CMB101RS Head Vol & clearance

[dwilfong]

Ian

My experience is not that vast with every thing yet still learning.

There are many things that change a setup and no two are the same. I could not give advice to your specific set up as I think it would be the same for any one else.

The same eng in two boats will not run the same. If you set up for RPM or if you set up for power the eng will be different. You have to decide where you will run it and base the prop choice off this. The load on the eng will change with prop load. Run less load at high RPM or more load at lower RPM. This is the choice that needs to be made. You cant have it both ways. Every boat will react different. Make a plan and stick with it.

You can run in circles real easy believe me I know.

That is the problem with giving advice on head design. You really need to know what RPM the eng is running with the set up. With out that it is all just conjecture.

The best thing you can do is get a data logger. It will make all the difference in tuning the boat. Knowing the RPM at MPH will tell you every thing you need to know.

It will be the best $300 investment you will ever make.

David

David,

I have previously calculated MSV but didn't go anywhere with it because it gave me a number, but I don't know what a good number will be. This is why I am interested in the origin of the 70-76 MPS figures and the effects of running figures different to this. Also there is the question of what RPM to calculate at, and the effect of doing that, ie should the MSV be calculated at peak torque (peak tuned pipe resonance), peak power or (if different) peak rpm? Without changing the head setup at all I have significantly increased the rev range on my 101 (with a different pipe setup and smaller props) without noticing anything different with detonation or the like, the MSV would have increased in that situation.

Also as I understand it the squish band adds to the heating of the mixture somewhat, so surely would inter-relate with the compression ratio in determining when detonation occurs? Does the 'good' range of MSV change with compression ratio and other factors like nitro %?

I may not be calculating MSV correctly, any chance of getting some data so that I can check I am working it out the same way?

I ran a logging tacho in a 90 mono about 10 years ago, it wasnt life changing. It did give some interesting readings, but after a while it broke down and it wasnt so useful that I needed to replace it. Since then I have an EagleTree logger but havent fitted it.

With the brass head buttons, Dave Marles has suggested the benefit of these is less damage from detonation, but if you are running hydros with lower compression (to not limit the top end revs too much) the deto wouldnt be a problem? Unless you are getting to the point of deto thru stinger size and cooling restriction?

Thank you.

Ian.

Ian

I am just starting to log and create files of my runs withe my eagle tree. Bin at it for about 6 month now. I am still messing with what info to log so far I use the GPS to get speed and I am in the process of over laying the runs on Goggle earth so I can see where on the course the info was collected. RPM and also head temp. Have bin messing with a ex gas probe but have just started to get info. It takes time to gather the info and study it then make changes and try again. But if you don't know RPM MPH eng temp ex gas temp how do you know what did what. You are just guessing.

As far as the MSV numbers. There is a lot of different feelings on if it matters or not. From what I have read and bin told 69-77 seems to work the best. As far as why pick a theory and go with it. From the source I go with it has bin checked on Dino runs and many years of experience.

If you can calculate MSV just input different RPM figures and see how much it changes. Decide what RPM range you will run in. Say 3000 RPM spreed and stay within the 69-77 change comp ratio and see what it changes change squash and see what changes. The tighter you make the squash the better more heat transfer.One source said he runs at .008 on his large engs and his boats are fast.

I think that the chamber shape means just as much as any thing. I had a theory of what shape to use and when making the new buttons the design I was handed was what I was thinking. All I can say is do some searching on the web for chamber design and do some home work.

I spent most of my effort on my 45RS but have a 91RS on the way to mess with. To this point detonation was just some thing I put up with. Only had stock buttons to mess with and that limits what you can do.

I think you answered your own question on lower compression in a hydro. I think there is a point that to much compression with high nitro will detonate no mater what you do. So if you push the limit and try to find the knife edge it will be much harder to tune and around and around you go. Settling on a lower compression will make tuning much easer and limit detonation witch result in more revs.

The problem with asking for a certain number is their is not one that will be the golden bullet. Like you said pipe ex temp nitro content prop load all change this number.Ex duration needs to be the first thing you set.and work from there.

I am in no way an expert in this field but laying out a plan and fallowing it one step at a time will get the best result.

David

 

[dwilfong]

Ian

My experience is not that vast with every thing yet still learning.

There are many things that change a setup and no two are the same. I could not give advice to your specific set up as I think it would be the same for any one else.

The same eng in two boats will not run the same. If you set up for RPM or if you set up for power the eng will be different. You have to decide where you will run it and base the prop choice off this. The load on the eng will change with prop load. Run less load at high RPM or more load at lower RPM. This is the choice that needs to be made. You cant have it both ways. Every boat will react different. Make a plan and stick with it.

You can run in circles real easy believe me I know.

That is the problem with giving advice on head design. You really need to know what RPM the eng is running with the set up. With out that it is all just conjecture.

The best thing you can do is get a data logger. It will make all the difference in tuning the boat. Knowing the RPM at MPH will tell you every thing you need to know.

It will be the best $300 investment you will ever make.

David

David,

I have previously calculated MSV but didn't go anywhere with it because it gave me a number, but I don't know what a good number will be. This is why I am interested in the origin of the 70-76 MPS figures and the effects of running figures different to this. Also there is the question of what RPM to calculate at, and the effect of doing that, ie should the MSV be calculated at peak torque (peak tuned pipe resonance), peak power or (if different) peak rpm? Without changing the head setup at all I have significantly increased the rev range on my 101 (with a different pipe setup and smaller props) without noticing anything different with detonation or the like, the MSV would have increased in that situation.

Also as I understand it the squish band adds to the heating of the mixture somewhat, so surely would inter-relate with the compression ratio in determining when detonation occurs? Does the 'good' range of MSV change with compression ratio and other factors like nitro %?

I may not be calculating MSV correctly, any chance of getting some data so that I can check I am working it out the same way?

I ran a logging tacho in a 90 mono about 10 years ago, it wasnt life changing. It did give some interesting readings, but after a while it broke down and it wasnt so useful that I needed to replace it. Since then I have an EagleTree logger but havent fitted it.

With the brass head buttons, Dave Marles has suggested the benefit of these is less damage from detonation, but if you are running hydros with lower compression (to not limit the top end revs too much) the deto wouldnt be a problem? Unless you are getting to the point of deto thru stinger size and cooling restriction?

Thank you.

Ian.

Ian

I am just starting to log and create files of my runs withe my eagle tree. Bin at it for about 6 month now. I am still messing with what info to log so far I use the GPS to get speed and I am in the process of over laying the runs on Goggle earth so I can see where on the course the info was collected. RPM and also head temp. Have bin messing with a ex gas probe but have just started to get info. It takes time to gather the info and study it then make changes and try again. But if you don't know RPM MPH eng temp ex gas temp how do you know what did what. You are just guessing.

As far as the MSV numbers. There is a lot of different feelings on if it matters or not. From what I have read and bin told 69-77 seems to work the best. As far as why pick a theory and go with it. From the source I go with it has bin checked on Dino runs and many years of experience.

If you can calculate MSV just input different RPM figures and see how much it changes. Decide what RPM range you will run in. Say 3000 RPM spreed and stay within the 69-77 change comp ratio and see what it changes change squash and see what changes. The tighter you make the squash the better more heat transfer.One source said he runs at .008 on his large engs and his boats are fast.

I think that the chamber shape means just as much as any thing. I had a theory of what shape to use and when making the new buttons the design I was haded was what I was thinking. All I can say is do some searching on the web for chamber design and do some home work.

I spent most of my effort on my 45RS but have a 91RS on the way to mess with. To this point detonation was just some thing I put up with. Only had stock buttons to mess with and that limits what you can do.

I think you answered your own question on lower compression in a hydro. I think there is a point that to much compression with high nitro will detonate no mater what you do. So if you push the limit and try to find the knife edge it will be much harder to tune and around and around you go. Settling on a lower compression will make tuning much easer and limit detonation witch result in more revs.

The problem with asking for a certain number is their is not one that will be the golden bullet. Like you said pipe ex temp nitro content prop load all change this number.Ex duration needs to be the first thing you set.and work from there.

I am in no way an expert in this field but laying out a plan and fallowing it one step at a time will get the best result.

David

P.S. Think of the piston as a bullet and the chamber as a gun barrel. What will shoot farther a 270 Weatherby or a blunder bust.

 

[DickJones]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

 

[dwilfong]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

Dick

Thanks for the info.

I was hoping the Weatherby -Blunder bust analogy would stir your interest.

What our your thoughts on MSV?

David

 

[Ian Inverarity]

Ian

I am just starting to log and create files of my runs withe my eagle tree. Bin at it for about 6 month now. I am still messing with what info to log so far I use the GPS to get speed and I am in the process of over laying the runs on Goggle earth so I can see where on the course the info was collected. RPM and also head temp. Have bin messing with a ex gas probe but have just started to get info. It takes time to gather the info and study it then make changes and try again. But if you don't know RPM MPH eng temp ex gas temp how do you know what did what. You are just guessing.

As far as the MSV numbers. There is a lot of different feelings on if it matters or not. From what I have read and bin told 69-77 seems to work the best. As far as why pick a theory and go with it. From the source I go with it has bin checked on Dino runs and many years of experience.

If you can calculate MSV just input different RPM figures and see how much it changes. Decide what RPM range you will run in. Say 3000 RPM spreed and stay within the 69-77 change comp ratio and see what it changes change squash and see what changes. The tighter you make the squash the better more heat transfer.One source said he runs at .008 on his large engs and his boats are fast.

I think that the chamber shape means just as much as any thing. I had a theory of what shape to use and when making the new buttons the design I was handed was what I was thinking. All I can say is do some searching on the web for chamber design and do some home work.

I spent most of my effort on my 45RS but have a 91RS on the way to mess with. To this point detonation was just some thing I put up with. Only had stock buttons to mess with and that limits what you can do.

I think you answered your own question on lower compression in a hydro. I think there is a point that to much compression with high nitro will detonate no mater what you do. So if you push the limit and try to find the knife edge it will be much harder to tune and around and around you go. Settling on a lower compression will make tuning much easer and limit detonation witch result in more revs.

The problem with asking for a certain number is their is not one that will be the golden bullet. Like you said pipe ex temp nitro content prop load all change this number.Ex duration needs to be the first thing you set.and work from there.

I am in no way an expert in this field but laying out a plan and fallowing it one step at a time will get the best result.

David

David,

So have you experimented with MSV specifically? What did you find if the MSV numbers were lower or higher than the 69-77MPS range? When you say "69-77 seems to work the best", best in what way?

I have been playing with making head buttons for probably about 12 years and certainly would not say I have found what is best, but I have done a bit of research and am happy with the results I am getting with some of the designs I have trying recently. The more I have researched the more I have found it is hard to experiment with changing only one variable, a change affects other aspects of the design which can muddy the experiments. Trying to separate MSV in testing from the effects of other geometry changes may be quite hard, so what may appear to give a good result may be the product of other changes?

Ian.

 

[Ian Inverarity]

P.S. Think of the piston as a bullet and the chamber as a gun barrel. What will shoot farther a 270 Weatherby or a blunder bust.

Sorry, I dont get this reference, I am not into firearms?

Ian.

 

[Jack ODonnell]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

Dick; You hit the nail on the head with the piston seal being #1. Jack.

 

[DickJones]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

Dick

Thanks for the info.

I was hoping the Weatherby -Blunder bust analogy would stir your interest.

What our your thoughts on MSV?

David

David

I believe the "MSV" is alot of fun to work with however if U take 10 different motors, of the same size and include different manufacturers,

set them all up with the same MSV numbers, put them in the same boat with the same set up, prop, fuel, pipe and length, carb, maybe 2 of the engines might run very close however the other 8 would be all over the place in performance. If U just rely on a set of nubers to shoot for and forget about all of the variables in previous post what then? Were the "nubers" wrong and do U shoot for a different set of numbers or look elswhere.

One of the biggest discrepencies I see is in fuel delivery thru the spray bar size. I have over the past 20 years, been researching this area and have measured spray bar sizes in more than three hundred different engines from .09 thru the new 101, from airplane thru cars and boats and it has been quite interesting to see how big the difference is in the same size engine but different manufacturers or even the same size engine by the same manufacturer but different year models. An example is the current line of CMB engines VS older CMB engines. An older CMB .21 engine I just recently measured had a spray bar size of .039, the new .21 has a size of .069 and the CMB 101 carb I have has a .077 size. Now if U just stop for a moment and think about this, .021 engine has a size of .069 and a .90 or 101 has a size spray bar only .008 thosands bigger, what happends to the fuel delivery on the big engines when they spool up into the higher RPM's?

I could go thru different engine manufacturers all the way back to the supertiger .61 side exhaust engines and the spray bar, "fuel delivery" numbers are all over the chart even for the same size engine. This variable alone will cause the fuel burn rate to accelerate in the higher RPM's where the engine starts building some heat and cause a super lean, "detonation" burn to occur and the driver has no control over what is happening in the combustion chamber except to richen the needle to slow the burn rate down which also slows the boat down. Like I said the "MSV" numbers are able to give boaters a target, however I belive the MSV numbers what ever U shoot for will be subject to the unique parameters with the type of racing we do.

I guess I should give an example, my 40 hydro boat has a piston and liner that is very wore out and will not launch with a 1462 prop, this engine has a MSV of 72, I replaced the liner which was the same "MSV" numbers and also had a very loose fit. The only difference in the liners is the replacement liner exhaust port was from the top down .098 thosands shorter on the bottom.

I then relaunched the hydro and it litteraly jumped up and took of from the shore runing very hard. After running for a few laps I replaced the the 1462 with a H32 and relaunched. to my surprise it did get up although not as fast as the previose launch and at top end U could tell it was reaslly loading the motor and would not RPM like the previous prop.

So what happened between the 2 liners? I call it one of the very important variables.

Just my 2 cents

dick

 

[DickJones]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

Dick; You hit the nail on the head with the piston seal being #1. Jack.

Jack

I appreciate your comments, with all of your background in these engines, you.ve been there-done that.

dick

 

[dwilfong]

David

I haver never heard of either the Weatherby or the blunder bust boats, U must be working on some seceret projects.

As far as the MSV numbers U give, none of my engines run even close to the numbers U posted, yes I do run all of my

engines at .008 thos. head clearance and they all turn lots of RPM's and very seldom is there any pre detonation,

and if there is its because I have not correctly matched all of the parimeters,IE (air & water temp, corrected density

altitude & dew point , correct plug to control fuel ignition, percentage of fuel, carb size, spray bar size, prop size,

pipe length, and the most important, the piston to liner seal).

It's the last one that I believe has caused so many boaters running engines with a very weak or no seal at all to be problamatic.

With out a good seal it is almost impossible to keep the engine from going lean at higher RPM's.

Just my 2 cents

dick

Dick

Thanks for the info.

I was hoping the Weatherby -Blunder bust analogy would stir your interest.

What our your thoughts on MSV?

David

David

I believe the "MSV" is alot of fun to work with however if U take 10 different motors, of the same size and include different manufacturers,

set them all up with the same MSV numbers, put them in the same boat with the same set up, prop, fuel, pipe and length, carb, maybe 2 of the engines might run very close however the other 8 would be all over the place in performance. If U just rely on a set of nubers to shoot for and forget about all of the variables in previous post what then? Were the "nubers" wrong and do U shoot for a different set of numbers or look elswhere.

One of the biggest discrepencies I see is in fuel delivery thru the spray bar size. I have over the past 20 years, been researching this area and have measured spray bar sizes in more than three hundred different engines from .09 thru the new 101, from airplane thru cars and boats and it has been quite interesting to see how big the difference is in the same size engine but different manufacturers or even the same size engine by the same manufacturer but different year models. An example is the current line of CMB engines VS older CMB engines. An older CMB .21 engine I just recently measured had a spray bar size of .039, the new .21 has a size of .069 and the CMB 101 carb I have has a .077 size. Now if U just stop for a moment and think about this, .021 engine has a size of .069 and a .90 or 101 has a size spray bar only .008 thosands bigger, what happends to the fuel delivery on the big engines when they spool up into the higher RPM's?

I could go thru different engine manufacturers all the way back to the supertiger .61 side exhaust engines and the spray bar, "fuel delivery" numbers are all over the chart even for the same size engine. This variable alone will cause the fuel burn rate to accelerate in the higher RPM's where the engine starts building some heat and cause a super lean, "detonation" burn to occur and the driver has no control over what is happening in the combustion chamber except to richen the needle to slow the burn rate down which also slows the boat down. Like I said the "MSV" numbers are able to give boaters a target, however I belive the MSV numbers what ever U shoot for will be subject to the unique parameters with the type of racing we do.

I guess I should give an example, my 40 hydro boat has a piston and liner that is very wore out and will not launch with a 1462 prop, this engine has a MSV of 72, I replaced the liner which was the same "MSV" numbers and also had a very loose fit. The only difference in the liners is the replacement liner exhaust port was from the top down .098 thosands shorter on the bottom.

I then relaunched the hydro and it litteraly jumped up and took of from the shore runing very hard. After running for a few laps I replaced the the 1462 with a H32 and relaunched. to my surprise it did get up although not as fast as the previose launch and at top end U could tell it was reaslly loading the motor and would not RPM like the previous prop.

So what happened between the 2 liners? I call it one of the very important variables.

Just my 2 cents

dick

Dick

I do agree that many things change the way a boat runs and all of these need to be taken in to consideration. The piston fit being the most important as it controls cly pressure whitch I feel controls MSV. Calculated compression ratio is just that calculated. cyl pressure is more important and that will vary with Cly fit and degree of tapper. I feel that you need to try and pick a base for all figures to make comparisons and MSV is a good a place as any when trying to find head volume number.You can run many scenarios and try to stay with in a specific range and make a decision. The fit is the one thing you will not know till you run the eng as the quality of the production piston is hit or miss.

Just my humble opinion.

David