Hi all, I originally wanted to power my 4*60 with a OS61FX but I am thinking of going four stroke now. I have a bunch of questions I hope I can get some help with :

1) What is the equivalent four stroke engine to a OS61FX ? Is it the OSFS70 or OSFS91 ? Where can I get a "2-stroke to 4-stroke conversion chart" ?

2) I notice that OS offers four stroke engines with and without pump. What is the purpose and pros/cons of the pump ?

3) Can I use the same engine mounting provided in the 4*60 kit for mounting a four stroke ?

Thanks a zillion !...............

Hm. Considered the 4C offerings by Saito or YS?

A Saito .72, YS .63 and Saito .91will outperform the similar OS offerings and weigh less.

You asked about the reason for the pump and that is for an airplane where you cannot achieve good tank placement or you want the tank on the cg. It will even out the fuel flow where the engine run the same inverted or not and straight up, down, or level. Generally you don't need this on a 4 *.

You should be able to use the same mount but the equilivent weight ouyt dront is a little more and you may have to move the battery back.

Jim

OS91FS will give a little more power,theOS70 will give less than the 61FX,w8ye @ post 3 answered the pump question,if you don't need it, then it's just one more thing to go wrong,think you may have to use a longer mount,has been many years past since I've built the 4* planes,the other brands of engines I'm not familiar with,hope this helps.
Have a goodun,John

Hi w8, if I were to get one without pump, will it be upgradable in the future, or will I have to get a standalone pump ?

Also, Terell mentioned about the OS91FS. What is the equivalent engine for Saito and YS ? Which is better in your opinion, in terms of power, user friendliness and maintenance ?

Will I need a stronger fuel tank as I heard about tanks bursting. Why do 4C engines generate so much tank pressure compared to 2C ?

On the subject of hovering, is this normally done with a 2C or 4C ?

Sorry for my inquisitiveness but thx in advance !...........

The OS 91's and Saito 91's as well as the Magnum and Thunder Tigers are all very simular engines and as to which one is best would cause some debate on here. You should buy the one you get the best deal on or the one you first come accross. The Saito 100 is a good user friendly, higher power, alternative if hoovering is your game. It is more powerful than all the others but about the same as the Y-S 91 in power.

The Y-S 91 is more powerful, heavy, and cost more than the other engines with the exception of the Saito 100. Although a new one generally runs extremely well, they can have trouble and due to their complexity, can be a real problem to get to run correctly unless you are very good at engines.

It is cheaper to just buy a stand alone pump for one of the above engines (with the exception of the Y-S) from Perry if you decide in the future that you may need one. The OS pump is nice but it costs a lot and they will obsolete it before you know it and then you will have to buy a stand alone pump anyway. Pumps are a added complexity that often cause as many problems as they cure. There are also demand regulators avaiable that help keep the fuel delivery from the pump constant. It is usually best to pick a plane design that has the tank positioned to where there is no need for a pump.

Any current R/C fuel tank should be fine for the above engines. The above mentioned 4 cycle engines do not produce anymore tank pressure than the two cycle engines do.

The question of bursting tanks refers to the Y-S engines (both 2 cycle and 4 cycle). They use ported crankcase pressure with a check valve to build up a lot of tank pressure. however, I havn't had any trouble with just using a standard Dubro tank with them. But you should relieve the pressure after use. Don't press your luck.

You can hoover with either 2 cycle or 4 cycle engines. It's just that we've been in a transition period to four cycles in recent years and everyone talks about them all the time.

The best things in life are simple!

good luck,

Jim

Hi w8, thank you very much for your superb explanation ! You know, maybe i should just stick to a simpler OS61FX after all and enjoy flying rather than getting bogged down with 4C issues. Rather fine tune my air skills than valves. Cheers !..........

Good decision, If you have something that you make work for you, stay with it and enjoy yourself.

Jim

One question I have is if you compare the 4C engines from OS, Saito and YS in the 70 and 90 classes, what are the nitro content requirements and the fuel consumption like ? From some of the threads I see, it seems like Saito and YS requires higher nitro (up to 30%) and their fuel consumption is higher compared to OS. Could you kindly comment on this ? Thanks again..........

Actually, the Saito's are quite content on the same fuel you use in the OS 4 Strokes. But they do take kindly to 2020 or 30 heli.

The Y-S engine does poorly on anything less than 15% and does much better with 2020 or 30 heli fuels.

don't run 4 stroke fuel in any of them.

Enjoy

Jim

Hi w8, what about fuel consumption comparison in the three ? Any difference ? Thanks............

You see all kinds of figures on here. But from my experience, the OS and Saito's in the same sizes have about the same consumption.

A fellow on here a few minutes ago reported 9 min on 8 oz with his Y-S 63.

The Y-S 91 has a much greater fuel consumption than the OS or Saito 91's.

Enjoy,

Jim

What about an equivalent 4s engine for a TT pro .46? I have a model that requires 2x .46 2s engines, but want to run 4s (LOVE the sound of a 4s). What should I use?

Thanks.

People are using Saito 56's, 72's, & Y-S 63's. The 56 should almost replicate your TT PRO 46. But the 3D hotdogs are using the bigger engines.

The OS 70 Surpass II has good power and friendlyness but is larger on the outside than the other engines. Some people use it though.

The OS 52 doesn't have the power of the TT PRO 46 and is better suited to a large wing - lite weight plane. Then you can have many hours of economical fun with one.

I have a couple Magnum 61's but they are not materially different from the 52.

Jim

Thanks!

Quote:"The Y-S 91 is more powerful, heavy, and cost more than the other engines with the exception of the Saito 100"

Actually the YS91AC I had on my 4*60(decided I didn't need outta sight unlimited vertical) weighed the same as the TT.61 2 cycle and I needed no adjustment in balance to fly with the 61.

As a matter of reference I once owned a 4-60 with a 61FX. Ran a MAS 12X6 on 15% Nitro with an OS #8 plug. The verticle was truly unlimited but not enough power to pull out from a hover but then again this is not a 3D air frame - its an everyday good second plane. I think any good 60 size engine will fly the 4-60 well enough for most to enjoy.

Hi Rajul.
Just done a very similar transplant, different plane 64" 80's pattern model, but similar engine swop.
I replaced a 91FX (absolute junk) with An OS91FS non pumped (cracking motor), the mounting holes are identical on all three engines 61FX,91FX and 91fs. Another interesting point I actually weighed the 91's and the four stroke is about 3oz lighter than the two strokes if you include the silencers, which is because if you read the OS specs they quote the weights without silencer and the one for the two strokes weighs about 7oz.
Model fly's much better on the FS with a 13x8 master prop.
Cheers futaba1024.

Hideho,
The biggest reason to go 4 stroke is the Torque. Swing a bigger, better prop and much less effort. Better fuel economy. 4 strokes have a much more linear throttle, thereby no flat spots or midrange transition problems.
Lower, more stable idle.
Ability to be installed and run inverted in planes without the starting and running problems associated with 2 strokes, (which are many)...like having to start your plane upside down if you have a two stroke installed inverted.
4 strokes expel much less gooo from the exhaust....rarely do I have to clean spooge off my planes that I have 4 strokes in.
4 Strokes sound much better.

Are two strokes more simple?
Yup.
Are 4 strokes worth the extra $$?
Every time.

Ask any 4 stroke owner if he would trade his 4 stroke for two 2 strokes of comparable power....
Answer?
Doubt it, I would'nt.