hi all. I got perry pump for my magnum 91rfs,
can I gain more rpm if I'll remove muffler? has someone made such thing with results?
thanks

The Perry pump, by itself, will not make your Saito have more power.

To remove the muffler will make the engine slightly louder and will make it only slightly more powerful.

Enjoy,

Jim

OK...I love my Magnum 91 but it seems to just not do it for you.... and that is fine.....You have done verything to add more power....



I really think that your only option is a larger engine.....

removing the muffler will make your engine noisier and messier......IMHO......

I think ti is time to just suck it up and buy a larger engine.....

just my .02

one problem here. to get better engine I need this:

sell this engine (only 20 people flying in my country [X(] )
financing from family
I have no local hobby shop. I have to wait about 45 days to get this engine from towerhobbies

i'm in the deepest ****

removing the muffler may be can give a very little bit power and another thing :what prop you use on this engine ? overloaded engine can give it full power

Several things that might help: Run at least 15% nitro fuel for starters. (is this available?) and these engines need several gallons thru them before they truly produce their potential. Remember, winding up a 4 stroke is not really a good thing as the valve springs will only take so much.
If I understand, you are in the country of Georgia? You might consider a FAI engine that requires no nitro fuel such as MVVS, a 91 2 stroke should do the trick real well.
Just my opinion......

yes. I'm from Georgia

every bit of power is so usefull for me . if I'll change engine, I think I'll go gas. maby zenoah g26.
I was using 15X6 top flight and broke it when taxiing back after land. don't have other
in 15 dasy I'll get 15X4W and 16X4W. if it will pull 5kg, I'll be happy. if no I'll be
engine has only 3 hours of running time. but it is idleing perfectly. on 15X6 it was sliighhtly rolling on tarmack. max thrust was 4.4kg.
and can sinthetic oil give me more power?
Gizmo. I bought 4 stoke engine, cause here we are hard in fuels. and my engine uses less fuel, than OS61fx. we need bring methanol castor and nitro from rusiia. and + shipping it cost 5$ for 5% nitro fuel and with only castor.
I have this engine on 3.4kg giles202. on tis one

Bako, I have an OS .91 Surpass 2 with pump. I have only had passing contact with other guys' Magnum .91 fourstrokes, enough to see that they are closely patterned after the OS equivalent. Therefore, for the purposes of this discussion, I'll assume that your Magnum .91 with perry pump and my OS .91 with OS pump are equal in terms of their stock performance characteristics and exhibit the same potential for improvement.

So, with this in mind, let me explain how I got considerably more power out of my OS.

As a stock baseline, my OS turned a 13x10 APC prop at 9,200 rpm on 15% Nitro and 18% Synth/Castor blend.

I removed the muffler and just ran the stock header and recorded no improvement in power.

I then removed the stock header and replaced it with the OS EX-502 header unit (available at Tower Hobbies) and immediately performance jumped from 9,200 rpm to a recorded peak of 9,600 rpm. Evidently the restriction was in the stock header rather than the muffler itself. Even with this straight pipe, the engine is still quieter than a stock OS 1.20 Surpass with muffler.

I noticed when running these tests that the engine really preferred to be spinning in the 9s and if loaded with an APC 14x8 (only a little more load than a 13x10), would drop way down to 8,800 rpm.

I recently pulled the cylinder head off to decoke the exhaust valve and port (she's done about 20-30 hours on castor blends) and noticed a missmatch between the inlet port and the inlet manifold. The inlet manifold has a diagonal oval shape mating up with a vertical oval shaped inlet port. Doing my own head mods on cars years ago taught me that this is not good. Naughty OS! So, I relieved the inlet port with a needle file so the manifold and port better matched, reassembled the engine and immediately got 200 more rpm on the same fuel (now 9,800, compared to the baseline 9,200 - an increase from 1.44 hp to 1.74 hp (Pe Reivers' Prop-Power) for the price of an OS header (US$23.99) and a bit of careful filing.

This engine spins the 13x10 faster than my Saito FA 100 and uses about two-thirds of the fuel compared to the Saito in so doing.

I now run the engine on a YS 20/20 blend and with the extra nitro, she'll reliably peak at 9,900 rpm.


I hope this helps. Good luck.

Hi,
You are starting to have an engine that should be broken in by now. You really need at least 10% nitro and some Castor oil in this engine. I use 15% in both of my 91's as well as my 30 and 52 Magnum 4 strokes. I use 14x6 or 15x4 props which work well for me depending on the plane.
You have a really nice looking plane that demands lots of power......you may find an FAI 91 is the best choice for you?Good luck, keep us posted.

Harry,

Thank you for your detailed report of OS .91 engine modifications. I looked up OS EX502 on the Tower Website and got three hits:

1. LXCC14 Tuned Pipe Set
2. LXCN34 Header Pipe In
3. LXCN35 Header Pipe Out

It appears that the Tuned Pipe Set requires either the LXCN34 Header Pipe In (Inside fuselage installation) or the LXCN35 Header Pipe Out (Outside fuselage installation) to operate using the tuned pipe. From your description, it looks like you used one of the two header pipes without the tuned pipe to achieve a 400 RPM power increase to 9600 RPM.

I have two questions:

1. Which header pipe did you use, LXCN34 or LXCN35?
2. Did you try running the OS .91 without any header pipe at all, and if so, what were the results?

Here is where I am headed with all this. I am starting to think that you might be experiencing a mild tuning effect from the header pipe installation rather than a reduction in exhaust system restriction (back pressure). This might account for the significant RPM drop when using an APC 14-8 prop if the engine dropped below the header pipe tuning band. This is sometimes referred to as "falling off the pipe". Two stroke engines can behave this way with tuned pipes, and it is my understanding that it can affect four strokes as well but to a much lesser extent. Any information that you might have would be appreciated.

Thank you,

Bruce

Bruce,

I used the LXCN35 Header Pipe Out - it just hangs out in the breeze at about the same angle as the original header/muffler.

Re: the tuning effect... I'm not sure about this. Given the engine is only doing about 9-10 grand, I'd imagine a tuned header would have to be over two feet in length. The EX-502 is about 4 3/4 inches long.

I ride dirtbikes - one of mine for example is a 400cc 55hp (at the crank, at 9,000 rpm) four-stroke. These four-strokes typically call for an ideal header length of between two and three feet. These engines put their maximum horsepower at much the same revs as our four-stroke model engines.

One thing about the EX502 header that is significant is that it is very thin-walled compared to the stock header and has a much better looking bend - perhaps it flows better. It's actually a nicely made piece of stainless pipe. You can even clean the castor stains off it with oven cleaner and it comes up shiny as new!

No, I didn't try an open exhaust port - that would have been a good test actually.

Your observation about the engine "getting on the pipe" is on the money. With the 14x8 at 8800, the engine is only putting out 1.3 hp and is harder to "needle" accurately, whereas with the 13x10 on it, it jumps up to 1.7 in the space of 1000 rpm and is a breeze to needle.

thanks harry. now i'll go and test fitting of intake manifold

Harry,

Thanks again for the additional information. It looks like you have found the best bargain ever in tuned pipes! I have an OS .91 and will order a LXCN35 Header Pipe today. Thanks for sharing your findings with us. [sm=thumbup.gif]

Bako,

Best of luck with your Giles202.

Bruce

harry. when I remowed intake manifold, the washer there was awfullty fitted and I replaced it. and the manifold was stupidly drilled from up and down and there were big mountins in side. I have polished them all, instead of 1 little, where i can't reach. thanks.
don't u know any headers whgich aren't bent?

Bako - good news! Be sure to let us know how she goes.

Bruce has kindly provided the Tower Hobbies part numbers for the OS parts in the post above - I'm sure there are other headers available in the configuration you require. There's also a flexible header if this helps.

Check out Tower's site.

harry. I want to ask u to tell me the inner diameter of your exaust header. I think my header will bit yours just tell me diameter
and os and magnum have same diameter headers? don't u know?

does anybody know???

Guys...I found that a piece of mild steel automotive gas line will work well for a header, and you can bend it easily, and make it any length you want.
I made a header for a Saito .80 this way...

You just need to make a flare on one end, and "massage" it a little bit to fit into the exh. port nicely...

And, it's a heck of a lot cheaper!

The header inner diameter is 9mm and it uses (according to Tower) an 11mm x .75mm thread to screw into the port.

thanks harry. magnum 91rfs has 8mm inner diameter. the thread is no problem, my friend can make it. he made 1 for me before this idea. he makes combat and CL, and timer engines, 2.5cc. wonderfull ones. I can swear they can bit many good manufacturer engines.
he made 3 or 4 ones, I don't remember