4 Stroke Fuels

Some time ago (in the fall) I spent some time speaking with Laura from Powermaster fuels. I was interested in understanding why YS 20/20 blend always seemed to perform better than other fuels (especially stunt fuels), even with the same nitro content. Long story short, I discovered that the YS blend is lower viscosity. It is blended with 1/3 very low viscosity oil and 2/3 high viscosity oil. The lower viscosity allows the engine to draw fuel much easier, and reduces what Doug and I call "the burn down effect". I used to think it was the nitro improving the performance, but now I am convinced it is most likely the improved fuel draw.

Laura suggested that we try the 23% "All Low Viscosity Heli" Blend. It is 100% low viscosity oil. It comes in 15% and 30% nitro.

I tried the 15% and it appeared to definitely improve the run. It had a noticeable positive effect on the OS Max 52 Surpass, but Doug still prefers even more nitro than the 15%.

'Zilla,

Well, it's what I've always said. The way to get more juice out of a 4 Stroke is by increasing the ability to get fuel into it. OK, it's not like I invented this or anything, but it is none the less true. I have to admit, I hadn't considered a lower viscosity oil as a way to aid this. Cool idea.

So my question is why doesn't simply opening the needle valve, or the hole in the spraybar, fix this draw problem?

>So my question is why doesn't simply opening the needle
>valve, or the hole in the spraybar, fix this draw problem?

It appears the loss is mostly in the fuel line.

The energy to draw the fuel into the venturi does not increase with a larger hole (I don't think?)

Eather has been using large diameter tubing in the tanks to aid in drawing fuel more effectively.

The thinner fuels seem to work best so far, and it is just as easy as trying some...

Godzilla,
I find that extermely hard to believe. For example, remove the spraybar and needle from your favorite engine. Attach it , via a long length of fuel tubing, to a tank of fuel, and get the siphon going. Hang the spraybar end down. Note the drip rate with the needle set at the typical setting that the engine uses. Now pull off the spraybar, and see how fast the fuel comes out on it's own. The effect of fuel tubing is really negligible. As I recall, someone (Noel Drindak??) did a test on the impedance of fuel tubing some years back in Stunt News, and found it truly doesn't do anything on the scale of what we do. I suggest a test stand study. Setup an engine on the test stand, peak it out and measure the rpm's. Then double the length of fuel tubing and get it running again. See if you have to richen the needle very much to get back to the peak rpm's.

I mean think if you think about it for a moment, if we were limited by the impedance of the fuel tubing, the needle valve wouldn't have much effect on the mixture--which it certainly does. I am sure almost everyone can go from screaming lean to sloppy rich on just changing the needle setting.

An analogy to think about is two resistors in series. The total resistance is just the sum. If one resistor is 1 meg ohm (the needle/spraybar), and the other 1kohm (the tubing), the total resistance (1.001 MOhm (~impedance) is completely dominated by the one meg resistor.

(note I find it amusing that I am using the electrical circuit analogy to "explain" simple fluid like flow, just opposite of most freshman physics books which use pressure and flow to "explain" electrical circuits!)

Godzilla,

I love ya, man, as you are never *ever* afraid of laying it on the line, tend to give full and complete details.

But I think you've gone off the res on this one. Yep, I like YS 20/20 fuel. And the doctored 25% and 30% blends.

Maybe I should do some some testing, and I will, but it's hard to wrap my mind around the viscosity of the fuel being a noticeable factor in the operation of a four-stroke.

How's the Perry Pumper working? And why didn't you just drive it off the case?

I'm looking at a couple old pumps from my RC days, may try one of them. But there is no way enough room over top of either Saito 56 or 72 to do anything other than just go straight up and through top block with the dump tubing.

>Godzilla,
>
>I love ya, man, as you are never *ever* afraid of laying it
>on the line, tend to give full and complete details.
>
>But I think you've gone off the res on this one. Yep, I like
>YS 20/20 fuel. And the doctored 25% and 30% blends.
>
>Maybe I should do some some testing, and I will, but it's
>hard to wrap my mind around the viscosity of the fuel being
>a noticeable factor in the operation of a four-stroke.

Actually, it is poor fuel draw that is the ultimate culprit. The lower viscosity fuel simply makes it easier for the engine to draw fuel.

Feel free to do some testing. Doug and I did a few of our own. Our first test was simply static test. Doug made up a test stand with a Black and Decker Workmate bench. We bolted the Saito 72 to the stand. We tried several different props and loads for comparison. What we were looking for was the "burn down effect".

The "burn down effect" is defined as a slow and continuous drop in RPM as the engine goes lean and starts to overheat. Doug noticed this first with his initial tests. If the proper fuel and prop were combined (even one that flies pretty descent) the engine could be made to slowly lose RPM, and would eventually bottom out at a total loss sometimes arounf 1500 RPM.

We would take the engine start it and tach it to peak RPM (note the RPM). Then take the bench and tilt it to 90 degrees and tach the engine again. It became evident that the engine could be made easily to start to "burn down" lean (something Doug and I had been seeing a lot of with the high RPM setup).

With the 14" prop we could make the engine burn down slightly even with 20% nitro. Take off the pressure line and it was nearly instanteously burning down!!!! Put in some Sig fuel and it got worse!!!

We tried several variations including:

1. Pressure.
2. No Pressure.
3. Stunt fuel.
4. Ys 20/20.
5. Powermaster 15% nitro Heli 23% low viscosity fuel.
6. Check valve on the pressure line (for higher ultimate pressure in the tank).
7. Perry Pump.

The worst combination was a high load, high viscosity fuel, and no pressure. The burn down was very evident and instantenous.

The lower viscosity fuel had almost zero burndown and made more RPM on less NITRO than the YS 20/20!!! With a middle load and muffler pressure it would run indefinately in the vertical position.

The check valve on the pressure line definately increased flow to the engine, but was unpredictable without a regulator.

The Perry Pump was simply awesome. The engine simply did not care were you pointed it. It just pounded out the exact RPM not matter how it was pointed. In fact, it could be set with slightly higher flow and make the engine go RICH in the vertical position.

Flight testing showed the static testing was correct.

>How's the Perry Pumper working? And why didn't you just
>drive it off the case?

I do drive the pump off the case. I use the spooge tube as per the instructions.

Brad Walker will be running pumps from now on, I believe. It is simply too "plug and play". The freedom to run the engine "however" is wonderful. I may even put my tank on the CG in the future like a pattern plane.

If I somehow choose to not run a pump I will be running the low viscosity fuel and muffler pressure.

>I'm looking at a couple old pumps from my RC days, may try
>one of them. But there is no way enough room over top of
>either Saito 56 or 72 to do anything other than just go
>straight up and through top block with the dump tubing.

This weekend I am looking to mount the pump in the backplate.

As far as being off the reservation, that must means I am doing something original...

>I mean think if you think about it for a moment, if we were
>limited by the impedance of the fuel tubing, the needle
>valve wouldn't have much effect on the mixture--which it
>certainly does. I am sure almost everyone can go from
>screaming lean to sloppy rich on just changing the needle
>setting.

In the case of poor fuel draw the engine will not richen no matter how much you open the needle. I know, I have done it... You must have enough energy available at the point of draw for the needle to work.

How about a more efficient venturi? Could we be getting more suck for the same amount of throttling?

>How about a more efficient venturi? Could we be getting
>more suck for the same amount of throttling?

That too.

I have no expertise in creating super venturis, though. I am capable of changing fuels and buying pumps.

I agree..... I was running my Saito .30 on the bench and when I tilted the test stand up, the engine would start to sag. No matter what I did to adjust the needle to (richening it), the engine would not speed back up! Using Powermaster 10/22 at the time. Once the engine had to draw against an increased resistance, it would not richen up.

From your previous posts, I'm going to try the Perry Pressure pump that runs off of crankcase pressure. Brad, I assume you are still using this type and that is what you are trying to nestle into the backplate.

[photo not recovered: 3fe0f5784e1567bc.jpg]

Standard Perry Pump.

'Zilla,

I am assuming it's mounted on the outside because there's no room on the inside.

What are you using for the pressure tap?
Did you drill the backplate or are you using the crankcase breather?
If you aren't using the breather outlet, does it reduce the available crankcase pressure?
If you are using the breather have you had any trouble with pressure build up inside the crankcase?
Would muffler pressure be enough to drive this regulator?
Did you try the Perry oscillating pump?

Enquiring minds want to know. You and Doug Moon have done a lot for our hobby with your experiments. I have stayed interested in four strokes since I came back to CLPA from RC, but I cannot build fast enough to keep up with your work. I finally have the Legacy working with the Saito .56 and the Time Machine is in primer with an OS .52 Pond Scum Special. So far, my results are very encouraging.

Keep up the good work.

>'Zilla,
>
>I am assuming it's mounted on the outside because there's no
>room on the inside.

It was easier for testing. I had no idea if the loaction of the pump mattered, or if the tank position was still critical. I still believe the engine still sees the tank in high G's even with the pump.

>What are you using for the pressure tap?
>Did you drill the backplate or are you using the crankcase
>breather?

Spooge breather with a T fitting as per the instructions.

>If you aren't using the breather outlet, does it reduce the
>available crankcase pressure?
>If you are using the breather have you had any trouble with
>pressure build up inside the crankcase?

No, the case still vents through the T fitting to other outlet as always. I still vent the spooge the same as always.

>Would muffler pressure be enough to drive this regulator?

I do not think it would like the heat, do you?

>Did you try the Perry oscillating pump?

No, got one to loan?

>Enquiring minds want to know. You and Doug Moon have done a
>lot for our hobby with your experiments. I have stayed
>interested in four strokes since I came back to CLPA from
>RC, but I cannot build fast enough to keep up with your
>work. I finally have the Legacy working with the Saito .56
>and the Time Machine is in primer with an OS .52 Pond Scum
>Special. So far, my results are very encouraging.
>
>Keep up the good work.

We will, try. Thanks.

Thanks for the info. I agree the pump should make tank position irrelevant. Some of the RC guys are mounting their tanks back at the CG.

I don't know about the heat. My first pumpers had the regulator mounted inside the backplate cavity and worked fine. They got their pulse directly from the crankcase. I don't know how much heat would remain from the muffler after the pressure pulse traveled up the tubing to the remote regulator. I may hook one up on the test stand and give it a shot. If all else fails, I can simply follow the instructions.

I have one oscillating pump and I'm trying to figure out how I can make it work inside a tight CLPA cowl. The mounting process is not so bad - the plumbing hook up might be the hard part. I'll let you know.

>Thanks for the info. I agree the pump should make tank
>position irrelevant. Some of the RC guys are mounting their
>tanks back at the CG.

I doubt that is true.

Even the YS with its high pressure tank and pump required tank shimming on the vertical.

diameter and length of the fuel line has got to matter, esp. if the fuel is thicker.

Had an interesting, related experience last summer. I forgot the muffler pressure line at home. I had about a foot of the small pink Prather tubing. so I just stuck the whole foot on and wrapped it around the cylinder to keep the excess out of the way. Well, wouldn't you know, the motor simply would not run. A prime, but no more, no matter how much I opened the needle valve. After about six tries, we gave up and cut a shorter piece of the large dia. silicon. Ran first flip.

the longer, smaller tubing was keeping the AIR from the muffler from flowing into the tank and providing enough pressure to push the fuel out. So I have no trouble at all believing that too small a fuel line, and/or thicker fuel could prevcent a marginal venturi setup from sucking enough fuel. Venturi suction does not provide much force to move fuel, that is for sure.

>>So my question is why doesn't simply opening the needle
>>valve, or the hole in the spraybar, fix this draw problem?

Because opening the needle changes the mixture. Lowering the fuel's viscosity just changes its characteristics. The amount you draw is the same, or very close to it.

"Burn Down Effect"

Brad and I noticed this right from the start with 4s motors. I even noticed it back in 97 when I had a saito 50 in a buccaneer 746. I always seemed to be searching for more from the motor.

It happens the most on a large prop with high pitch in the dead of summer. The air thins and the motor struggles. How you will notice it is after three loops in a row it is deffinently flying slower and running slower at the end of the loops as opposed to the beginning of the loops. Pretty much and overheated situation. Then after a lap it is back on and running fine.

Brad went nuts with the 4s and he really began to figure this thing out. The more he worked the more he reduced this effect. It is almost gone but from time to time in really hot still days you will feel it creep in. ESPECIALLY at the top of the hourglass where you really need it to be very strong.

To feel this effect for yourself setup your 4s with the largest Daimeter 6 picth prop it will turn. Fly along and do 6 consecutive loops and really pay close attention to it. You feel what I am talking about. Or try it with 4 consecutive square eights. It will need to be hot day to really feel this. But after flying these things for a while I can tell when it is doing it even on a 50 degree day. And it really hacks me off!

Funny thing is when I see it happen to other people's motors and then they say it is not there...????

One day in August Brad and I sat out there and tried and tried to figure out away to keep the fuel pressure up in the motor during the top of the hourglass. Without pumps and bladders. The fuel kept coming up. Then he found some really cool stuff. It works tooooo. Then he got a really nice pump so he has got either way if he wants.

The lower viscosity fuels really let the motor pull the fuel with much more ease. The gravity has less effect. Say what you want but I proved it to myself about dragging fuel uphill. It really hurts the 4s because it has nothing else to do but overlean. It cant break into another cycle like a 2s. We already start out pretty close to or right on dead lean from level setup so point it uphill and it will have lean out and go "Over the Top" or "Burn Down".

I plan on much more testing with this stuff for sure.

I have never claimed that you may have lousy fuel draw with a four stroke, I just claim it isn't due to viscosity and the fuel tubing!

Any engine will lean out when the nose is put up, and the venturi is too big, or the tank is too far back. This is just rho*g*h. The only significant drop in pressure due to the fuel flow and its viscosity is across the needle seat and perhaps the hole in the spraybar if that is too small. That can be corrected by opening the needle up. The fuel tubing is just not an effect.

Enough of the Voodoo 4 stroke analysis.

>I have never claimed that you may have lousy fuel draw with
>a four stroke, I just claim it isn't due to viscosity and
>the fuel tubing!

I never said that higher viscosity CAUSED the poor fuel draw, it simply made the starving of the engine worse.

If you do not think there is a significant effect on the "draw" from changing fuels, I submit you do very simple test.

Take a bottle of Sig or Powermaster GMA and draw some fuel into a syringe using standard size fuel tubing.

Now switch to the heli blend. The heli blend will require half the force.

Now switch to 1/8" tubing and try again...

It's not Voodoo it's practical. Obviously, your theoretical calcualtions are missing something, because the effect is obvious and evident.

> Any engine will lean out when the nose is put up, and the
>venturi is too big, or the tank is too far back. This is
>just rho*g*h.

Or conversely the velocity across the "correct" size thrttle opening (venturi) is too low. Reducing the venturi size is like throwing away HP, not an option for me.

The only significant drop in pressure due to
>the fuel flow and its viscosity is across the needle seat
>and perhaps the hole in the spraybar if that is too small.
>That can be corrected by opening the needle up. The fuel
>tubing is just not an effect.
>
>Enough of the Voodoo 4 stroke analysis.

Feel free to prove me wrong...

Here's an easier and much more obvious test. Get a milkshake, insert straw, suck for all you're worth. Switch same straw to glass of milk. Suck on this. Guess what, only difference is the viscosity of the "fuel" and same "engine", "venturi", "fuel line" and only difference is the "fuel". Pretty obvious which has the easier draw. Viscosity of fluids matters. Period.

>Enough of the Voodoo 4 stroke analysis.

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=6906&forum=DCForumID1&viewmode=all

>I have never claimed that you may have lousy fuel draw with
>a four stroke, I just claim it isn't due to viscosity and
>the fuel tubing!

How can you say that. An even easier test than Brad's test is this. Go to MacDonalds and buy a coke and a chocolate shake, or vanilla if that is your fancy. Then get a straw and trade it from shake to coke. Tell me if there isnt a difference in the ability to "pull" the two liquids. One with much less viscosity than the other. Pretty simple logic.

The sig fuels are much thicker and require much more suction to pull through the fuel line. The thinner heli fuel pulls through like the coke in the above test.

I have no experience with the tubing sizes. I use the standard sizes like everyone else so that has been a constant in all my testing.

>
> Any engine will lean out when the nose is put up, and the
>venturi is too big, or the tank is too far back.

Yep and a lean situation for the 4s is VERY bad and hard not to have due to the way the setups have been so far.(shrinking the venturi will never ever fix this problem on a four stroke) On the ground in level flight they run right up near or at max RPM so they lean out in a nose up attitude and that is BAD. Try to "pull" shake through the fuel line or a coke through the fuel. The engine works alot less for the coke. It can more easily keep the fuel it needs to run the load applied at the desired rpm. the attitude has less of an effect. In my tests gravity is playing a MUCH larger role than load as to how far the engine will lean out.

This is
>just rho*g*h.

What does that mean?

The only significant drop in pressure due to
>the fuel flow and its viscosity is across the needle seat
>and perhaps the hole in the spraybar if that is too small.
>That can be corrected by opening the needle up. The fuel
>tubing is just not an effect.

If fuel tubing sizes are not an effect than how come top fuel dragsters use a 4" diameter fuel line? Once the pressure is equal at most fuel line sizes it should get what it needs right? Wrong. They need almost 16 gallons of fuel to travel 1310 feet. They cant get that much through in a smaller line in just 4.5 seconds. The tubing size can play a role. To a certain extent.

Take the shake for insatance. You try to suck it through a coffee stir stick and you will be there a while. Try to suck it through a Big Gulp big straw and you will pull alot more shake through there alot faster with alot less work. Get the tubing too big and the motor cant create enough suction to pull the fuel. But we are talking very small sizes here and the differences are still in the working ranges.

I have no experience with the tubing. I might try soon but I dont think I will go that route.

Opening the needle changes the mixture. It just doesnt do the same thing. I have tried and tried and tried and it just doesnt work.

>
>Enough of the Voodoo 4 stroke analysis.

All we did was take a very common sense approach and do some very common sense testing that proved to be right on in flight testing. Not much VooDoo to it.

I don't think it's voodo. The maximum amount of suction that can be produced is fixed by the venturi/needle valve configuration and engine displacement and speed.

The soda straw analogy hits it right on the head. For a fixed amount of suction, higher viscosity fluids will flow less than lower viscosity fluids. We are varying fuel flow with the needle not suction so if we are running close to max flow capabilities at normal operating conditions then there is no additional latitude when additional resistance is added by conditions such as raising the nose of the aircraft. Lowering the fuel viscosity provides more latitude under these conditions.

The 4 cycle fuel draw is poor when compared to the 2 cycle. I do wonder if the fact that the 4 cycle draws fuel at half of the number of cycles of a 2 cycle might be part of the problem. Although the fuel flow probably stops for both engines between intake strokes, the 4 cycle fuel is at rest longer. I wonder if we might not be seeing a situation much like a water hammer. The 2 cycle might have some damping oscillation of the fuel pressure due to the kinetic energy of the fuel and the fuel line pressure might not be at zero by the time the next intake cycle comes along. Because of the longer time periods between intake cycles of a 4 stroke, the kinetic energy from the fuel flowing has completely dissipated and the 4 cycle has to overcome this inertia on each cycle.

Just thinking out loud.

>
>Just thinking out loud.

Good post. Brett said something similar. I think that may be it.

There is also no case volume to buffer the stroke in time.

>There is also no case volume to buffer the stroke in time.

That's a really good point. The case acts like an accumulator.

I have to say, the fuel draw/viscosity/pipe diameter analysis is top notch thinking. Well done to all concerned.

Brett

p.s. When is UHP coming out with a Saito 72 intake plenum?

Intake Plenum? That is a really good idea. How would you suggest that be built?

>Intake Plenum? That is a really good idea. How would you
>suggest that be built?

Ahem.

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=7187&forum=DCForumID1&viewmode=all#26

>>Intake Plenum? That is a really good idea. How would you
>>suggest that be built?
>
>Ahem.
>
>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=7187&forum=DCForumID1&viewmode=all#26
>
>

Huh...

>>>Intake Plenum? That is a really good idea. How would you
>>>suggest that be built?
>>
>>Ahem.
>>
>>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=7187&forum=DCForumID1&viewmode=all#26
>>
>>
>
>Huh...

Godzirra, see post #26 of that thread...by Mr. Taib. He suggested a plenum. There isn't much room there, but maybe it would be worth a try. Steve http://www.nwskyraiders.com/index.html

I was thinking, last night, that perhaps one could use a 4 stroke muffler as the plenum. So you'd have two of the things sticking out on either side of the engine.. so it's just a matter of plumbing. Or you could take a page out of Joe Wagner's book and put a really long extension on the intake manifold tube, push the fuel tank all the way back to the CG, and put the venturi and needle valve just in front of the fuel tank.

Sorry Doug, I jumped in with out reading your analogy. Samo, samo and true.

Brad, it looks like you are using Perry Pump VP-30. It sounds like it is supposed to be driven by crankcase pressure on a 2 stroke. Wouldn't think the blowby would provide enough pressure to do much pumping. I am wondering why you didn't get the VP-20, which runs off vibration? It sounds like the one to use, according to their website. http://www.perrypumps.com/prod02.htm Steve

>Brad, it looks like you are using Perry Pump VP-30. It
>sounds like it is supposed to be driven by crankcase
>pressure on a 2 stroke. Wouldn't think the blowby would
>provide enough pressure to do much pumping. I am wondering
>why you didn't get the VP-20, which runs off vibration? It
>sounds like the one to use, according to their website.
>http://www.perrypumps.com/prod02.htm Steve
>
>http://www.nwskyraiders.com/index.html

Becasue the guy at Perry Pumps said not too.

Using the analogy of an electrical circuit.

I = E/R

I = current (in our case fuel volume)

E = voltage (the suction at the needle/spraybar)

R = resistance (the needle/spraybar fuel line and fuel viscosity)

If we want to increase (I) but can't increase (E) then all we have to work with is (R). If the needle is open giving us max flow then the resistance is the hole in the spray bar and the fuel tubing. But reducing the fuel viscosity which will drop (R) and increase (I). So using fuel witha lower viscosity will increase fuel flow for a given set of mechanical conditions, which is what Brad and Doug have done.

Just made me wonder if the spraybar hole could be enlarged to help this problem. Might be too restrictive as is. My gut feeling is that it would only work if all of the physical plumbing was also increased in size (fuel tubing, spraybar I.D., etc.). Me thinks that using lower viscosity fuel is easier!

A question for Brad and Doug. Are you using the stock Saito carb or an after market needle/spraybar assembly?

>A question for Brad and Doug. Are you using the stock Saito
>carb or an after market needle/spraybar assembly?

After market Venturi with an NVA.

There already is a plenum of sorts in the intake. Consider the amount of fuel charge that resides in the intake above the venturi (or carb) and before the intake valve and it is probably about 20% to 25% or more of the engine displacement.

I think a there might be some charge dilution occuring when the air flows over the nose creating eddies and swirls at the intake. This dilution would cause a chronic lean condition and couple that with the fact that the fuel to air ratio is lean at the start of the intake stroke until the velocity increases thru the venturi and that produces the current lean condition. That intial lean condition would be worsened by using high viscosity fuel. So depending on the particular configuration of the airplane's nose, some installations maybe affected more than others. Maybe a ram air intake tube to pack the charge or a Bru-line type foam filter over the intake to prevent any air penetration or dilution might help.

I am still puzzled as to why muffler pressure isn't adequate to overcome the fuel piping system/fuel viscosity problem (assuming that you buy into that theory.... which I do). I wonder if the modifications that Brad and Doug made to the muffler of boring out the end dropped the muffler pressure to the point that it isn't effective.

Again just thinking out loud.

As mentioned earlier, I have some case pressure-operated Perry pumps. And if I can remember which piped 60s (RC Pattern motors) have these things stuck in their back doors, guess I'm going to have to take a deep breath and fit at least one to a four-stroke. Sigh...

However, there was also mention of the oscillating Perry pumps in this thread. While I will not state that these do not work, I have tried them on RC motors and had less than stellar results.

My suggestion is to try what we know works (case pressure pumps) to decide if you like this sort of setup. And then if there is some reason to try a shaker pump, and it doesn't work, at least one can reasonably assume it's a hardware problem, not a conceptual problem.

Also notice the Perry guys told 'Zilla to use a pump driven by case pressure.

The purpose of the oil is lubrication. It keeps the parts from going metal to metal. The lower viscosity oil provides less lubrication. Of course, a big four stroke with rings and ball bearings doesn't need as much as a Fox 35. What you may be experiencing is that the 20/20 YS fuel is more than adequate to lubricate a 4S. So you decrease the oil content or lower the viscosity. The friction on the cyl walls is less, power is more. As long as the parts don't go metal to metal, your fine. When they do, as in an overheat, ouch!

>The purpose of the oil is lubrication. It keeps the parts
>from going metal to metal. The lower viscosity oil provides
>less lubrication.

I simply do not think this is true.

Powermaster said there low viscosity oil has the highest lubricity of any oil they use... It is there Premium package and certainly is more expensive on their end.

There has always been (I think) an incorrect correlation between viscosity and lubricity. Thick oils can lose lubricity at the microscopic surfaces and actually provide much poorer lubrication,

There hs been many remarks about trying a vibration driven pump.

Three or four years ago I built a profile Zero for an Enya 53. I tried a vibration Perry Pump on this model. I messed with that thing for many flights with no luck. It seemed to make no difference in how the motor ran. I tried it mounted on the provided mount like the instructions show and then on the model itself like a few other RC guys told me to try it. It never seemed to add any pressure to the fuel system. Finally I just gave up and flew without it. Motor ran exactly the same. I think the circular path of our models renders these vibration pumps pretty useless. I know someone out there has used them but I know I couldnt get mine to work. Tried all the adjustments and nothing. After consulting with RC guys they too came to the conclusion that the circular path was probably locking up the pump during flight and even more so in a hard maneuver where there is more pressure on the pump. The fuel just passes through as a filter but doesnt receive any added push. I gave mone back to the RC flier I borrowed it from and he put it back on his model and it is working fine.

If anyone else has gotten them to work I would like to hear how they set it up.

If the shaker don't work, increase the shaking. Use an unbalanced prop.

I've never seen one, but I expect you'd have to mount it relative to the cylinder axis, to get the vibration going the right direction? My guess is that vibration beats G's, like rock beats scissors. Steve