Run in stand/dyno build.

[Wasted wages]

Looking for 3-500 rpm/sec between 15 and 25K or so: http://performancetrends.com/Calculators/Engine-Inertia-Dyno/Engine-Inertia-Dyno.php

Engineering added a centrifugal clutch and one-way bearing in case of engine seizure:

Gotcha.....thanks for the clarification... I just pictured major carnage happening if something locked up in the engine at WOT..

 

[Terry Keeley]

That oxygen sensor setup was developed by a South African who builds hot saws among other small two strokes. About as far from California as you can get. I also think Terry's flywheel is a little big. Our 5.13" diameter x 3" long flywheel managed to load 11cc nitro engines enough that they melted pistons. We mostly tested gasoline engines from 2 1/2 hp to almost 12 hp at up to 25,000 rpm.

Lohring Miller

I was reading somewhere (I think it was that Kiwi forum you put me on to) about what Charles mentioned, ie: the EGT getting hotter as the mixture is leaned but cooling when over center as detonation started and the piston and head absorbed a lot of heat. Maybe that's why OS used CHT? Maybe a combination of both would work better but the ultimate would be an O2 sensor as you posted, got a link to the sensor above?

When you guys were running your 67's on the dyno how exactly did you set the needle? Did you just kinda just know where it should be from on the water testing? How did you cool the motors? Did you monitor EGT's or CHT's?

I purposely started with the wheel big, I want slow acceleration for the smoothest possible curves, plus I'll probably run 91 VAC's on it down the road.

If it turns out to be too big it's an easy fix, not so much going the other way...

edit: O2 sensor discussion: Oxygen sensor used to tune a two stroke?

 

[Marty Davis]

Did you guys put the thermocouple in the header pipe? As mentioned I've read that kart/bike guys shoot for 3 X the bore from the piston face. Remember what sort of temps you were seeing?

With Mike Rappold's help am pretty sure what I'm going to order for EGT.

https://www.pyromation.com/Literature/Catalog.aspx
Looking at a 1/16" "shielded" probe that has a 0.01 sec. reaction time. Initially I was looking at a "grounded" junction with a 0.3 sec. time but figured it would be too slow, especially for a mixture control.

For the CHT I'm thinking this will work:

https://www.zoro.com/tempco-thermocouple-type-k-trw00113/i/G2205183/

We put the thermocouple in the largest part of the pipe. Mid 600's Get the fastest TC that you can.

 

[dwilfong]

Terry it dose not matter that much where you put it .
It is just a reference so you can see what it needs to be with the best HP figures on your dyno.
HP is what matters the EGT is just a reference so you can work on the fuel flow when you are ready.
It will reacted quicker the closer it is.
But like Marty stated you need a fast acting K probe or it is just a fart in the breeze.

 

[Michael Mooers]

This is the EGT telemetry setup I use on my gas boats with a Futaba T4PV system. The thermocouple comes from TCDirect.com and the SBUS input board comes from RCSense.com. The probe goes through a pressure tap in the header and the silicone tube just helps keep it in place. I log every heat, and adjust accordingly. The sweet spot varies a little from boat to boat, but once you know where it is, it makes everything else a little easier.

 

[Terry Keeley]

Terry it dose not matter that much where you put it .
It is just a reference so you can see what it needs to be with the best HP figures on your dyno.
HP is what matters the EGT is just a reference so you can work on the fuel flow when you are ready.
It will reacted quicker the closer it is.
But like Marty stated you need a fast acting K probe or it is just a fart in the breeze.

Yup, that's why I decided to use the same "exposed sheild" as Mike, 0.01 sec. response time. I'm going to put it in the header though, seems most of the other two stroke tuners (bikes, karts, sleds etc.) do that. I'm also looking at the EngMod2T simulation software that uses EGT from that location (I've been told): Engine Simulation Software: EngMod2T Introduction

This is the EGT telemetry setup I use on my gas boats with a Futaba T4PV system. The thermocouple comes from TCDirect.com and the SBUS input board comes from RCSense.com. The probe goes through a pressure tap in the header and the silicone tube just helps keep it in place. I log every heat, and adjust accordingly. The sweet spot varies a little from boat to boat, but once you know where it is, it makes everything else a little easier.

Thanks for posting that! Obviously gas motors run hotter than nitro, I'm hearing I might see about 900F in the header, your 634*C is 1173*F.

From what I've seen gas guys don't mess with the needle much, when you say you found "the sweet spot" is that the needle setting or other factors? Ever go "over center" and burn a piston/plug electrode? If so any idea what temp it was at? Is that a modded Zenoah?

That TCDirect has some K types down to 0.010" diameter: TC Direct for Temperature Sensing, Measurement and Control

 

[Michael Mooers]

Almost everything I run is a Gizmo GZ2 or 30 plus. I did get one up to about 670C but didn't break anything. I'm not one of those guys who can watch and listen to a boat on the water and say it needs to go one way or the other, so I had to find another way to find the sweet spot. The gas carbs don't need a huge amount of adjustment, but both the low and high end needles are in play at full throttle. When I'm testing a new combination, I start rich and get the low end needle dialed in first, and then adjust the high end to get the right EGT. From there, it's usually a small adjustment after the first heat and I'm good for the day. I also use RPM telemetry to find small differences in EGT, pipe length and prop size. I've been able to gain about 400-600 rpm in engine speed by getting from "sounds good" to "the numbers are right." Here's the RPM telemetry from the same time period as the EGT telemetry. In this case, I could see that I could pull .005 more pitch with no problem, and maybe .010 more. Having this kind of data on a dyno would certainly help speed up the process of finding the best carb, needle and pipe combination for a particular motor, that's for sure.

 

[LohringMiller]

Terry, you are hooked up with all the best two stroke guys I know about. Don't be afraid to ask them questions. My experience with EngMod2T has been mostly with gasoline engines. You need very different settings for glow ignition and not many people can help. That's why measurements on real engines on your dyno will be important. Once you can reproduce the dyno results in the simulation, you will be able to "test" dozens of pipes in the time it takes to build one. If you decide to buy the program, I would be glad to help.

Lohring Miller

 

[Terry Keeley]

Terry, you are hooked up with all the best two stroke guys I know about. Don't be afraid to ask them questions. My experience with EngMod2T has been mostly with gasoline engines. You need very different settings for glow ignition and not many people can help. That's why measurements on real engines on your dyno will be important. Once you can reproduce the dyno results in the simulation, you will be able to "test" dozens of pipes in the time it takes to build one. If you decide to buy the program, I would be glad to help.

Lohring Miller

Thanks again for that, I'll definitely be tapping into that resource when I have some good data to work with. I see right away our pipes need improving when I look at the MB 40 pipe:

Wonder if Scott Bouchie was using EngMod2T? Hmmm...

Right again, there's not a lot of info for glow engines, and if there is it's for FAI fuel. Adding 60-80% nitro to the mix probably changes things a bit, lol.

Can I ask you again?

"When you guys were running your 67's on the dyno how exactly did you set the needle? Did you just kinda just know where it should be from on the water testing? How did you cool the motors? Did you monitor EGT's or CHT's?"

I'm trying to figure out how to set the needle so it's just slightly rich of peak before doing a dyno pull, I could see how a motor would easily go over-lean as the wheel is taking time to spin up. I was thinking of running my fan unit with a particular setup to find a good needle first, then switching to the dyno wheel but that's a lot of work going back and forth. Maybe watching EGT and CHT will help?

Making a pull, leaning the needle, rinse and repeat seems like a recipe for disaster on a dyno...

 

[Marty Davis]

Let me ask Brian Callahan about the placement of the TC.

Brian built in a way to get the needle correct. It is shown on theses dyno pull as the RPM/Time and also in the smooth HP curve. The smoother the curves the closer to the needle you are. Also, the engine will make more HP if it is on the rich side of the needle, just like it is in our boats.

Brian also built in an adjustment for atmospheric conditions in the dyno cell to compensate for the days conditions.

He also came up with an output that is called just "n" with is the useful output of the engine as we use them.

The thermocouple was not working at these runs.

I typically used BMEP to see if I was close to the needle. Several places to check the optimum.

By the way... We tried a one way clutch bearing and they failed on the first or second runs. That was done with 67, 90 sized engines. We were never able to use the dyno for big engines well at all. Based on the inertial dyno wheel you show and the one we used, I AGREE that the wheel is WAY TO BIG.

 

[Marty Davis]

Thanks again for that, I'll definitely be tapping into that resource when I have some good data to work with. I see right away our pipes need improving when I look at the MB 40 pipe:

Wonder if Scott Bouchie was using EngMod2T? Hmmm...

Right again, there's not a lot of info for glow engines, and if there is it's for FAI fuel. Adding 60-80% nitro to the mix probably changes things a bit, lol.

Can I ask you again?

"When you guys were running your 67's on the dyno how exactly did you set the needle? Did you just kinda just know where it should be from on the water testing? How did you cool the motors? Did you monitor EGT's or CHT's?"

I'm trying to figure out how to set the needle so it's just slightly rich of peak before doing a dyno pull, I could see how a motor would easily go over-lean as the wheel is taking time to spin up. I was thinking of running my fan unit with a particular setup to find a good needle first, then switching to the dyno wheel but that's a lot of work going back and forth. Maybe watching EGT and CHT will help?

Making a pull, leaning the needle, rinse and repeat seems like a recipe for disaster on a dyno...

I had a long conversation with the Hines in Vance and Hines (the Old Man) about pipes and the big thing that he said to me was not to mess with the sloping baffle and diffuser cones to make them other than straight until I had the best simple cones, angles, diameters, stingers, etc that I could come up with. Test on the dyno. To many variables, stick with the simple things first.

 

[Terry Keeley]

Let me ask Brian Callahan about the placement of the TC.

Brian built in a way to get the needle correct. It is shown on theses dyno pull as the RPM/Time and also in the smooth HP curve. The smoother the curves the closer to the needle you are. Also, the engine will make more HP if it is on the rich side of the needle, just like it is in our boats.

Brian also built in an adjustment for atmospheric conditions in the dyno cell to compensate for the days conditions.

He also came up with an output that is called just "n" with is the useful output of the engine as we use them.

The thermocouple was not working at these runs.

I typically used BMEP to see if I was close to the needle. Several places to check the optimum.

By the way... We tried a one way clutch bearing and they failed on the first or second runs. That was done with 67, 90 sized engines. We were never able to use the dyno for big engines well at all. Based on the inertial dyno wheel you show and the one we used, I AGREE that the wheel is WAY TO BIG.

I found from running the Eagle Tree and my fan unit that the rpm varies quite a bit on a rich needle but smooths out a bunch when it gets closer to optimum. At first I thought it was noise and found a circuit to filter it out, tested it on my Eagle tree and it took out the big spikes but on a rich needle the small variations are still there. I think what's happening is the motor is "four stroking" (not firing every cycle) and the sensor is picking that up. At very rich settings it might miss say one in every ten cycles, leaner maybe one in a hundred etc. The Performance trends stuff has bigger sensors and works at 50 hz vs 10 for the Eagle Tree so when I see ragged rpm I'm pretty sure it's the motor. It also has different levels of filtering I haven't played with yet and air sampling that compensates for atmospheric variations.

Would sure like to hear what Brian says about getting the needle right, that would save me a lot of time (and parts!). Any way to get him on here? He could add a lot of great info to this.

Dunno what's going to happen when I crank this thing up in a week or two, I'm sure there will be "adjustments" to be made just like when running the fan. I'm hoping that including a centrifugal clutch will "soften the blow" on the system to get the wheel spinning initially so I don't break the one-way bearing, drive pins etc.

Yup, the wheel is bigger than what most have tried, except maybe Dave Marles latest unit. I see yours only took 5-6 sec. to wind up a .21, I'm hoping to see 30-45 sec. As mentioned I can easily trim it down, as you know cutting down the O/D has the biggest effect on inertia.

 

[Mike Rappold]

Terry,
If you decide to go with EngMod2T, let me know. I have been using it for a few years to design carbon fiber tuned pipes used on a 21 size glow ignition RC drag car. Like all things, there is a learning curve to the program. The author of the program has been very helpful in answering questions and making some bug fixes for the glow ignition portion. It does allow numerous designs to be simulated. I do not have a dyno (yet) to compare results so have to use on-track performance and logger data to validate EngMod2T general results. Overall it has been a great tool that got me much farther ahead than just random trial and error.

Mike

 

[Terry Keeley]

As Joe Ingrao used to say "it won't be long now"...

 

[Terry Keeley]

Terry,
If you decide to go with EngMod2T, let me know. I have been using it for a few years to design carbon fiber tuned pipes used on a 21 size glow ignition RC drag car. Like all things, there is a learning curve to the program. The author of the program has been very helpful in answering questions and making some bug fixes for the glow ignition portion. It does allow numerous designs to be simulated. I do not have a dyno (yet) to compare results so have to use on-track performance and logger data to validate EngMod2T general results. Overall it has been a great tool that got me much farther ahead than just random trial and error.

Mike

Very nice work! I was starting to think about how to make pipes and even looked into some resins etc. for CF work, I'll havta pick your brain some more.

Once I get this thing running and getting consistent results there's a few "off the shelf" things I want to try (bigger carbs, fuels, a few different pipes etc.) and then I'll be looking to EngMod2T for more. As you say it looks like a great tool rather than just "cut and try".

 

[LohringMiller]

As an example, I'm designing an opposed piston 60 cc engine with Fusion 360 and EngMod2T. Since there's almost no data on gasoline opposed piston engines, I'm hoping to get in the ball park before I build anything. I compared various crankshaft lead angles, single versus dual exhausts and a lot of different pipe designs. Starting with a simple two cone pipe with a parallel center section I was able to improve the power band by subtle diffuser changes. I bet I "tested" over 50 pipe designs.

Lohring Miller

 

[RaceMechaniX]

Sorry to derail the conversation. Lohring, what are you using for an ignition source? Years ago I worked on the mini Opposed Piston Opposed Cylinder engine with similar bore dimensions to a Zenoah. We had to develop a cross-bore spark plug to try and get a spark centered in the cylinder. This was a uniflow engine with asymmetric crank timing so a little different than your symmetric OP layout. We used a CDI ignition system with 115-200mJ of energy, that's about 1/4 of a ProMag 44 Top fuel ignition. It would erode those spark plugs in a matter of hours.

 

[Brian Spitzer]

Almost everything I run is a Gizmo GZ2 or 30 plus. I did get one up to about 670C but didn't break anything. I'm not one of those guys who can watch and listen to a boat on the water and say it needs to go one way or the other, so I had to find another way to find the sweet spot. The gas carbs don't need a huge amount of adjustment, but both the low and high end needles are in play at full throttle. When I'm testing a new combination, I start rich and get the low end needle dialed in first, and then adjust the high end to get the right EGT. From there, it's usually a small adjustment after the first heat and I'm good for the day. I also use RPM telemetry to find small differences in EGT, pipe length and prop size. I've been able to gain about 400-600 rpm in engine speed by getting from "sounds good" to "the numbers are right." Here's the RPM telemetry from the same time period as the EGT telemetry. In this case, I could see that I could pull .005 more pitch with no problem, and maybe .010 more. Having this kind of data on a dyno would certainly help speed up the process of finding the best carb, needle and pipe combination for a particular motor, that's for sure. View attachment 287315

Michael,
What type of rpm sensor are you using? Thank you.

 

[LohringMiller]

Sorry for getting completely off track. I plan to use the Power Spark ignition with two plugs on opposite sides of the cylinder. This layout has been tested on a larger gasoline engine. I'm running a 4 degree exhaust piston lead. I "tested" a lot of different leads and found that that was a good compromise. Lower leads boosted the bottom end at the expense of over rev, and higher leads did the opposite. See below.

The big question was scavenging. A friend did some CFD studies of various layouts. We had issues translating from Fusion 360 to Solidworks, but I decided on a central squish with a little swirl on the transfers. The piston deflects the flow up the center. The problem is getting flow to go up the cylinder walls as well as the center of the bore. Another builder is trying a dished piston with flow into it to create tumble in his larger engine. We'll see. Below are a couple of the CFD studies and the final transfer and exhaust design.

Lohring Miller

 

[dwilfong]

What ever happened with the Hard drive magnet disk break set up?
I see you used this idea for a brake on your system Terry
.