WTB - A set of Rotax 912 Intake Manifolds.

[murrayg]

Looking to buy a set of Rotax 912 Intake Manifolds to install a larger crossover tubes, a la    https://www.flygas.info/2017/06/18/311/

 

Anyone got any spares?

 

Cheers

 

Murray

 

 

[skippydiesel]

Can't quit see the benefit(s) .

 

The promotional words seem to focus on poorly maintained carby's (not balanced) and the loss of one carby control cable (more poor maintenance). Talks about power but does not quantify.

 

In the immortal words of our lady of the chip shop - please explain??

 

 

[Thruster88]

The only benefit I can see is his wallet will be lighter. Those lazy bum engineers from Rotax have had 25 years now to put this system on the 912, actually they don't seem to have made any improvements in all time? 

 

 

[murrayg]

I did a Carburettor balance and made a larger ( temporary) crossover pipe and all ican say is it made a huge difference. Smooth as silk at idle and cruise. I cannot say how much was due to the balance as they were both done at the same time, but logic says to me that a larger crossover will help to make up for any inequalities.

 

So the reason for getting another set of manifolds is so that I can compare the two. I am quite prepared to accept that I am wasting my time, but progress is not made by sitting on ones arse.

 

 

[skippydiesel]

Fair enough! Good luck - perhaps you will tell us how it all went.

 

 

[Thruster88]

I did a Carburettor balance and made a larger ( temporary) crossover pipe and all ican say is it made a huge difference. Smooth as silk at idle and cruise. I cannot say how much was due to the balance as they were both done at the same time, but logic says to me that a larger crossover will help to make up for any inequalities.

 

So the reason for getting another set of manifolds is so that I can compare the two. I am quite prepared to accept that I am wasting my time, but progress is not made by sitting on ones arse.

 

In the intake manifold there is pulsation caused caused by the intake valve only being open for about 30% of the time. By adding this large additional chamber you could get a standing wave that resonates at certain rpm, the effect on mixture could be nothing or it could be detonation, burned exhust valve etc. If an incident were to happen the modified engine will do you no favours. Rotax have been producing this engine for 25 years and 40,000? examples, if it needed a bigger cross over i think they would have done it.   

 

 

[facthunter]

The system as it is, is unevenly phased and doesn't give a good mixture distribution There's no room for anything else like a crossover system so just set it up "perfectly" with each cable pulling evenly idle stops set correctly and live with it.. You need a damper/ restrictor in the pipe to the vacuum gauge to stop it pulsing.

 

 

[Kyle Communications]

We have been doing a lot of work on these issue. The throttle arms are not exactly the same in travel the way some of the throttle cables are setup this causes uneven mixtures. Solved by making extra arm fitted to one of the carbs and measuring the openings by adjusting the length of the arms to suit the throat opening. The larger cross tube made and fitted on several engines now and a much bigger improvement to burn pattern and idle and cruise smoothness. I think Rotax do not want to change anything because of all the extra paperwork for certification this is why. No different than when they made the new IS engine and changed the oil pump to a 6 lobe pump instead of keeping the original 4 lobe and they also changed the oil pressure relief valve design...because it was a new engine they did this as the was no extra cost. They fixed their mistakes without any extra real cost

 

 

[Kyle Communications]

 

[facthunter]

What you say is perfectly correct Kyle  but it's not really a good idea to have different ideas floating around with varying abilities to do "corrections" when the original set up is never going to be ideal and the carbs are pretty ordinary. One of the reasons the 912 gives reliability is generally it's left alone and not fiddled with. A bigger balance tube could transfer a back fire to the other bank. I would suggest it could work fairly well without any balance tube which has it's major effect at idle speed. The springs pulling the throttle to OPEN are 1/2 the problem with stiff and uneven cables. One cable to a linkage would be an improve.. Nev

 

 

[skippydiesel]

........................One cable to a linkage would be an improve.. Nev

 

Couldn't agree more. I have often contemplated trying to come up with an improved  throttle control system for the 912 but as yet haven't put any of my musings into action.

 

 

[murrayg]

Just to add fuel to the fire ?

 

https://teamkitfox.com/Forums/threads/8116-Carb-sync-Never-again?p=66172#post66172

 

The kitfox group have a discussion on this.

 

 

[murrayg]

And RANS

 

http://www.ransclan.com/forums/archive/index.php/t-5186.html

 

 

[murrayg]

And Zenith too

 

http://www.zenith.aero/forum/topics/flygas-intake-manifold

 

Interesting reading - but as with anything like this - subjective

 

 

[Kyle Communications]

Measure the length of travel of the throttle lever if its out just make a extension for one then you can even up the travel of the butterfly

 

Doing the 19mm tube mod also bought all 4 EGT to almost exactly the same where before 2 were more than 80deg higher than the others now they have come back to the same. The engine idles better and runs smoother

 

The mcFarlane twin cable throttle lever is the best around but really needs to be mounted in the centre of the dash not off to one side. But its a lot better than the savannah setup which has too much flex in the mounting plate and too much difference in cable lengths

 

 

 

[Tucano]

PM me I have a set

 

Gary

 

 

[murrayg]

PM sent

 

 

[Tucano]

Hi,

 

Found a set

 

 

[Tucano]

Murry,

 

I owe you a HUGE appology - This had left my mine TOTALLY

 

Ring me on 0490500605 URGENTLY

 

I will refund you money or ship this weekend

 

I APPOLIGIZE with no reservation.

 

Gary