head buttons

[Marty Davis]

Has any one tryed two plugs in a 21 and what would the out come be.I beleave this would help the fuel to burn more even.Just thinking out loud.
Dave Roach

Not enough room, I have thought about that....

Marty Davis

 

[Marty Davis]

We routinely run a test on our Dyno that is what we call a friction test.

The process is: We take an engine and get it primed with fuel and then run it up to the maximum rpm that we can using a regular starter motor and then trigger the Dyno to start measuring the time, etc that the engine takes to run down to some set low rpm. Remember that we have a wheel of substantial weight that the engine is spinning. That is the principle of an inertial dyno.

We can thus measure the internal friction of the engine. We spend a LOT of time trying to reduce the friction and we get big gains in performance as a result.

The squishing of the charge as a result of various compression ratios seems to be something that would directly affect the friction of the engine. GUESS WHAT, that will be a test that we will run this "off season" to see if it is a correct analogy.

I can't help but think that it will show that either a wider/close squish band or a higher compression ratio will produce more friction and thus limit peak rpm. WE will see....

Marty Davis

 

[Charles Perdue]

Marty, I wish I knew the answers on head design. I'm running with a very small angle squish with a 1mm flat on on the outside edge so that I know when I'm measuring the squish clearance correctly Your MSV at 60 to 70 metres per sec seems incredibly high. You sure thats correct? My program caculates MSV on my 3.5 at 34,000 rpm with 0.3mm squish and just under .19 chamber at just over 27 m/s which I thought was a bit high. I always stick with the same squish clearance on all of my nitro engines which is as close to 0.35mm as possible but have played a lot with squish band width which is very important for allowing the motor to rev out or not as the case may be.

Here is a link to an interesting article written by Neils Vannik a well respected tuner and two stroke software designer. Heads

Dave

Dave; Could you explain with a little more detail on the squish band width,which is very inportant for allowing the motor to rev out or not as the case may be. Jack

Jack, I just extracted some testing info from my files but firstly as I said I don't know the answers on head design and I can say nothing definitive except what works for me. I found in general that when I had a session of serious testing on the 3.5 to extract more performance, I could increase the compression ratio by various means and get improved throttling, pulling away from the shore and a shade bigger on the prop but actual lap times did not fall because top speed was down which I put down to less revving past peak hp. ie overrev. My files show my motor running with 8.5:1 trapped CR, squish 0.4mm and squish of 60%. This was my good race motor which was fast and easy to use but I'm always looking for better. I reduced the squish to 0.2mm which increased the compression ratio to 10:1 and the motor was instantly better out of the corners and better acceleration but top rpm on the water was down by close to 800 rpm. After a lot of playing around I found I could run the same 10:1 with .2mm squish and maintain rpm if I used a head with reduced squish area of around 45%. I don't know the reason for that, only the result.

Dave

Dave; I have found the same thing as you on head volume. The bigger i can make the head volume and still get the engine on the pipe, the more top rpm`s/overrev the engine has. And i have read studies on tuned pipes that say a properly tuned pipe will most often require a bigger head volume. I also found that the ABC piston/sleeve fit has a big influence on head volume. Jack.

Jack and Dave:

Think of it this way: The higher the compression ratio the more difficult that the engine will have to squish the trapped charge as the piston comes up. That is kind of like putting on the brakes for the rotating assembly. The less compression ratio, the less difficulty the piston and the rest of the rotating components have in squishing the trapped charge. The same thing with the squish band. The more area, the harder it is to squish the trapped charge and the more of a brake is put on the rotating mass. The trade off is that you will not have nearly as much torque across the band which will make you have to use rpm with smaller props. Both ways will work for sure. As you said Dave, with 8.5:1 you get great rpm but suffer in torque. You have found that you want the rpm and can live without the torque. For Jack, as long as his teather car can have enough torque to get on pipe, the less squish band area and the less compression ratio, the greater the potential rpm. For Jack's use, and going over 200 mph, I would think that the head would be the most important part of the puzzle, other than the pipe design.

For SAW, the lower the CR and the less squish area you can get away with the better if you are looking for HIGH RPM. Exactly the same as for Jack's Teather Cars.

Marty Davis

One other thing that you have to consider is that we are running approximately 6 to 1 air to fuel ratio with a compression ratio at approximately 10 to 1, the fuel/air mixture in the combustion chamber at top dead center, except for the fact that we are not filling the cylinder to 100%, is almost compressed back to a liquid or am I completely off base?

Charles:

You might be about right on that. I know that the mixture is VERY rich in volume with high nitro fuels.

AND, that makes even harder to compress.

Marty Davis

The liquid part of the fuel/air mixture will not compress, only the air. With the volume of the head buttons being so critical, we may be approching hydraulic lock where the mixture will be very difficult to compress. This would have a negative effect on the engines ability to RPM. Just something else to think about.

 

[DaveMarles]

Has any one tryed two plugs in a 21 and what would the out come be.I beleave this would help the fuel to burn more even.Just thinking out loud.
Dave Roach

Not enough room, I have thought about that....

Marty Davis

Been there, done that. twin coneplug heads

 

[dave roach]

Dave-Marty

Thanks for the pictures

Did you see any differance in usings two plus in a 21.This would up the CC and if you cut the squish band on 1.5 deg on 1/3 of the area and set at .006 clearance would this be a good start.By changing the angles of the plugs would this make a differance.Mybe one glow plug set it on a angle so the plug is facing toward the intakes.Shooting in the dark on this one.

Dave Roach

 

[Chris Wood]

Dave-MartyThanks for the pictures

Did you see any differance in usings two plus in a 21.This would up the CC and if you cut the squish band on 1.5 deg on 1/3 of the area and set at .006 clearance would this be a good start.By changing the angles of the plugs would this make a differance.Mybe one glow plug set it on a angle so the plug is facing toward the intakes.Shooting in the dark on this one.

Dave Roach

Dave,

we used to do the dbl plug head thing.. it is a waste of time..you will see no power if little gains for the headache it is to try and find what cc and bowl size to use. plus if a plug does go bad it may run but falls off terrible.

we tried to change the direction of the plugs.. offset them.. it just wasn't producing anything that you could say WOW this might be worth it.

chris

 

[DaveMarles]

Dave,

I tested the twin (taper seal cone plug) plug head on the 3.5 but could find nothing conclusive except deto problems possibly down to the narrow squishband that was required to get the plugs in. I tested it only once.

Chris, Twin standard plug heads are a waste of time in my experience but I race all my .45's and .91's with twin cone plug heads. What I gain is higher torque, much easier setting up and throttling reliability, better power out of the corners and good plug life. I lose in much higher fuel consumption but thats all. I would never run anything else. A well setup single plug head in the .45 can be competitive with mine but not the .91 in my experience, also when others are struggling to find the needle (all use radio needles here) I'm putting in solid laptimes with no blown plugs.

Dave

 

[DaveMarles]

A couple of people have PM'd me to ask why cone plugs would make the difference when running twin plugs. Cone plugs have one main attribute that makes them work much better than a single standard plug in 21's and .45's and not so much better in .90's.

Dave

 

[steve wood]

A couple of people have PM'd me to ask why cone plugs would make the difference when running twin plugs. Cone plugs have one main attribute that makes them work much better than a single standard plug in 21's and .45's and not so much better in .90's.
Dave

dave,

do you think the the cone lock plugs work better in a dbl plug head due to seal?? and have tried any o'donniel plugs in a dbl plug head as they are supposed to have a much better seal on a convential plug than say a mccoy.

 

[Jack ODonnell]

A couple of people have PM'd me to ask why cone plugs would make the difference when running twin plugs. Cone plugs have one main attribute that makes them work much better than a single standard plug in 21's and .45's and not so much better in .90's.
Dave

Dave; What would that attribute be, that makes the cone seat plug better in the 21`s & 45`s ? Jack

 

[DaveMarles]

Steve, Jack,

When I first used cone plugs on .21's I thought the performance increase was because of a better combustion chamber shape or somethinmg to do with the cooling of the plug but a pylon racing friend told me it was down to the the fact that on a normal plug, the plug threads are wasted volume in the combustion chamber, the same efffect as on a head thats not a tight fit in the liner. So we bench tested back to back by glueing a plug into a head with araldite epoxy and its true we got the same approx 500 rpm increase that the cone plug gave. I figure thats why the 21 has the best improvement , the 45 somewhat less and the .90 very little difference.

Dave

 

[Jack ODonnell]

Steve, Jack,When I first used cone plugs on .21's I thought the performance increase was because of a better combustion chamber shape or somethinmg to do with the cooling of the plug but a pylon racing friend told me it was down to the the fact that on a normal plug, the plug threads are wasted volume in the combustion chamber, the same efffect as on a head thats not a tight fit in the liner. So we bench tested back to back by glueing a plug into a head with araldite epoxy and its true we got the same approx 500 rpm increase that the cone plug gave. I figure thats why the 21 has the best improvement , the 45 somewhat less and the .90 very little difference.

Dave

Dave;; We have done a lot of testing of plugs, and we have found that if there was a drop in rpm`s from a cone seat plug to std.gasket seat plug,most of the time it was do to the coppre gasket leaking or more often it was the stem seal leaking. The cone seat plug seal`s better and it elimiates the copper gasket. I think your right ,the cone plug does give a better combustion shape. Jack

 

[Marty Davis]

Marty, I wish I knew the answers on head design. I'm running with a very small angle squish with a 1mm flat on on the outside edge so that I know when I'm measuring the squish clearance correctly Your MSV at 60 to 70 metres per sec seems incredibly high. You sure thats correct? My program caculates MSV on my 3.5 at 34,000 rpm with 0.3mm squish and just under .19 chamber at just over 27 m/s which I thought was a bit high. I always stick with the same squish clearance on all of my nitro engines which is as close to 0.35mm as possible but have played a lot with squish band width which is very important for allowing the motor to rev out or not as the case may be.

Here is a link to an interesting article written by Neils Vannik a well respected tuner and two stroke software designer. Heads

Dave

Do you run .013-.014" squish clearance on your .21's?

Tha seems amazingly high.

I shoot for .007" (.18mm) for the .21's, about .010" for the .45's, .013" for the .67's.

Marty Davis

 

[AndyBrown]

Marty, I wish I knew the answers on head design. I'm running with a very small angle squish with a 1mm flat on on the outside edge so that I know when I'm measuring the squish clearance correctly Your MSV at 60 to 70 metres per sec seems incredibly high. You sure thats correct? My program caculates MSV on my 3.5 at 34,000 rpm with 0.3mm squish and just under .19 chamber at just over 27 m/s which I thought was a bit high. I always stick with the same squish clearance on all of my nitro engines which is as close to 0.35mm as possible but have played a lot with squish band width which is very important for allowing the motor to rev out or not as the case may be.

Here is a link to an interesting article written by Neils Vannik a well respected tuner and two stroke software designer. Heads

Dave

Do you run .013-.014" squish clearance on your .21's?

Tha seems amazingly high.

I shoot for .007" (.18mm) for the .21's, about .010" for the .45's, .013" for the .67's.

Marty Davis

Just a little hint here Marty! Ask Dave how much nitro he runs in his .21's.

 

[Marty Davis]

Marty, I wish I knew the answers on head design. I'm running with a very small angle squish with a 1mm flat on on the outside edge so that I know when I'm measuring the squish clearance correctly Your MSV at 60 to 70 metres per sec seems incredibly high. You sure thats correct? My program caculates MSV on my 3.5 at 34,000 rpm with 0.3mm squish and just under .19 chamber at just over 27 m/s which I thought was a bit high. I always stick with the same squish clearance on all of my nitro engines which is as close to 0.35mm as possible but have played a lot with squish band width which is very important for allowing the motor to rev out or not as the case may be.

Here is a link to an interesting article written by Neils Vannik a well respected tuner and two stroke software designer. Heads

Dave

Do you run .013-.014" squish clearance on your .21's?

Tha seems amazingly high.

I shoot for .007" (.18mm) for the .21's, about .010" for the .45's, .013" for the .67's.

Marty Davis

Just a little hint here Marty! Ask Dave how much nitro he runs in his .21's.

Andy:

I realize that he runs low nitro mostly for fuel economy and cost of the nitro.

I am just trying to get a handle on why he runs such a high squish clearance. I believe that he really wants his engines to rpm, as he stated that he runs at 35k. The best that I have run that I can document is 32,500 with telemetry. The engine was running VERY well at 32.5k. In order for him to be able to get to that rpm, he probably has to have a lot of squish clearance. He also must not need as much low end because of the setup that he uses. Not sure if they are still running the geared setup, but if they are, that takes a lot less low and mid range power.

What do you think of the anaology that I used about the reason for loss of rpm with increased compression ratio and/or reduced squish clearance. Do you agree that the engine is being forced to squish the charge more and thus makes the engine work harder to ge that done. That in itself reduces the peak rpm potential.

With a high nitro mixture, you have to run MUCH richer to provide enough cooling, which also makes the charge much more dense and harder to compress.

Your thoughts.....

Marty Davis

 

[Norm Doerr]

Marty, I wish I knew the answers on head design. I'm running with a very small angle squish with a 1mm flat on on the outside edge so that I know when I'm measuring the squish clearance correctly Your MSV at 60 to 70 metres per sec seems incredibly high. You sure thats correct? My program caculates MSV on my 3.5 at 34,000 rpm with 0.3mm squish and just under .19 chamber at just over 27 m/s which I thought was a bit high. I always stick with the same squish clearance on all of my nitro engines which is as close to 0.35mm as possible but have played a lot with squish band width which is very important for allowing the motor to rev out or not as the case may be.

Here is a link to an interesting article written by Neils Vannik a well respected tuner and two stroke software designer. Heads

Dave

Do you run .013-.014" squish clearance on your .21's?

Tha seems amazingly high.

I shoot for .007" (.18mm) for the .21's, about .010" for the .45's, .013" for the .67's.

Marty Davis

Just a little hint here Marty! Ask Dave how much nitro he runs in his .21's.

Hmmmmmmmmmm

 

[DaveMarles]

I don't run low nitro in the .21, I run more than Andy told me he was running in his 21 rigger at the World Champs in France the first year he attended. I do run geared drive in 3.5 and would run higher rpm if I thought the motor would last long enough to survive a weekends racing. I have run very small squish clearances in riggers but in my geared motors in FSRV racing if I run less than I stated, I will have problems.

Dave

 

[AndyBrown]

I don't run low nitro in the .21, I run more than Andy told me he was running in his 21 rigger at the World Champs in France the first year he attended. I do run geared drive in 3.5 and would run higher rpm if I thought the motor would last long enough to survive a weekends racing. I have run very small squish clearances in riggers but in my geared motors in FSRV racing if I run less than I stated, I will have problems. Dave

"I don't run low nitro in the .21, I run more than Andy told me he was running in his 21 rigger at the World Champs in France the first year he attended."

I like that one Dave! Now you'll have everyone wondering what your doing because they know I run a lot of nitro.

 

[SayMikey]

I don't run low nitro in the .21, I run more than Andy told me he was running in his 21 rigger at the World Champs in France the first year he attended. I do run geared drive in 3.5 and would run higher rpm if I thought the motor would last long enough to survive a weekends racing. I have run very small squish clearances in riggers but in my geared motors in FSRV racing if I run less than I stated, I will have problems. Dave

"I don't run low nitro in the .21, I run more than Andy told me he was running in his 21 rigger at the World Champs in France the first year he attended."

I like that one Dave! Now you'll have everyone wondering what your doing because they know I run a lot of nitro.

I love it when the BIG DOGS TALK ! If i could use one tenth the information you guys are saying here id be winning more races. Good to see you guys talking avout these things to us small fry. When your done here lets talk pipes. My eyes are peeled and my mind is focused,..........WRITE ON.

 

[Rokieboater]

Wouldn't it be great if someone could post diagrams for us to really take in all this info. Such as the angled squish band, larger volume bowls with less squish band and so and so on.

Does it make a difference if the head button is smooth as oppsed to roughed up a little? Any thoughts????

Thanks,

Robert