1.01 cmb burning holes in pistons

[Joe Warren]

Tom I`am really surprised you did not see the difference in the brass head button. We believe the more fuel the engine is able to burn (larger Bore engine) the larger the cooling cycle is on each intake stroke (dragging the head button temp down) & the brass head button helps the engine combustion area retain heat and not go thru the Big cooling cycle each stroke. (methonal is a refrigerate) it would be no different than throwing a car-trk on the ground with a fixed needle you know it will take a couple of laps for the heat to rise & the little engine to heat up and step up on the pipe. Now if you slow back down for 2 3 laps the engine will cool right back down and go back rich & all of this was done with the same needle setting. Only thing different is you came into a needle with Heat....... Not Leaner fuel setting. A small engine that burns less fuel Will Not go thru the same Intake cooling effect & may not see the results of a Brass Head button that retains heat. The Brass head button Adds RPM because of the Heat. I could Only guess it helps light a larger percentage of the Nitro for the Added power. they are the same spec as the alum head buttons we were running. a larger bowl volume and a tight Squish helps make heat also. Steve wood knows what volume to cut the heads for racing. p.s. pay attention to Jerry`s temp when he comes out of the water at the winter nats & the cowl comes off. The Engine is Smoking & Sizzling Hot........ He found power in Combustion HEAT a long time ago..........

 

[Tom Foley]

Like I said I had been running this piston and sleeve for the past season going into Charleston with a 1.0 CC aluminum button successfully on 60 % at about .013 " or so head clearance . All I changed was the head button and I was dead in 2 laps . It didn't sound real lean or anything but the compression ratio was higher adding to the problem . I'm going to open up the head button to 1 CC open up the needle and go .

 

[charles siler]

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.

I got some new parts in from Dave at Got nitro for my OPS 90 the rods are lightened and semi knifegded and they have already

cut the piston and sleave all strait from the factory . I to have had simalar problems with burning holes in pistons in my twin I also

just ordered a gen 4 Boris meter to tune the motors better.

 

[Piston1]

The last time I ran my twin Roadrunner RS 101 was Sept last year. I ran it with a couple of very used up RS 101 motors. I ran it with a couple of Canto cup 7.5 1667 props. The boat did 89mph on a very heat race tight set up as measured with a speed gun radar. The rpm was out of the roof. Motors were originally set by master tuner Steve Wood maybe three years ago. That was money well spent. As a minimum open the head volume to .95 - 1.0 cc then play from there to be on the safe side. If you do not have a lathe do it with primitive tools. It does not have to be pretty but get the volume right.

JOSE

 

[RodneyPierce]

Charles, that OPS stuff looks VERY NICE!!! I didnt think they updated any of there stuff, but appears that they may have?

 

[Tom Foley]

The last time I ran my twin Roadrunner RS 101 was Sept last year. I ran it with a couple of very used up RS 101 motors. I ran it with a couple of Canto cup 7.5 1667 props. The boat did 89mph on a very heat race tight set up as measured with a speed gun radar. The rpm was out of the roof. Motors were originally set by master tuner Steve Wood maybe three years ago. That was money well spent. As a minimum open the head volume to .95 - 1.0 cc then play from there to be on the safe side. If you do not have a lathe do it with primitive tools. It does not have to be pretty but get the volume right.

JOSE

I've got the machine tools and actually opened up the brass head button today to .95 cc or so . checked it 20 times with a 1 CC syringe under very controlled circumstances and each time it was just a smidge different . I opened it up with a .750 " ball end mill just a little at a time . It's in a Mono , we'll see in a few days.

 

[Piston1]

Tom, I run flat piston at .012 clearance. Powermaster 55 nitro fuel.

 

[charles siler]

Charles, that OPS stuff looks VERY NICE!!! I didnt think they updated any of there stuff, but appears that they may have?

Rodney any chance of shipping 70% fuel to Anchorage Alaska 99502 through seatle and bardge to Anchorage. A fue guys I know were saying to talk to ya about it . Ya sooper happy with the newer OPS 90 parts later Charlie

 

[RodneyPierce]

Charles, no go on that my friend. It was made very clear to me when I became a distributor. Sorry!

 

[Tom Foley]

Tom, I run flat piston at .012 clearance. Powermaster 55 nitro fuel.

Thank you , I'm hoping for good things !

 

[steve wood]

i'm 100% confident now that head volume and head clearance is not putting holes in the pistons,it's a lean condition caused by inadequate fuel delivery.

if you guys are making brass head buttons with the same volume and head clearance,i think you are going in the wrong direction.my testing started with the nova 21,as that was where we were have detonation issues.my first brass button was made to the same volume as the aluminum one we were running at the time .19 cc.this first brass button showed no detonation after a full day of running,with no difference in performance.we are now running a smaller volume button,higher compression ratio,higher exhaust timing at 30°blowdown,and shorter pipe= more rpm and speed.if you are using brass at the same volume as aluminum,all you're doing is making the boat heavier.

just my opinion.

also more testing needs to be done with every different engine size,and thats hard for me to do when i don't run that particular engine.

 

[Buckshot]

i'm 100% confident now that head volume and head clearance is not putting holes in the pistons,it's a lean condition caused by inadequate fuel delivery.

if you guys are making brass head buttons with the same volume and head clearance,i think you are going in the wrong direction.my testing started with the nova 21,as that was where we were have detonation issues.my first brass button was made to the same volume as the aluminum one we were running at the time .19 cc.this first brass button showed no detonation after a full day of running,with no difference in performance.we are now running a smaller volume button,higher compression ratio,higher exhaust timing at 30°blowdown,and shorter pipe= more rpm and speed.if you are using brass at the same volume as aluminum,all you're doing is making the boat heavier.

just my opinion.

also more testing needs to be done with every different engine size,and thats hard for me to do when i don't run that particular engine.

Now you got it!!!! Feed it the fuel!!!!!!

 

[Tom Foley]

i'm 100% confident now that head volume and head clearance is not putting holes in the pistons,it's a lean condition caused by inadequate fuel delivery.

if you guys are making brass head buttons with the same volume and head clearance,i think you are going in the wrong direction.my testing started with the nova 21,as that was where we were have detonation issues.my first brass button was made to the same volume as the aluminum one we were running at the time .19 cc.this first brass button showed no detonation after a full day of running,with no difference in performance.we are now running a smaller volume button,higher compression ratio,higher exhaust timing at 30°blowdown,and shorter pipe= more rpm and speed.if you are using brass at the same volume as aluminum,all you're doing is making the boat heavier.

just my opinion.

also more testing needs to be done with every different engine size,and thats hard for me to do when i don't run that particular engine.

I wasn't going to send it out the same way as when I had a problem . I am just using it as a test , I will richen till way fat and lean down till its running fat and happy . I am going to set the head clearance lower and now that my comb. chamber is a bit larger I have room for more mixture . We shall see this weekend .

 

[Michael Caruso]

Hi Guy's,

Question for guys with flow bench setups.

Does anyone have carb flow numbers vs. spray bar draw? I have not flowed anything in many years but I did have success by increasing the spray bar draw cfm at the same carb flow cfm. Electric fuel pump might work good set up with a bypass fuel system less to go wrong. I am not running any of the engines like you guys. I would like to know if anyone has measured their spray bar draw?

Thanks,

Mike

 

[richard jones]

Just a thought,anyone ever give any thought to boring a hole in the skirt near the transfer ports to try and spray the bottom of the piston? Much like a cooling jet

Mike since the 101 came out we have been cutting a slot and series of holes in the slot about 1/4 inch below the exhaust port to cool the exhaust side of the piston and prevent sticking and it works.

I had a thought of doing something on the transfer ports just below the top of the port to spray fuel across the piston. Again since the brass head button's we have not burned any holes.

What were you running in Charleston when you burned one down ? I switched to a brass button that measured .85 CC , flat top piston and burned right away , too lean . Brass , Aluminum , I don't think it matters but too lean REALLY matters!

You are most definitely right lean is lean brass or not. CR dose not matter head clearance dose not matter lean is lean.

Lean is what is holing pistons. no more no less.

Now what you do to get the power you need and not run lean that is a whole different story.

Like I said the mods I do are just a band aid to help keep the eng alive.

The mods I had done did not prevent it.

"Now what you do to get the power you need and not run lean that is a whole different story'

David,it's righjt in front of your nose!!!!!!!

dick

 

[dwilfong]

David,

What size is the spray bar ID on your mega carbs??

For heat racing, has anyone seen any advantage in running 60% in the RS .91/1.01's?

.125

 

[Buckshot]

David,

What size is the spray bar ID on your mega carbs??

For heat racing, has anyone seen any advantage in running 60% in the RS .91/1.01's?

.125

So how did your .650" bore w/ .125" I.D. spray bar run??

 

[dwilfong]

Ran Good as long as you didn't go below half throttle.

Had to try that AB 67/80 muffled pipe. It dose not race well on a 1.01.!!!!!!!!!!!

Would tail walk for 30' when you launched it. looked like a wet water Turkey trying to take off. :lol:

I know you told me so. <_< But you know I have to find out on my own.

Will have some time this weekend to run with the AB 90-1.01 billet pipe and header like you have in your pic of the twin.

Will see how it goes.

 

[dwilfong]

Well popped a wheelie and did a 540 on the prop like a ballet dancer first launch. :lol: :lol:

Needs more prop!!!! 1667 are way to small.

Lites up in the corner and sags on the straits.

Striped the steering servo gears. next week will try again with 50% in steed of 60%.

The .125 spray bar big bore carb works real nice.

 

[dwilfong]

Just figured I would pass on some testing results.

Have bin running my 1.01 with a .87 cc chamber at 9.7cr with 187 ex timing with a .010 clearance with 60% 20% nitro oil mix.

33 on the BM flow meter.

The button is my own design brass.

No holes !!!

A few blown plugs finding the sweet spot.

Also no groves or holes in the sleeve under the ex port.

Big carb and .125 spray bar with the transfer angle change.