Crossover pipe of Rotax 912 Carbys

[BrendAn]

10 minutes ago, facthunter said:

It was brought up if there was a risk of the Pipe collapsing, remember. I wouldn't be altering the original set up which is multiples lower in Volume. without a lot of testing including throttle response.  Nev

I understand that but I can't see how joiners would collapse.

[facthunter]

You Pull a pretty high vacuum with the throttle closed if the engine is in good Nick. Bigger dia Hoses are More susceptible, but it wouldn't be the end of the world in any case . You have to allow for a slight change of length. Nev

[Blueadventures]

Info building, they are out there.  Just saw this on a VG advertisement.

 

Also, last weekend was shown over a 912 supercharged that had a crossover pipe setup. Yep supercharged, great info for me to consider.

[Kyle Communications]

Mike you been looking at Tony's aircraft..he did it himself. Seems to be going well. Did you head up Townsville way or was he down your way

 

[Blueadventures]

8 hours ago, Kyle Communications said:

Mike you been looking at Tony's aircraft..he did it himself. Seems to be going well. Did you head up Townsville way or was he down your way

 

Met up at Burdekin breakfast a week ago. Like his bigger diameter prop. Very interesting setup by a talented mechanic. Cheers.

[BrendAn]

What hp is getting with the blower

[T510]

Do you know what supercharger is he using?

 

Be great to see some pics if anyone has some to share

[BrendAn]

5 hours ago, T510 said:

Do you know what supercharger is he using?

 

Be great to see some pics if anyone has some to share

there are many to choose from these days. there some nice small superchargers on jetskis.

[Kyle Communications]

On 16/02/2026 at 6:54 AM, Blueadventures said:

Met up at Burdekin breakfast a week ago. Like his bigger diameter prop. Very interesting setup by a talented mechanic. Cheers.

That was the prop I had bought for my S21. He managed to break his original Eprop dropping the noseleg into a deep wet hole one day. He has more hp so apparently he still had enough ground clearance to fit my larger prop as it was the only prop I had here. Its a 190cm because my engine will be close to 120hp. Although Eprop now are recommending going to a 4 blade if your 115hp or more rather than using a bigger 3 blade

[skippydiesel]

How about  some photos of the "supercharger" installation😈

[skippydiesel]

https://www.flygas.info/supercharger-rotax-91214/😈

[facthunter]

Boost THROUGH a carburetter is not a great idea. Full stop.  Nev

[turboplanner]

20 hours ago, facthunter said:

Boost THROUGH a carburetter is not a great idea. Full stop.  Nev

No + compression ratio to be considered. Make an interesting sound when they blow in street racing, but there the occupants can step out and push it off the road.

[409tonner]

Rotax has been successfully blowing through carburettors for many years on the 914

[BrendAn]

21 hours ago, facthunter said:

Boost THROUGH a carburetter is not a great idea. Full stop.  Nev

What do you base that idea on 

[Marty_d]

22 hours ago, skippydiesel said:

https://www.flygas.info/supercharger-rotax-91214/😈

I hope their engineering is better than their spelling.

Their manual has a "Foreward" (foreword), and talks about the "lubrification" system.

[facthunter]

It's not often done and is generally considered not to be  the way to go with float carburetters.. Nev

[onetrack]

Pressurising a carburettor via a supercharger brings with it a substantial number of problems. For a start, all carburettors operate on vacuum and venturi principles.

 

When you pressurise a carburettor, it reverses all the basic carburettor principles. Supercharger pressure means all shafts must be sealed to prevent fuel leaks.

The standard venturi effect does not compensate for air pressure. As boost rises, the carburettor can lean out, leading to dangerous combustion chamber temperatures, even broken internal engine components (pistons/rings).

 

It is difficult to keep a supercharged carburettor from running too rich at idle and light throttle, because the idle circuits are pressurised.

 

Carburettor gaskets must be seriously modified or eliminated, as standard carburettor gaskets can blow out, or leak fuel under pressure.

 

The boost pressure from the supercharger can force fuel past the carburettors needle and seat, causing the float bowl/s to overfill, flooding the engine.

 

 Standard fuel pumps cannot handle a supercharged carburettor setup. You must use a boost-referenced fuel pressure regulator that increases fuel pressure in direct proportion to boost pressure. If the fuel pressure does not remain higher than the boost pressure, fuel will be forced backward, emptying the float bowl/s.

 

If the carburettor floats are not designed for high pressure, standard floats can collapse under the intense pressure of the supercharger, leading to a catastrophic loss of fuel control.

 

Supercharging a carburettor can lead to intake icing. As the supercharger compresses the air, the cooling effect of fuel vaporisation can cause intake temperatures to drop below freezing inside the carburettor, leading to ice formation on the throttle plates, even in warm weather.

 

The high-velocity air forced into the carburettor may not supply all air or emulsion bleeds in the carburettor evenly, causing some cylinders to run leaner than others.

 

In summary, the addition of supercharging to an aircraft engine via carburettor pressurisation, brings with it a substantially increased level of complexity in components and tuning requirements, which is not desirable in an application where that level of complexity lays the groundwork for increased engine unreliability.

[facthunter]

VERY well explained. Simply put, the carburetter is not designed for it  and can't really be.  Injection would be fine. Direct preferably  That would stop damaging backfires, that can happen on start up Nev

[Blueadventures]

47 minutes ago, onetrack said:

Pressurising a carburettor via a supercharger brings with it a substantial number of problems. For a start, all carburettors operate on vacuum and venturi principles.

 

When you pressurise a carburettor, it reverses all the basic carburettor principles. Supercharger pressure means all shafts must be sealed to prevent fuel leaks.

The standard venturi effect does not compensate for air pressure. As boost rises, the carburettor can lean out, leading to dangerous combustion chamber temperatures, even broken internal engine components (pistons/rings).

 

It is difficult to keep a supercharged carburettor from running too rich at idle and light throttle, because the idle circuits are pressurised.

 

Carburettor gaskets must be seriously modified or eliminated, as standard carburettor gaskets can blow out, or leak fuel under pressure.

 

The boost pressure from the supercharger can force fuel past the carburettors needle and seat, causing the float bowl/s to overfill, flooding the engine.

 

 Standard fuel pumps cannot handle a supercharged carburettor setup. You must use a boost-referenced fuel pressure regulator that increases fuel pressure in direct proportion to boost pressure. If the fuel pressure does not remain higher than the boost pressure, fuel will be forced backward, emptying the float bowl/s.

 

If the carburettor floats are not designed for high pressure, standard floats can collapse under the intense pressure of the supercharger, leading to a catastrophic loss of fuel control.

 

Supercharging a carburettor can lead to intake icing. As the supercharger compresses the air, the cooling effect of fuel vaporisation can cause intake temperatures to drop below freezing inside the carburettor, leading to ice formation on the throttle plates, even in warm weather.

 

The high-velocity air forced into the carburettor may not supply all air or emulsion bleeds in the carburettor evenly, causing some cylinders to run leaner than others.

 

In summary, the addition of supercharging to an aircraft engine via carburettor pressurisation, brings with it a substantially increased level of complexity in components and tuning requirements, which is not desirable in an application where that level of complexity lays the groundwork for increased engine unreliability.

Agree that is why the Rotax 914 cab bowl is held in place with a bolt in the bottom of the float bowl (the spring on the 9i2's is not strong enough).  Over time the bowl to cab gasket leaks and people tighten the nut and redo it a number of times this causes the bowl to deform and the carb float pins splay out and effect the movement of the floats.  Attention is needed for this when servicing and maintaining the 914's.  I'm personally happy with the 912's. 

Edited yesterday at 12:07 AM by Blueadventures

[Moneybox]

There's a lot of speculation here guys. If Rotax can successfully produce a turbo charged engine on basically the same principal then I'm sure it can be reliably done.

 

Some of you're statements just don't add up like fuel being forced back past the needle. You're talking of an area within the venturi, a low pressure area drawing fuel by low pressure produced by the rapid flow of air. The float bowl is vented to atmospheric pressure, there'll be no pressure pushing fuel back down the line. Sure in a standard setup the breather for the float bowl is within the air intake but that would be a minor modification. How is compressed air going to increase the risk of icing?

 

Lots of unsubstantiated negative comments, just what we expect from from the masses when we see new innovation. We should embrace new inventions and technology and enjoy the outcome.

[facthunter]

Rubbish Mate. Face FACTS. Facts can't hurt you. Blind trust can. It's NOT a new principle. and O/T covered it thoroughly. I don't see that  as unsubstantiated. Quite the Opposite. Nev

[Moneybox]

Nev, what you're trying to tell us is that Rotax stuffed up badly when they produced the 914 Turbo, as 409tonner pointed out, it works on a similar principal. And the FACT is it obviously works. Why all the negativity? 

[Siso]

I reckon, back in the day they use to put carb in a box and pressurise the box. The floats would have neded modifying.

[facthunter]

This Obviously WORKS is NOT the answer. That's confirmed by the Bolt instead of a spring  and extra inspections which Indicates excess pressure in the Bowl which has predictable consequences. It's NOT negativity to  investigate  and comment on such things no Matter What brand of Jigger it is ON. That particular Carburettor is a Pretty cheap and Nasty thing to have on a modern (and expensive) engine in an aeroplane. It's way out of date. There's infinitely Better stull on good ride on Lawnmowers with one throat to each individual cylinder. nev