1.01 cmb burning holes in pistons

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I have bin doing this mod from the start.

Have only holed one piston and that was using the pipe Scott made for me.

It was my fault trying to push the envelop to the max to see where it would go.

Got happy with it and only took a 1 second to bite me.

Blowing the fuel across the top of the piston will cool it down right now not after it soaks thew the other side.

This is just a band aid to a eng that is choked up from not enough AIR FLOW.

Look at it this way a 80 runs a .500 carb now a 1.01 is .21 larger and a .21 runs what size carb add it up!
 
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Greg Robertson said:
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
Click to expand...
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
 
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Greg Robertson said:
How can you get a lean condition from a lack of air flow
Click to expand...
Good question. I don't think that is the case. It would cause a lack of RPM's & Power which is not the case with the 1.01.

Do all carbs of the same bore have the same flow? Probably so in the simple idea of how much volume you can put thru a specific size orifice? But I bet there is big differences in fuel draw from the spray bar in all cases. Changes in bell shape, venturi length, and tract length make them all different.

I wouldn't think just making a big bore carb with a big bore spray bar is going to work or solve the holed piston issue. It might just make it worse!? Besides that, the Int port in the case is only so big right?

It might be that the factory carbs are working too efficiently! Maybe they draw the fuel soo well under load that the fuel supply system can not keep up. :eek:
 
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Buckshot said:
Greg Robertson said:
How can you get a lean condition from a lack of air flow
Click to expand...
Good question. I don't think that is the case. It would cause a lack of RPM's & Power which is not the case with the 1.01.

Do all carbs of the same bore have the same flow? Probably so in the simple idea of how much volume you can put thru a specific size orifice? But I bet there is big differences in fuel draw from the spray bar in all cases. Changes in bell shape, venturi length, and tract length make them all different.

I wouldn't think just making a big bore carb with a big bore spray bar is going to work or solve the holed piston issue. It might just make it worse!? Besides that, the Int port in the case is only so big right?

It might be that the factory carbs are working too efficiently! Maybe they draw the fuel soo well under load that the fuel supply system can not keep up. :eek:
Click to expand...
You are right on the big bore carb. It will make the problem worse. If you slow the air down to much you will not be able to get the motor to move the fuel and this is what a big bore does. The bigger the bore the more twicky the motor will be which works for record runs but not good for heat racing in a twin. I found that .530 is about the best for big motors in a twin. But you also have to play with end position of the spray bar in the bore. By cutting the end off the spray bar is how you tune the bottom and mid range of the motor. Go back and watch the video and listen to the motors on my twin and find the first 100mph pass that Andy Brown made some years back. You will find that they sound about the same on the bottom end. The reason is I made the carb that Andy ran.

The problem is like I said before the 101 motor goes thru a big cooling cycle each stroke. And it is enough to make it hard to build heat in the motor. And everyone that does not understand will crank the needle down or cut the water off which will cause the 101 motor to hole the piston.
 
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Mark Bullard said:
Buckshot said:
Greg Robertson said:
How can you get a lean condition from a lack of air flow
Click to expand...
Good question. I don't think that is the case. It would cause a lack of RPM's & Power which is not the case with the 1.01.

Do all carbs of the same bore have the same flow? Probably so in the simple idea of how much volume you can put thru a specific size orifice? But I bet there is big differences in fuel draw from the spray bar in all cases. Changes in bell shape, venturi length, and tract length make them all different.

I wouldn't think just making a big bore carb with a big bore spray bar is going to work or solve the holed piston issue. It might just make it worse!? Besides that, the Int port in the case is only so big right?

It might be that the factory carbs are working too efficiently! Maybe they draw the fuel soo well under load that the fuel supply system can not keep up. :eek:
Click to expand...
You are right on the big bore carb. It will make the problem worse. If you slow the air down to much you will not be able to get the motor to move the fuel and this is what a big bore does. The bigger the bore the more twicky the motor will be which works for record runs but not good for heat racing in a twin. I found that .530 is about the best for big motors in a twin. But you also have to play with end position of the spray bar in the bore. By cutting the end off the spray bar is how you tune the bottom and mid range of the motor. Go back and watch the video and listen to the motors on my twin and find the first 100mph pass that Andy Brown made some years back. You will find that they sound about the same on the bottom end. The reason is I made the carb that Andy ran.

The problem is like I said before the 101 motor goes thru a big cooling cycle each stroke. And it is enough to make it hard to build heat in the motor. And everyone that does not understand will crank the needle down or cut the water off which will cause the 101 motor to hole the piston.
Click to expand...
 
The Giant bore Carbs dont get me too excited I have seen Andy run 630`s on a Mac 84 and they were tricky to get the boat up off the launch. They seemed to help mostly on High RPM. You must also consider that the intake rotor stays closed more crank degrees than it stays open. The trick is to have a Strong Signal at the carb venturi. I earlier stated that the Fuel systems starts at the pipe pressure fitting and ends at the Spray Bar. This is just to check ability to flow fuel at a high rate without restrictions.... But it stills haves to flow thru the intake valve & transfers then to the Plug to get lit. p.s. Dont forget the nitro percentage is the multiplier for the Oxygen the fuel is going to make & The 15cc pipe gives back a ton of hot fuel when she finally steps up on pipe. This is why we run Big pipes in florida races in the hot humid weather... cause you cannot get anymore thru the carb. DAVID, Jerrry Crowther Changed More Intake Transfer Angles & sizes with success & I`am sure he make mistakes too??But I would almost bet they still had angle torwards the plug & not blowing straight across the piston. Most of Jerry motors the transfer port was on the chrome side of the liner Not the Outside of the liner like stock. Thats right... He dug the chrome off the liner & piston ported the piston to make a primary transfer ( shortest path to the top of the piston) and the case port acted like a secondary transfer on 90 engines the liner is much thicker so you had other options.
 
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We have Won a Ton of races with Slight Engine Mods with the RS101. Julian set the Twin record late 2011 with Steve Wood prepped engines, Mark has the record with Bullard Prepped Motors, I know for a fact they are almost exact the same with just a few differences that Mark likes in his head button angles. Out of the RS101 Engines I see and help Keep running in Our camp, Joes 15 - Rs101s, Ralph 4 - Rs101s, Julians 6 Rs -101s,Charles 4 - RS101s thats 29total - RS101 Engines alone. Plus I know the numbers Jose Ortiz operates his 4 - RS101 on. I promise we dont have 1 percent of the broken parts that David has between the 33 engines total. Our parts are Worn out from Winning Races. Maybe we need to post the Winnings. 2012 Ralph - Atlanta Twin Spring Shootout Champ! Joe - Evansville Little thunder Champ in TWIN class and F MONO Both with RS101s & the following race Huntsville Open Mono and F mono Champ with RS101s, Jose - Huntsville Twin Shootout RS101s, Charles - Evansville Twin Shootout CHAMP, Cliff - Evansville F Mono Champ. And to Finish out the year a few of us arrrived at Huntsvile to see Mark reset the Twin IMPBA 2 lap record. Now I would say those Races were Won with All RS101s & those same engines are setting in boxes today waiting for 2013 racing season to start.... Special Thanks to Steve Wood & Mark Bullard on the Engine machine and building help & Ralph Almirola @ Roadrunner & Jerry Crowther @ Seaducer. A lot of RS101 boaters were in the Winners Circle in 2012!!!!! Plus I hear Buckshot went to Hobart and ROCKED the DOCK with his RS101s & took home TWIN AWARD & the CLOCK too. You know... Stu dont give that clock up easily.... Point is these RS101 engines are Winning Many Many races. Not setting on the bank broken!!! & they are in Common Heat racing Boats that You Can Buy ..... NOT SOME SKI RAMP BOAT that the Ski Ramp ( prop planing surface) is Longer than the Boat itself..... Rumor is......Stu has a New Batch of Engines. Cannot wait to get my hands on a New Set of 2013 RS101s.......
 
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Joe Warren said:
We have Won a Ton of races with Slight Engine Mods with the RS101. Julian set the record late 2011 with Steve Wood prepped engines, Mark has the record with Bullard Prepped Motors, I know for a fact they are almost exact the same with just a few differences that Mark likes in his head button angles. Out of the RS101 Engines I see and help Keep running in Our camp, Joes 15 - Rs101s, Ralph 4 - Rs101s, Julians 6 Rs -101s,Charles 4 - RS101s thats 29total - RS101 Engines alone. Plus I know the numbers Jose Ortiz operates his 4 - RS101 on. I promise we dont have 1 percent of the broken parts that David has between the 33 engines total. Our parts are Worn out from Winning Races. Maybe we need to post the Winnings. 2012 Ralph - Atlanta Twin Spring Shootout Champ! Joe - Evansville Little thunder Champ in TWIN class and F MONO Both with RS101s & following Huntsville Open Mono and F mono Champ with RS101s, Jose - Huntsville Twin Shootout RS101s, Charles - Evansville Twin Shootout CHAMP, Cliff - Evansville F Mono Champ. And to Finish out the year a few of us arrrived at Huntsvile to see Mark reset the Twin IMPBA 2 lap record. Now I would say those Races were Won with All RS101s & those same engines are setting in boxes today waiting for 2013 racing season to start.... Special Thanks to Steve Wood & Mark Bullard on the Engine machine and building help & Ralph Almirola @ Roadrunner & Jerry Crowther @ Seaducer. A lot of RS101 boaters were in the Winners Circle in 2012!!!!! Plus I hear Buckshot went to Hobart and ROCKED the DOCK with his RS101s & took home TWIN AWARD & the CLOCK too. You know... Stu dont give that clock up easily.... Point is these RS101 engines are Winning Many Many races. Not setting on the bank broken!!! & they are in Common Heat racing Boats theat You Can Buy . NOT SOME SKI RAMP BOAT that the Ski Ramp ( prop plaining surface) is Longer than the Boat itself..... Rumor is......Stu has a New Batch of Engines. Cannot wait to get my hands on a New Set of 2013 RS101s.......
Click to expand...
Joe thats not even adding 2009-2011 races LOL thats alot of wins for Team Roadrunner thats all using CMB101RS engines
 
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Someone said it was time to add fuel pumps to our boats.........here you go, get busy.

http://iansboats.co....ew_products.htm

pump%20jp.jpg
 
Buckshot said:
No secret.....

http://www.intlwater...523#entry514446

a lot of guys have been doing it for a while. ;)

As well as flat roof int. ports. :)
Click to expand...
This is interesting. Some need to go back to a fixed needle setting (mainjet) and run there water thru the third channel....... this way they could get there fix on playing with the third channel knob & the engine would stay in the boat longer??
 
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.
 
Last edited by a moderator:
dwilfong said:
Greg Robertson said:
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
Click to expand...
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
Click to expand...
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.
 

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