CMB101RS Head Vol & clearance

[mark voorhies]

Well. I`am running 60 Techonology fuel & Will be running 65 percent in the fall races...... Low Nitro is NOT the direction for POWER!!!

That may be true, just gotta keep mine alive to find out?? Slow process, maybe, but I'll be back in Sept.

 

[Piston1]

Will a hydro have the same burning issue? I have a new 101 and can switch to a 91 hr if its going to eat pistons

Mikey, I can tell you I run Sig 55% in my 101s with 1cc volume at .014 clearance. The Klotz package from Sig works good for me. My head inserts look like mirrors. Ask me to show them to you the next time I see you. B)

Hose-A

 

[Joe Warren]

Will a hydro have the same burning issue? I have a new 101 and can switch to a 91 hr if its going to eat pistons

Let Mark Bullard open the head up to .9 & set it @ .012 .014 squish.....

 

[Ian Inverarity]

Will a hydro have the same burning issue? I have a new 101 and can switch to a 91 hr if its going to eat pistons

Let Mark Bullard open the head up to .9 & set it @ .012 .014 squish.....

Joe,

Is that for hydro engines or monos?

Ian.

 

[Mark Bullard]

Will a hydro have the same burning issue? I have a new 101 and can switch to a 91 hr if its going to eat pistons

Let Mark Bullard open the head up to .9 & set it @ .012 .014 squish.....

Joe,

Is that for hydro engines or monos?

Ian.

We run the same on both.

 

[Joe Warren]

Will a hydro have the same burning issue? I have a new 101 and can switch to a 91 hr if its going to eat pistons

Let Mark Bullard open the head up to .9 & set it @ .012 .014 squish.....

Joe,

Is that for hydro engines or monos?

Ian.

AS Mark Said Same on both applications Hydro - Mono

 

[Ian Inverarity]

Thanks guys, I will try 0.9cc and 0.12 to 0.14 clearance.

 

[Ian Inverarity]

As I work it out, 0.83cc (stock volume) with 0.019 clearance is 1.25cc total volume at TDC including the squish volume and piston dish. With the bowl volume of 0.9cc and 0.013 clearance is 1.22cc total volume.

 

[steve wood]

As I work it out, 0.83cc (stock volume) with 0.019 clearance is 1.25cc total volume at TDC including the squish volume and piston dish. With the bowl volume of 0.9cc and 0.013 clearance is 1.22cc total volume.

the squish volume is already accounted for in the program.just add bowl and piston volume

 

[Ian Inverarity]

Steve,

I use a CAD program to work out head volumes, and also to design my head buttons. B)

Ian.

 

[dwilfong]

The squash velocity is what you should base all your calculations off of. Then adjust your clearance and volume to get say 70 to76 MPS. On a hydro don't go to high on compression it will hold your RPM in check. You don't have the load to move as you do with a mono so the compression can be lower to let the eng rev. On a mono bump the compression up to move the load.

You need to decide what RPM you will run the eng at to make adjustments to the head. All calculation are based on running RPM. So pick a target MPH and aim for it with prop calculations and then RPM needed to achieve your target with that prop. Then aim for MPS basing compression on the weight of the boat.

Almost forgot ex duration will change the MPS so you need to know the timing with out knowing all this it is just a shot in the dark.

Got a good lesson from Marty this weekend making some brass head buttons.We used the new to be released version of his engine analysis software. It has all the info you will need to figure every aspect of tuning in it.

David

 

[Ian Inverarity]

David,

Out of interest, where does the 70 to 76 MPS come from? What would be the effects above and below those figures?

I must admit I have different findings to you relating to compression in hydros and monos. I found that it was critical to run higher compression in my rigger to be able to launch the props and didnt notice a gain in RPM when lowering the comp, but the same engine in a mono would have a noticable drop in peak revs if I increased the compression. Monos and riggers have different load characteristics on the engines, a mono has less drag at launch than a rigger but more at full speed.

Ian.

 

[dwilfong]

David,

Where does the 70 to 76 MPS come from? What are the effects above and below those figures? Also, as I understand it, the squish velocity is related to RPM, and I dont have a tacho on my 101's. So what RPM is used to calculate the squish velocity (or how is it estimated?)

I must admit I have different findings to you relating to compression in hydros and monos. I found that it was critical to run higher compression in my rigger to be able to launch the props and didnt notice a gain in RPM when lowering the comp, but the same engine in a mono would have a noticable drop in peak revs if I increased the compression. Monos and riggers have different load characteristics on the engines, a mono has less drag at launch than a rigger but more at full speed.

Ian.

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

 

[steve wood]

The squash velocity is what you should base all your calculations off of. Then adjust your clearance and volume to get say 70 to76 MPS. On a hydro don't go to high on compression it will hold your RPM in check. You don't have the load to move as you do with a mono so the compression can be lower to let the eng rev. On a mono bump the compression up to move the load.

You need to decide what RPM you will run the eng at to make adjustments to the head. All calculation are based on running RPM. So pick a target MPH and aim for it with prop calculations and then RPM needed to achieve your target with that prop. Then aim for MPS basing compression on the weight of the boat.

Almost forgot ex duration will change the MPS so you need to know the timing with out knowing all this it is just a shot in the dark.

Got a good lesson from Marty this weekend making some brass head buttons.We used the new to be released version of his engine analysis software. It has all the info you will need to figure every aspect of tuning in it.

David

got any idea what alloy brass you are using?

 

[dwilfong]

The squash velocity is what you should base all your calculations off of. Then adjust your clearance and volume to get say 70 to76 MPS. On a hydro don't go to high on compression it will hold your RPM in check. You don't have the load to move as you do with a mono so the compression can be lower to let the eng rev. On a mono bump the compression up to move the load.

You need to decide what RPM you will run the eng at to make adjustments to the head. All calculation are based on running RPM. So pick a target MPH and aim for it with prop calculations and then RPM needed to achieve your target with that prop. Then aim for MPS basing compression on the weight of the boat.

Almost forgot ex duration will change the MPS so you need to know the timing with out knowing all this it is just a shot in the dark.

Got a good lesson from Marty this weekend making some brass head buttons.We used the new to be released version of his engine analysis software. It has all the info you will need to figure every aspect of tuning in it.

David

got any idea what alloy brass you are using?

That is some thing Marty would have to chime in on. not my place to say even if I knew. Did not ask.

 

[DaveMarles]

Any free machining brass will be OK for a head button. No rocket science needed.

Dave

 

[steve wood]

Any free machining brass will be OK for a head button. No rocket science needed.

Dave

is it better than aluminum,and if so,why

 

[DaveMarles]

I use brass because the head does not get damaged by detonation. Performance is unchanged as far as I can see.

Dave

 

[steve wood]

I use brass because the head does not get damaged by detonation. Performance is unchanged as far as I can see.

Dave

i assume the motor is still detonating,just not showing it on the head,right

 

[Ian Inverarity]

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 didnt go anywhere with it because it gave me a number, but I dont 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.