os 70 surpass II RPM

ground I richened to 10900

this engine to produce these readings. what type of readings are others getting from this engine

I don't own the OS, but I get 10,300 richened from 10,800 on my 1.2HP rated Saito .72 () running an APC 13x6 on only 10% Cool Power. Your tach readings seem to be in the same ballpark for this size engine and prop.

On the other hand, I think ThrustHP's results are best taken with healthy dose of salt. It calculates 1.338HP, 9.09lb thrust for an APC 13x6 at

10,300RPM. That supposed 9lb of thrust can barely hover my 6.8lb(wet) SU- 31.

That is not unreasonable with that amount of nitro. Most four strokes thrive on higher nitro content in the fuel.

82% humidity is just below "goldfish bowl" specs. Where do you live?

I have two OS 70 Surpass II's. I've never believed OS's ratings on these engines. If you compare the hp ratings between the 70 and the

91 there's a 1/2 hp difference. I hardly think so. I've flown the same plane with both of these engines and there's is not a nearly 50% increase in hp between the 70 and the 91.

I run my 70 on 15% Cool Power and get in the vicinity of 11,000 rpm with mine, so your readings seem in the ball park.

I'm confused. I have the OS.70 in a VMAR Cessna 182, I was told to buy (I am a returning newbie) synthetic fuel with 10% nitro and I did just that. When I went to my local model supplier they were horrified that I would use 10% in this engine and advised me to use 5% instead. The shop owner and all his staff are model builders and fliers, the owner uses the OS .70 himself and is adamant that 5% is what I should use.

Is he talking crap? Will I be in danger of damaging this very nice engine by using 5%? The OS.70 is at the top end of the requirements for the aircraft it is in so maximum RPM is not such a crucial factor I am thinking....

Advice please :) Regards, Jeff.

82% isn't that high at lower temps. 82% at 90deg would be horrible!

He is talking crap. Typical Brit attitude that since nitro costs more you should use less of it. I heard that all the time at the flying sites in the UK (until they saw mine running).

Every four stroke I have ever had the pleasure of using has run MUCH BETTER on 15-25% nitro.

-- Paul Mc>

Contrary to what Paul says, the shop owner has a valid point for as far as he goes into the subject. However, Paul is right if you NEED screaming performance. For that more nitro works just fine. You decide what your usage is and buy accordingly.

Not far from the norm here in south east Texas in the summer.

Actually the norm I am familiar with is 100+ with humidity 98%+ . But that is NOT in Houston.

OS rates the engine at 1.1hp @ 11000 rpm today I was running MA 13x6 on 30% helix fuel and peeked at 11400 on the ground I richened to 10900 to fly according to thrust hp calculator 1.585hp, it seams unreasonable for this engine to produce these readings. what type of readings are others getting from this engine the temp was 62 f and humidity 82% and pressure of 29.91 in Hg

"the temp was 62 f and humidity 82% and pressure of 29.91 in Hg" Wow! An oasis! It would be for us, here in Central Florida (Orlando). Temps everyday 92-98, humidity in the 90's to 100 every summer day, humidity up there even in the slightly cooler evenings. Not that I'm complaining. Nothing like flying in the dead of winter, temps in the 60's-70's. I can live with it!

Contrary to what you say, nitro isn't just for screaming performance. It has the same effect as turbocharging. It makes the engine seem larger than its physical capacity. You can comfortably use larger, more efficient props with higher nitro.

The secondary benefit (one of the primary for me) is that idle and transition are MUCH better with 15% and above. Compression levels are fairly low in most four strokes. This means that they run worse on lower nitro levels. If you could bump up the compression a bit, you might even be able to get good performance with no nitro.

I too use 15% in my 4 strokes. They become more reliable and have more power.

Hi, I'm fairly new to four stroke model engines an have just started to play with my OS 70 Surpass. (not Surpass II). The instructions say that for break-in, use a 11X8~9, 12X7~8, 12.5X6 for sport and stunt models. For fuel they recomend synthetic and/ or castor oil with 5 to 15% nitro. I have 6 tanks of fuel thru mine with an 11X8 Zinger, 15% Wildcat and it turns

10,000 rpm on the ground. Idle is a little fast and it makes it hard to slow down for a landing. I have just put on an APC 13X6 and will try it tomorrow. Dan.

Paul, You do it your way, and I will do it my way. I admit my way takes a little more care and attention in dialing in the needle settings. However, I do try to get my engines right so that I can run them hard and inexpensively. That is why I have the opinion that all nitro does is aid top end preformance.

DO NOT RUN HIGH CASTOR CONTENT IN 4 STROKE ENGINES! It causes a large build up of carbon around the exhaust valve that degrades performance significantly. Some mfgr's even withdraw the warranty if you use castor in the fuel. Some of that information has been developed since the .70 came out.

If you run a castor/synthetic blend, make sure that the castor is no more than 2-3% of the total fuel makeup. The higher combustion temperatures in many four strokes will cause a lot of hard deposites from the castor. Syntheic deposits tend to be a lot softer and easier to remove if needed.

So, you haven't actually TRIED it? Most people I know say the same thing until they try a little higher nitro and they don't go back.