other. This makes for a lot of "fixing." That engine had its displacement increased a few times. It started out with a 77 mm bore (650 cc and maybe smaller before that) and is currently at an 84 mm bore(754 cc). The basic lower cases are the same. The casting of the cylinders has changed very little with the increase in bore size. When they made the bore larger, because of the upward angle of the transfer ports into the cylinder, it decreased the angle area of the transfer timing. On the exhaust side, since the port is angled downward, its timing became milder. This was compensated for - to some extent, but not completely. The 84 mm version of that engine has transfer ports that are way too small and angled incorrectly for high output. This says something about the lower end of the motor and 2 strokes in general too. Increases in displacement by changing the bore only are usually fine with no changes to the crankcase volume - other than what is increased as the bore is made larger. The modern 2 stroke cycle bottom end is small, compact and void of pockets or space which might hide or allow mixture not be used to produce power. The case reed design is probably better at lubricating the lower bearings than the cylinder reed. Usually when an engine design is presented and put into production there are design parameters in place for future displacement increases. Especially in the area of the bore size and sometimes in the area of stroke as well. This is very easy to notice with V-8 engines. The Ford 260 grew to 400 inches as a small block. The Chevy 283 grew to 400 inches as well (did it start smaller than 283 - I forget). The bore centers of the block allowed for future castings to have larger pistons fitted. All out pure racing designs usually have much less growth potential because they are specifically produced to compete in a particular displacement class. This gives them the freedom the pour all the technology they have into the design, pull out the stops and produce the lightest, most compact piece they can - without having to worry about the future. Engine tuners will extract all the power they can for the type of racing they are involved in. Development stops when it has been determined that it reached its full potential. You can be sure that when that development has stopped, the designers have already produced the next generation of "state of the art." They will give the new engine to their engine tuners to develop it until it outlives its usefulness - and the process starts over again. With current technology, the speed at which information can be gathered, sorted out and introduced into a new engine is faster and more accurate than at any time before it. Rick