Holey Piston!!

[Ken Retallick]

Shorts,

Already thought of that one, cant go much tighter on squish band without bits bumping into each other.

Once i have this engine sorted, there are a few rather unusual things to try.....

 

[Don Ferrette]

Shorts,

Already thought of that one, cant go much tighter on squish band without bits bumping into each other.

Once i have this engine sorted, there are a few rather unusual things to try.....

Ken I might be wrong but I think perhaps Craig meant deeper in the actual bowl depth of the head button & widening the surface area of squish band to keep bowl volume the same. BTW- what is the bowl volume? :blink:

 

[Ken Retallick]

Ken I might be wrong but I think perhaps Craig meant deeper in the actual bowl depth of the head button & widening the surface area of squish band to keep bowl volume the same. BTW- what is the bowl volume? :blink:

Don, 1cc. Squish is 50%. I may machine another head button with more volume to try aswell.

I kept to compression ratio up high to try and make torque and not huge rpm

 

[Don Ferrette]

Ken I might be wrong but I think perhaps Craig meant deeper in the actual bowl depth of the head button & widening the surface area of squish band to keep bowl volume the same. BTW- what is the bowl volume? :blink:

Don, 1cc. Squish is 50%. I may machine another head button with more volume to try aswell.

I kept to compression ratio up high to try and make torque and not huge rpm

I think more bowl volume might be a good thing here. I understand the desire to keep compression high but You've also got to have enough volume to properly & completely compress & light off the incoming charge, especially with that huge carb you're trying to run. I would try to increase bowl volume some while keeping your squish area tight. Too little bowl volume and/or too much squish band clearance ain't good either. That was something I forgot to mention, in your pic it looks like you've got combustion occurring all the way out at the edges of the piston. What is the actual head clearance set at?? :unsure:

 

[Ken Retallick]

Don, I have squish at 13 thou.

 

[Don Ferrette]

Don, I have squish at 13 thou.

That seems ok BUT you still have the mixture burning outside of the bowl so I would try to increase the bowl volume.

 

[EatMyShortsRacing]

Yeppers what I was trying to get to was increasing the distance from the piston (TDC) to the plug. Also are you using a twin taper on the squish band? I did some testing a while ago and it seemed like the radius required where the squish meets the bowl was larger if the squish band was totally flat. If using the second angle on the squish band very little radius was required to prevent detonation.

Also I found with a totally flat squish and high compression the High RPM seemed to be limited. This i assumed (there is my disclaimer) that the detonation became full on pre-ignition and basically the engine was firing too soon. If the engine fires, for example, at TDC the force is going in a straight line down the rod and then the crank attempts to transfer the force laterally, but most has to be absorbed by the rod and crank if it all happens at TDC.... Also there would be nowhere for the heat to go but into the piston and head button as well as more of the explosion energy would result in heat as the gas expansion is limited.... If the flame front hits the piston later then more power is transferred to the crank rotation, more of the energy of the explosion goes into gas expansion, and the cooling charge of the new fuel arrives earlier...

My deduction was that the squish/head transition was providing equal ignition to the glow plug... but earlier in the stroke... Therefore the piston burning like that would be more likely under that scenario...

But yet again this is just one more scenario!!!

 

[Tim_Duggan]

Ken,

Whats the fuel composition you are running? Not the cause of the problem but could possibly explain one of the side effects that some of the guys are discussing.

IMO it's the pipe doing the damage to the piston in your case. Fix the pipe and the rest of the effects will go away.

Tim.

 

[EatMyShortsRacing]

Ken,

Whats the fuel composition you are running? Not the cause of the problem but could possibly explain one of the side effects that some of the guys are discussing.

IMO it's the pipe doing the damage to the piston in your case. Fix the pipe and the rest of the effects will go away.

Tim.

at 10:1 compression???? (yes I know that the trapped compression ratio is less than that but technically when the pipe is operating correctly the full contents of the cylinder should be compressed.....)

Lots of other issues spring up with that kind of compression especially on a big block engine...

From memory one of the best heads on my A90 was around 1.15 - 1.2cc

EMS Racing - I can feel a side bet coming on....

 

[Tim_Duggan]

Not the MAIN cause of the problem but could possibly explain one of the side effects

That better?

 

[Ken Retallick]

Also I found with a totally flat squish and high compression the High RPM seemed to be limited. This i assumed (there is my disclaimer) that the detonation became full on pre-ignition and basically the engine was firing too soon. If the engine fires, for example, at TDC the force is going in a straight line down the rod and then the crank attempts to transfer the force laterally, but most has to be absorbed by the rod and crank if it all happens at TDC.... Also there would be nowhere for the heat to go but into the piston and head button as well as more of the explosion energy would result in heat as the gas expansion is limited...

Craig, what you say certainly could be true. I am running a totally flat squish band. More things to think about :blink:

Underneath the piston is rather dark, so definatly a heat issue

Tim, just the usual mix i run, 40% Nitro, 5 Castor, 15 Klotz.

I wonder if someone would like to donate some Neo to try?? hehehe

Ken

 

[Don Ferrette]

Running castor oil also seems to raise combustion temps. I stopped using castor years ago & found engine temps came down when I switched to all synthetic oil.

 

[Anders_Martinelle]

Ken, what pipe length are you running??(centerline engine to end of first cone?)

As you can see some things don`t add upp here and that gives you problem.

You say that the engine is setup for torque and not rev, correct??

If you set it up for torque why use a 14,5mm carb on it???

You don`t need a 14,5mm carb unless you plan to run 24k rpm+.

I agree with Don that the carb is to big. Does it generate the problems you have?? I THINK NOT.

My feeling is that the pipe is the main problem.

I have learned over years that some pipes and some engines don`t like each other....... why?? I have not a clue. Just is....

Just an example of that is that i tested a prestwich pipe on a K90 and that just generated heat and no speed.

Didn`t matter that changes i made......

Then you have ALOT of people that runs the prestwich pipe on CMB engines and that works fine.

I can see that the "setup" you have is not ok.

The fuel i run is 40% nitro and 20% castor in all of my 90 engines and i have not seen that amount of black carbon in any of my engines......

Also the prop seems to be small compered what i normaly use.

When i run my RS91 i have been useing 1667 with 5,9-6,0cup from AB and 22-24k rpm.

If you have 1cc in bowl volume should be OK.

Have you tested the MAC 1389 or 1399 pipe on that engine??

So test a nother pipe and it might be ok....

Anders

 

[Don Ferrette]

I have learned over years that some pipes and some engines don`t like each other....... why?? I have not a clue. Just is....

Anders on this I couldn't agree with you more. B)

 

[Ken Retallick]

Anders, Pipe length to front cone is 320. Your sure right about some pipes dont like some engines!!

This problem i have isnt to be seen as a big problem, just a small problem in the huge world of testing, modifying, and trying something different

Thanks for everyones input, always good to have more than one opinion to what is why and how!

Will let u know how things go.

Ken

 

[EatMyShortsRacing]

Also I found with a totally flat squish and high compression the High RPM seemed to be limited. This i assumed (there is my disclaimer) that the detonation became full on pre-ignition and basically the engine was firing too soon. If the engine fires, for example, at TDC the force is going in a straight line down the rod and then the crank attempts to transfer the force laterally, but most has to be absorbed by the rod and crank if it all happens at TDC.... Also there would be nowhere for the heat to go but into the piston and head button as well as more of the explosion energy would result in heat as the gas expansion is limited...

Craig, what you say certainly could be true. I am running a totally flat squish band. More things to think about :blink:

Underneath the piston is rather dark, so definatly a heat issue

Tim, just the usual mix i run, 40% Nitro, 5 Castor, 15 Klotz.

I wonder if someone would like to donate some Neo to try?? hehehe

Ken

Next time you are over come grab some

 

[Don Ferrette]

Something that needs to be considered is nitromethane can be lit off by pressure. You can put a dime size puddle of pure nitro on your shop floor & throw a match on it & the match will probably go out. But if you were to strike that same little puddle with a hammer you'd have a sizeable divot in your floor from the resulting explosion (DON'T try this!) Too much compression can force premature ignition & may explain the burn pattern all the way out at the piston crown edge. We know the optimum burn pattern is a circle on top of the piston the same size & location as the head button's combustion chamber. Based on the picture you posted combustion seems to be occuring outside of that area. Since the head clearance sounds about right I'm wondering about what the actual physical compression ratio is? Also keep in mind that with that huge carb you are supplying a tremendous amout of air/fuel to try to ignite & you can only compress a given quantity so much before it will ignite. Just a thought.......

 

[carlnoki]

I have to agree with what Don is saying.

REMEMBER, our glo engines are classified as SEMI-DIESEL motors. The main ignition is the cause of the alcohol and the physical make up of the glo plug element itself. The 1.5 volts is used to start the motor but not needed to keep them running. (althoug in the past i have been able to start an engine BY ACCIDENT with out the battery hooked up. (just the right conditions at the wrong time.))

With the HUGE carb you are trying to run on the engine, the huge amount of mixture is being or trying to be compressed in a given amount of physical space that would normally work great with say, a 11MM bore carb.

With such a greater amount to compress, the mixture with your compression is igniting TOO early and that is where you are experiencing the almost total coverage burn pattern on your piston top.

Take Don's advice and try a smaller carb on it. That in my opinion will probably take care of your problem.

Remember, BIGGER is not always BETTER,,,,,,,,,,,,,,,,,,,,,,,

Just my 2 cents worth.

have a great one.

carl

 

[Drew Hamilton]

When I first started running 1.0 engines, I had the same problem...almost. Not as severe as yours! The plug would turn black and almost blow the center out of the plug! Alot of head scratching went on and after talking to a very fast boater friend who was use to working on EVOs, he told me to check rotor clearance.

Well, it was excessive. Machine the block, machine the rotor smooth, make sure the cover plate is smooth and true. Drop clearance down to .003/.004. Made a world of differance!

You could not get the air fuel mixture to stay the same before this, and it would go lean on the top end. This cured my problem, hope this helps you.

 

[Ken Retallick]

With the HUGE carb you are trying to run on the engine, the huge amount of mixture is being or trying to be compressed in a given amount of physical space that would normally work great with say, a 11MM bore carb.

Carl, You have uncovered the reason behind the huge carb which has many hours of flow testing and mods done to it. It draws and vapourises better than any other carb i tested. I would post a picture of my carb flow bench but you would probably laugh

Im going for better crankcase filling which leads to a bigger bang upstairs. All the mods i have done are reversable, just trying to see what i can achieve without big port timing numbers.

Also keep in mind that with that huge carb you are supplying a tremendous amout of air/fuel to try to ignite & you can only compress a given quatity so much before it will ignite. Just a thought.......

Don,

very true, by keeping the temp below ignition point long enough so that it can all be compresed for the plug to light it off at the right time there should be a bigger bang

Pipe stinger has a huge influence on engine temp, i have modified it so its all ready to test again.

Ken