new 91 engine

[rjsanders]

I need some input on my next engine choice! Originally, I had decided on a ys 91 and have heard that it has some tuning problems on low nitro HV oil fuel? I currently use wildcat 15% helimix and like it alot especially the cost. Recently, I started looking at the new OS 91 sz-h and it seems to be the better choice as far as my fuel preference goes. I like the pressurized fuel delivery of the YS and was hoping someone who already has a OS 91 sz could provide some feedback to help me in my decision? Would it be a good option to get a c spec as an alternative to the 91 sz? Thanks a lot for the advice :)

[rjsanders]

any advice would be helpful to me :!:

[Mille aka Fredrik]

C spec with cline and Big bore is an awesome combination :noteworthy

[DavidH]

To get the most power from any engine, your going to have to use at least 30% nitro fuel.
The YS or OS will run fine on 15% nitro fuel. The downside to 15% nitro fuel. If you get around someone using 30% nitro fuel and the same setup as you have. I can assure you the 30% nitro fuel setup is going to have more noticeable power by a significant margin.

Both motors will run fine on High Viscosity oil. The difference I have noticed when using the Low Viscosity oil, is the motor will accelerate quicker with the LV oil.

If your just a sport flyer and on a budget. Then use the 15% nitro fuel. Just don't make the mistake of trying to needle the motor to get the same power as 30% nitro fuel. If you try to do that, you will be replacing cylinders, rings, and pistons often.

David

[rjsanders]

Thanks very much Fredrik and David for the info :!: At this point in my flying, I do some 3d stuff, and I realize that 30% nitro fuel would definitely give more power. I just am not sure how much I would benefit from using that much more nitro in my fuel when my skills probably would not allow me to take advantage of having the extra power. Alot of people say that the YS 91 is a set and forget needle adjustment and no additional mods are needed. That is definitely a positive selling point to me! The OS szh 91 claims to put out 3.3hp in it's current form so I wonder how it compares in power to the ys 91 :?: I will probably wait a little longer to see how people are liking their OS 91 SZ before I make my final decision. Thanks again!

Rex

[DavidH]

Rex,
I will throw another equation into your decision making. I flew YS motors for 10 years. I switched to the OS Cspec with Cline setup a couple of years ago. The OS motors run well and produce more power than the YS. I switched to the OS because it runs quieter than the YS. I do contest flying and quietness is a big factor in that part of the hobby.
Also look at the availability of the YS engines over the last few months. Till a couple of weeks ago they have been non-existent. I have seen this cycle before. Also parts were/are hard to come by in that period also.
I saw a few of the OS 91SZ's run this weekend. They all were purring really nice and producing power. Every one that had one was pleased, at least that is what they said.
Don't take this as me downing YS engines, Mr. Yamada makes a good engine. Just the supply chain is not consistent at times. OS is a large company and keeps the supply chain flowing nicely.

David

[rjsanders]

Hi David,

You absolutely right about the YS's always being in short supply. I waited forever like a bunch of other people for the YS 51 to come out and I never did hear about it being available except maybe in on shipment which was a very small one at best :( That is what I like about my two hyper 50's is that there are always parts available for them and I am familiar with them too. I have been hearing the same good things about the os 91 sz's and how smooth and powerful they are now. I think the only mod that James at omi is doing is the cline reg :?: I take it that the carb on the sz is good enough that it doesn't need any mods at all. What about the factory pumped version that is supposed to be out in March? I guess I could get one now and have it upgraded later if necessary? Do you see that the viper head would be a worthwhile upgrade for the 91 sz? Thanks,

Rex

[DavidH]

James was with all of us at Clints event this weekend. James installs the Cline on the 60M-C ( SZ carb). He also enlarges the needle openings some. He does not bore the carb barrel and case. The SZ is 10.6 mm, I seriously doubt .2 mm is going to make any difference. The BB and Cline 60K is only 10.8 mm.
I don't know if a Viperhead is needed on the SZ. The ones I saw running Saturday I did not see a VH on them. They seemed to run well and have plenty of power. As for the pump system for the SZ. Marcus Kim has been using that system for several months now on his Cspec. He should be able to comment how that system works. The regulator is built onto the carb and the pump is bolted to the back plate.
Upgrading to the pump/regulator system at a later date is probably going to be expensive.

David

[Jerry]

Rex,

I've been running the OS factory system on my SZ for about 5 gallons. The pump mounts to the backplate, and supplies the OS regulator with fuel under pressure for delivery in the carb. The pump's output is high enough that muffler pressure or crank pressure (via checkvalve) are NOT required.

Advantages:

The only thing in your fuel tank is fuel. No corrosive exhaust gasses. No more quickly eaten fuel magnets or fuel lines.

Plumbing issues are reduced, as pressure does not exist within the system. No troublesome plumbing leaks or checkvalves causing strange tuning issues

The system works with a 10.6mm carburetor, similar to the 60M-C. There are different internal diameters, however. Obtaining the pump/regulator in the future would require carb modifications to the 60M-C.

The 60M-C has been reported to work well in it's stock configuration as a 3 needle carb. If you elect to go the Cline route..... James has to modify the internals for the Cline to work properly - similar to the mod he does to the Cspec's 60K.

Some of the advantages the SZ have over the black Cspecs, outside the power arena:

The engine is beefier. The case has been re-designed. I believe this will help the engine and possibly bearings last longer.

The piston has been redesigned with a slightly higher piston to liner tolerance. In addition, a groove has been used under the compression ring, aiding lubrication. These two features work together to reduce 'ease of destruction' when working the engine extremely hard under 'less than optimum' conditions.

The Viperhead does work with the SZ. I have found both the stock head and the viperhead to work very well with this motor.

Hope all this helps.

Jerry

[rjsanders]

Hi David and Jerry,

The info you all have provided has been very helpful in my decision for which engine I will eventually get. David, I thought I read another of your post that you were going to wait for the factory 91sz with the pump setup to come out in march. Is this right? Jerry, what factory OS pump system are you using on your sz? Is is from a c spec? I think I would prefer the same system you are using now! The new 91sz seems to be my choice at this time, but if OS will be releasing the factory pumped version soon! I can wait for a while longer to make sure the engine I get will be what I really want. Also, what is Jame's website or contact #? Thanks alot!

Rex

[DavidH]

Rex,
The new OS SZ with the pump and regulator will not be out till later this spring is what I have been told.
The system Jerry is using is the pump and regulator that will be on that motor when it comes out. There is a few pilots here in the USA that have been testing the pump/regulator system that will on the OS91SZ for a few months.
Here is James website. The best way to contact him is by phone.

http://www.oneals.com/Omitro.html

David

[rjsanders]

Thanks David! Looks like that setup is the way to go. Hopefully it won't be too long of a wait until it goes into production!


Rex

[Jerry]

Here are some pictures of the setup.

http://members.aol.com/ctseaplane/regulator1.jpg

(above) Here you can see the regulator portion of the system mounted to a 60M-C carburetor. This particular carb was modified to match what has been tested and will eventually be released by OS in the USA later this year.


http://members.aol.com/ctseaplane/pump.jpg

(above) This photo is of the backplate. The backplate is is tapped for a pressure tap - just like with the Cline system. A short piece of fuel line connects between this pump body and the pressure nipple. Unregulated crankcase pressure drives this high output pump. This pump supplies enough fuel to the regulator to supply the necessary fuel for the carburetor.


http://members.aol.com/ctseaplane/regulator2.jpg

(above) This is the complete system and it's plumbing. We have a feed line coming off of the tank from the clunk. (Through gold Hangar 9 filter) This flows to the IN nipple on the pump. Fuel is then fed to the regulator via the OUT nipple on the pump. From here, it goes into the carburetor via the high speed needle. You can also see that the tank is simply vented to the atmosphere via a vent line. This line exits below the tank level when upright on it's skids. Therefore, considering the outlet is on TOP of the tank, fuel will not leak out. When inverted, since the vent opening is above the level of the fuel, fuel will not leak out. No check valve required.

Jerry

[rjsanders]

Thanks Jerry for sharing the great pics! Is there anyway of knowing about how long it will be before OS puts this setup on the market and what the price range will be? Thanks,

Rex

[WayneBrown]

Thats a cool setup.
I may have to bail on YS over this one if it works.

[Jerry]

Rex,

I've been hearing March for the engine's availability with this setup. I am not sure of the price though.

The availability of the pump/regulator/carb as an affordable 'upgrade' package is something that probably won't happen - at least right away.

Jerry

[rjsanders]

Thanks Jerry! March isn't that long of a wait :)

[DavidH]

Thats a cool setup.
I may have to bail on YS over this one if it works

Wayne would you think it works by the way that way that Marcus Kim's engine runs? Marcus has been running the OS pump and regulator like pictured above for several months now. <G>

David

[Lemuel C.]

Hello,
I'm new to this site, Been flyin heli since 97 here in Orange County, CA. Quit for 3 years.
What would be a best match muffler for the OS 91sxh c spec with pump .
Hatoris or Muscle pipe(CY)?

Thanks for the Help in advance.I used to fly freya with YS st2, It s good for Chaos(piroutte flip) 3D :arggg:

[Lemuel C.]

Never mind,
I got the answer from Curtis FAQ

[WillJames]

The Hatori's seen to be more popular at he fields from what I am seeing at events.