Was wondering if anybody had experience with the fLygas intake manifold for the rotax 912 it has a very large crossover tube it's supposed to eliminate carburetor synchronization.

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HI David,

Never heard of the fLgas intake manifold crossover, but the claim of eliminating carb synchronization is interesting. When you synchronize the Rotax carbs you are adjusting the throttle cable of one and comparing and manifold pressure to each carb, so I don't see how you would want that adjustment and setting eliminated. There is already a small crossover tube that can balance that somewhat, and maybe the bigger tube carries that fudge factor even more, but ultimately you still want and need those carbs synced. Maybe the larger tube allows you to "cheat" a little more if you'd like. 

Walt Snyder

Y'all,

My version was to drill out the original threaded hole on the intake manifolds for the cross over from about 3/8" to 3/4." Rule of thumb is double the cross section of a pipe and quadruple the flow. Then rounded up some 90 degree fittings ,3/4" barbed on one end and had an AN fitting on the other end. I cut off the AN fitting on one end and inserted into the manifold and had a friend TIG in place. Then used a good quality 3/4 hose with hose clamps for the cross over. I will say that it made a great difference, now silky smooth at all RPMs from idle  right on through the mid range.Before one could not really get it right, at all the different RPM settings even being extra careful. This mod along with getting the prop pitch right, so the engine can develop the needed RPM on climb out, has really transformed the way this plane performs.

Bill Alexander

Attachments:

A few more pictures.

Attachments:

Hi there,

Very nice modification. Did you gain any extra HP ? Flygus says it made some difference...

Should also be less critical on synchronization ???

Let us knowe !

Norm

Normand,

The cross over mod just made the engine run very smooth at all RPMs, What I did was get the carbs sinked as close as I could with a Twin Max, Then made the cross over mod and that really smoothed the motor out. Before the mod if you got it dead on say at 2000 RPM  it would be off a little at 2500 or 3000 or visa versa. 

Now on the HP thing I think it is most important to pitch the prop where you are getting at least 5450 to 5500 on climb out. Remember the HP of the Rotax is most dependent on RPMs. Anyway thats where I have mine set. I cruze at 5300 to 5400 RPMs, at about 95 MPH ind. At WOT level flight I can get 5850 RPMs at 108 MPH ind. Now with the prop set as it is the motor is a little more unloaded at cruse resulting in the EGTs running real close together. Of course it is cooler weather now,  and I am getting 900 to 1000 FPM climb rate, with 20 gals fuel and 210 lb me.

Bill

Bill,

I'm not at my plane right now, so I hope this question is correct.

What did you do about the parts that are in the middle of the crossover tube ? I think there is a tap which might be for manifold pressure, and some other parts in the middle of the tube. What parts did you change or modify ? Could you give additional info on the parts if some were replaced ?

Thanks,

             Jim

Jim ,

 If you look at picture 86 and 87 you can see a straight 3/4 nipple with a small tube teed in for the manifold pressure. Of course if you do not have a inflight adjustable prop, manifold  pressure is almost useless. I do not have an inflight adjustable prop but just happen to have a 3/4 nipple with the small tube teed in so I elected to use it, although not needed.

Bill

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