WILDGAS

I have a Bobcat 52 with an OS 55 with a Ducted Pipe Rossi and I need to tuned this combo.

The original RPM with the stock exaust was 13,000 RPM (The propeller is APC 11x7 pusher), after put the Ducted Pipe Rossi the RPM was the same (13,000 rpm), and them I would need to tuned this combo, but I don't know How to do this?

A friend talked me about, I would cut the header to find more rpm, but I want to be sure.

Could you help me?

Flyboy Dave

My Feedback: (21)

....try a smaller prop, maybe a different brand as well.

I think your prop is restricting the RPM, that's why it stayed the same, even though
you changed the pipe. I don't know what kind of port timing that engine has, but I
don't think it will come on the pipe....like I said, too much prop.

FBD.

Razor-RCU

My Feedback: (50)

I would do a search for "tuned pipe" because there are a few really good tutorials on here about how to tune a pipe--- Cutting 1/4 inch at a time and observing the RPM, etc.

Dave made a good point, half the battle is finding the right prop. for the engine/pipe combo. Because if you cut and set the pipe for the wrong pipe then you have an issue.

Keep us posted- I would also PM "Bob27" also, as he has a TON of experience in this field---

rcflyer1970

My Feedback: (212)

Only had very little experience with the 55AX with stock muff in a Phoenix Mustang 40 the engine was happy with a 10x7 or 10x8 apc. We tried 9.5x7 and some 11x7 they didn't perform as well.

airbusdrvr

See if this helps: http://www.macspro.com/tuning.asp

Also, http://www.jettengineering.com/ and then navigate to their technical library for a page on pipe tuning.

"bob27s" is a great source of knowledge. You can do a "by author" search for him on this RCU.

Trundle

A 55AX should turn a 11x7 APC no problem.

WILDGAS

Many thanks for all recomendations. I'll cut the header 1/4" to make a test, and if the rpm increase, I'll cut again.

Razor-RCU

My Feedback: (50)

I am not that familiar with the 55AX but 11x7 seems large- what rpm's should he expect?

Keep us posted!

rmenke

My Feedback: (13)

WILDGAS:

IMHO, you are wasting your time and money on the OS-AX. It is tuned for sport, and only a great grinder can get much more than 16,000 out of them. For a relatively cheep and quick engine, get the new Webra 55. Then buy the Jett tuned pipe for same. Break in with lots of bench time, then slap a apc 9 X 10 on the thing. If it does not give you 18K, you are doing something wrong. I know 18k does not sound like a bunch, but consider the 6 or 7 pitch prop of the OS and think in terms of a 10. I run my nephew down consistantly on our pilon course with identical airframes, he is Jett 60LX powered. I may be a better pilot, but man I close on him hard, and thats not pilot. The jett 60LX is still my favorite engine of all time, but for a cheap (relatively) thrill, try that Webra 55. Its a flat beast. ENJOY

WILDGAS

I'm loocking for a 16000 rpm.

freakingfast

My Feedback: (3)

You wont get 16,000 rpm on a 11x7 prop with the 55 AX. Not even 15,000 with a 11x6 with the best adjusted tuned pipe on 20%
If you need to get that performance, you need a bigger/different motor.

Sorry

Flyboy Dave

My Feedback: (21)

....yep, I would bet money that engine won't come on the pipe with an 11-7 APC prop. []

FBD.

Razor-RCU

My Feedback: (50)

15K on a 55 is AMBITIOUS to say the least. I admit I do not have the 55 AX and I do like my 50SX but 15K? I don't think my Tower-75 will do that...



R menke is making a VERY compelling argument for the Webra-55 however... 9x10? Outrunning the Jett-60LX? I gotta get one of those

WILDGAS

And them, Which is the top rpm by an OS 55 AX?

freakingfast

My Feedback: (3)

The better question is; what's the best operating RPM. You could spin a toothpick to 23K with it, but it won't get any work done up there. I think this engine was ported with the 3D folks in mind. From what I've seen the 55 AX is at its best power at about 14,000 @ 2.0 HP with the right tuned pipe. That's about the speed you can turn a 11X 7 apc.
One thing you could try, is to go with a 10X7 @ 15,900 on the ground but don't expect it to unload much in the air like a Webra. A Tower 75 and a 11 X 7 looks pretty good about now(still won't see 16K).

Flyboy Dave

My Feedback: (21)

Displacement: 0.545 cu in (8.93cc)
Bore: .906 in (23mm)
Stroke: 0.846" (21.5mm)
Practical RPM: 2,000-17,000
Power Output: 1.75 ps/16,000 RPM
Weight: 14.25oz (404g)
Recommended Props: 12x7-8, 13x6-7

The specs give mixed signals. On one hand the engine RPM looks good for some potential.
On the other hand, the prop recommendation are too high (normally) more like the prop
recommendations for a .75 engine or a .90 two stroke. I'm guessing that this engine is of
the newer design....more grunt (torque), and less screaming (rpm/noise).

I would try a Tower muffler (if it fits) and see if the power can be boosted. Then perhaps I
would think about a Performance Specialty or Jett muffler if the engine responds.

Only if the engine turns out to be a sreamer would I think about a tuned pipe, and
doubt that this engine will scream, but you never know till you experiment.

FBD.

LGM Graphix

My Feedback: (22)

Another thing to consider is the pipe itself. Cutting the header may not even get you in the ball park if the pipe is to long, a rossi ducted fan pipe doesn't mean much, what size rossi is it for? If it's a 90 size pipe you'll never get the header short enough, if it's like most ducted fan pipes it will be even longer from the opening to the high point since most of them are designed to mount right up to the head of the engine with just a stub of a header. You'd probably get further with a Mac's pipe and header designed for a 50 size engine. Like others have already said, you'll need to use a smaller prop if you want a higher RPM as well, which may not gain you any advantage in the dirty air of a pusher.