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Magnum .91FS!

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Old 03-26-2005, 12:44 PM
  #1
Cogburn
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Default Magnum .91FS!

Just got done running in my new magnum .91fs. 150$ on sale at tower! Adjusted the valves and tried a few props. Here's what i'm getting!

39'f , 30.15"pressure
15% omega with 2% castor added

11x9 apc 11600rpm 1.47hp
12x8k ma 10650rpm 1.43hp
14x6k ma 10250rpm 1.77hp
Peaked
HP from thrusthp
These things must fall off fast after 10000rpm.
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Old 03-31-2005, 11:51 AM
  #2
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Default RE: Magnum .91FS!

don't trust thrusthp calculator.
I have same engine, running on 5%nitro and 18% castor
here are some results

MA 13X8k 8.3lb
MA 13X8 3blade same, but more speed
top flight 15X6 9.7 lb
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Old 04-14-2005, 05:13 PM
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Default RE: Magnum .91FS!

I dont touch the valves. I ran 2 tanks through my $149 tower motor too! I put a Master Airscrew 14x6 and pulled consistently 10,500 static. I put a 15x6 APC on it and pulled 8900. This is with Cool Power 30% Heli. This motor is a hog man, I love it.
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Old 04-27-2005, 11:35 PM
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Default RE: Magnum .91FS!

I ran mine a couple years ago and was 9500 with a 14-8 APC 1,100' @40F.

It was stronger than my OS 91 Surpass I which was 9400 with a 14-6.

Saito 80 was 9200 with a 14-6.

All same day with Omega 10%
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Old 05-08-2005, 09:49 PM
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Default RE: Magnum .91FS!

Now 3 gallons through my Magnum .91 for $149 on 30% Heli..... I spin an APC 15x6 at 10,000 even. This motor is incredible. Stronger than my newer .91 OS Max!!
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Old 05-12-2005, 12:25 AM
  #6
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Default RE: Magnum .91FS!

thats joke yea? how can 91 magnum spit 15X6 on 10k? I can't believe. check thrust or recheck tchometer. if it'sso, lets god be with u. just wonderfull
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Old 05-12-2005, 05:36 PM
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Default RE: Magnum .91FS!

It the 2nd one I have that turns a 15x4 or 6 at static 10,000. I have a Magnum tac and a Glow Bee tach. Both the same. The motor is screaming, I believe it. I will get some vid clips up soon. Take in mind, I run 30% nitro too... I run them rich, always run afterrun oil, and let the good times roll. Its 3D, So I dont need to wind them up, but they will!
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Old 05-18-2005, 09:39 PM
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Default RE: Magnum .91FS!

14x6 APC 9900 rpm on Wildcat 15% full synthetic
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Old 11-21-2005, 06:59 AM
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Default RE: Magnum .91FS!

HOw long after break in does it take to get to these rpmĀ“s

I was breaking mine in yesterday and with a 14X6 MA prop and 10% fuel I was getting around 7500. It was super rich but I cant see another 2500 RPMĀ“s coming out of this engine.
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Old 11-21-2005, 07:07 AM
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Default RE: Magnum .91FS!

I just looked through some tach readings on other four strokes and you guys are getting close to the same readings that guys are reporting on Saito 100.

I just dont see how that is possible. Am I the only one not getting huge numbers on a Magnum 91?
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Old 11-22-2005, 01:25 PM
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Default RE: Magnum .91FS!

High nitro helps a lot in 4-stroke engines nowadays. Usually you can get 500+ rpm gain going from 15% nitro to 30% nitro.

Having said that, the Saito 100 and Magnum 91 4-stroke differ in power by about 500 rpm on the same prop and same nitro. So I can believe that Magnum 91 on 30% nitro will catch up with Saito 100 on 15% nitro, if both use the same prop that's within comfortable range of the 91. However, running expensive 30% nitro fuel on a Magnum sort of defeats the benefit of Magnum's economy. I've found that 20/20 fuel is a good compromise between fuel cost and performance.

Saito 100 will out-pull a 4-stroke 91 significantly when you go to larger prop, like APC 16x4W.
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Old 11-23-2005, 07:56 AM
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Default RE: Magnum .91FS!

I think you will lose a couple of hundered Revs when it is over 80 degrees out. Anybody rememember what they were getting last summer?
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Old 11-23-2005, 05:22 PM
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Default RE: Magnum .91FS!

Over 80 degrees. We hardly fly when its under 95!
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Old 12-12-2005, 07:16 PM
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Default RE: Magnum .91FS!

Magnum calls for no more than 15% nitro, so what happens when you run 30%? Are any of you running into detonation issues?
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Old 12-13-2005, 04:47 PM
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Default RE: Magnum .91FS!

Quote:
ORIGINAL: Gringo Volador

I just looked through some tach readings on other four strokes and you guys are getting close to the same readings that guys are reporting on Saito 100.

I just dont see how that is possible. Am I the only one not getting huge numbers on a Magnum 91?
Gringo, I'm with you. Some of these numbers are just incredible. I bet some of these guys have got the special "one that got past QA" car that does 1000 mpg too.

I mean...., one guys gets 10,000 with an "APC 15x4 or a 15x6". Well which one - or were they the same load?

Also, 9500 with an APC 14x8 on 10% nitro. This is not only at least 600 rpm stronger than any OS, Saito or TT .91 I've ever tested (and I've tached a few now) but is more than 200 rpm stronger than my Saito FA100 can get on 20% nitro.

I wish some guys would take more care when reporting rpms.
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Old 12-14-2005, 01:05 PM
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Default RE: Magnum .91FS!

I have 3 of these motors, two of which I regularly fly with Powermaster 20/20 fuel. I'm near enough to sea level and generally fly in typical Southern California 72 degree weather.

One is in Funtana 40 spinning an APC 15x4W prop. Not sure of exact tach readings, but I do remember that it is reguarly right around 9900 - 10000 slightly rich (I always run rich for 3D stuff to keep it from leaning out in manuevers).

However, my other one is in a Corsiar warbird. Looking for speed here, but I just don't seem to be getting a lot of love. For instance, a 13x9 prop only spins in the 8000 range which seems low. I've had to resort to running 12" props... right now I'm at a 12x11 that spins in the 9000 rpm range, and performance is decent for level flight but not a lot of thrust (as to be expected).

I've tried everything... adjusted the valves (both tappet clearance and pulling the head to clean the seats) and even checked the cam timing.

Perhaps I'm just expecting too much, but there seems to be a noticible power difference between the two motors. I certainly do not seem to be getting anywhere near the numbers being reported in this thread with that second motor...
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Old 12-14-2005, 03:20 PM
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Default RE: Magnum .91FS!

Endor, to see if your engines are performing up to par, try this: if you have an APC 13x8 handy, put this prop on and tach your peak reading on both your engines.

If your engines are in the .91 four-stroke ballpark, you'll get mid to high nines. On the same day, on 10% nitro, I did this with a guy's TT .91 and another guy's Saito .91. They both got around 9800 rpm at sea level.

Remember that from day to day, up to at least 200 rpm variation in readings can take place due to, among other things, temperature and humidity.
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Old 12-15-2005, 11:53 AM
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Default RE: Magnum .91FS!

Harry,

Thanks for that tip. Some time ago I did try a 13x8 and seem to recall that it was only running in the mid-8000's on YS 20/20 fuel, but the motor was relatively new then and may not have been fully broken in. I'll grab that prop, a bit of my friend's 10% nitro fuel, and tach it out.
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Old 12-25-2005, 11:59 PM
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Default RE: Magnum .91FS!

A follow-up...

Ran an APC 13x8 on the Mag 91FS. With Powermaster 20/20 fuel it pulled right at 10k on a cool day (mid-60s).

Wow, it must have finally broken in (it has about a gallon through it) because I do remember it not pulling anywhere near that RPM when the engine was newer.

Thanks for that tip Harry, at least I know I'm in the ballpark with other motors.
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Old 12-27-2005, 04:26 AM
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Default RE: Magnum .91FS!

Endor,

Thanks for the followup post. It sounds like she's a good strong engine and it should get even better with a few more hours up.
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Old 01-14-2006, 09:56 AM
  #21
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Default RE: Magnum .91FS!

wow! I must say that some people are getting really impressive rpm`s out of this engine. Mine runs 10400 on dynathrust 13/6. 9200 on apc 14/6 and 8800 on master airskrew 13/8 k- series. I must be doing something wrong I guess. I run a 15/15 fuel.I`ve just installed a new liner and ring and set the valve clearances, so hopefully mine will run stronger than this when it`s fully broken in again.
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Old 02-18-2006, 03:22 PM
  #22
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Default RE: Magnum .91FS!

Here is an engine tuners calculator that might explain some of the RPM variations.
http://www.wahiduddin.net/calc/calc_hp.htm

[8D]
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Old 02-22-2006, 02:32 PM
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Default RE: Magnum .91FS!

I set the needles on a friends new Magnum 91 Four stroke last Thursday. It turned a 14-6 MAS at 9900 with Omega 15%. It was about 70 F outside.

Enjoy,

Jim
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Old 03-18-2006, 12:00 PM
  #24
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Default RE: Magnum .91FS!

I see a lot of you guys are running 15% nitro in the magnum. I am running 5% and now that it is fully broken in I getting close to 10000 on a MA 14X6 .

Mine has about 3 quarts of fuel through it.

All that to say is that this engine runs just as well on low nitro so some of you guys could save a few bucks on fuel.
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Old 11-27-2006, 12:57 PM
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Default RE: Magnum .91FS!

To kick an old thread...

Broke in my .91 yesterday. We're at about 700' above sea level and it was 60 deg. F. Spent all day running and cooling the engine. Granted it's still new with only maybe and hour of run time, but I was a bit disapointed in the RPM readings as they seem low. I have it on an Astro Hog so I'm not looking for speed I just want to be sure it's running right.

I tried to run it mostly with good smoke for the break in but when I leaned it out, it maxed out at 9250 with a wood 14x6 break-in prop. Of course I would richen it for flight but I was checking the max a couple of times.

Backing it off to 8900 to simulate a flight setting did not produce much smoke or goop on the wing. The manual says to fly with a smoke trail but I have to drop 600+ RPM to do that.

I'm running 20% oil, 6% nitro home brew fuel. I mixed a few gallons for break-in of a couple engines.

Oh, I'm running the McCoy Miracle 4stroke plug.
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