Gas props on nitro rigger

[Michael Costanzo]

mb .40

dam those pylon guys get all the good stuff! h34r:

 

[BigChuck]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

 

[John Finch]

Interesting reading. Some good stuff. Let me speak from someone who has driven the IMPBA course at over 100 mph. A little over two seconds to go from buoy 6 to buoy one. Two seconds through the corners. A bit over two seconds down the back straightaway, and another two seconds around buoy 4.5. and 6. How in the world would you heat race a boat like that. Think about it. When Kentley and I did the f record the boat was clocked at 103 going into buoy one with a stalker radar gun and 98 miles per hour coming out of the corner on buoy 6. You can't race a boat that fast! When you straighten up at buoy 6 you will be at buoy one in two seconds. How would you not run over another boat! I set up a heat racing boat about 8 years ago for the very reason of going to the internats to do ovals, run over 100 on saw and heat race. The boat did 107 at a SAW event with a 2160 stock diameter, and would heat race with a 1667. Never made it to the nats, but I would not even attempt to say the boat could be heat raced at anything over 85 mph. One ripple and the boat is an air ship at those speeds.

 

[dwilfong]

Interesting reading. Some good stuff. Let me speak from someone who has driven the IMPBA course at over 100 mph. A little over two seconds to go from buoy 6 to buoy one. Two seconds through the corners. A bit over two seconds down the back straightaway, and another two seconds around buoy 4.5. and 6. How in the world would you heat race a boat like that. Think about it. When Kentley and I did the f record the boat was clocked at 103 going into buoy one with a stalker radar gun and 98 miles per hour coming out of the corner on buoy 6. You can't race a boat that fast! When you straighten up at buoy 6 you will be at buoy one in two seconds. How would you not run over another boat! I set up a heat racing boat about 8 years ago for the very reason of going to the internats to do ovals, run over 100 on saw and heat race. The boat did 107 at a SAW event with a 2160 stock diameter, and would heat race with a 1667. Never made it to the nats, but I would not even attempt to say the boat could be heat raced at anything over 85 mph. One ripple and the boat is an air ship at those speeds.

John

I here what you are saying. IF I can get this speed out of the boat dose not mean I have to use it all the time BUT it would be nice to be able to pull the trigger when I need it.

The boat was tested in 10- 15 MPH wind and about 3" of cross rip last weekend and it never flipped out. got some air a few times.

But it flies real nice. there is no rudder input used to keep the boat strait so far. Set the ruder with a strait edge and never had to trim it.

So far prop walk has not bin a problem. Will see how it progresses as testing continues.

Just because you have it dose not mean you have to use it.

David

 

[Jim Allen]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

Well, if you can understand that, consider the following. Dyno test show that a domed piston, combined with a matching squish band, upward radiused transfers & a radiused piston top edge, produce the most HP at High RPMs. When comparing transfers that are cut straight in, with a sharp edge piston, to those that are cut at an upward angle, the angled transfers always will have less area. However, the incomming streams created from the angled stuff do not collide violently in the middle of the cylinder & there will be an initial upward movement of the streams after they collide. This type of flow will follow the piston crown, reducing turbulence while cooling the piston crown, which is absolutely necessary to enable efficient cooling of the piston.

When looking at the radius on the piston edge, consider the following. As any transfer or exhaust port is opened, the piston becomes the inside edge of that port until BDC is reached. Sharp edged opening points create turbulence that will be proportional to the pistons speed. That turbulence causes loss of pressure in the flows & lost HP. Take a close look at the bottom edge of ports on some manufactured engines. Why should the bottom edge of any port be below the pistons top edge at BDC? It is probably done to enable easier cutting of the transfer windows. IT DOES NOT IMPROVE THE FLOW OR THE HP!!

Jim Allen

 

[dwilfong]

Jim you have enlightened me as always. How much time dose the piston reside at BDC in the time of its travel in the window. also when dose the port velocity reach its maximum. these are questions I ask my self. also how much dose the pipe reduce cly pressure when ex port is open. this would help with the pressure difference in the cylinder and change velocity in the intake ports. It would take one hell of a simulator to calculate all this.

Some times you have to use the simulator you are given a birth and go with your instincts.

The information you have given is a great and very informative please keep it coming.

I will not sleep for days now. :lol:

David

 

[John Finch]

David,

I have found that when you get to the 90 to 100 mph range that less rudder correction is needed than in the 70 to 80 mph range. I can only conclude that has something to do with more water pressure on the rudder at higher speeds or the front sponsons are aired out more.

Jim can definitely give you a large amount to think about when it comes to engines. Good stuff! I wish I had more time to get on the web.

John

 

[dwilfong]

David,

I have found that when you get to the 90 to 100 mph range that less rudder correction is needed than in the 70 to 80 mph range. I can only conclude that has something to do with more water pressure on the rudder at higher speeds or the front sponsons are aired out more.

Jim can definitely give you a large amount to think about when it comes to engines. Good stuff! I wish I had more time to get on the web.

John

John thanks for your input. I will need all the info I can get to make this work out.

Love to here form as many as I can. Different point of view help in making a good decision.

David

 

[Jim Allen]

Jim you have enlightened me as always. How much time dose the piston reside at BDC in the time of its travel in the window. also when dose the port velocity reach its maximum. these are questions I ask my self. also how much dose the pipe reduce cly pressure when ex port is open. this would help with the pressure difference in the cylinder and change velocity in the intake ports. It would take one hell of a simulator to calculate all this. Some times you have to use the simulator you are given a birth and go with your instincts. The information you have given is a great and very informative please keep it coming. I will not sleep for days now. :lol: David

The development of advanced simulator programs, CFD (computational fluid dymamics) programs, flow benches, dynamometers & metallurgy has made continued two cycle engine development possible. All the features of what appears to be a very simple engine design can be analyzed before any metal is cut. The information is available in SAE papers, on technical web sites & any good engineering library. The application of this information is up to the engine builder.

It is possible for model engine users to greatly improve their engines without the benefit of the previously mentioned high tech tools. For example, understanding how to calculate any engines exact timing numbers does not require, & should not require the use of a degree wheel. Basic trigonometry or an accurate drawing on .100 grid graph paper, drawn at a 10 to 1 scale, will tell you where to cut any liner to make whatever timming is desired. All you need to know is the stroke of the engine, the connecting rod holes center distance & the distance from wrist pin center hole to the top of the piston crown. A machinist scale will give you the correct answer by direct measurement & since the number will be divide by 10 the results will be very accurate.

There is enough dyno tested information on the web about tuned pipes to make the following observations. The material selected for the construction of whatever pipe will greatly effect its performance. Aluminum is the worst material to be used followed by mild steel, stainless steel & titanium. Coatings & various wraps will help with materials that have high thermal conductivity. Poor exhaust duct design & head pipe design cannot be erased with a good pipe design. Both the exhaust duct in the engine & the head pipe must be tappered. Straight head pipes, even those made with larger diameters will always result in decreased HP. Tuned pipe volumes when compared to the engines displacement should be at least 32 times greater. Stinger lengths should be 13 times the stingers inside diameter to be effective.

Jim Allen

 

[Charles Perdue]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

Well, if you can understand that, consider the following. Dyno test show that a domed piston, combined with a matching squish band, upward radiused transfers & a radiused piston top edge, produce the most HP at High RPMs. When comparing transfers that are cut straight in, with a sharp edge piston, to those that are cut at an upward angle, the angled transfers always will have less area. However, the incomming streams created from the angled stuff do not collide violently in the middle of the cylinder & there will be an initial upward movement of the streams after they collide. This type of flow will follow the piston crown, reducing turbulence while cooling the piston crown, which is absolutely necessary to enable efficient cooling of the piston.

When looking at the radius on the piston edge, consider the following. As any transfer or exhaust port is opened, the piston becomes the inside edge of that port until BDC is reached. Sharp edged opening points create turbulence that will be proportional to the pistons speed. That turbulence causes loss of pressure in the flows & lost HP. Take a close look at the bottom edge of ports on some manufactured engines. Why should the bottom edge of any port be below the pistons top edge at BDC? It is probably done to enable easier cutting of the transfer windows. IT DOES NOT IMPROVE THE FLOW OR THE HP!!

Jim Allen

Mr. Allen, what size radius are you talking about on the edge of the piston? A radius should affect the piston/port timing. Do you still calculate the timing #'s from the top of the piston, the bottom of the radius or somewhere in between? How much affect does leaving some of the unburned fuel in the crevice formed by the radius of the piston to the cylinder wall or do you machine a lip on the squish band of the head to fill this crevice?

Charles

 

[Jim Allen]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

Well, if you can understand that, consider the following. Dyno test show that a domed piston, combined with a matching squish band, upward radiused transfers & a radiused piston top edge, produce the most HP at High RPMs. When comparing transfers that are cut straight in, with a sharp edge piston, to those that are cut at an upward angle, the angled transfers always will have less area. However, the incomming streams created from the angled stuff do not collide violently in the middle of the cylinder & there will be an initial upward movement of the streams after they collide. This type of flow will follow the piston crown, reducing turbulence while cooling the piston crown, which is absolutely necessary to enable efficient cooling of the piston.

When looking at the radius on the piston edge, consider the following. As any transfer or exhaust port is opened, the piston becomes the inside edge of that port until BDC is reached. Sharp edged opening points create turbulence that will be proportional to the pistons speed. That turbulence causes loss of pressure in the flows & lost HP. Take a close look at the bottom edge of ports on some manufactured engines. Why should the bottom edge of any port be below the pistons top edge at BDC? It is probably done to enable easier cutting of the transfer windows. IT DOES NOT IMPROVE THE FLOW OR THE HP!!

Jim Allen

Mr. Allen, what size radius are you talking about on the edge of the piston? A radius should affect the piston/port timing. Do you still calculate the timing #'s from the top of the piston, the bottom of the radius or somewhere in between? How much affect does leaving some of the unburned fuel in the crevice formed by the radius of the piston to the cylinder wall or do you machine a lip on the squish band of the head to fill this crevice?

Charles

Great question. The radius that I use in a 26 cc engine is .0469" & the radius that I use in a 15 cc engine is .0312". What happens as a result of this according to pulsed flow bench studies is the initial pulse happens at a latter time than when compared to sharp edges, but it is of greater intensity & duration, because there is less turbulence. This penomenon is sometimes explained as acting like a De Laval nozzle.

When & if you can get the engines ports geometry correct as well as the head design, you will be able close the squish band until it just touches the piston crown at TDC during maxium RPMs. This is necessary to tumble the burning gasses which speeds up the combustion process. A functioning squish with a high squish velocity increases flame speed, creates high turbulence, reduces detonation & allows more combustion gasses to burn faster. Forget about the crevice, it has no adverse effect. Remember that the squish band is 50% of the bores area & if it is not working the engine will not make high amounts of HP.

As a timing example, take a liner with a wall thickness of .100". Lets cut an exhaust window at a 15 deg angle top & bottom to give 184 deg timing. The inside of the exhaust will be .027" higher than the outside at the 15 deg angle. In the middle of this exhaust, over a distance of 2/3 of the total width cut a 33 deg 49 minute angle. Cut this from the same point as the 184 deg exhaust. This should give an exhaust timing of 194 deg, if the math is correct, in this area. Of course this exhaust has its top edge cut in a straight line & its width is 80% of the bores ID. Many dyno studies have shown that oval shapped exhaust tops reduce the blowdown time area number. They may increase out flow but will decrease inflow.

In the above example, after applying the radius, I do not know the exact timming, but it probably is approaching 200 deg. I don't care what the actual geometric timming number is but I do care how much I can increase the flow without turbulence losses.

Jim Allen

 

[dwilfong]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

Well, if you can understand that, consider the following. Dyno test show that a domed piston, combined with a matching squish band, upward radiused transfers & a radiused piston top edge, produce the most HP at High RPMs. When comparing transfers that are cut straight in, with a sharp edge piston, to those that are cut at an upward angle, the angled transfers always will have less area. However, the incomming streams created from the angled stuff do not collide violently in the middle of the cylinder & there will be an initial upward movement of the streams after they collide. This type of flow will follow the piston crown, reducing turbulence while cooling the piston crown, which is absolutely necessary to enable efficient cooling of the piston.

When looking at the radius on the piston edge, consider the following. As any transfer or exhaust port is opened, the piston becomes the inside edge of that port until BDC is reached. Sharp edged opening points create turbulence that will be proportional to the pistons speed. That turbulence causes loss of pressure in the flows & lost HP. Take a close look at the bottom edge of ports on some manufactured engines. Why should the bottom edge of any port be below the pistons top edge at BDC? It is probably done to enable easier cutting of the transfer windows. IT DOES NOT IMPROVE THE FLOW OR THE HP!!

Jim Allen

Mr. Allen, what size radius are you talking about on the edge of the piston? A radius should affect the piston/port timing. Do you still calculate the timing #'s from the top of the piston, the bottom of the radius or somewhere in between? How much affect does leaving some of the unburned fuel in the crevice formed by the radius of the piston to the cylinder wall or do you machine a lip on the squish band of the head to fill this crevice?

Charles

Great question. The radius that I use in a 26 cc engine is .0469" & the radius that I use in a 15 cc engine is .0312". What happens as a result of this according to pulsed flow bench studies is the initial pulse happens at a latter time than when compared to sharp edges, but it is of greater intensity & duration, because there is less turbulence. This penomenon is sometimes explained as acting like a De Laval nozzle.

When & if you can get the engines ports geometry correct as well as the head design, you will be able close the squish band until it just touches the piston crown at TDC during maxium RPMs. This is necessary to tumble the burning gasses which speeds up the combustion process. A functioning squish with a high squish velocity increases flame speed, creates high turbulence, reduces detonation & allows more combustion gasses to burn faster. Forget about the crevice, it has no adverse effect. Remember that the squish band is 50% of the bores area & if it is not working the engine will not make high amounts of HP.

As a timing example, take a liner with a wall thickness of .100". Lets cut an exhaust window at a 15 deg angle top & bottom to give 184 deg timing. The inside of the exhaust will be .027" higher than the outside at the 15 deg angle. In the middle of this exhaust, over a distance of 2/3 of the total width cut a 33 deg 49 minute angle. Cut this from the same point as the 184 deg exhaust. This should give an exhaust timing of 194 deg, if the math is correct, in this area. Of course this exhaust has its top edge cut in a straight line & its width is 80% of the bores ID. Many dyno studies have shown that oval shapped exhaust tops reduce the blowdown time area number. They may increase out flow but will decrease inflow.

In the above example, after applying the radius, I do not know the exact tomming, but it probably is approaching 200 deg. I don't care what the actual geometric tomming number is but I do care how much I can increase the flow without turbulence losses.

Jim Allen

Jim

So using different angles in the ex roof is the same idea some do with the top hat cut. but the way you do it keeps the window the same hight at the out side of the liner with a strait line. Very interesting. as far as the with of the port at the top. 80% of the bore? all this with should only go down as far as the top of the transfers then narrow to get the timed area right to 30% of the boost and transfer area numbers?

 

[Jim Allen]

Thats correct. Compare an exhaust that is oval shaped at the top with one that is flat across the top & it can easily been seen which one has the greater time area number in the blowdown area. You will definitely want this if the tuned pipe is really doing its job.

 

[dwilfong]

Thats correct. Compare an exhaust that is oval shaped at the top with one that is flat across the top & it can easily been seen which one has the greater time area number in the blow down area. You will definitely want this if the tuned pipe is really doing its job.

I do make the top of the ex flat but the different angle sounds real nice. I was always on the mind set that the ex should come out all at once to get that high pressure wave moving all in one shot.

So 80% of the timed area should be the number of the wide area that is above the transfers and the the rest of the window should make up the rest?

With a total area of the ex to be 30% of the combined transfer and boost area?

Just got my new mill set up to day will mess with some old sleeves and do some test cutting.

The bottom of radius on the piston should line up with the bottom of the ports. what kind of transition to the transfers would work best.

Should the sleeve be a sharp edge on the OD or should this be a transition radius? then again the piston dose not spend much time at the bottom.

 

[dwilfong]

Here are some pics of the Eagletree V4 installation .

I have it set to show MAX RPM and MAX MPH on the screen. It will reset after the power is turned off.

The cable for the USB hookup will be accessed thew the hole with tape on it to keep it dry.

This way I can read the runs and make a file for each run I want to keep on the PC at the pond.

Can review each run and see what the RPM and speed are at any point on the course.

This will tell what the load on the eng is and how good the prop is working at any point on the course.

This is what I use to tune my mono old 666. It is a very fast 40 mono! hence the name 666 runs like a boat possessed.

 

[Tom Foley]

You ready for the Rumble ?? !! Keep up the good work David !!

 

[Terry Keeley]

Here are some pics of the Eagletree V4 insulation .

I have it set to show MAX RPM and MAX MPH on the screen. It will reset after the power is turned off.

The cable for the USB hookup will be accessed thew the hole with tape on it to keep it dry.

This way I can read the runs and make a file for each run I want to keep on the PC at the pond.

Can review each run and see what the RPM and speed are at any point on the course.

This will tell what the load on the eng is and how good the prop is working at any point on the course.

This is what I use to tune my mono old 666. It is a very fast 40 mono! hence the name 666 runs like a boat possessed.

You're gonna like the Eagle Tree, best tuning tool I've ever used.

 

[dwilfong]

You ready for the Rumble ?? !! Keep up the good work David !!

Brutus will be ready to rumble!!!

Just don't know if I will be ready to control the beast?. :unsure:

Thanks Tom

 

[Jim Allen]

Thats correct. Compare an exhaust that is oval shaped at the top with one that is flat across the top & it can easily been seen which one has the greater time area number in the blow down area. You will definitely want this if the tuned pipe is really doing its job.

I do make the top of the ex flat but the different angle sounds real nice. I was always on the mind set that the ex should come out all at once to get that high pressure wave moving all in one shot.

So 80% of the timed area should be the number of the wide area that is above the transfers and the the rest of the window should make up the rest?

With a total area of the ex to be 30% of the combined transfer and boost area?

Just got my new mill set up to day will mess with some old sleeves and do some test cutting.

The bottom of radius on the piston should line up with the bottom of the ports. what kind of transition to the transfers would work best.

Should the sleeve be a sharp edge on the OD or should this be a transition radius? then again the piston dose not spend much time at the bottom.

I think we have a little misunderstanding here. The 80% number shows the relatonship between the exhaust width at its widest point & the engine bore diameter. For example; a K-90 has an exhaust width of .895" & a bore of 1.0635", which equals 84%; OS MAX .91 has a .902" wide exhaust & a bore of 1.090" which gives 83%; CMB .90 has a .968" wide exhaust & a bore of 1.102" which gives 88%; Rossi 1.05 has a 1.096" wide exhaust & a bore of 1.1425" which gives 96%. Whats interesting here is that some of the most powerful piped engines such as K & B .40 & .82, Nelson .45 & Picco hydro .90 have exhaust widths that do not exceed 75%.

Could excessive exhaust width & poor exhaust port shape coupled with poor transfer geometry restrict the main transfer areas & cause HP killing short circuiting? Dyno testing says the answer is a definite yes!!

The radius is applied to the top edge of the piston only.

Jim Allen

 

[Charles Perdue]

Thank you Mr. Allen. .......I understood all of that!!! The light bulb got brighter!!!!

Well, if you can understand that, consider the following. Dyno test show that a domed piston, combined with a matching squish band, upward radiused transfers & a radiused piston top edge, produce the most HP at High RPMs. When comparing transfers that are cut straight in, with a sharp edge piston, to those that are cut at an upward angle, the angled transfers always will have less area. However, the incomming streams created from the angled stuff do not collide violently in the middle of the cylinder & there will be an initial upward movement of the streams after they collide. This type of flow will follow the piston crown, reducing turbulence while cooling the piston crown, which is absolutely necessary to enable efficient cooling of the piston.

When looking at the radius on the piston edge, consider the following. As any transfer or exhaust port is opened, the piston becomes the inside edge of that port until BDC is reached. Sharp edged opening points create turbulence that will be proportional to the pistons speed. That turbulence causes loss of pressure in the flows & lost HP. Take a close look at the bottom edge of ports on some manufactured engines. Why should the bottom edge of any port be below the pistons top edge at BDC? It is probably done to enable easier cutting of the transfer windows. IT DOES NOT IMPROVE THE FLOW OR THE HP!!

Jim Allen

Mr. Allen, what size radius are you talking about on the edge of the piston? A radius should affect the piston/port timing. Do you still calculate the timing #'s from the top of the piston, the bottom of the radius or somewhere in between? How much affect does leaving some of the unburned fuel in the crevice formed by the radius of the piston to the cylinder wall or do you machine a lip on the squish band of the head to fill this crevice?

Charles

Great question. The radius that I use in a 26 cc engine is .0469" & the radius that I use in a 15 cc engine is .0312". What happens as a result of this according to pulsed flow bench studies is the initial pulse happens at a latter time than when compared to sharp edges, but it is of greater intensity & duration, because there is less turbulence. This penomenon is sometimes explained as acting like a De Laval nozzle.

When & if you can get the engines ports geometry correct as well as the head design, you will be able close the squish band until it just touches the piston crown at TDC during maxium RPMs. This is necessary to tumble the burning gasses which speeds up the combustion process. A functioning squish with a high squish velocity increases flame speed, creates high turbulence, reduces detonation & allows more combustion gasses to burn faster. Forget about the crevice, it has no adverse effect. Remember that the squish band is 50% of the bores area & if it is not working the engine will not make high amounts of HP.

As a timing example, take a liner with a wall thickness of .100". Lets cut an exhaust window at a 15 deg angle top & bottom to give 184 deg timing. The inside of the exhaust will be .027" higher than the outside at the 15 deg angle. In the middle of this exhaust, over a distance of 2/3 of the total width cut a 33 deg 49 minute angle. Cut this from the same point as the 184 deg exhaust. This should give an exhaust timing of 194 deg, if the math is correct, in this area. Of course this exhaust has its top edge cut in a straight line & its width is 80% of the bores ID. Many dyno studies have shown that oval shapped exhaust tops reduce the blowdown time area number. They may increase out flow but will decrease inflow.

In the above example, after applying the radius, I do not know the exact timming, but it probably is approaching 200 deg. I don't care what the actual geometric timming number is but I do care how much I can increase the flow without turbulence losses.

Jim Allen

Thanks Mr. Jim. Just one more question....will you build me an engine for christmas, I will not tell anyone.

Charles