OS .91 Confusion

[Ots]

My Hirobo Freya has an OS .91 SZ engine. That's what it says on the side.

I'm going to build a new JR Vibe 90 and I went to the OS website to make sure I ordered the right engine. There are two engines (of interest) on their website: a .91SZ-H PH-Hyper and a .91SZ-H Ringed engine. It says that the Hyper is a pumped engine.

My Raptor 90 has a YS engine that pressurizes the fuel tank through a check valve. I find this to be a bit of an irritation as I have to pay attention to the fuel tank to make sure I open and close the vent valve when I fuel, shut down, etc. Not a big deal, but I don't like it. And the performance difference between the two is small for my level of flying.

So, my question is, which would be the better engine for me with respect to this new build? Is the Hyper with the pump a better choice? It appears from the photo on their website that the pumping action happens within the engine and does not pressurize the fuel tank like the YS. If this is true, then which would be better and why? The website says that they both make 3.3 hp. It appears that my Hirobo has the non-pumped .91SZ-H, and it makes great power.

[Shawn K]

The non-pumped SZ is - in my opinion - the better choice.

The Perry Pump the O.S. includes with the pumped SZ is a nice enough pump, but the regulator and the carb that come with the pumped SZ aren't very good. They just don't do what they're designed to do, which is to offer the utmost consistency from the first drop of fuel to the last.

The pump may be physically attached to the engine, but it doesn't pressurize "within the engine" as you thought. It's just mounted to the backplate of the engine because (a) it's convenient, and (b) the pump operates using crankcase pressure, and the pressure tap is on the backplate. The pump uses the crankcase pulses to pressurize the fuel delivery to the fuel tank, so yes, the tank is pressurized, just like on a YS system.

The non-pumped SZ may be the better choice for you mostly because there's "less stuff to break" (as my father would say). You're not going to find a difference in maximum power, because fuel pressure does not equal power. The goal of a pressurized system is to build a pressure head above what the engine needs to operate, and then use a regulator to bring the pressure down to a level that the engine can actually use, and then keep it there. (If any of you know anything about SCUBA diving, it's the same principle as a first-stage and second-stage regulator). The problem with the pumped SZ is that O.S. hasn't really figured out how to make a good regulator yet, and they haven't quite got the hang of metering a carb for use in a pressurized system.

The non-pumped SZ with an OMI Fuel Magnet pickup will work beautifully for you. I use a Fuel Magnet and a C-Spec in my machine, and it's served me well for over a year now.

[Ots]

Thank you very much, Shawn. I really appreciate complete answers such as this one.

[GMONEY]

I am with Shawn on this one. I own the pumped version and it works good for my style flying but the NON pumped version is much nicer and runs twice as consistent as my motor.. I have been finding myself fliping back and forth from idle up to normal mode because is seems to run better in Normal mode.. My next motor will be either the nonpmped O.S. or the big block TT motor.. Only time will tell..

G
Hey OTS where do you fly in SoCal? I'm in Upland

[Ots]

Thanks - I have the non-pumped version in my Freya and it performs really well. I was just wondering if the pumped version was better as I'm in the market for a new engine. But we'll stick with the non-pumped one for this build.

Just a curiosity though as you mentioned norm vs idle up - are you running a governor?

It really changes everything. Throttle curves become a thing of the past and all of my pitch curves are linear from 0 to 100 percent. No drama switching from one to the other. But you probably know all of this already.

[GMONEY]

Governer? Yes i have a Gov on the R90 but its the ACE Governer and its not all that.. I am going to keep working with it until I have some more cash to replace it with something a little more hands off.. As it stands i am able to work around it OK.. I have my fingers crossed TT delivers the big power in the next couple months...

G

[Ots]

The Futaba GV-1 is super. It's not the cheapest but it's great.

[Shawn K]

I've been using a GV-1 on my machine, and I'm pleased. It's no longer the top-o'-the-heap in terms of absolute headspeed lock (newer gov's hold a little tighter, but even then you're talking about a very small difference), but the nice thing about it is that with the display screen and menu structure, you can plug in your gear ratio and desired headspeed, and know that it'll be correct. No tachometer required, and no sequence of flashing lights to interpret. It's also very well integrated with Futaba radios, so if all of your shirts are orange and black to begin with, you're golden. (Makes me wish Airtronics would come out with a governor...)

There's also one other thing I like about the GV-1. Changes in headspeed occur much more smoothly than with other governors I've used. I still have the Throttle Jockey Pro that I used for a couple of years, and the one thing I didn't like about it (besides the need for a headspeed tach) was that whenever you'd change flight modes, the TJ Pro would *slam* the throttle open or closed. It's not that I ever damaged anything, it was just annoying how on-and-off the response was. The GV-1 ramps up much more smoothly. In fact, the rate of change is adjustable across a certain range.

The downside to the GV-1? The price. As far as I'm concerned, it costs way too much for what it is, especially since they've been around for ages now. Just one man's opinion.

[WiscHeli]

i use the youngblood Gov ,,, ez to program with the display and the disply is not on the heli to add weight like a GV-1 ,, the programer sits in you flight box ,,, futaba its in your heli adding weight :eek:

[tdswan]

....for what it is, especially since I've been around for ages now. Just one man's opinion.

Shawn, I edited your post so that it's gramatically correct! ;)

[cbflys]

Shawn, I edited your post so that it's gramatically correct! ;)
Good work Troy, it's not only gramatically correct now, it's technically correct ;)

[tdswan]

LOL!
I'm sure I'll get sent back to the corner for that one! :D

[Lota Fun R]

I've got an old SX 91 C spec pump and it works very well. Seems to have as much power as any SZ I've seen fly. I did change out the control valve to make it work right and has worked good since. Carb Smart helps.

My next engine is either an SZ or a TT big bore. Likely the TT. and I'll be mad at myself if it has problems. I love new stuff but hate being a beta tester.

[Ots]

There are lots of problems with the new Redline series.

[Lota Fun R]

I've got a TT53 for my 600. It's one of the first few off the production line so if they have problems, then mine surely has the same problems. Don't know yet since it's not flying.

[GMONEY]

There are lots of problems with the new Redline series.


REALLY??? I have some time with this motor and have some friends in very low places That would certainly hear and be hands ON with any PROBLEMS.. Could you expand on PROBLEMS.. I know of two motors with PROBLEMS 1. early preproduction motor granaded while testing too lean (ON purpose) 2. motor sent back for PROBLEM needles so far off it wouldnt run (needles adjusted and sent back)

G

[blax1]

REALLY??? I have some time with this motor and have some friends in very low places That would certainly hear and be hands ON with any PROBLEMS.. Could you expand on PROBLEMS.. I know of two motors with PROBLEMS 1. early preproduction motor granaded while testing too lean (ON purpose) 2. motor sent back for PROBLEM needles so far off it wouldnt run (needles adjusted and sent back)

G

Hi G
A few of the boys down-under have been having issues with this motor, some have problems others dont, I dont have one so I cant really comment, but at one stage there was a lot of negative stuff written about this engine, I'll leave it to you to decide, here's the thread, grab a beer, kick back relax, it's a long read...... :)

http://www.archeli.com.au/cobra/showthread.php?t=113432

Cheers Ralph

[Ots]

It's been a problem associated with "chasing the lean." Set up as instructed the engine runs hot. Richen it to lower the temp and it has no power. Lean it to get the power back and temps rise - to the high 200's.

Ace has had my engine for a two months or more. I don't know when I'll get it back. Don't really care.

However, I saw JF fly a Rap 50 with one and it kicked ass big time. So, when it's right it's good. When it's not it's not. I'm not the only one who has had this problem.

[heli-cuzz]

The Futaba GV-1 is super. It's not the cheapest but it's great.

I have a GV-1 governor and agree with you 100%. Although I do love how my RevMax limiters perform. In the end they both produce the same result... Consistent headspeed.

[GMONEY]

It's been a problem associated with "chasing the lean." Set up as instructed the engine runs hot. Richen it to lower the temp and it has no power. Lean it to get the power back and temps rise - to the high 200's.

Ace has had my engine for a two months or more. I don't know when I'll get it back. Don't really care.

However, I saw JF fly a Rap 50 with one and it kicked ass big time. So, when it's right it's good. When it's not it's not. I'm not the only one who has had this problem.


"chasing lean" Well I havent seen it yet! Blax I will read that thread on Monday while at work. OTS for the meantime ACE having your motor for two months is stupid. Monday morning 7:30 call and ask for Rocky he is head of that department (CS) You will need to tell him when you shipped your motor. GAbe is the in house motor guy leave him a message if in fact it has been two months. They either need to replace with new today or have acceptable results by end of day Monday with phone call for "back up" If you dont get the resutls your after please call me at 909-581-5492.. I have a very small amount of pull over there but I will use every ounce to get your motor back to you and running right..

Gmoney

[Ots]

Thanks, I appreciate it, but it's not really a problem. As soon as I realized that we weren't going to have success with the new Redline motor I put an OS in my new Evo 50.

My LHS sent the Redline back to Ace - and thinking about it now, it was the last week in March. So it hasn't been two months. My LHS sat on it for a month - that's where the two months came from. So Ace has only had it for four or five weeks.

It's unlikely I'll use it when they get done with it, so it's no big deal. I was just pointing out that there have been some problems with the the new engine. I tend to be an "early adopter" and sometimes this is what you get!

Like I said, I saw one running well and it kicked some major butt.

[GMONEY]

Nothing like O.S. reliabilty! Hopefully they come out with there big block soon.. I have a call in about your motor. Four or five weeks is still four weeks to long. There turn around on any motor should be no longer than two days.. Morons doing nothing all day.. yeah I know your reading this get to work BIATCH!

After reading that thread it seems like TT is going to have some issues on there hands. I saw JF's motor and have seen about a dozen more run soooo good bums me out...CUZ when there good they are awesome the OS doesnt even hold a candle to it..

Gmoney