Author Topic: OS 40 Surpass FS vs Saito FA-40a (Read 7349 times)

Colin McRae · « **on:** May 03, 2025, 12:13:06 PM »

I have both of these engines NIB and plan to use a 40 size FS on a future CL stunt/sport build. Probably a profile warbird model. For those that have direct experience with these engines, which one is considered to be more powerful? If I was guessing at this point, the warbird model will weigh in the neighborhood of 48 oz, with a wing loading around 14.

The Saito FA-40a is interesting as it is a full 2 oz lighter that the OS 40 Surpass FS.

Thanks in advance.

Martin Quartim · « **Reply #1 on:** May 06, 2025, 05:54:02 PM »

Mike Alimov · « **Reply #2 on:** May 22, 2025, 05:39:08 PM »

I don't have the Surpass 40, but the Saito FA-40a is a lovely engine, very impressive power! Comparable or better than most 46-size two strokers. You are a lucky guy!

Dennis Toth · « **Reply #3 on:** May 23, 2025, 10:47:55 AM »

Saito 40 is 2oz lighter, go with that. At a wing load of 14 you need to save all the weight you can. If you need more power adjust the prop and nitro. The 40 will turn a wide blade BBY&O 11x5 at a good rpm (could tweak to a 5 1/2" or go to a 6" pitch and trim diameter to 10 3/4'). For nitro, 10 - 15% is a good starting point and could go up to 20%.

Best, DennisT

Robert Zambelli · « **Reply #4 on:** May 23, 2025, 03:43:38 PM »

I have/had three of each.
The SAITO 40 is a wonderful piece of engineering, perfect for our needs.
I consider the Supass 40s, on the other hand, to be "Reverse Excedrin"* engines.
Of the three I HAD, the performance was nowhere near that of the SAITO.
Each one was carefully broken in EXACTLY according to OS instructions.
Inconsistent runs, broken crank pin, difficult starting, etc.
One of my close friends had one with which he experienced similar issues.
I've owned over 100 4 cycle engines including ENYA, OS, SAITO, WEBRA and HP and Morton.
I still have well over 60.
In defense of the OS, I've owned every one from the 20 up to the 70 and the only one that had issues was the Surpass 40.

Bob Z.

*doesn't cure headaches, it causes them!

Colin McRae · « **Reply #5 on:** September 06, 2025, 05:46:53 PM »

After careful break-in on the Saito 40 with about a full hour on the bench, I decided to bolt it to my P40 ARF just to see how it does in the air. My model is set up with an Evolution 36 NT which low and behold has the exact same bolt pattern as the Saito 40. So, it was easy to just bolt on and fly. I did have to raise the fuel tank a bit to center it with the carb. But that was very easy.

I'm quite impressed with the Saito. Very easy to start, 1 or 2 flips each time. And it pulled the model around just fine on 15 nitro. I wanted to just use the stock carb but also wanted to be able to start it at say 1/3 throttle for a short warm-up. I figured out a simple spring arrangement on the throttle arm. Being a profile model, I could just use my finger to hold the throttle approximately where I want, then go to full throttle and launch. Worked great.

My future build plan is to put together a Hellcat warbird using the Saito 40. The Brodak Hellcat is the same size +/- as the P40.

Dennis Toth · « **Reply #6 on:** September 07, 2025, 07:26:51 AM »

Colin,
Sounds great. I like the spring throttle idea for start. Might be able to expand that idea to use a cable with small loop at the tail hooked into the stooge for having it idle while going to the handle then release for full throttle at take-off. Other option would be a two-line stooge approach with one for the throttle release and the second for the plane. J

Just some thoughts, let us know how this works out. BTY what prop are you using, what l lines and length and lap time.

Best, DennisT

Colin McRae · « **Reply #7 on:** September 07, 2025, 04:43:47 PM »

Quote from: Dennis Toth on September 07, 2025, 07:26:51 AM

Colin,
Sounds great. I like the spring throttle idea for start. Might be able to expand that idea to use a cable with small loop at the tail hooked into the stooge for having it idle while going to the handle then release for full throttle at take-off. Other option would be a two-line stooge approach with one for the throttle release and the second for the plane. J

Just some thoughts, let us know how this works out. BTY what prop are you using, what l lines and length and lap time.

Best, DennisT

Hi Dennis

The simple spring throttle adjustment I used only really works on a profile model. I can easily slip my finger between the engine and fuel tank to move the throttle arm where I want it against the spring to start (+/- 1/3 throttle to warm up a bit, then release to full throttle before I walk out to my handle). If everything was inside a fuselage there would need to be a different method for throttle /adjustment. But your ideas sound intriguing.

Then I only did a couple of flights with the Saito 40 on my Brodak P40 ARF. I run 64' lines on this model. And I did not bother to get lap times. I just wanted to get an idea of the available power for the Saito 40. I first tried 10 nitro and an APC 11-5 sport prop. Model was too slow. Probably around 6 seconds. So, I went to 15 nitro and an APC 11-6 prop. Was much better. Ground launch rpm at 9,200.

What I really like about FS's for CL is the constant power. Once I set the desired ground rpm, it pretty much stays right there throughout the entire flight. And repeatable. And BTW, I was not using muffler pressure, just ram air vent to the wide wedge uniflow tank.

(I did have another FS related general question. Is the use of the double nut that came with the Saito necessary? Reason for my question. My Saito came with the double nut. But I have OS 26 & 40 FS's and OS does not provide them as standard. Then I heard that the double nut does not really offer much on these 'smaller' FS engines. But the double nut system should be used on large FS's. Your thoughts are welcome. Thx)

Colin

Steve Dwyer · « **Reply #8 on:** September 16, 2025, 06:18:37 AM »

I have a Surpass 40 I've been flying all summer on a lumbering old 1.15 size foam wing Prowler I acquired back some time ago. When I initially test ran it with only one prop nut and a Brodak 2" plastic spinner the prop came lose. I will add I am also one to really horse the prop nut when tightening. It not only came lose but nut broke the spinner allowing the 11 x 4.5 prop to fly about 10' away. I was fortunate not to get hit this could have been a disaster. The second back up nut is a must; I've not had a problem using it since. The 4 cycle by nature appears to be a higher torque engine than the typical 2 cycle we fly. It may be a difference in the stroke-displacement I'm sure Bobby Z can shed some light on this.

Regarding the performance I have no complaints with the Surpass 40. It's a consistent runner, same lap time 5.2 and holds the Prowler where it's supposed to be in every maneuver. I do have a Saito 40 I've only bench run, but no flying comparison. I think the Prowler likes the added nose weight with the Surpass.

Colin McRae · « **Reply #9 on:** September 16, 2025, 07:57:16 AM »

Quote from: Steve Dwyer on September 16, 2025, 06:18:37 AM

The second back up nut is a must; I've not had a problem using it since.

I will certainly use the double nut system on the Saito 40.

Interesting that the Saito 30 doesn't even come with a double nut. The shaft isn't even long enough for one.

And the OS 26 and 40 FS's I have don't come with a double nut system.

In any event, I routinely check for prop nut tightness every couple of flights on any prop, and especially with a wood prop.

Colin

Dennis Toth · « **Reply #10 on:** September 16, 2025, 03:53:21 PM »

Steve,
You didn't mention the fuel mix you were running when it popped the prop. Also, what was the temperature that day. Was it a wood prop? I have run the Surpass 40 on a few ships on 10%N, 20% total oil fuel and never had a issue. But just like with 2 stokes they can pop one every now and then. The second nut is a good idea it should at least keep it from throwing the prop off completely. One thing is you need to check the prop tightness every few flights at least with a wood prop.

Colin,
Another thing I want to try on the FS (maybe on the bench first) is a long aluminum exhaust tube to move the exhaust off the plane kinda like a tuned pipe does.

Best, DennisT

Best, DennisT

Steve Dwyer · « **Reply #11 on:** September 17, 2025, 06:10:57 AM »

Dennis,

The prop was an APC 11x4, I don't recall the weather that day I suspect it was in the low 80s and I was using Randy's recommended 20% N with 20% blended oil. Looking at the Saito literature, I don't have it for the Surpass they recommend in two places to use the lock nut. They also recommend 10 to 15% N. I suspect the 20% N contributed to the Surpass kicking on starting, it probably backfired causing the prop to loosen but I don't recall the details except the prop, broken spinner and nut went flying.

Steve

Steve Dwyer · « **Reply #12 on:** September 17, 2025, 10:46:42 AM »

It turns out I do have the Surpass operating literature I discovered buried in the engine literature file. It's interesting there is no mention of using a backup nut on the prop shaft. Surpass recommends the same Nitro % as Saito and they recommend starting in the clockwise rotation and to expect the prop to snap back into the counterclockwise direction. I don't know why Randy recommended using the higher Nitro levels in the 4 strokers but I suspect this can contributes to the start torque. I did notice the literature is written around using the engines for RC and to start with the throttle partially open. We wire the throttle wide open for CL and it starts screaming.

Steve

Colin McRae · « **Reply #13 on:** September 18, 2025, 10:06:26 AM »

Quote from: Steve Dwyer on September 17, 2025, 10:46:42 AM

It turns out I do have the Surpass operating literature I discovered buried in the engine literature file. It's interesting there is no mention of using a backup nut on the prop shaft. Surpass recommends the same Nitro % as Saito and they recommend starting in the clockwise rotation and to expect the prop to snap back into the counterclockwise direction. I don't know why Randy recommended using the higher Nitro levels in the 4 strokers but I suspect this can contributes to the start torque. I did notice the literature is written around using the engines for RC and to start with the throttle partially open. We wire the throttle wide open for CL and it starts screaming.

Steve

Not sure why but people seem to just use 20% nitro on the Saito's. I have been using 10 & 15 nitro on my OS and Saito FS's, per the owner's manuals, depending on the power I need and also adjusting the props I use. Have not needed to go to 20% nitro (yet).

On a smallish Yak 9 w/ OS 26 FS, I was looking for 10,000 rpm on an APC 9-7 sport prop (to obtain the lap time I was looking for). 10% was to slow and 15% too fast. So, I just blended the 2 fuels 50/50 for 12.5% nitro and the 26 settled in nicely at 10k.

On my P40 (Saito 40) 10% nitro was too slow (lap time), and on 15% it settled in where I wanted it. There was no need to go to 20% nitro power wise.

So just pick a nitro / prop combination that gets you were you need to be power wise.

Also, to my understanding higher nitro can be harder on an engine and also glow plugs. So, I use as low a nitro as needed along with prop selection for a particular model to get the lap time I need.

Colin

Colin McRae · « **Reply #14 on:** November 05, 2025, 02:18:32 PM »

Quote from: Steve Dwyer on September 17, 2025, 10:46:42 AM

I did notice the literature is written around using the engines for RC and to start with the throttle partially open. We wire the throttle wide open for CL and it starts screaming.

Steve

I'm using the stock carb on my FS's. (Not jerry-rigged with a venturi.) But I have a manual throttle control setup. I can start the engine at say 1/3 throttle for a brief warmup, then go to full throttle for launch. My FS's have been easily starting with 1 or 2 flips in the normal rotation direction (not backflipping). Maybe the 1/3 start throttle setting is helping w/ the easy starts.

Colin McRae · « **Reply #15 on:** November 05, 2025, 02:47:17 PM »

Quote from: Steve Dwyer on September 16, 2025, 06:18:37 AM

I have a Surpass 40 I've been flying all summer on a lumbering old 1.15 size foam wing Prowler I acquired back some time ago. When I initially test ran it with only one prop nut and a Brodak 2" plastic spinner the prop came lose. I will add I am also one to really horse the prop nut when tightening. It not only came lose but nut broke the spinner allowing the 11 x 4.5 prop to fly about 10' away. I was fortunate not to get hit this could have been a disaster. The second back up nut is a must; I've not had a problem using it since. The 4 cycle by nature appears to be a higher torque engine than the typical 2 cycle we fly. It may be a difference in the stroke-displacement I'm sure Bobby Z can shed some light on this.

Regarding the performance I have no complaints with the Surpass 40. It's a consistent runner, same lap time 5.2 and holds the Prowler where it's supposed to be in every maneuver. I do have a Saito 40 I've only bench run, but no flying comparison. I think the Prowler likes the added nose weight with the Surpass.

On a couple of my models, I can't use a spinner if I use the FS double nut system. The shaft is not long enough.

As a test, in lieu of a double nut, I tried this thin steel 'spring' washer on a 26 FS on my Yak 9. Spring washers are designed for vibration type loads. With an APC sport prop and Dubro plastic spinner, and after snugging up the prop nut, I flew 6 flights. I checked the prop nut tightness and it was still tight. No loosening at all.

So, the spring washer seems fine for a smaller 26 FS. I'll also try it on the larger Saito 40 when the time comes.

Dan McEntee · « **Reply #16 on:** November 05, 2025, 10:46:08 PM »

Quote from: Colin McRae on November 05, 2025, 02:18:32 PM

I'm using the stock carb on my FS's. (Not jerry-rigged with a venturi.) But I have a manual throttle control setup. I can start the engine at say 1/3 throttle for a brief warmup, then go to full throttle for launch. My FS's have been easily starting with 1 or 2 flips in the normal rotation direction (not backflipping). Maybe the 1/3 start throttle setting is helping w/ the easy starts.

The partially closed throttle is the thing helping your start up. It's acting like a butterfly choke. I've mentioned this many time before, that if you are using a stock carb for a C/L model, close off the throttle about 1/4 to reduce the open area in the throat of the carb and lock it there. It's way bigger than a normal venturi and can make for difficult needle settings, especially if the throttle barrel is loose and rattles around. Closing off the throttle decreases the choke area, and once started, then you adjust the needle for the RPM you desire. Four strokes are all about fuel draw, and you can get the venturi diameter quite small without losing any power. The aftermarket venturi I have on my Saito .56 in a 70 ounce Top Flite Score was about 7mm and still too big, so I added a screw than comes into the throat 90 degrees from the side, as per Bob Reeves writings on a high pitch/low RPM set up. By the time I test ran it to get to the recommended RPM range, the throat was probably 6mm or smaller, and with a through the venturi spray bar. It still makes more than enough power and swings a 13-7 prop with great authority and around 8000 RPM, and uses about 3 3/4 ounces typically of YS-20/20 fuel for a pattern. The screw lets you adjust that a bit for air temperature, humidity and altitude and such. On that small of a 4 stroke, the throttle opening at full throttle may be small enough as it is if you don't have trouble getting and holding a needle setting. But on bigger engines I have played with, it is an issue.
Type at you later,
Dan McEntee

spare_parts · « **Reply #17 on:** November 06, 2025, 03:02:01 PM »

Normal running doesn't need the double nut. The double nut reduces the chances of a thrown prop if leaned to the point of detonation. Truturn had double nuts for short shafts. I learned the FS-40S will happily throw props, even with no nitromethane in the fuel. I was doing some testing for max power, leaning it to the point of knock. With a double nut, it would run long enough to hear knock. Single nut, the prop simply left the chat.

Robert Zambelli · « **Reply #18 on:** November 06, 2025, 07:09:51 PM »

I’ve had similar experiences with ENYA four cycle engines.
The 53 was the worst.
Adding one head gasket (supplied with the engine) solved the problem.
Bob Z.

Author Topic: OS 40 Surpass FS vs Saito FA-40a (Read 7349 times)

Colin McRae

OS 40 Surpass FS vs Saito FA-40a

Martin Quartim

Re: OS 40 Surpass FS vs Saito FA-40a

Mike Alimov

Re: OS 40 Surpass FS vs Saito FA-40a

Dennis Toth

Re: OS 40 Surpass FS vs Saito FA-40a

Robert Zambelli

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Dennis Toth

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Steve Dwyer

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Dennis Toth

Re: OS 40 Surpass FS vs Saito FA-40a

Steve Dwyer

Re: OS 40 Surpass FS vs Saito FA-40a

Steve Dwyer

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Colin McRae

Re: OS 40 Surpass FS vs Saito FA-40a

Dan McEntee

Re: OS 40 Surpass FS vs Saito FA-40a

spare_parts

Re: OS 40 Surpass FS vs Saito FA-40a

Robert Zambelli

Re: OS 40 Surpass FS vs Saito FA-40a