balance tube

by bill martin in General Tech Discussion 11 years ago

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Re: balance tube

by Nate Dyk » 8 years ago

Nate Dyk

5 6 0

How has that balance tube been working for you?
It seems like a great idea.
Thank you for your post.
It is very tricky adjusting the throttle stetting so the Rotax 912 is balance through it entire rpm range.
Throttle cable set up is very critical.
It seems from your finding that increasing the diameter of the cross over tube might mitigate throttle linkage discrepancies between the carbs.

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Re: balance tube

by Nate Dyk » 8 years ago

Nate Dyk

5 6 0

you might look at this link another Bill used a 3/4 inch cross over tube. he did not mention any roughness at higher rpm. His mod also did not change the location of the carb.
http://www.zenith.aero/forum/topics/flygas-intake-manifold?page=1&commentId=2606393%3AComment%3A488645&x=1#2606393Comment488645

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Re: balance tube

by Roger Lee » 8 years ago

Roger Lee

125 5.12k 4.52k

Anyone ever think that Rotax picked a 3/8" tube for a reason? Why they didn't pick a smaller or larger one? Why with the thousands of hours of testing and research they deemed the current tube the correct size?

If you changed something you must have a good reason why the current items doesn't work and why your idea would out perform the current part. Surely this isn't just a shot in the dark.

Anyone able to answer these?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Ken Ryan

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Re: balance tube

by James Ott » 8 years ago

James Ott

22 322 358

Just a thought Roger, but I know that race car engines tune their intake manifolds (also exhaust systems) to very specific volumes and lengths to achieve a boost effect from the air column as it resonates with valves opening and closing. Could it be that Rotax has tested this effect and found that a larger or smaller crossover tube with a different volume actually reduces the intake efficiency? Something like that is very easy to test on a dyno and I can't imagine that Rotax has not done it.

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Re: balance tube

by Roger Lee » 8 years ago

Roger Lee

125 5.12k 4.52k

Hi James,

I truly don't know since that was in the design phase and during other research through the years, but I do know they had their reasons. I'm sure those engineers are a bit smarter than me and have money and the tools to do research we can't afford or duplicate.
I'm sure Rotax has done dyno test and that's another reason not to change the size of the intake tube inadvertently. Unless you do the testing then anything else is just a shot in the dark without a target. I see people all the time adding or removing parts on Rotax engines without a shred of testing, engineering understanding or a handle on the unintended consequences issues and doing it just because it sounds good. Not a good basis for messing with an engine that keeps you thousands of feet in the air with friends and family members onboard and then have an engine die or at a minimum a costly thousand dollar repair..
I have no problem with people who use science and facts to make changes or a better mousetrap, but doing it in a helter skelter fashion has never made good sense to me.

Could rotax make some new changes after all these years like an different reg/rec, probably and why they don't I don't know. may be just a time and money issue?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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