OK so it's not the only engine used in SPA events, but darn near. Why? I can understand using four strokes, but Saito weighs less and has a bit more power. Why do I hardly see it used? Magnum looks and weighs the same and the latest ones have more power. OK I know pattern guys would not be caught dead with a four stroke that cost less than $200, but the Magnum would do as well performance wise. Also there are a few .60 two strokes that at least come close to the same power. Such as the Webra, HP, K&B twist, Fox, Tower,etc. Also many others that have the same power but weigh more. OK I know the pattern guys are not enamored with the Fox, but it would be a contender if properly set up.

I'm on my second Magnum .91. I haven't compared it directly to an OS .91 four-stroke powerwise, so I don't know if it measures up. Probably not by a few hundred rpm. Just a guess though.

I like the OS four-strokes, but to me, they are just too big for a .60 sized plane. I don't like carrying tail weight. This is why I have been considering the Saito .91. It may be down a few hundred rpms (don't know - just the rumor), but to me it would more than make up for that by weighing a LOT less. When all is said and done, its all up weight should be just about the same as a modern two-stroke .61 with muffler.

I have decided to swim against the current. I'm going to use my new Rossi .60 with an Ultrathrust muffler (which in combo may be as heavy as an OS FS-91 Surpass <G&gt. It's just for kicks with me. I don't stand a chance against the old pattern pros anyway (SPA). But I do believe I can convince them that I was there, on a good day. We shall see. I may be too optimistic, but I plan on having fun even if I finish dead last. When you get older, you realize that the fun was the trip, not arriving at the destination. Just being around folks with similar interests is fun it and of itself.

The Fox .60 can be a bear, no doubt.

Maybe it is the fact that the OS.91 Surpass uses a black valve cover (hint: looks like a YS from a few feet away).

There may be a market going untapped for black Magnum .91 four-stroke valve covers!

Ed,
Thought the newer Magnums were more powerfull, from reading the Tach reports. Now getting above 10,000 with a 14-6 prop. Also the Saito 91S is getting in or close to that range. Someone said the S version has a hotter cam?

How bout using the Magnum with an OS valve cover? LOL

you'll have fun with the Rossi. I flew my first SPA meet last year at Cullman, in the "open class", so we had a piped Rossi and a piped YS60, and the guys loved them. The only place you may have an issue with the Rossi is at the Knoxville meet, they have noise regs there. I believe that may have been why the 4-cycles were allowed in the first place, because at one time, it was all 2 strokes. Dennis Hunt and Ed Hartley are the CDs there, so you can check with them for your specific application. I loved my Rossi, if it makes you happy, run with it, that's what it's all about anyway!

Putting a HP gold cup on a Tower .60 Kaos, maybe I should get a pipe for open class? As for as noise, maybe an old SF turning less than 10,000 with a three blade prop would meet the noise restrictions? Come to think of it, may need a better muffler or something for the HP. What is the noise limit in Knoxville?

not sure what the noise limit is. If you go to www.seniorpattern.com I think they have email addresses there for a couple of the officers, you could send them an email to get the lowdown. "Open Class" is only flown at Cullman, the contest run by Steve Byrum. He offered that last fall as "bait" to get more people involved in SPA. If worked on my brother and myself. I think he's offering it this spring as well, but I wouldn't expect to see it beyond that. Last fall, there were only a few true "open class" planes there, and judging by the response to Steve's recent post here, there may not be any coming next month. Beyond that, there are no pipes allowed. To my knowledge, Ultrathrust type mufflers are legal though.

I will e-mail them some day. I don't plan on going to all of the meets, maybe just the one in Paulding Co. That field is about 6 miles from me, my club is Cobb Co which is just past 3 miles. I checked to make sure my transmitter tests would not cause a crash! I checke the Knoxville club site and they don't say anything about noise limits. Trees seem close in for a pattern competition. Is there more than one Knoxville club?

I'm not sure if there is more than one Knoxville club or not. The club in question is KCRC, here's their site:
http://www.kcrctn.com/
If you go to "about KCRC" on the left, there is a rules and regs page that talks about their noise situation. From what I understand, they're not doing a noise reg out of preference, they have a beautiful field and some "high dollar" homes were built within ear-shot of loud engines, so they were forced to, to keep their site.
Cobb County reminds me of when I was a kid and watched WWF wrestling, there was a character on there "the big boss man", and the story of the character was he was a cop at the "Cobb County Georgia" correctional facility.

Funny, Cullman makes me think of wrestling. Don't know why.

I asked the same question on the SPA Bulletin Board and Bruce Underwood told me that 4 strokes were favored because of reliabity and torque (prop selection). With respect to the OS, he felt the OS broke in easier, was less fussy to adjust (and keep adjusted), and requred much less maintenance. I'm building a Sun Fli III right now, and I'm putting an OS 91FS in it. I'm hopeful of attending a few SPA events this year. Regards,..WarpedWing.

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Generally, engines that produce less power are in a lower state of tune and are not as fussy on adjustments. For those wishing to have fun, but are not four-stroke experts, I can see the appeal of an OS .91 Surpass II and the Magnum .91 clone of same.

The Saito break-in isn't all that difficult. Just time consuming. I've seen folks pop them onto a plane and just set them up rich and broke them in that way without horrible consequences. I think that is a non issue. At least it is to me.

I like OS engines, but the Saito .91s is so light and small that it just begs to be used in this application. I also suspect that the Saito .91 utilizes nitro a bit better.

After saying all of that, I have two Saito .82s NIB, so I'm going to substitute an .82 for a .91 and see how well it handles the models. If worse comes to worse, I can put the .82 in the Kaos 40 ARF and be powered more than adequately, especially when running higher nitro fuel.

I'm not giving up on the Rossi .60 and Ultrathrust combo, however. There's too many great choices in this hobby. Know what ah mean, Vern?

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I thought so too, to be honest with you.

I just ordered an OS FS-91 II, so we shall have a bench running contest between the two of them.

Which prop, manufacturer and size, is the most popular amongst the SPA guys for the OS .91 II Surpass? Any ideas?

13x9 is pretty standard.

APC that is.

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That figures. It's the one size I don't have as yet. Oh well, more paint stirrers to add to the pile.

Are you sure about that size? I recall that the OS FS .91 would only turn about 9,500 with a 13-8. I never tried a 13-9 figuring it was too much prop. That was the original Surpass, don't know if performance was improved with the Surpass II.

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I have 13x8 APC props, just for .91 four-strokes.

Maybe they are pulling more pitch when using 30% nitro heli fuel? I don't think that I will be doing that. YS 20/20, maybe.

I don't think the OS FS can run 30% heli fuel. I recall that 20% was the limit, in the summer anyway. But again the II may be differant.

pretty much SPA standard is Morgan Fuels Cool Power 30% heli thru the OS, with anywhere from a 13*9, 13.5*9. Turn up the nitro and she runs. The extra oil (full synthetic) keeps them cool. There are SPA members with 4-500 flights on the same set of bearings with this fuel. All applies to I and II.

Well I think my OS must have been a lemon. Never was satisfied with the performance. Got rid of it after a year or so.

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I have a new OS .91 II on the way, but I'm also thinking of trying a Saito .91. I can't help but believe the Saito would be stronger, especially on higher nitro fuels. We shall see.

Just kinda lookin around this SPA arena. I've always been interested in 70's pattern. Are most guys using the pumped, or non-pumped OS 91FS? I noticed in the MA article pumps were "legal"

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Pumps are legal, just not oversized carbs. If the carb comes with the engine, it is not oversize.

They are against supercharging, so all YS four-strokes are not legal. A good move as far as I'm concerned. Otherwise, it turns into another wallet competition.

I've never owned/operated an OS four-stroke with a pump. With that said, it is just another thing to break or cause problems. Now, if it was a geared pump, such as those used by Enya, I'd be all for trying one. But Enya's .91 four-stroke is really heavy, so I hear.

Guys

Having run the OS91 pumper for about 7 years, the only complaint I've had is that the regulator cover begins to drip fuel after about 6 months of use. They have finally fixed this with a replacement cover that lacks the cute OS logo and has reenforcing ribs instead. Otherwise, the engine is extremely reliable.

13x8 is the standard prop on less than Heli fuel. Otherwise, the larger prop is fine. I put on a 14x10 a few years ago. The plane was very slow and constant speed. Great vertical, but my rates were too slow and I didn't feel like reworking everything, so I went back to 14x8. I've also flown 13x8 3 blades successfully. Several guys have also used 11x9 4 blades.