1.01 cmb burning holes in pistons

[dwilfong]

David my .21 runs a .390 carb so add those numbers up

Even @ .350 for a .21 scaled up 5 times is 1.750 lol

This stuff doesn't scale like that

Greg thats what the program I have said .390 at 36000 for a .21 it also said a 1.01 at 26000 needs .730 and a 80 at 28000 needs a .550

That is what I am trying to get across.

so put a .250 on your eng and let me know what happens?

What size is the hole in your crank for the air to go thew?

David

David; What does your program say about what stinger diameter to use on your 101 at 26,000 with 50% nitro.You say the 101 needs 12cfm to run at 26,000rpm.Is your stinger capable of flowing 12 cfm.At some point the stinger become's a plug. J.

I have opened up the stinger on the new setup with the AB 67/80 muffled pipe to .500

Their has to be some difference between the cab boar and the ex stinnger ID to give back pressure for sure.

what the difference is in a percentage I am not sure but there must be a constant.

The calculation on flow are rudimentary figures easy found on line. the variable is the efficiency of the eng to pump air. also what the pipe will bring to the table. 80% is a conservative number when doing VE calculations.

the pipe is the wild card with a two stroke.

I have not run the pipe thew the program I have yet. Lazy is all it is. That and I am not completely sure how to load all the parameters in.

Marty gave me allot of stuff to play with. still sorting thew it all. Bin over two years and still have not comprehended it all yet.

Wish I had more time to play.

 

[Tim_Duggan]

Excellent point Jack!

Even if one was to go to a fuel pump to take variable fuel pressure out of the equasion (which could be good thing IMO along with carbs that can meter fuel at idle & partial throttles) the stinger diameter and length still plays an important role in both the ability of the engine to pump air, and also to control temps!

For those considering pumps - considered how to switch it off if the engine stops so that you don't pump all the fuel into the lake and starve the pump?

 

[dwilfong]

Would be great if we could go with a carb like that on bikes with a fuel bowl.

put the needle at the bottom of the emulsification tube on the main jet.

Only problem is fitting it in a rigger.

 

[Joe Warren]

looks like there is soon going to be a CMB RS/EVO 91 according to Ians web site. Whatever that is?????

Joe do you have a link to this website?

iansboats.com

 

[Tom Foley]

You know Greg asked what dose a bigger carb and more air flow have to do with leaning the eng.

Here is my take on it.

You need a certain amount of air to burn a certain amount of fuel. now if you don't have the air to support the fuel you remove some of the fuel.

What plays a big factor in cooling theses eng?

Water or fuel?

Now add more air and you get more fuel flow thew the eng.

This way you can run on the lean side of the needle and build good power with out the heat getting away from you and going to high.

As the heat goes up the more nitro you burn and the eng goes lean.

Think of the fuel as a radiator. If the radiator is to small for the eng it will over heat.

Water cooling the head brings down the combustion chamber temps. This is bad. more fuel flowing thew the case cools the case and flowing across the piston top cools the piston. But the head is keep hot with just a small amount of water to cool it.

Separate the head and water cooling cap from the eng. this way you can run a hot head and the fuel will cool the case and piston.

The two need to be two separate systems.

Less air = less fuel = less temp control = runaway heat build up = HOLED PISTON

Take a piston and put it in the sleeve now line it up with the transfer port bottoms. now take a small drill bit and glue it to the transfer angle closes to the ex port on both sides. look at where the air fuel mix is going across the top of the piston.

Bet it dose not go across the top very much. with a angled top port it never even goes near the piston.

The incoming fuel mix under the piston in the crankcase is cooling the entire piston at all times the engine is running . Most transfer / boost ports are angled up to evacuate spent gasses more completely as the exhaust port is open and ensure a more filled combustion chamber

 

[dwilfong]

How about instead of using a fuel bowl carb

Use one of the pumps listed on the site that David posted

But use the brushless version and hook the esc into your throttle channel

Now you can vary the fuel pressure depending on throttle position

I'm sure it's not going to be as simple as that but you get the idea

What about the pulse driven pumps picco used to have bottled onto there 90 motors

I tried a Perry pump but as the RPMS got higher it seamed to stall out.

The diaphragm I don't think can react quick enough.

A gear pump would reacted to RPM change but I don't think it would not reacted under load change.

Have a ESC to mess with but have not had the time to play with it to much.

Writing the code is a pain.

I think Tim was messing with it also.

Time if I only had more time.

I will keel over before I can try every thing in my head.

Tom evacuating the cly is a mute point if the piston melts.

Take a cutting torch and put it on a flat plate. now run water on the under side. bet you can blow a hole in it. now run the water on the top side and do the same thing. bet you can't blow a hole thew it.

Some Dino test on the CMB35 are what sent me in this direction to start. Then Jim stated his angle change. This all contributed to what I have now.

This is just my take on it dose not mean it is the gospel.

Always open to a good deduction on any thing.

 

[Tim_Duggan]

http://www.hpt-sport.us/flowrivr.htm

 

[Tim_Duggan]

Have a ESC to mess with but have not had the time to play with it to much.

Writing the code is a pain.

I think Tim was messing with it also.

Time if I only had more time.

My thoughts were to treat the fuel pump as a constant (just on and off switched by a FET - simple code) and to still use the remote needle for WOT, but to use a metering system similar to the one used in OS 21D carb for mid and low throttle positions. That design is robust, and has minimal obstruction in the carb bore with the discharge nozzle to reduce effective airflow, but the variable fuel pressure from our pipes brings it unstuck on high nitro.

I have the same time issue - especially in regards to the programming of a logic controller when I have boats that currently don't "need" the item in question for me to enjoy them.... I got to a point where I needed to get some basic data with a logger and then got very side tracked! I was more pre-occupied with throttle position variable on-board glow control at the time which is a little trickier code wise.

Having said that, a logic controller would not be needed to prove the concept. a simple spare channel switch can be used to switch the pump on and off manually at the TX.

 

[dwilfong]

I still think a EGT sensor to control a needle right on the carb is the way to go.

Some day I will get it going.

 

[Joe Warren]

Installing big carbs or carving out a huge exhaust port won't do much good if the transfers restrict the flow rate of a mixture, and vice-versa. READ THAT AGAIN........ The flow through the port begins at the entry, down in the crankcase. Any restriction through velocity and power, and the biggest problem areas are at the port's roof and the neck size just below the port window. If the charge is misdirected or restricted at the window. where the incoming charge's velocity is high, many problems may occur

 

[dwilfong]

Installing big carbs or carving out a huge exhaust port won't do much good if the transfers restrict the flow rate of a mixture, and vice-versa. READ THAT AGAIN........ The flow through the port begins at the entry, down in the crankcase. Any restriction through velocity and power, and the biggest problem areas are at the port's roof and the neck size just below the port window. If the charge is misdirected or restricted at the window. where the incoming charge's velocity is high, many problems may occur

Read post #2 again

 

[Tim_Duggan]

I still think a EGT sensor to control a needle right on the carb is the way to go.

Some day I will get it going.

You could try adapting your 555 servo driver to work with a K type thermocouple instead of the thermistor!! No code! I'd want to be able to override it with CH3 though.

 

[Tom Foley]

I still think a EGT sensor to control a needle right on the carb is the way to go.

Some day I will get it going.

You could try adapting your 555 servo driver to work with a K type thermocouple instead of the thermistor!! No code! I'd want to be able to override it with CH3 though.

You also have to be able to finish a race without things malfunctioning . Complication sometimes is a bad thing . I did some major gutting inside the case on my 101 just as you get past the disc valve trying to open up the entry to the 3 ports as well as some major profiling of the outside of the sleeve in the port tunnels . Hoping for good results .

 

[dwilfong]

I still think a EGT sensor to control a needle right on the carb is the way to go.

Some day I will get it going.

You could try adapting your 555 servo driver to work with a K type thermocouple instead of the thermistor!! No code! I'd want to be able to override it with CH3 though.

I was thinking the same but put it on the back shelf last year for the VAC 1.05 build.

Will revisit it this year. Have a new project started. Turning a OPS.90 in to a 1.27.

This is first on the list.

Going to push the envelop as far as I can. the OPS.90 has a bigger disk than the CMB RS

Can really open it up and the jug has tons of room to hog out to make good port Cross sections.

Also easy to work the ports with the mill having a removable jug.

Can change timing also by shimming the jug and not messing up the port sleeve interface.

Drop a stock VAC91 rod right in no mods to any thing. End up with a 1.8 R/S ratio this will drop the power curve right where it will need to be for this big eng.

This is a win win design as far as I see it.

The RS is a dead end with its small disk and small case and the VAC is limited by the drum size and design.

Have already talked with Steve and as soon as he is back on his feet we will start the build.

Have bin colecting some small Dellorto carbs to play with.

Will see where this will lead.

 

[Joe Warren]

I still think a EGT sensor to control a needle right on the carb is the way to go.

Some day I will get it going.

You could try adapting your 555 servo driver to work with a K type thermocouple instead of the thermistor!! No code! I'd want to be able to override it with CH3 though.

You also have to be able to finish a race without things malfunctioning . Complication sometimes is a bad thing . I did some major gutting inside the case on my 101 just as you get past the disc valve trying to open up the entry to the 3 ports as well as some major profiling of the outside of the sleeve in the port tunnels . Hoping for good results .

We call this anytime metal hits the floor from inside the intake rotor...you replace it with more fuel. The only fuel you have to push up top is the fuel that is sealed in the case when the intake rotor closes. The only thing that limits it to flow to the top now is the transfer window size and shape.

 

[Bob Morton]

Tryed the EGT thing hook to a third channel software to slow for all the changes. But if held at WOT it did work. I tryed this along time ago. So maybe the software has improved. Hard to beat a Boris Meter. And Ferrette needles. The only time I burnt a piston was when the water line broke the motor came in steaming. So I tryed to restart the motor and a ton of fuel came out of the carb not good. Pulled the head ther was a hole in the piston. So I say keep the water flowing. This was on a twin. Keep the needles RICH.

Data recorder is the why to go.

Nails

 

[Buckshot]

Here is a snap shot of my Eagle Tree head temp readings from a run in open water at Hobart 2012.

 

[Buckshot]

You'll notice how fast the temp drops at the end of the run.

IR temp guns after a run are only good for guessing.

IR temp guns are a great tool on the bench for tuning along with the good 'ol ear.

 

[Rick Doane]

Here is a snap shot of my Eagle Tree head temp readings from a run in open water at Hobart 2012.

Excellent data!

 

[Mark Bullard]

You'll notice how fast the temp drops at the end of the run.

IR temp guns after a run are only good for guessing.

IR temp guns are a great tool on the bench for tuning along with the good 'ol ear.

I assume that you slowed down a couple of time in the run? Also great data.