Carb Flowbench Testing

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Lohring, although the oxygen sensors are useful, you have to know your scavenging and delivery ratio otherwise the data is meaningless.

In our big 2 stroke 2 cylinder testing we run four of the 4.2 or 4.9 sensors, one for each exhaust stub, one combined pre turbine and one post turbine. We measure the fresh air and fuel mass flow to know what the total percentage is, but have to use a simulated table for delivery ratio and scavenging to approximate what is in the cylinders.

Tracer gas analysis is the best way, but I doubt any of us are going to that extent for these engines.

BR,

Tyler
 
Tyler, you're doing real engineering, and I'm an amateur. I use the engine's power output as a measure of scavenging efficiency. My favorite test of that showed a power increase with Mike Bontoft's transfer port modification on the second liner from the left below. I think the grooves create a stream that deflects outgoing flow away from the exhaust port. Fancier flow testing equipment would show what's happening.

liners transfer.JPG

Most of the people I talk to are using oxygen sensors as part of a two stroke electronic engine management system. A few are thinking of it as a way to check carb settings under load. I'm thinking of it as a replacement for the flowmeter. The problem is providing a load. No sensor will fit in a boat, so you need to load the engine on the shore. Dynos are the obvious way, but a simpler brake system would also work. I'm interested in what the lambda for best power would be with our nitro fuels. it should still be a little less than 1 even with the fuel's oxygen content.

Lohring Miller
 
julianconde said:
I used to run 67/80 zoom carbs on my CMB 101's and they work perfect to me.

Julian
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Hello Julian, where are you now and how are you?

Thanks for the compliment on the Zoom carbs. The check is in the mail to pay you for these kind words.
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Charles
 
lohring said:
The sensor is a Bosch 4.9 LSU, a heated sensor. I'm shocked at how low cost these sophisticated things are.

Lohring Miller
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Nice site. I believe that fuel injection will be the future of our fuel systems. It will have to be done just for the love of the accomplishment, not for monetary reasons.

Charles
 
Charles Perdue said:
julianconde said:
I used to run 67/80 zoom carbs on my CMB 101's and they work perfect to me.

Julian
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Hello Julian, where are you now and how are you?Thanks for the compliment on the Zoom carbs. The check is in the mail to pay you for these kind words.
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Charles
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Your welcome.

I still have my 101's with my zoom carb there in permanent storage. The best thing I love about these carbs is that I can crawl very slow like the gas guys with my twin and then stab the throttle and it comes right back on pipe. Throttle response is excellent thru low,mid, and full throttle. My carbs are actually smaller than the original carbs the engines comes with I think there 410 or 467.

So not bad ;-)

Julian
 
And by the way you can have the biggest carb on your engines and it really don't mean crap if your engine can't burn it properly. But I like what I have and what worked. Unfortunately my engines won't run again. Charles I'm currently on the other side of the world ;-) I'll be in Florida very soon.

Julian
 
Loading the eng is the whole trick with burning high nitro. You can play with the needle all you want this dose not make the eng run better.

The prop is the key to the load on the eng. You can dump all the nitro and air you want in the eng.

But if you can not load it right it will not burn.

Nitro need load to burn. The burn rate is the key to this and will change with load.

Have tried some very good pipes and found out on the big engs 1.01 it was not helping any.

It was more of a problem to load the eng to make it work.

OK so you say just put a bigger prop on. It don't work that way you still have to launch it and have good low speed reaction.

Harnessing the potential of high nitro is the main problem.

Not getting it in the eng.

A dino can not replicate a boat running a prop on the water.

What will work on a dino under proper load is hard to replicate in a boat.

High nitro is a very fickle beast..........................................................It has a life of its own.

Most of the time you stumble on the right setup by trial and error. The problem is it will all change the next day.

So conservative setups are the way to go as thy do not change as much.

Gust my ranting at the beast........................................!!!!!
 
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David, I agree.

I was very, very lucky to have Mr. Jim Wilson do a lot of the prototype testing on the Zoom carbs in the beginning. If not for his help and expertise, the Zoom carb would not have been anywhere near as successful.

He was one of the first to learn about loading the engine to burn more of the nitro and the relationship to higher performance of the engines. He and Mark Sholunds great prop work contributed a lot to our understanding about adding progressively more pitch and angle to the prop blades to accomplish this. With their feed back and my flow bench, I began to understand more about our fuel systems, just what the numbers meant and how to apply this to on-the-water-testing. I learned how to control the fuel curve of the carbs in relation to the requirements of the engines and also how to vaporize the fuel much better than had been done before. The better the fuel vaporization, the smaller the fuel droplets and the better and more consistent that they would burn. A side benefit of vaporizing the fuel more was it cooled the fuel/air charge giving better driveability and allowing certain engine mods to deliver more power. As each change was made, they had to made changes in the engines and props to maximize these benefits. It was not an overnight success. It took many, many hours of building, testing and burning nitro to get as far along as we did.

Our fuel systems still have a long way to go to be perfect.

It is great to have good friends,

Charles
 
Charles Perdue said:
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David, I agree.

I was very, very lucky to have Mr. Jim Wilson do a lot of the prototype testing on the Zoom carbs in the beginning. If not for his help and expertise, the Zoom carb would not have been anywhere near as successful.

He was one of the first to learn about loading the engine to burn more of the nitro and the relationship to higher performance of the engines. He and Mark Sholunds great prop work contributed a lot to our understanding about adding progressively more pitch and angle to the prop blades to accomplish this. With their feed back and my flow bench, I began to understand more about our fuel systems, just what the numbers meant and how to apply this to on-the-water-testing. I learned how to control the fuel curve of the carbs in relation to the requirements of the engines and also how to vaporize the fuel much better than had been done before. The better the fuel vaporization, the smaller the fuel droplets and the better and more consistent that they would burn. A side benefit of vaporizing the fuel more was it cooled the fuel/air charge giving better driveability and allowing certain engine mods to deliver more power. As each change was made, they had to made changes in the engines and props to maximize these benefits. It was not an overnight success. It took many, many hours of building, testing and burning nitro to get as far along as we did.

Our fuel systems still have a long way to go to be perfect.

It is great to have good friends,

Charles
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"He was one of the first to learn about loading the engine to burn more of the nitro and the relationship to higher performance of the engines. He and Mark Sholunds great prop work contributed a lot to our understanding about adding progressively more pitch and angle to the prop blades to accomplish this."

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Sorry to butt in these OS Venturi are awesome ! Having a little getting it to center up on the 9B carb but it does fit great on the OS 40A with a plastic shim I found in the shop I work in. Was a end cap to keep dirt out that came on a new trans oil cooler line

image.jpg
 
 
Great fun this hobby we'll have EFI Closed loop before we know it. I spent hours of fun on a S/F 300 in 1977 just on Carb flow Vs. spray bar draw using an extra manometer on the spray bar. Makes you feel like you know something LOL but did improve drive ability.
 
yes very interesting indeed......................................................
 
Tom v.d Brink said:
Seem to have found back an older topic,

anyway I couldn't help myself......very interesting
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Am I reading this right? Is the Zoom carb the only one that makes the mid-range richer? Is this an accident...... or just maybe it is designed this way to give it better driveability under different throttle settings, hmmmmmm...........
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Charles
 
We did some testing on Walbro carbs for gasoline engines. It was interesting to see how much anything in or even near the venturi restricted the flow.

Lohring Miller
 
Yes, Lohring is correct, carb inlet clearance is much more sensitive than most people think. I have not tested the gas carbs for this but I have tested the nitro engines. On our toy nitro motors ANYTHING within 1/2 inch in front of or around the venturi will effect the consistent airflow into the carb. And if you really want to disturb the airflow going into the carb, allow air to blow ACROSS the venturi as in front rotor engines with the carb sticking up into the air stream. I am surprised that they run as well as they do. Many boater fight this problem without realizing what the problem is.

Charles
 
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