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HomeAircraftHelicopterAlignOther › 91HZ to 105HZ (non-R) on 30% to 105-HZR on 15% - how much of a difference?
07-26-2018 09:40 PM  86 days agoPost 1
cudaboy_71

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sacramento, ca, u.s.

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I got an old v1 Trex 700 Nitro Pro going again for this year. I've just put my first full case of 30% through it and it's running fantastic.

Obviously, it's never going to perform like a powerful 700 electric. But, I know the 105 on 15% does offer a bit more power. But, specifically on this airframe--how much of a difference?

I know that's hard to quantify. But, someone who has flown the old 91HZ on this airframe and has upgraded would be able to give a relative answer.

Worth the $$$ to upgrade? Or is is just a nominal amount of power? Like I said, the 91HZ is running great. No need to throw $600 at it to only yield modest gains. It would take a lot of gallons to make the fuel savings pay for the upgrade if there's not a significant performance gain to make it worth it otherwise.

if it ain't broke, break it.

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07-27-2018 01:36 PM  86 days agoPost 2
wjvail

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Meridian, Mississippi

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Very difficult question. It's made more difficult by the fact I run my 1.05s (and .91s) on 30%.

But to your question.... I recently built a 700XN. When I built the kit, I had a .91HZ-R not installed in anything so I chucked it in the new build. I flew it with that engine for a while.

A few weeks passed and the 1.05HZ-R I had on order arrived. The question is muddied because the .91 was well broken in and I was flying it pretty hard. Of course the 1.05 was brand new so there was a brake-in period. It's not as if I could immediately see the difference because I had to run the 1.05 rich. It took a gallon or two to start leaning on the 1.05 a bit and by then I had forgotten exactly how the .91 flew.

But there is no question the 1.05 is a refinement of the .91. It does everything better. My personal impression is that it is easier to tune and has less vibration.

With the above said, I can't tell you it's worth $600 for the upgrade. I have 3, 91HZ-Rs and 4, 1.05HZ-R. They all run well. The 1.05s run better. But unless you really fly hard, or just want to impress your friends, run the .91. If your pocket book will allow, the 1.05 is a better engine but I can't tell you it is a must item.

"Well, Nothing bad can happen now."

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07-27-2018 02:03 PM  86 days agoPost 3
cudaboy_71

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sacramento, ca, u.s.

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Thanks. Those are just the kind of remarks I was hoping to hear. Of course, you didn’t make the decision any easier ;-)

I just need to manage the collective a little better when loading up the head. On big electrics it just plows through everything you throw at it. If the 105 can keep the revs up on that bleeding edge, it may make it worth the upgrade—one day.

But, for now I’ll keep the 91 in. It is a blast.

if it ain't broke, break it.

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07-27-2018 03:47 PM  86 days agoPost 4
wjvail

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Meridian, Mississippi

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cudaboy_71
If the 105 can keep the revs up on that bleeding edge, it may make it worth the upgrade—one day.

But, for now I’ll keep the 91 in. It is a blast.
It occurred to me... OS publishes horse power ratings for it's engines. Those numbers can be very misleading but using a like for like comparison may help. That is, comparing OS-HZ to OS-HZ may give some relative idea of how much the 1.05 adds.

Using the manuals in the link below, the power for these engines is:
OS .91HZ-R --- 3.4
OS 1.05HZ-R --- 3.75

My gut impression is the increase in power from the .91 to the 1.05 is about what the numbers suggest. It "feels" like a 10% gain. You can feel a clear increase in power but you won't drop your transmitter in amazement. Is .35HP worth 6 hundred? I wouldn't dare to guess.

I don't have enough experience to compare the 91 on 30% to a 1.05 on 15%. My guess is that it would end up being very nearly a wash power wise but you would save on fuel cost.

https://www.osengines.com/manuals/index.html

"Well, Nothing bad can happen now."

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