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Thread: Stroker 340 Lean Test

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    Senior Member turbopilot's Avatar
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    Default Stroker 340 Lean Test

    The last time I flew an airplane with a carburetor was the mid 1970's. How easy we forget.

    Anyway I have continued to investigate all the potential areas to lower cruise and climb CHT's. Since getting my Carbon Cub last April I have noticed how the CHT's move around as the mixture setting was changed but never really took the time to understand what was going on.

    So today I decided to run a lean test. The last time I flew a carbureted airplane there was no CHT or EGT, much less a multichannel version. Pretty much just looked at the oil temperature and leaned for peak RPM. How things have changed. Anyway after flying for years behind fuel injected engines with tuned injectors where every cylinder was running within .1 or .2 gallons of the same mixture I am enjoying a walk down memory lane with Carbon Cub's old carburetor. Yes, it is light and simple but very crude.

    So here is the lean test today.



    First thing that jumps out on this test is that the front half of the motor is in a different mixture world than the back half. There is a .9 gph difference between the leanest cylinder #2 and the richest cylinder #4. So if you were to lean this motor to best power (50 dF rich of peak EGT on the leanest cylinder) you would be running around 6.1 gph no where near the "best power" available to the engine at this throttle setting. The good news is you would see lower CHT's.

    Since there is such a gap between the leanest and richest cylinders "best power" (based on the RPM readings, I have a cruise prop) is somewhere around 5.1 gph. At this fuel flow setting #1 and #2 are running near peak EGT while #3 and #4 have not yet reach best power EGT levels.

    Of interest in the airplane I was able to run without missing as #1 and #2 went 20 to 30 dF lean of peak, just as #3 and #4 were hitting peak. So it looks like at this power setting I don't need all the fancy equipment, just lean until #1 and #2 are so lean LOP they miss, then richen until smooth and you are probably at the best point.

    It would certainly be good news if we could figure out a way to get the same mixture to each cylinder since it would appear you could then run 20 or 30 dF LOP and get very efficient power and much lower CHT's.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member RanRan's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by turbopilot View Post
    There is a .9 gph difference between the leanest cylinder #2 and the richest cylinder #4. .
    That's approaching a 20% difference between front and back cylinders. That should be fixable with a simple baffle or two within the induction box to equalize the mist feed.

    It would be interesting to see if or how ECI regulates air flow in their cold induction box on their fuel injected version of the engine.

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    Senior Member John Hodges's Avatar
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    Default Re: Stroker 340 Lean Test

    Do other engine builders or manufacturers use intake manifold plenum baffles or dividers to equalize mixture distribution?

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    Senior Member turbopilot's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by 8zq View Post
    Do other engine builders or manufacturers use intake manifold plenum baffles or dividers to equalize mixture distribution?
    Certainly worth looking into.

    I would like to know the weight penalty to convert this engine to fuel injection. If we could run the motor cooler and more efficiently LOP with fuel injection any weight penalty may be easily made up by the reduced fuel (and associated weight) required to operate the engine compared to a carbureted engine.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member RanRan's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by 8zq View Post
    Do other engine builders or manufacturers use intake manifold plenum baffles or dividers to equalize mixture distribution?
    Yes, (and even plastic baffles) but typically it's taken care of by the design of the manifold itself - larger passageways to the furthest cylinders from the air intake. But the Stroker uses a warm induction box to heat the mixture up - so it's not a manifold per se.
    Last edited by RanRan; 10-11-2010 at 07:00 AM.

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    Senior Member RanRan's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by turbopilot View Post
    Certainly worth looking into.

    I would like to know the weight penalty to convert this engine to fuel injection. If we could run the motor cooler and more efficiently LOP with fuel injection any weight penalty may be easily made up by the reduced fuel (and associated weight) required to operate the engine compared to a carbureted engine.
    ECI's fuel-injection is mechanical. There is no computer or O2 sensor. The injectors are squirting ALL the time and not into the cylinder but before the valve. The pilot still has to lean the mixture. But it should run cooler since the FI mixture is not pre-heated. If there is an increase in HP (there should be), then you can bet that they solved the distribution problem IN their cold induction box or simply by feeding colder air to the cylinders - or both.

    But if the FI air distribution is still not equal then you'd have the same lean/rich differences between cylinders and have solved nothing.
    Last edited by RanRan; 10-11-2010 at 07:54 AM.

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    Senior Member turbopilot's Avatar
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    Default Re: Stroker 340 Lean Test

    Based on a brief look at the ECI web site it looks like the Stroker 340 could be easily converted to fuel injection. Looks like it would require conversion to the cold induction system.

    Fuel Injection Retrofit Kit is $2,591.
    Cold Induction Retrofit Kit is $2,162.

    So for $4,753 plus labor it looks like the Carbon Cub could be fuel injected. Could someone from CubCrafters or ECI comment about whether this conversion can work in the Carbon Cub. I would be inclined to do it on my E-LSA if it appears feasible.
    Last edited by turbopilot; 10-11-2010 at 07:24 AM.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member RanRan's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by turbopilot View Post
    So for $4,753 plus labor it looks like the Carbon Cub could be fuel injected.
    Crudely fuel injected without any guarantee of fixing the initial problem.

    Here's what I would do...(I'm not recommending anything to anyone)

    Weld a 1/2 nut to the intake pipes of the rich cylinders. Screw in a 1/2 bolt (it will act like a baffle) until the temp numbers get more in line with each other. Lock down the bolts and enjoy.

    Talk to your mechanic - it's an elegant fix because it's adjustable.
    Last edited by RanRan; 10-11-2010 at 08:43 AM.

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    Senior Member turbopilot's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by RanRan View Post
    Crudely fuel injected without any guarantee of fixing the initial problem.

    Here's what I would do...(I'm not recommending anything to anyone)

    Weld a 1/2 nut to the intake pipes of the rich cylinders. Screw in a 1/2 bolt (it will act like a baffle) until the temp numbers get more in line with each other. Lock down the bolts and enjoy.

    Talk to your mechanic - it's an elegant fix because it's adjustable.
    That's an interesting suggestion. Have you had experience with this solution?

    It would appear the air/fuel mixture is richer in the front induction tubes than it is in the rear tubes. Just wondering how restricting flow in the front tubes would help since the ratio of fuel and air should stay the same.

    I have checked the induction tubes on my aircraft for leaks. I don't see any. I also see no evidence of a gasket between the intake tube and cylinder head on all four cylinders. Should there be a gasket?. Appears to be metal to metal fit though I don't see any obvious gaps in the junction. An induction leak can cause mischief but in my case it would have to be same size leak on both sides based on the lean test results.

    I wonder about a calibrated air leak on the induction tubes with the rich mixture.
    Last edited by turbopilot; 10-11-2010 at 09:18 AM.
    Bob Anderson, CC11-00435, N94RA

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    Senior Member RanRan's Avatar
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    Default Re: Stroker 340 Lean Test

    Quote Originally Posted by turbopilot View Post
    That's an interesting suggestion. Have you had experience with this solution?
    Yes. Years ago I worked for and with a former WWII Luftwaffe mechanic. He was amazing when it came to engines. He'd pull plugs on an air-cooled Porsche engine. "Do you zee za difference?" And then routinely baffle the rich running cylinder/s if he knew the problem wasn't with the spark or rings or carbs.

    As an aside - We worked on a lot of Rolls Royce cars. He said they had the best engines of all. Many Messerschmitt 109s were powered by Rolls engines and said they were better than the M-B engines. He would know.

    To answer your questions - if you don't see a gasket then there is probably an 'O' ring at the junction. And the mixture wouldn't change, just the pathway, and therefore, amount sucked in by each cylinder. The question to ask is if the front cylinders are just running cooler or starving the back cylinders because of bad or no baffling in the induction chamber? It might be both. A cooler running cylinder will always suck in more mixture...and there's the rub...you want more fuel to the hot cylinders. The only way to do that is baffle or add another carb.
    Last edited by RanRan; 10-11-2010 at 11:10 AM.

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