Carb Flowbench Testing

[lohring]

We were asked to test some gas carbs several years ago. Below is from the report.

"We could not test your carbs on the engine. Since we have a flow bench, we did airflow testing on all the carbs. In the past, differences in the carb airflow has translated into power differences. Specifically, the M&D modified WT-257 carb produces higher power than my modified WT-257 carb when tested on the same engine, even though my carb has a larger bore. Tiny details make the M&D carb flow better. All your carbs have the same .500 inch venturi bore. Below is the flow at 13 inches of water:

Modified WYK 81 cfm (.610 bore, barrel style carb)

M&D modified WT-257 65.5 cfm

Miller modified WT-257 63 cfm

WT-257 61.8 cfm

WT-287 58 cfm

WT-813 56 cfm

WT-745 55 cfm

WT-644 53 cfm (Modified WT-644 61 cfm)

WT-EX520 48 cfm

You can see why everyone runs the WT-257. I’m not sure why some carbs that look the same flow differently. You can see the effect of choke butterflies and protruding jets."

We mounted a Quickdraw cylinder on the flow bench and tested the flow through it. Below is the flow bench setup we used. The difference between a WYK and a WT-257 carb on a Quickdraw was around 1/4 hp on a 7 1/2+ hp engine



Lohring Miller

 

[RaceMechaniX]

Lohring,

I can also attest to the power gains on the QD motor with the prepped WYK with the right fuel. An unbeatable combo.

Have you been able to measure the crankcase mean vacuum to determine what test pressure to use? I make a simple approximation of airflow through the engine from displacement, VE and RPM. Then just used three pressures to sweep the flow rate.

TG

 

[Terry Keeley]

Great info Tyler, thanks for taking time with this.

I've tried 12, 13 & 14mm new style carbs on my 67 in the SAW boat and found the 14 (.550") too big, working with the 12 (stock) and 13mm sizes.

 

[RaceMechaniX]

Hey Terry,

Makes sense based on the volume a 67 can ingest compared to a larger motor even at ludicrous RPM's. You run a 9B in your 67 boats, so the bellmouth may just give you that little extra or you need to get yourself a Zoom carb to test.

BTW, I freely admit to picture stalking in your gallery



TG

 

[lohring]

Flow bench testing in two strokes is a problem since the actual engine is dominated by pulsating flows. People have built pulsating flow benches, but the flow through a carb can reverse direction. The engine's power is a sensitive indicator of how well the various parts of an engine work. We usually tested various components on the dyno using a standard engine. We have a welded M&D pipe we have used as a standard for years. Pipe testing compared new pipes to this on the same engine. You don't get absolute results, but it's easy to decide what carb or other component, is the best. In the above case we found several defective engine castings so were unable to run the carbs on the supplied engine.

That said, it is fun to see what little things do to the flow. You can see how much clearance you need around the carb. The effect of obstructions in the bore becomes obvious. You can see the effect of various bell mouths. It all needs to be confirmed on a running engine, though. That's why we didn't spend a lot of time trying to decide what pressures to run on the flow bench.

Lohring Miller

PS Thanks for sharing your results, Tyler

 

[Terry Keeley]

Hey Terry,

Makes sense based on the volume a 67 can ingest compared to a larger motor even at ludicrous RPM's. You run a 9B in your 67 boats, so the bellmouth may just give you that little extra or you need to get yourself a Zoom carb to test.

BTW, I freely admit to picture stalking in your gallery

normal_ScanImage282.jpg

TG

You Gallery Stalker you!

I've actually switched to the new style CMB carbs with the low end needle and really like how they work, sold off my 9B's.

I made an adapter plate to fit the 13 & 14mm carbs to the 67 and tried them, as stated the 14mm would work if you came up on the throttle really slow, open it too fast and it would just quit lean. The 13mm seems to work well but I'm not sure it's any faster than the stock 12mm. The 12mm throttles up quicker so might be better through the traps.

 

[Marty Davis]

I think that this type testing using comparison between available products is a good thing.

Several years ago, I offered a service for carb optimization which was a completely different approach to flow. This was designed to optimize an individual carb. It optimized the angle, the spray bar and the the bell mouth so that it was more efficient. All done on a flow bench at an air speed simulated with our use.

Both are important to us. Finding the best carb among many is probably a good first step. It can be done in a variety of ways including comparison using a flow bench or "on water testing". Most of us have to use the later because we don't have the flow bench.

John Ackerman worked at an aircraft maintenance company for 40 years and decided to look at the inlet on a jet engine for a clue as to the shape of the intake. Could this shape improve our carbs? The answer was YES. We started adding bellmouths that were shaped like that and the improvements were obvious. We did have the flow expert test these to see the result and they were impressive.

The topic is interesting for sure and the comparisons are good info. I just wish that I still had the contact for the flow guy who used to do this work for me. My racing partner has the only optimized carb that we still have and he won't let me have it

 

[dwilfong]

The spray pattern in the carb and how it enters the case will make more difference than any thing else.

Say Charles you taught me some thing to look at.

That is the reason for a wet flow box that is clear. thay way you can look down the throught of the beast and see light at the end of the tunnel.

Can also see how it enters the box.

Robin gave me the idea of using a strobe light.LOL

It worked................................. stops the droplets in mid flow.

Kinda transindental with the howl of the vacuum and the strobe going.................................................wooooow duuuude.

Give it a try you may like it.

Then again it may just give you a head ach.

The jet eng intake gave a good pattern but Dale Powel's advice gave the best results.

The dang carb iced over LOL

What works the best dose not look like or seam like it will work.

Flow is not the answer.

Pressure drop threw the carb at a specific point is.

when introducing large volumes of fuel in to the air stream you clog the carb. Air flow with out taking into consideration how the fuel will affect it is only a rule of thumb. It will change with designed fuel delivery to the air stream.

Let me ask this. Those that have run a eng under load on pipe with a dino. Was there a plum in front of the carb at this point in the run?

 

[moparbarn]

I told ya a strobe or engine timing light would show & teach you a lot (-; it's a trick I learned way longer ago than I care to admit. I used it to help jet multi carb setups on mopars. Just synching air flow is only part of it. Without a Boris meter or third channel, we would use a timing light under the hood to literally "eyeball" fuel flow with the engine running at different rpm's. You would be surprised at how much different jets having the same part# can be!! Remember that when you get the 'stream back in the water, David.

 

[dwilfong]

Yes I will try the timing light in the carbs trick. Don't want to melt down a 300+HP Merc 2.5

I think it will be a little more $$$$$$$$$$$$$$$$$$$$$$$$$ than a 1.01 LOL

Getting close now..................

Pretty strong for a old man now aaaaaaaaa

 

[Charles Perdue]

I do not think that you can separate any one facet of the carb and its affect on performance. It is like most everything else, it is the entire package that matters (for a good example of this, look at a woman). All areas and how they relate to the other are very important.

Yes, a strobe light allows you to see fuel/air patterns. I used it for a while. I now use a ultaviolet dye in the fluid that I flow the carb with and when I turn out the lights and use an ultaviolet light source to view the spray patterns, they become very visible. Another use for the ultraviolet dye is in the smoke generator that I use in this chamber to see the airflow patterns in and around the carb.

On the flowbench, the entire carb assembly is mounted inside of a sealed plexiglass chamber with air flow measured as it enters the chamber. I not only take fuel draw readings on the spraybar, I have a tiny probe that I can move to any area of the carb while it is being flowed in this chamber for very precise spot readings.

I did not develop my test apparatus instantly. It was developed over a period of years as I tried to learn as much as I could about our fuel systems. A lot of what I learned is in the Zoom carbs as they evolved over time.

I like to see others working on these things to. No one knows it all, and I still play with carbs ever once in a while.

Charles

 

[Derret]

Terry- Funny how modelers are now getting 'it' about tuning motors using a low speed needle-

The biggest reason I stopped offering the RPM carbs was the endless tuning problems that came up with them.

The average boater most often failed to (Could?) understand the tuning with both hi & low speed needles & how much you can move the torque curve with different settings- sorta like NASCAR left turn only deal-

Surprising how much supposed 'experts' don't know about carb /engineering tuning- I sure found that out-

In recent times the advent of gas carbs/motors use has forced this learning curve-

Nitro is easier to tune I think- think of it as being a crutch to cover many bad ideas for most tuners-

Once past the carb now you get to a tuned pipe- getting it to work right with the carb- now we have a whole new game over & over again tween the carb & pipe-

I'm no quitter but had to stop the carb deal to stay sane & healthy-

Retirement is great-

Be well-

Dave Richardson

 

[dwilfong]

Glow in the dark fuel with the black light.

Now we are talking........................... Woooow duuude.

Have that setup in my service truck to find oil leaks. Will give it a try when I get back at it.

So right Charles a carb is like a woman.

Don't let it control your destiny.....................................................Try a different one. LOL

 

[John Beardslee]

This all reminds me of the old days when Ford and GM viewed an intake manifolds as a carburetor bracket and Chrysler was working on flow with Tim Connely the lead and really making giant steps in performance. circa 1976.

Thanks, John

 

[Terry Keeley]

Terry- Funny how modelers are now getting 'it' about tuning motors using a low speed needle-

The biggest reason I stopped offering the RPM carbs was the endless tuning problems that came up with them.

The average boater most often failed to (Could?) understand the tuning with both hi & low speed needles & how much you can move the torque curve with different settings- sorta like NASCAR left turn only deal-

Surprising how much supposed 'experts' don't know about carb /engineering tuning- I sure found that out-

In recent times the advent of gas carbs/motors use has forced this learning curve-

Nitro is easier to tune I think- think of it as being a crutch to cover many bad ideas for most tuners-

Once past the carb now you get to a tuned pipe- getting it to work right with the carb- now we have a whole new game over & over again tween the carb & pipe-

I'm no quitter but had to stop the carb deal to stay sane & healthy-

Retirement is great-

Be well-

Dave Richardson

Hey Dave:

I ran your carbs for years, used to mark a little arrow on the body to show which way to lean the low end.

Allowed me to run bigger carbs but still have good idle and transition, never understood why many guys cut the low needle out?

 

[Charles Perdue]

Glow in the dark fuel with the black light.

Now we are talking........................... Woooow duuude.

Have that setup in my service truck to find oil leaks. Will give it a try when I get back at it.

So right Charles a carb is like a woman.

Don't let it control your destiny.....................................................Try a different one. LOL

David, just do not do what I did....I took a pee with the dye on my hand and it made my Rooster glow in the dark.

You doing this could cause your wife to get hurt........She could fall out of the bed laughing when she sees you.

Charles

PS: Can anyone tell that we are snowed and iced in with not much to do?????

 

[John Beardslee]

Yup!!!!! Been there, done that. It's cabin fever for sure!!!

 

[lohring]

This is way off topic, but I'm considering an oxygen sensor for needle setting under load. The pictures below show a stinger setup a friend uses over the stinger of hot saw engines on his dyno. The silicone disk is replaceable for various stinger sizes. Several people say they don't have problems with oil in the fuel. A wide band sensor is fairly low cost these days. I have a drawing if anyone is interested.

Lohring Miller

 

[Charles Perdue]

Mr. Lohring,

Is the oxygen sensor in your photos the heated sensor? The reason that I asked is that for an oxygen to work accurately, it must be at a minimum working temperature of 600 degrees fahrenheit. Other than using the exhaust temperature, the manufactures also install a heating unit in the O2 sensor to reach this temperature. I could not tell from the photos if the sensor was a heated sensor which uses 4 wires and a 12vdc power source to the sensor instead of the 2 or 3 wired sensor which are not the heated units.

Charles

 

[julianconde]

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

Julian